[history-ot] initial implementation of using doc-level history-ot (#25054)

* [history-v1-ot] initial implementation of using doc-level history-v1-ot

* [web] fix advancing of the otMigrationStage

Use 'nextStage' for the user provided, desired stage when advancing.

Co-authored-by: Brian Gough <brian.gough@overleaf.com>

* [document-updater] document size check in editor-core

* [history-ot] rename history-v1-ot to history-ot and add types

* [history-ot] apply review feedback

- remove extra !!
- merge variable assignment when processing diff-match-match output
- add helper function for getting docstore lines view of StringFileData

Co-authored-by: Alf Eaton <alf.eaton@overleaf.com>

* Revert "[document-updater] add safe rollback point for history-ot (#25283)"

This reverts commit d7230dd14a379a27d2c6ab03a006463a18979d06

Signed-off-by: Jakob Ackermann <jakob.ackermann@overleaf.com>

---------

Signed-off-by: Jakob Ackermann <jakob.ackermann@overleaf.com>
Co-authored-by: Brian Gough <brian.gough@overleaf.com>
Co-authored-by: Alf Eaton <alf.eaton@overleaf.com>
GitOrigin-RevId: 89c497782adb0427635d50d02263d6f535b12481

libraries/overleaf-editor-core/index.js

@@ -18,6 +18,7 @@ const MoveFileOperation = require('./lib/operation/move_file_operation')
 const SetCommentStateOperation = require('./lib/operation/set_comment_state_operation')
 const EditFileOperation = require('./lib/operation/edit_file_operation')
 const EditNoOperation = require('./lib/operation/edit_no_operation')
+const EditOperationTransformer = require('./lib/operation/edit_operation_transformer')
 const SetFileMetadataOperation = require('./lib/operation/set_file_metadata_operation')
 const NoOperation = require('./lib/operation/no_operation')
 const Operation = require('./lib/operation')
@@ -43,6 +44,8 @@ const TrackingProps = require('./lib/file_data/tracking_props')
 const Range = require('./lib/range')
 const CommentList = require('./lib/file_data/comment_list')
 const LazyStringFileData = require('./lib/file_data/lazy_string_file_data')
+const StringFileData = require('./lib/file_data/string_file_data')
+const EditOperationBuilder = require('./lib/operation/edit_operation_builder')
 
 exports.AddCommentOperation = AddCommentOperation
 exports.Author = Author
@@ -58,6 +61,7 @@ exports.DeleteCommentOperation = DeleteCommentOperation
 exports.File = File
 exports.FileMap = FileMap
 exports.LazyStringFileData = LazyStringFileData
+exports.StringFileData = StringFileData
 exports.History = History
 exports.Label = Label
 exports.AddFileOperation = AddFileOperation
@@ -65,6 +69,8 @@ exports.MoveFileOperation = MoveFileOperation
 exports.SetCommentStateOperation = SetCommentStateOperation
 exports.EditFileOperation = EditFileOperation
 exports.EditNoOperation = EditNoOperation
+exports.EditOperationBuilder = EditOperationBuilder
+exports.EditOperationTransformer = EditOperationTransformer
 exports.SetFileMetadataOperation = SetFileMetadataOperation
 exports.NoOperation = NoOperation
 exports.Operation = Operation

libraries/overleaf-editor-core/lib/file_data/string_file_data.js

@@ -88,6 +88,14 @@ class StringFileData extends FileData {
     return content
   }
 
+  /**
+   * Return docstore view of a doc: each line separated
+   * @return {string[]}
+   */
+  getLines() {
+    return this.getContent({ filterTrackedDeletes: true }).split('\n')
+  }
+
   /** @inheritdoc */
   getByteLength() {
     return Buffer.byteLength(this.content)

libraries/overleaf-editor-core/lib/operation/edit_operation_builder.js

@@ -36,6 +36,20 @@ class EditOperationBuilder {
     }
     throw new Error('Unsupported operation in EditOperationBuilder.fromJSON')
   }
+
+  /**
+   * @param {unknown} raw
+   * @return {raw is RawEditOperation}
+   */
+  static isValid(raw) {
+    return (
+      isTextOperation(raw) ||
+      isRawAddCommentOperation(raw) ||
+      isRawDeleteCommentOperation(raw) ||
+      isRawSetCommentStateOperation(raw) ||
+      isRawEditNoOperation(raw)
+    )
+  }
 }
 
 /**

package-lock.json

@@ -42539,6 +42539,7 @@
         "lodash": "^4.17.21",
         "minimist": "^1.2.8",
         "mongodb-legacy": "6.1.3",
+        "overleaf-editor-core": "*",
         "request": "^2.88.2",
         "requestretry": "^7.1.0"
       },

services/document-updater/app.js

@@ -212,8 +212,6 @@ app.use((error, req, res, next) => {
     return res.status(422).json(error.info)
   } else if (error instanceof Errors.FileTooLargeError) {
     return res.sendStatus(413)
-  } else if (error instanceof Errors.ProjectMigratedToHistoryOTError) {
-    return res.status(422).send(error.message)
   } else if (error.statusCode === 413) {
     return res.status(413).send('request entity too large')
   } else {

services/document-updater/app/js/DiffCodec.js

@@ -1,4 +1,5 @@
 const DMP = require('diff-match-patch')
+const { TextOperation } = require('overleaf-editor-core')
 const dmp = new DMP()
 
 // Do not attempt to produce a diff for more than 100ms
@@ -16,8 +17,7 @@ module.exports = {
     const ops = []
     let position = 0
     for (const diff of diffs) {
-      const type = diff[0]
-      const content = diff[1]
+      const [type, content] = diff
       if (type === this.ADDED) {
         ops.push({
           i: content,
@@ -37,4 +37,24 @@ module.exports = {
     }
     return ops
   },
+
+  diffAsHistoryV1EditOperation(before, after) {
+    const diffs = dmp.diff_main(before, after)
+    dmp.diff_cleanupSemantic(diffs)
+
+    const op = new TextOperation()
+    for (const diff of diffs) {
+      const [type, content] = diff
+      if (type === this.ADDED) {
+        op.insert(content)
+      } else if (type === this.REMOVED) {
+        op.remove(content.length)
+      } else if (type === this.UNCHANGED) {
+        op.retain(content.length)
+      } else {
+        throw new Error('Unknown type')
+      }
+    }
+    return op
+  },
 }

services/document-updater/app/js/DocumentManager.js

@@ -11,10 +11,16 @@ const RangesManager = require('./RangesManager')
 const { extractOriginOrSource } = require('./Utils')
 const { getTotalSizeOfLines } = require('./Limits')
 const Settings = require('@overleaf/settings')
+const { StringFileData } = require('overleaf-editor-core')
 
 const MAX_UNFLUSHED_AGE = 300 * 1000 // 5 mins, document should be flushed to mongo this time after a change
 
 const DocumentManager = {
+  /**
+   * @param {string} projectId
+   * @param {string} docId
+   * @return {Promise<{lines: (string[] | StringFileRawData), version: number, ranges: Ranges, resolvedCommentIds: any[], pathname: string, projectHistoryId: string, unflushedTime: any, alreadyLoaded: boolean, historyRangesSupport: boolean, type: OTType}>}
+   */
   async getDoc(projectId, docId) {
     const {
       lines,
@@ -75,6 +81,7 @@ const DocumentManager = {
         unflushedTime: null,
         alreadyLoaded: false,
         historyRangesSupport,
+        type: Array.isArray(lines) ? 'sharejs-text-ot' : 'history-ot',
       }
     } else {
       return {
@@ -87,16 +94,25 @@ const DocumentManager = {
         unflushedTime,
         alreadyLoaded: true,
         historyRangesSupport,
+        type: Array.isArray(lines) ? 'sharejs-text-ot' : 'history-ot',
       }
     }
   },
 
   async getDocAndRecentOps(projectId, docId, fromVersion) {
-    const { lines, version, ranges, pathname, projectHistoryId } =
+    const { lines, version, ranges, pathname, projectHistoryId, type } =
       await DocumentManager.getDoc(projectId, docId)
 
     if (fromVersion === -1) {
-      return { lines, version, ops: [], ranges, pathname, projectHistoryId }
+      return {
+        lines,
+        version,
+        ops: [],
+        ranges,
+        pathname,
+        projectHistoryId,
+        type,
+      }
     } else {
       const ops = await RedisManager.promises.getPreviousDocOps(
         docId,
@@ -110,15 +126,21 @@ const DocumentManager = {
         ranges,
         pathname,
         projectHistoryId,
+        type,
       }
     }
   },
 
   async appendToDoc(projectId, docId, linesToAppend, originOrSource, userId) {
-    const { lines: currentLines } = await DocumentManager.getDoc(
+    let { lines: currentLines, type } = await DocumentManager.getDoc(
       projectId,
       docId
     )
+    if (type === 'history-ot') {
+      const file = StringFileData.fromRaw(currentLines)
+      // TODO(24596): tc support for history-ot
+      currentLines = file.getLines()
+    }
     const currentLineSize = getTotalSizeOfLines(currentLines)
     const addedSize = getTotalSizeOfLines(linesToAppend)
     const newlineSize = '\n'.length
@@ -153,22 +175,42 @@ const DocumentManager = {
       throw new Error('No lines were provided to setDoc')
     }
 
+    // Circular dependencies. Import at runtime.
+    const HistoryV1OTUpdateManager = require('./HistoryV1OTUpdateManager')
     const UpdateManager = require('./UpdateManager')
+
     const {
       lines: oldLines,
       version,
       alreadyLoaded,
+      type,
     } = await DocumentManager.getDoc(projectId, docId)
 
     logger.debug(
       { docId, projectId, oldLines, newLines },
       'setting a document via http'
     )
-    const op = DiffCodec.diffAsShareJsOp(oldLines, newLines)
-    if (undoing) {
-      for (const o of op || []) {
-        o.u = true
-      } // Turn on undo flag for each op for track changes
+
+    let op
+    if (type === 'history-ot') {
+      const file = StringFileData.fromRaw(oldLines)
+      const operation = DiffCodec.diffAsHistoryV1EditOperation(
+        // TODO(24596): tc support for history-ot
+        file.getContent({ filterTrackedDeletes: true }),
+        newLines.join('\n')
+      )
+      if (operation.isNoop()) {
+        op = []
+      } else {
+        op = [operation.toJSON()]
+      }
+    } else {
+      op = DiffCodec.diffAsShareJsOp(oldLines, newLines)
+      if (undoing) {
+        for (const o of op || []) {
+          o.u = true
+        } // Turn on undo flag for each op for track changes
+      }
     }
 
     const { origin, source } = extractOriginOrSource(originOrSource)
@@ -203,7 +245,11 @@ const DocumentManager = {
     // this update, otherwise the doc would never be
     // removed from redis.
     if (op.length > 0) {
-      await UpdateManager.promises.applyUpdate(projectId, docId, update)
+      if (type === 'history-ot') {
+        await HistoryV1OTUpdateManager.applyUpdate(projectId, docId, update)
+      } else {
+        await UpdateManager.promises.applyUpdate(projectId, docId, update)
+      }
     }
 
     // If the document was loaded already, then someone has it open
@@ -224,7 +270,7 @@ const DocumentManager = {
   },
 
   async flushDocIfLoaded(projectId, docId) {
-    const {
+    let {
       lines,
       version,
       ranges,
@@ -245,6 +291,11 @@ const DocumentManager = {
 
     logger.debug({ projectId, docId, version }, 'flushing doc')
     Metrics.inc('flush-doc-if-loaded', 1, { status: 'modified' })
+    if (!Array.isArray(lines)) {
+      const file = StringFileData.fromRaw(lines)
+      // TODO(24596): tc support for history-ot
+      lines = file.getLines()
+    }
     const result = await PersistenceManager.promises.setDoc(
       projectId,
       docId,
@@ -294,6 +345,7 @@ const DocumentManager = {
       throw new Errors.NotFoundError(`document not found: ${docId}`)
     }
 
+    // TODO(24596): tc support for history-ot
     const newRanges = RangesManager.acceptChanges(
       projectId,
       docId,
@@ -360,6 +412,7 @@ const DocumentManager = {
   },
 
   async getComment(projectId, docId, commentId) {
+    // TODO(24596): tc support for history-ot
     const { ranges } = await DocumentManager.getDoc(projectId, docId)
 
     const comment = ranges?.comments?.find(comment => comment.id === commentId)
@@ -381,6 +434,7 @@ const DocumentManager = {
       throw new Errors.NotFoundError(`document not found: ${docId}`)
     }
 
+    // TODO(24596): tc support for history-ot
     const newRanges = RangesManager.deleteComment(commentId, ranges)
 
     await RedisManager.promises.updateDocument(
@@ -420,7 +474,7 @@ const DocumentManager = {
   },
 
   async getDocAndFlushIfOld(projectId, docId) {
-    const { lines, version, unflushedTime, alreadyLoaded } =
+    let { lines, version, unflushedTime, alreadyLoaded } =
       await DocumentManager.getDoc(projectId, docId)
 
     // if doc was already loaded see if it needs to be flushed
@@ -432,6 +486,12 @@ const DocumentManager = {
       await DocumentManager.flushDocIfLoaded(projectId, docId)
     }
 
+    if (!Array.isArray(lines)) {
+      const file = StringFileData.fromRaw(lines)
+      // TODO(24596): tc support for history-ot
+      lines = file.getLines()
+    }
+
     return { lines, version }
   },
 
@@ -476,6 +536,11 @@ const DocumentManager = {
     if (opts.historyRangesMigration) {
       historyRangesSupport = opts.historyRangesMigration === 'forwards'
     }
+    if (!Array.isArray(lines)) {
+      const file = StringFileData.fromRaw(lines)
+      // TODO(24596): tc support for history-ot
+      lines = file.getLines()
+    }
 
     await ProjectHistoryRedisManager.promises.queueResyncDocContent(
       projectId,
@@ -684,6 +749,7 @@ module.exports = {
         'ranges',
         'pathname',
         'projectHistoryId',
+        'type',
       ],
       getDocAndRecentOpsWithLock: [
         'lines',
@@ -692,6 +758,7 @@ module.exports = {
         'ranges',
         'pathname',
         'projectHistoryId',
+        'type',
       ],
       getCommentWithLock: ['comment'],
     },

services/document-updater/app/js/Errors.js

@@ -5,7 +5,15 @@ class OpRangeNotAvailableError extends OError {}
 class ProjectStateChangedError extends OError {}
 class DeleteMismatchError extends OError {}
 class FileTooLargeError extends OError {}
-class ProjectMigratedToHistoryOTError extends OError {}
+class OTTypeMismatchError extends OError {
+  /**
+   * @param {OTType} got
+   * @param {OTType} want
+   */
+  constructor(got, want) {
+    super('ot type mismatch', { got, want })
+  }
+}
 
 module.exports = {
   NotFoundError,
@@ -13,5 +21,5 @@ module.exports = {
   ProjectStateChangedError,
   DeleteMismatchError,
   FileTooLargeError,
-  ProjectMigratedToHistoryOTError,
+  OTTypeMismatchError,
 }

services/document-updater/app/js/HistoryV1OTUpdateManager.js

@@ -0,0 +1,158 @@
+// @ts-check
+
+const Profiler = require('./Profiler')
+const DocumentManager = require('./DocumentManager')
+const Errors = require('./Errors')
+const RedisManager = require('./RedisManager')
+const {
+  EditOperationBuilder,
+  StringFileData,
+  EditOperationTransformer,
+} = require('overleaf-editor-core')
+const Metrics = require('./Metrics')
+const ProjectHistoryRedisManager = require('./ProjectHistoryRedisManager')
+const HistoryManager = require('./HistoryManager')
+const RealTimeRedisManager = require('./RealTimeRedisManager')
+
+/**
+ * @typedef {import("./types").Update} Update
+ * @typedef {import("./types").HistoryV1OTEditOperationUpdate} HistoryV1OTEditOperationUpdate
+ */
+
+/**
+ * @param {Update} update
+ * @return {update is HistoryV1OTEditOperationUpdate}
+ */
+function isHistoryOTEditOperationUpdate(update) {
+  return (
+    update &&
+    'doc' in update &&
+    'op' in update &&
+    'v' in update &&
+    Array.isArray(update.op) &&
+    EditOperationBuilder.isValid(update.op[0])
+  )
+}
+
+/**
+ * Try to apply an update to the given document
+ *
+ * @param {string} projectId
+ * @param {string} docId
+ * @param {HistoryV1OTEditOperationUpdate} update
+ * @param {Profiler} profiler
+ */
+async function tryApplyUpdate(projectId, docId, update, profiler) {
+  let { lines, version, pathname, type } =
+    await DocumentManager.promises.getDoc(projectId, docId)
+  profiler.log('getDoc')
+
+  if (lines == null || version == null) {
+    throw new Errors.NotFoundError(`document not found: ${docId}`)
+  }
+  if (type !== 'history-ot') {
+    throw new Errors.OTTypeMismatchError(type, 'history-ot')
+  }
+
+  let op = EditOperationBuilder.fromJSON(update.op[0])
+  if (version !== update.v) {
+    const transformUpdates = await RedisManager.promises.getPreviousDocOps(
+      docId,
+      update.v,
+      version
+    )
+    for (const transformUpdate of transformUpdates) {
+      if (!isHistoryOTEditOperationUpdate(transformUpdate)) {
+        throw new Errors.OTTypeMismatchError('sharejs-text-ot', 'history-ot')
+      }
+
+      if (
+        transformUpdate.meta.source &&
+        update.dupIfSource?.includes(transformUpdate.meta.source)
+      ) {
+        update.dup = true
+        break
+      }
+      const other = EditOperationBuilder.fromJSON(transformUpdate.op[0])
+      op = EditOperationTransformer.transform(op, other)[0]
+    }
+    update.op = [op.toJSON()]
+  }
+
+  if (!update.dup) {
+    const file = StringFileData.fromRaw(lines)
+    file.edit(op)
+    version += 1
+    update.meta.ts = Date.now()
+    await RedisManager.promises.updateDocument(
+      projectId,
+      docId,
+      file.toRaw(),
+      version,
+      [update],
+      {},
+      update.meta
+    )
+
+    Metrics.inc('history-queue', 1, { status: 'project-history' })
+    try {
+      const projectOpsLength =
+        await ProjectHistoryRedisManager.promises.queueOps(projectId, [
+          JSON.stringify({
+            ...update,
+            meta: {
+              ...update.meta,
+              pathname,
+            },
+          }),
+        ])
+      HistoryManager.recordAndFlushHistoryOps(
+        projectId,
+        [update],
+        projectOpsLength
+      )
+      profiler.log('recordAndFlushHistoryOps')
+    } catch (err) {
+      // The full project history can re-sync a project in case
+      //  updates went missing.
+      // Just record the error here and acknowledge the write-op.
+      Metrics.inc('history-queue-error')
+    }
+  }
+  RealTimeRedisManager.sendData({
+    project_id: projectId,
+    doc_id: docId,
+    op: update,
+  })
+}
+
+/**
+ * Apply an update to the given document
+ *
+ * @param {string} projectId
+ * @param {string} docId
+ * @param {HistoryV1OTEditOperationUpdate} update
+ */
+async function applyUpdate(projectId, docId, update) {
+  const profiler = new Profiler('applyUpdate', {
+    project_id: projectId,
+    doc_id: docId,
+    type: 'history-ot',
+  })
+
+  try {
+    await tryApplyUpdate(projectId, docId, update, profiler)
+  } catch (error) {
+    RealTimeRedisManager.sendData({
+      project_id: projectId,
+      doc_id: docId,
+      error: error instanceof Error ? error.message : error,
+    })
+    profiler.log('sendData')
+    throw error
+  } finally {
+    profiler.end()
+  }
+}
+
+module.exports = { isHistoryOTEditOperationUpdate, applyUpdate }

services/document-updater/app/js/HttpController.js

@@ -9,6 +9,7 @@ const Metrics = require('./Metrics')
 const DeleteQueueManager = require('./DeleteQueueManager')
 const { getTotalSizeOfLines } = require('./Limits')
 const async = require('async')
+const { StringFileData } = require('overleaf-editor-core')
 
 function getDoc(req, res, next) {
   let fromVersion
@@ -27,7 +28,7 @@ function getDoc(req, res, next) {
     projectId,
     docId,
     fromVersion,
-    (error, lines, version, ops, ranges, pathname) => {
+    (error, lines, version, ops, ranges, pathname, _projectHistoryId, type) => {
       timer.done()
       if (error) {
         return next(error)
@@ -36,6 +37,11 @@ function getDoc(req, res, next) {
       if (lines == null || version == null) {
         return next(new Errors.NotFoundError('document not found'))
       }
+      if (!Array.isArray(lines) && req.query.historyV1OTSupport !== 'true') {
+        const file = StringFileData.fromRaw(lines)
+        // TODO(24596): tc support for history-ot
+        lines = file.getLines()
+      }
       res.json({
         id: docId,
         lines,
@@ -44,6 +50,7 @@ function getDoc(req, res, next) {
         ranges,
         pathname,
         ttlInS: RedisManager.DOC_OPS_TTL,
+        type,
       })
     }
   )
@@ -84,6 +91,11 @@ function peekDoc(req, res, next) {
     if (lines == null || version == null) {
       return next(new Errors.NotFoundError('document not found'))
     }
+    if (!Array.isArray(lines) && req.query.historyV1OTSupport !== 'true') {
+      const file = StringFileData.fromRaw(lines)
+      // TODO(24596): tc support for history-ot
+      lines = file.getLines()
+    }
     res.json({ id: docId, lines, version })
   })
 }

services/document-updater/app/js/PersistenceManager.js

@@ -95,6 +95,13 @@ function getDoc(projectId, docId, options = {}, _callback) {
           status: body.pathname === '' ? 'zero-length' : 'undefined',
         })
       }
+
+      if (body.otMigrationStage > 0) {
+        // Use history-ot
+        body.lines = { content: body.lines.join('\n') }
+        body.ranges = {}
+      }
+
       callback(
         null,
         body.lines,

services/document-updater/app/js/Profiler.js

@@ -1,68 +1,52 @@
-/* eslint-disable
-    no-unused-vars,
-*/
-// TODO: This file was created by bulk-decaffeinate.
-// Fix any style issues and re-enable lint.
-/*
- * decaffeinate suggestions:
- * DS206: Consider reworking classes to avoid initClass
- * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
- */
-let Profiler
-const Settings = require('@overleaf/settings')
 const logger = require('@overleaf/logger')
 
-const deltaMs = function (ta, tb) {
+function deltaMs(ta, tb) {
   const nanoSeconds = (ta[0] - tb[0]) * 1e9 + (ta[1] - tb[1])
   const milliSeconds = Math.floor(nanoSeconds * 1e-6)
   return milliSeconds
 }
 
-module.exports = Profiler = (function () {
-  Profiler = class Profiler {
-    static initClass() {
-      this.prototype.LOG_CUTOFF_TIME = 15 * 1000
-      this.prototype.LOG_SYNC_CUTOFF_TIME = 1000
-    }
+class Profiler {
+  LOG_CUTOFF_TIME = 15 * 1000
+  LOG_SYNC_CUTOFF_TIME = 1000
 
-    constructor(name, args) {
-      this.name = name
-      this.args = args
-      this.t0 = this.t = process.hrtime()
-      this.start = new Date()
-      this.updateTimes = []
-      this.totalSyncTime = 0
-    }
+  constructor(name, args) {
+    this.name = name
+    this.args = args
+    this.t0 = this.t = process.hrtime()
+    this.start = new Date()
+    this.updateTimes = []
+    this.totalSyncTime = 0
+  }
 
-    log(label, options = {}) {
-      const t1 = process.hrtime()
-      const dtMilliSec = deltaMs(t1, this.t)
-      this.t = t1
-      this.totalSyncTime += options.sync ? dtMilliSec : 0
-      this.updateTimes.push([label, dtMilliSec]) // timings in ms
-      return this // make it chainable
-    }
+  log(label, options = {}) {
+    const t1 = process.hrtime()
+    const dtMilliSec = deltaMs(t1, this.t)
+    this.t = t1
+    this.totalSyncTime += options.sync ? dtMilliSec : 0
+    this.updateTimes.push([label, dtMilliSec]) // timings in ms
+    return this // make it chainable
+  }
 
-    end(message) {
-      const totalTime = deltaMs(this.t, this.t0)
-      const exceedsCutoff = totalTime > this.LOG_CUTOFF_TIME
-      const exceedsSyncCutoff = this.totalSyncTime > this.LOG_SYNC_CUTOFF_TIME
-      if (exceedsCutoff || exceedsSyncCutoff) {
-        // log anything greater than cutoffs
-        const args = {}
-        for (const k in this.args) {
-          const v = this.args[k]
-          args[k] = v
-        }
-        args.updateTimes = this.updateTimes
-        args.start = this.start
-        args.end = new Date()
-        args.status = { exceedsCutoff, exceedsSyncCutoff }
-        logger.warn(args, this.name)
+  end() {
+    const totalTime = deltaMs(this.t, this.t0)
+    const exceedsCutoff = totalTime > this.LOG_CUTOFF_TIME
+    const exceedsSyncCutoff = this.totalSyncTime > this.LOG_SYNC_CUTOFF_TIME
+    if (exceedsCutoff || exceedsSyncCutoff) {
+      // log anything greater than cutoffs
+      const args = {}
+      for (const k in this.args) {
+        const v = this.args[k]
+        args[k] = v
       }
-      return totalTime
+      args.updateTimes = this.updateTimes
+      args.start = this.start
+      args.end = new Date()
+      args.status = { exceedsCutoff, exceedsSyncCutoff }
+      logger.warn(args, this.name)
     }
+    return totalTime
   }
-  Profiler.initClass()
-  return Profiler
-})()
+}
+
+module.exports = Profiler

services/document-updater/app/js/RedisManager.js

@@ -48,6 +48,7 @@ const RedisManager = {
       timer.done()
       _callback(error)
     }
+    const shareJSTextOT = Array.isArray(docLines)
     const docLinesArray = docLines
     docLines = JSON.stringify(docLines)
     if (docLines.indexOf('\u0000') !== -1) {
@@ -60,7 +61,10 @@ const RedisManager = {
     // Do an optimised size check on the docLines using the serialised
     // length as an upper bound
     const sizeBound = docLines.length
-    if (docIsTooLarge(sizeBound, docLinesArray, Settings.max_doc_length)) {
+    if (
+      shareJSTextOT && // editor-core has a size check in TextOperation.apply and TextOperation.applyToLength.
+      docIsTooLarge(sizeBound, docLinesArray, Settings.max_doc_length)
+    ) {
       const docSize = docLines.length
       const err = new Error('blocking doc insert into redis: doc is too large')
       logger.error({ projectId, docId, err, docSize }, err.message)
@@ -324,13 +328,6 @@ const RedisManager = {
             } catch (e) {
               return callback(e)
             }
-            if (docLines != null && !Array.isArray(docLines)) {
-              return callback(
-                new Errors.ProjectMigratedToHistoryOTError(
-                  'refusing to process doc that was migrated to history-ot'
-                )
-              )
-            }
 
             version = parseInt(version || 0, 10)
             // check doc is in requested project
@@ -468,6 +465,7 @@ const RedisManager = {
     if (appliedOps == null) {
       appliedOps = []
     }
+    const shareJSTextOT = Array.isArray(docLines)
     RedisManager.getDocVersion(docId, (error, currentVersion) => {
       if (error) {
         return callback(error)
@@ -507,7 +505,10 @@ const RedisManager = {
       // Do an optimised size check on the docLines using the serialised
       // length as an upper bound
       const sizeBound = newDocLines.length
-      if (docIsTooLarge(sizeBound, docLines, Settings.max_doc_length)) {
+      if (
+        shareJSTextOT && // editor-core has a size check in TextOperation.apply and TextOperation.applyToLength.
+        docIsTooLarge(sizeBound, docLines, Settings.max_doc_length)
+      ) {
         const err = new Error('blocking doc update: doc is too large')
         const docSize = newDocLines.length
         logger.error({ projectId, docId, err, docSize }, err.message)

services/document-updater/app/js/UpdateManager.js

@@ -15,9 +15,10 @@ const RangesManager = require('./RangesManager')
 const SnapshotManager = require('./SnapshotManager')
 const Profiler = require('./Profiler')
 const { isInsert, isDelete, getDocLength, computeDocHash } = require('./Utils')
+const HistoryV1OTUpdateManager = require('./HistoryV1OTUpdateManager')
 
 /**
- * @import { DeleteOp, InsertOp, Op, Ranges, Update, HistoryUpdate } from "./types"
+ * @import { Ranges, Update, HistoryUpdate } from "./types"
  */
 
 const UpdateManager = {
@@ -80,7 +81,11 @@ const UpdateManager = {
     profile.log('getPendingUpdatesForDoc')
 
     for (const update of updates) {
-      await UpdateManager.applyUpdate(projectId, docId, update)
+      if (HistoryV1OTUpdateManager.isHistoryOTEditOperationUpdate(update)) {
+        await HistoryV1OTUpdateManager.applyUpdate(projectId, docId, update)
+      } else {
+        await UpdateManager.applyUpdate(projectId, docId, update)
+      }
       profile.log('applyUpdate')
     }
     profile.log('async done').end()
@@ -110,12 +115,16 @@ const UpdateManager = {
         pathname,
         projectHistoryId,
         historyRangesSupport,
+        type,
       } = await DocumentManager.promises.getDoc(projectId, docId)
       profile.log('getDoc')
 
       if (lines == null || version == null) {
         throw new Errors.NotFoundError(`document not found: ${docId}`)
       }
+      if (type !== 'sharejs-text-ot') {
+        throw new Errors.OTTypeMismatchError(type, 'sharejs-text-ot')
+      }
 
       const previousVersion = version
       const incomingUpdateVersion = update.v

services/document-updater/app/js/types.ts

@@ -1,12 +1,17 @@
 import {
   TrackingPropsRawData,
   ClearTrackingPropsRawData,
+  RawEditOperation,
 } from 'overleaf-editor-core/lib/types'
 
+export type OTType = 'sharejs-text-ot' | 'history-ot'
+
 /**
  * An update coming from the editor
  */
 export type Update = {
+  dup?: boolean
+  dupIfSource?: string[]
   doc: string
   op: Op[]
   v: number
@@ -18,6 +23,11 @@ export type Update = {
   projectHistoryId?: string
 }
 
+export type HistoryV1OTEditOperationUpdate = Omit<Update, 'op'> & {
+  op: RawEditOperation[]
+  meta: Update['meta'] & { source: string }
+}
+
 export type Op = InsertOp | DeleteOp | CommentOp | RetainOp
 
 export type InsertOp = {

services/document-updater/package.json

@@ -34,6 +34,7 @@
     "lodash": "^4.17.21",
     "minimist": "^1.2.8",
     "mongodb-legacy": "6.1.3",
+    "overleaf-editor-core": "*",
     "request": "^2.88.2",
     "requestretry": "^7.1.0"
   },

services/document-updater/test/acceptance/js/ApplyingUpdatesToADocTests.js

@@ -31,6 +31,12 @@ describe('Applying updates to a doc', function () {
       op: [this.op],
       v: this.version,
     }
+    this.historyV1OTUpdate = {
+      doc: this.doc_id,
+      op: [{ textOperation: [4, 'one and a half\n', 9] }],
+      v: this.version,
+      meta: { source: 'random-publicId' },
+    }
     this.result = ['one', 'one and a half', 'two', 'three']
     DocUpdaterApp.ensureRunning(done)
   })
@@ -284,6 +290,260 @@ describe('Applying updates to a doc', function () {
     })
   })
 
+  describe('when the document is not loaded (history-ot)', function () {
+    beforeEach(function (done) {
+      this.startTime = Date.now()
+      MockWebApi.insertDoc(this.project_id, this.doc_id, {
+        lines: this.lines,
+        version: this.version,
+        otMigrationStage: 1,
+      })
+      DocUpdaterClient.sendUpdate(
+        this.project_id,
+        this.doc_id,
+        this.historyV1OTUpdate,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          setTimeout(() => {
+            rclientProjectHistory.get(
+              ProjectHistoryKeys.projectHistoryFirstOpTimestamp({
+                project_id: this.project_id,
+              }),
+              (error, result) => {
+                if (error != null) {
+                  throw error
+                }
+                result = parseInt(result, 10)
+                this.firstOpTimestamp = result
+                done()
+              }
+            )
+          }, 200)
+        }
+      )
+    })
+
+    it('should load the document from the web API', function () {
+      MockWebApi.getDocument
+        .calledWith(this.project_id, this.doc_id)
+        .should.equal(true)
+    })
+
+    it('should update the doc', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) done(error)
+          doc.lines.should.deep.equal(this.result)
+          done()
+        }
+      )
+    })
+
+    it('should push the applied updates to the project history changes api', function (done) {
+      rclientProjectHistory.lrange(
+        ProjectHistoryKeys.projectHistoryOps({ project_id: this.project_id }),
+        0,
+        -1,
+        (error, updates) => {
+          if (error != null) {
+            throw error
+          }
+          JSON.parse(updates[0]).op.should.deep.equal(this.historyV1OTUpdate.op)
+          JSON.parse(updates[0]).meta.pathname.should.equal('/a/b/c.tex')
+
+          done()
+        }
+      )
+    })
+
+    it('should set the first op timestamp', function () {
+      this.firstOpTimestamp.should.be.within(this.startTime, Date.now())
+    })
+
+    it('should yield last updated time', function (done) {
+      DocUpdaterClient.getProjectLastUpdatedAt(
+        this.project_id,
+        (error, res, body) => {
+          if (error != null) {
+            throw error
+          }
+          res.statusCode.should.equal(200)
+          body.lastUpdatedAt.should.be.within(this.startTime, Date.now())
+          done()
+        }
+      )
+    })
+
+    it('should yield no last updated time for another project', function (done) {
+      DocUpdaterClient.getProjectLastUpdatedAt(
+        DocUpdaterClient.randomId(),
+        (error, res, body) => {
+          if (error != null) {
+            throw error
+          }
+          res.statusCode.should.equal(200)
+          body.should.deep.equal({})
+          done()
+        }
+      )
+    })
+
+    describe('when sending another update', function () {
+      beforeEach(function (done) {
+        this.timeout(10000)
+        this.second_update = Object.assign({}, this.historyV1OTUpdate)
+        this.second_update.op = [
+          {
+            textOperation: [4, 'one and a half\n', 24],
+          },
+        ]
+        this.second_update.v = this.version + 1
+        this.secondStartTime = Date.now()
+        DocUpdaterClient.sendUpdate(
+          this.project_id,
+          this.doc_id,
+          this.second_update,
+          error => {
+            if (error != null) {
+              throw error
+            }
+            setTimeout(done, 200)
+          }
+        )
+      })
+
+      it('should update the doc', function (done) {
+        DocUpdaterClient.getDoc(
+          this.project_id,
+          this.doc_id,
+          (error, res, doc) => {
+            if (error) done(error)
+            doc.lines.should.deep.equal([
+              'one',
+              'one and a half',
+              'one and a half',
+              'two',
+              'three',
+            ])
+            done()
+          }
+        )
+      })
+
+      it('should not change the first op timestamp', function (done) {
+        rclientProjectHistory.get(
+          ProjectHistoryKeys.projectHistoryFirstOpTimestamp({
+            project_id: this.project_id,
+          }),
+          (error, result) => {
+            if (error != null) {
+              throw error
+            }
+            result = parseInt(result, 10)
+            result.should.equal(this.firstOpTimestamp)
+            done()
+          }
+        )
+      })
+
+      it('should yield last updated time', function (done) {
+        DocUpdaterClient.getProjectLastUpdatedAt(
+          this.project_id,
+          (error, res, body) => {
+            if (error != null) {
+              throw error
+            }
+            res.statusCode.should.equal(200)
+            body.lastUpdatedAt.should.be.within(
+              this.secondStartTime,
+              Date.now()
+            )
+            done()
+          }
+        )
+      })
+    })
+
+    describe('when another client is sending a concurrent update', function () {
+      beforeEach(function (done) {
+        this.timeout(10000)
+        this.otherUpdate = {
+          doc: this.doc_id,
+          op: [{ textOperation: [8, 'two and a half\n', 5] }],
+          v: this.version,
+          meta: { source: 'other-random-publicId' },
+        }
+        this.secondStartTime = Date.now()
+        DocUpdaterClient.sendUpdate(
+          this.project_id,
+          this.doc_id,
+          this.otherUpdate,
+          error => {
+            if (error != null) {
+              throw error
+            }
+            setTimeout(done, 200)
+          }
+        )
+      })
+
+      it('should update the doc', function (done) {
+        DocUpdaterClient.getDoc(
+          this.project_id,
+          this.doc_id,
+          (error, res, doc) => {
+            if (error) done(error)
+            doc.lines.should.deep.equal([
+              'one',
+              'one and a half',
+              'two',
+              'two and a half',
+              'three',
+            ])
+            done()
+          }
+        )
+      })
+
+      it('should not change the first op timestamp', function (done) {
+        rclientProjectHistory.get(
+          ProjectHistoryKeys.projectHistoryFirstOpTimestamp({
+            project_id: this.project_id,
+          }),
+          (error, result) => {
+            if (error != null) {
+              throw error
+            }
+            result = parseInt(result, 10)
+            result.should.equal(this.firstOpTimestamp)
+            done()
+          }
+        )
+      })
+
+      it('should yield last updated time', function (done) {
+        DocUpdaterClient.getProjectLastUpdatedAt(
+          this.project_id,
+          (error, res, body) => {
+            if (error != null) {
+              throw error
+            }
+            res.statusCode.should.equal(200)
+            body.lastUpdatedAt.should.be.within(
+              this.secondStartTime,
+              Date.now()
+            )
+            done()
+          }
+        )
+      })
+    })
+  })
+
   describe('when the document is loaded', function () {
     beforeEach(function (done) {
       MockWebApi.insertDoc(this.project_id, this.doc_id, {
@@ -390,6 +650,58 @@ describe('Applying updates to a doc', function () {
     })
   })
 
+  describe('when the document is loaded (history-ot)', function () {
+    beforeEach(function (done) {
+      MockWebApi.insertDoc(this.project_id, this.doc_id, {
+        lines: this.lines,
+        version: this.version,
+        otMigrationStage: 1,
+      })
+      DocUpdaterClient.preloadDoc(this.project_id, this.doc_id, error => {
+        if (error != null) {
+          throw error
+        }
+        DocUpdaterClient.sendUpdate(
+          this.project_id,
+          this.doc_id,
+          this.historyV1OTUpdate,
+          error => {
+            if (error != null) {
+              throw error
+            }
+            setTimeout(done, 200)
+          }
+        )
+      })
+    })
+
+    it('should update the doc', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) return done(error)
+          doc.lines.should.deep.equal(this.result)
+          done()
+        }
+      )
+    })
+
+    it('should push the applied updates to the project history changes api', function (done) {
+      rclientProjectHistory.lrange(
+        ProjectHistoryKeys.projectHistoryOps({ project_id: this.project_id }),
+        0,
+        -1,
+        (error, updates) => {
+          if (error) return done(error)
+          JSON.parse(updates[0]).op.should.deep.equal(this.historyV1OTUpdate.op)
+          JSON.parse(updates[0]).meta.pathname.should.equal('/a/b/c.tex')
+          done()
+        }
+      )
+    })
+  })
+
   describe('when the document has been deleted', function () {
     describe('when the ops come in a single linear order', function () {
       beforeEach(function (done) {
@@ -596,6 +908,160 @@ describe('Applying updates to a doc', function () {
     })
   })
 
+  describe('with a broken update (history-ot)', function () {
+    beforeEach(function (done) {
+      this.broken_update = {
+        doc: this.doc_id,
+        v: this.version,
+        op: [{ textOperation: [99, -1] }],
+        meta: { source: '42' },
+      }
+      MockWebApi.insertDoc(this.project_id, this.doc_id, {
+        lines: this.lines,
+        version: this.version,
+        otMigrationStage: 1,
+      })
+
+      DocUpdaterClient.subscribeToAppliedOps(
+        (this.messageCallback = sinon.stub())
+      )
+
+      DocUpdaterClient.sendUpdate(
+        this.project_id,
+        this.doc_id,
+        this.broken_update,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          setTimeout(done, 200)
+        }
+      )
+    })
+
+    it('should not update the doc', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) return done(error)
+          doc.lines.should.deep.equal(this.lines)
+          done()
+        }
+      )
+    })
+
+    it('should send a message with an error', function () {
+      this.messageCallback.called.should.equal(true)
+      const [channel, message] = this.messageCallback.args[0]
+      channel.should.equal('applied-ops')
+      JSON.parse(message).should.deep.include({
+        project_id: this.project_id,
+        doc_id: this.doc_id,
+        error:
+          "The operation's base length must be equal to the string's length.",
+      })
+    })
+  })
+
+  describe('when mixing ot types (sharejs-text-ot -> history-ot)', function () {
+    beforeEach(function (done) {
+      MockWebApi.insertDoc(this.project_id, this.doc_id, {
+        lines: this.lines,
+        version: this.version,
+        otMigrationStage: 0,
+      })
+
+      DocUpdaterClient.subscribeToAppliedOps(
+        (this.messageCallback = sinon.stub())
+      )
+
+      DocUpdaterClient.sendUpdate(
+        this.project_id,
+        this.doc_id,
+        this.historyV1OTUpdate,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          setTimeout(done, 200)
+        }
+      )
+    })
+
+    it('should not update the doc', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) return done(error)
+          doc.lines.should.deep.equal(this.lines)
+          done()
+        }
+      )
+    })
+
+    it('should send a message with an error', function () {
+      this.messageCallback.called.should.equal(true)
+      const [channel, message] = this.messageCallback.args[0]
+      channel.should.equal('applied-ops')
+      JSON.parse(message).should.deep.include({
+        project_id: this.project_id,
+        doc_id: this.doc_id,
+        error: 'ot type mismatch',
+      })
+    })
+  })
+
+  describe('when mixing ot types (history-ot -> sharejs-text-ot)', function () {
+    beforeEach(function (done) {
+      MockWebApi.insertDoc(this.project_id, this.doc_id, {
+        lines: this.lines,
+        version: this.version,
+        otMigrationStage: 1,
+      })
+
+      DocUpdaterClient.subscribeToAppliedOps(
+        (this.messageCallback = sinon.stub())
+      )
+
+      DocUpdaterClient.sendUpdate(
+        this.project_id,
+        this.doc_id,
+        this.update,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          setTimeout(done, 200)
+        }
+      )
+    })
+
+    it('should not update the doc', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) return done(error)
+          doc.lines.should.deep.equal(this.lines)
+          done()
+        }
+      )
+    })
+
+    it('should send a message with an error', function () {
+      this.messageCallback.called.should.equal(true)
+      const [channel, message] = this.messageCallback.args[0]
+      channel.should.equal('applied-ops')
+      JSON.parse(message).should.deep.include({
+        project_id: this.project_id,
+        doc_id: this.doc_id,
+        error: 'ot type mismatch',
+      })
+    })
+  })
+
   describe('when there is no version in Mongo', function () {
     beforeEach(function (done) {
       MockWebApi.insertDoc(this.project_id, this.doc_id, {
@@ -716,6 +1182,84 @@ describe('Applying updates to a doc', function () {
     })
   })
 
+  describe('when sending duplicate ops (history-ot)', function () {
+    beforeEach(function (done) {
+      MockWebApi.insertDoc(this.project_id, this.doc_id, {
+        lines: this.lines,
+        version: this.version,
+        otMigrationStage: 1,
+      })
+
+      DocUpdaterClient.subscribeToAppliedOps(
+        (this.messageCallback = sinon.stub())
+      )
+
+      // One user delete 'one', the next turns it into 'once'. The second becomes a NOP.
+      DocUpdaterClient.sendUpdate(
+        this.project_id,
+        this.doc_id,
+        {
+          doc: this.doc_id,
+          op: [{ textOperation: [4, 'one and a half\n', 9] }],
+          v: this.version,
+          meta: {
+            source: 'ikHceq3yfAdQYzBo4-xZ',
+          },
+        },
+        error => {
+          if (error != null) {
+            throw error
+          }
+          setTimeout(() => {
+            DocUpdaterClient.sendUpdate(
+              this.project_id,
+              this.doc_id,
+              {
+                doc: this.doc_id,
+                op: [
+                  {
+                    textOperation: [4, 'one and a half\n', 9],
+                  },
+                ],
+                v: this.version,
+                dupIfSource: ['ikHceq3yfAdQYzBo4-xZ'],
+                meta: {
+                  source: 'ikHceq3yfAdQYzBo4-xZ',
+                },
+              },
+              error => {
+                if (error != null) {
+                  throw error
+                }
+                setTimeout(done, 200)
+              }
+            )
+          }, 200)
+        }
+      )
+    })
+
+    it('should update the doc', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) return done(error)
+          doc.lines.should.deep.equal(this.result)
+          done()
+        }
+      )
+    })
+
+    it('should return a message about duplicate ops', function () {
+      this.messageCallback.calledTwice.should.equal(true)
+      this.messageCallback.args[0][0].should.equal('applied-ops')
+      expect(JSON.parse(this.messageCallback.args[0][1]).op.dup).to.be.undefined
+      this.messageCallback.args[1][0].should.equal('applied-ops')
+      expect(JSON.parse(this.messageCallback.args[1][1]).op.dup).to.equal(true)
+    })
+  })
+
   describe('when sending updates for a non-existing doc id', function () {
     beforeEach(function (done) {
       this.non_existing = {

services/document-updater/test/acceptance/js/GettingADocumentTests.js

@@ -13,11 +13,6 @@ const { expect } = require('chai')
 const MockWebApi = require('./helpers/MockWebApi')
 const DocUpdaterClient = require('./helpers/DocUpdaterClient')
 const DocUpdaterApp = require('./helpers/DocUpdaterApp')
-const Settings = require('@overleaf/settings')
-const docUpdaterRedis = require('@overleaf/redis-wrapper').createClient(
-  Settings.redis.documentupdater
-)
-const Keys = Settings.redis.documentupdater.key_schema
 
 describe('Getting a document', function () {
   before(function (done) {
@@ -114,59 +109,6 @@ describe('Getting a document', function () {
     })
   })
 
-  describe('when the document is migrated (history-ot)', function () {
-    before(function (done) {
-      ;[this.project_id, this.doc_id] = Array.from([
-        DocUpdaterClient.randomId(),
-        DocUpdaterClient.randomId(),
-      ])
-
-      MockWebApi.insertDoc(this.project_id, this.doc_id, {
-        lines: this.lines,
-        version: this.version,
-      })
-      DocUpdaterClient.preloadDoc(this.project_id, this.doc_id, error => {
-        if (error != null) {
-          throw error
-        }
-        sinon.spy(MockWebApi, 'getDocument')
-        docUpdaterRedis.set(
-          Keys.docLines({ doc_id: this.doc_id }),
-          JSON.stringify({ content: this.lines.join('\n') }),
-          err => {
-            if (err) return done(err)
-
-            DocUpdaterClient.getDoc(
-              this.project_id,
-              this.doc_id,
-              (error, res, body) => {
-                if (error) return done(error)
-                this.res = res
-                this.body = body
-                done()
-              }
-            )
-          }
-        )
-      })
-    })
-
-    after(function () {
-      MockWebApi.getDocument.restore()
-    })
-
-    it('should not load the document from the web API', function () {
-      MockWebApi.getDocument.called.should.equal(false)
-    })
-
-    it('should return an error', function () {
-      expect(this.res.statusCode).to.equal(422)
-      expect(this.body).to.equal(
-        'refusing to process doc that was migrated to history-ot'
-      )
-    })
-  })
-
   describe('when the request asks for some recent ops', function () {
     before(function (done) {
       ;[this.project_id, this.doc_id] = Array.from([

services/document-updater/test/acceptance/js/SettingADocumentTests.js

@@ -196,6 +196,167 @@ describe('Setting a document', function () {
     })
   })
 
+  describe('when the updated doc exists in the doc updater (history-ot)', function () {
+    before(function (done) {
+      numberOfReceivedUpdates = 0
+      this.project_id = DocUpdaterClient.randomId()
+      this.doc_id = DocUpdaterClient.randomId()
+      this.historyV1OTUpdate = {
+        doc: this.doc_id,
+        op: [{ textOperation: [4, 'one and a half\n', 9] }],
+        v: this.version,
+        meta: { source: 'random-publicId' },
+      }
+      MockWebApi.insertDoc(this.project_id, this.doc_id, {
+        lines: this.lines,
+        version: this.version,
+        otMigrationStage: 1,
+      })
+      DocUpdaterClient.preloadDoc(this.project_id, this.doc_id, error => {
+        if (error) {
+          throw error
+        }
+        DocUpdaterClient.sendUpdate(
+          this.project_id,
+          this.doc_id,
+          this.historyV1OTUpdate,
+          error => {
+            if (error) {
+              throw error
+            }
+            setTimeout(() => {
+              DocUpdaterClient.setDocLines(
+                this.project_id,
+                this.doc_id,
+                this.newLines,
+                this.source,
+                this.user_id,
+                false,
+                (error, res, body) => {
+                  if (error) {
+                    return done(error)
+                  }
+                  this.statusCode = res.statusCode
+                  this.body = body
+                  done()
+                }
+              )
+            }, 200)
+          }
+        )
+      })
+    })
+
+    after(function () {
+      MockProjectHistoryApi.flushProject.resetHistory()
+      MockWebApi.setDocument.resetHistory()
+    })
+
+    it('should return a 200 status code', function () {
+      this.statusCode.should.equal(200)
+    })
+
+    it('should emit two updates (from sendUpdate and setDocLines)', function () {
+      expect(numberOfReceivedUpdates).to.equal(2)
+    })
+
+    it('should send the updated doc lines and version to the web api', function () {
+      MockWebApi.setDocument
+        .calledWith(this.project_id, this.doc_id, this.newLines)
+        .should.equal(true)
+    })
+
+    it('should update the lines in the doc updater', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) {
+            return done(error)
+          }
+          doc.lines.should.deep.equal(this.newLines)
+          done()
+        }
+      )
+    })
+
+    it('should bump the version in the doc updater', function (done) {
+      DocUpdaterClient.getDoc(
+        this.project_id,
+        this.doc_id,
+        (error, res, doc) => {
+          if (error) {
+            return done(error)
+          }
+          doc.version.should.equal(this.version + 2)
+          done()
+        }
+      )
+    })
+
+    it('should leave the document in redis', function (done) {
+      docUpdaterRedis.get(
+        Keys.docLines({ doc_id: this.doc_id }),
+        (error, lines) => {
+          if (error) {
+            throw error
+          }
+          expect(JSON.parse(lines)).to.deep.equal({
+            content: this.newLines.join('\n'),
+          })
+          done()
+        }
+      )
+    })
+
+    it('should return the mongo rev in the json response', function () {
+      this.body.should.deep.equal({ rev: '123' })
+    })
+
+    describe('when doc has the same contents', function () {
+      beforeEach(function (done) {
+        numberOfReceivedUpdates = 0
+        DocUpdaterClient.setDocLines(
+          this.project_id,
+          this.doc_id,
+          this.newLines,
+          this.source,
+          this.user_id,
+          false,
+          (error, res, body) => {
+            if (error) {
+              return done(error)
+            }
+            this.statusCode = res.statusCode
+            this.body = body
+            done()
+          }
+        )
+      })
+
+      it('should not bump the version in doc updater', function (done) {
+        DocUpdaterClient.getDoc(
+          this.project_id,
+          this.doc_id,
+          (error, res, doc) => {
+            if (error) {
+              return done(error)
+            }
+            doc.version.should.equal(this.version + 2)
+            done()
+          }
+        )
+      })
+
+      it('should not emit any updates', function (done) {
+        setTimeout(() => {
+          expect(numberOfReceivedUpdates).to.equal(0)
+          done()
+        }, 100) // delay by 100ms: make sure we do not check too early!
+      })
+    })
+  })
+
   describe('when the updated doc does not exist in the doc updater', function () {
     before(function (done) {
       this.project_id = DocUpdaterClient.randomId()

services/document-updater/test/setup.js

@@ -31,6 +31,7 @@ SandboxedModule.configure({
   requires: {
     '@overleaf/logger': stubs.logger,
     'mongodb-legacy': require('mongodb-legacy'), // for ObjectId comparisons
+    'overleaf-editor-core': require('overleaf-editor-core'), // does not play nice with sandbox
   },
   globals: { Buffer, JSON, Math, console, process },
   sourceTransformers: {

services/document-updater/test/unit/js/DocumentManager/DocumentManagerTests.js

@@ -49,6 +49,9 @@ describe('DocumentManager', function () {
         applyUpdate: sinon.stub().resolves(),
       },
     }
+    this.HistoryV1OTUpdateManager = {
+      applyUpdate: sinon.stub().resolves(),
+    }
     this.RangesManager = {
       acceptChanges: sinon.stub(),
       deleteComment: sinon.stub(),
@@ -66,6 +69,7 @@ describe('DocumentManager', function () {
         './Metrics': this.Metrics,
         './DiffCodec': this.DiffCodec,
         './UpdateManager': this.UpdateManager,
+        './HistoryV1OTUpdateManager': this.HistoryV1OTUpdateManager,
         './RangesManager': this.RangesManager,
         './Errors': Errors,
         '@overleaf/settings': this.Settings,
@@ -222,6 +226,7 @@ describe('DocumentManager', function () {
           ranges: this.ranges,
           pathname: this.pathname,
           projectHistoryId: this.projectHistoryId,
+          type: 'sharejs-text-ot',
         })
         this.RedisManager.promises.getPreviousDocOps.resolves(this.ops)
         this.result = await this.DocumentManager.promises.getDocAndRecentOps(
@@ -251,6 +256,7 @@ describe('DocumentManager', function () {
           ranges: this.ranges,
           pathname: this.pathname,
           projectHistoryId: this.projectHistoryId,
+          type: 'sharejs-text-ot',
         })
       })
     })
@@ -263,6 +269,7 @@ describe('DocumentManager', function () {
           ranges: this.ranges,
           pathname: this.pathname,
           projectHistoryId: this.projectHistoryId,
+          type: 'sharejs-text-ot',
         })
         this.RedisManager.promises.getPreviousDocOps.resolves(this.ops)
         this.result = await this.DocumentManager.promises.getDocAndRecentOps(
@@ -290,6 +297,7 @@ describe('DocumentManager', function () {
           ranges: this.ranges,
           pathname: this.pathname,
           projectHistoryId: this.projectHistoryId,
+          type: 'sharejs-text-ot',
         })
       })
     })
@@ -333,6 +341,7 @@ describe('DocumentManager', function () {
           unflushedTime: this.unflushedTime,
           alreadyLoaded: true,
           historyRangesSupport: this.historyRangesSupport,
+          type: 'sharejs-text-ot',
         })
       })
     })
@@ -400,6 +409,7 @@ describe('DocumentManager', function () {
           unflushedTime: null,
           alreadyLoaded: false,
           historyRangesSupport: this.historyRangesSupport,
+          type: 'sharejs-text-ot',
         })
       })
     })

services/document-updater/test/unit/js/HttpController/HttpControllerTests.js

@@ -26,6 +26,7 @@ describe('HttpController', function () {
     this.Metrics.Timer.prototype.done = sinon.stub()
 
     this.project_id = 'project-id-123'
+    this.projectHistoryId = '123'
     this.doc_id = 'doc-id-123'
     this.source = 'editor'
     this.next = sinon.stub()
@@ -65,7 +66,9 @@ describe('HttpController', function () {
             this.version,
             [],
             this.ranges,
-            this.pathname
+            this.pathname,
+            this.projectHistoryId,
+            'sharejs-text-ot'
           )
         this.HttpController.getDoc(this.req, this.res, this.next)
       })
@@ -77,17 +80,16 @@ describe('HttpController', function () {
       })
 
       it('should return the doc as JSON', function () {
-        this.res.json
-          .calledWith({
-            id: this.doc_id,
-            lines: this.lines,
-            version: this.version,
-            ops: [],
-            ranges: this.ranges,
-            pathname: this.pathname,
-            ttlInS: 42,
-          })
-          .should.equal(true)
+        this.res.json.should.have.been.calledWith({
+          id: this.doc_id,
+          lines: this.lines,
+          version: this.version,
+          ops: [],
+          ranges: this.ranges,
+          pathname: this.pathname,
+          ttlInS: 42,
+          type: 'sharejs-text-ot',
+        })
       })
 
       it('should log the request', function () {
@@ -115,7 +117,9 @@ describe('HttpController', function () {
             this.version,
             this.ops,
             this.ranges,
-            this.pathname
+            this.pathname,
+            this.projectHistoryId,
+            'sharejs-text-ot'
           )
         this.req.query = { fromVersion: `${this.fromVersion}` }
         this.HttpController.getDoc(this.req, this.res, this.next)
@@ -128,17 +132,16 @@ describe('HttpController', function () {
       })
 
       it('should return the doc as JSON', function () {
-        this.res.json
-          .calledWith({
-            id: this.doc_id,
-            lines: this.lines,
-            version: this.version,
-            ops: this.ops,
-            ranges: this.ranges,
-            pathname: this.pathname,
-            ttlInS: 42,
-          })
-          .should.equal(true)
+        this.res.json.should.have.been.calledWith({
+          id: this.doc_id,
+          lines: this.lines,
+          version: this.version,
+          ops: this.ops,
+          ranges: this.ranges,
+          pathname: this.pathname,
+          ttlInS: 42,
+          type: 'sharejs-text-ot',
+        })
       })
 
       it('should log the request', function () {

services/document-updater/test/unit/js/UpdateManager/UpdateManagerTests.js

@@ -331,6 +331,7 @@ describe('UpdateManager', function () {
         pathname: this.pathname,
         projectHistoryId: this.projectHistoryId,
         historyRangesSupport: false,
+        type: 'sharejs-text-ot',
       })
       this.RangesManager.applyUpdate.returns({
         newRanges: this.updated_ranges,
@@ -502,6 +503,7 @@ describe('UpdateManager', function () {
           pathname: this.pathname,
           projectHistoryId: this.projectHistoryId,
           historyRangesSupport: true,
+          type: 'sharejs-text-ot',
         })
         await this.UpdateManager.promises.applyUpdate(
           this.project_id,

services/project-history/app/js/UpdateCompressor.js

@@ -2,6 +2,7 @@
 
 import OError from '@overleaf/o-error'
 import DMP from 'diff-match-patch'
+import { EditOperationBuilder } from 'overleaf-editor-core'
 
 /**
  * @import { DeleteOp, InsertOp, Op, Update } from './types'
@@ -230,6 +231,15 @@ function _concatTwoUpdates(firstUpdate, secondUpdate) {
     return [firstUpdate, secondUpdate]
   }
 
+  const firstUpdateIsHistoryV1OT = EditOperationBuilder.isValid(firstUpdate.op)
+  const secondUpdateIsHistoryV1OT = EditOperationBuilder.isValid(
+    secondUpdate.op
+  )
+  if (firstUpdateIsHistoryV1OT !== secondUpdateIsHistoryV1OT) {
+    // cannot merge mix of sharejs-text-op and history-ot, should not happen.
+    return [firstUpdate, secondUpdate]
+  }
+
   if (
     firstUpdate.doc !== secondUpdate.doc ||
     firstUpdate.pathname !== secondUpdate.pathname
@@ -276,6 +286,15 @@ function _concatTwoUpdates(firstUpdate, secondUpdate) {
     return [firstUpdate, secondUpdate]
   }
 
+  if (firstUpdateIsHistoryV1OT && secondUpdateIsHistoryV1OT) {
+    const op1 = EditOperationBuilder.fromJSON(firstUpdate.op)
+    const op2 = EditOperationBuilder.fromJSON(secondUpdate.op)
+    if (!op1.canBeComposedWith(op2)) return [firstUpdate, secondUpdate]
+    return [
+      mergeUpdatesWithOp(firstUpdate, secondUpdate, op1.compose(op2).toJSON()),
+    ]
+  }
+
   if (
     firstUpdate.op.trackedDeleteRejection ||
     secondUpdate.op.trackedDeleteRejection
@@ -440,8 +459,7 @@ export function diffAsShareJsOps(before, after) {
   const ops = []
   let position = 0
   for (const diff of diffs) {
-    const type = diff[0]
-    const content = diff[1]
+    const [type, content] = diff
     if (type === ADDED) {
       ops.push({
         i: content,

services/project-history/app/js/UpdateTranslator.js

@@ -7,7 +7,7 @@ import * as OperationsCompressor from './OperationsCompressor.js'
 import { isInsert, isRetain, isDelete, isComment } from './Utils.js'
 
 /**
- * @import { AddDocUpdate, AddFileUpdate, DeleteCommentUpdate, Op, RawScanOp } from './types'
+ * @import { AddDocUpdate, AddFileUpdate, DeleteCommentUpdate, HistoryV1OTEditOperationUpdate, Op, RawScanOp } from './types'
  * @import { RenameUpdate, TextUpdate, TrackingDirective, TrackingProps } from './types'
  * @import { SetCommentStateUpdate, SetFileMetadataOperation, Update, UpdateWithBlob } from './types'
  */
@@ -60,6 +60,16 @@ function _convertToChange(projectId, updateWithBlob) {
     }
     operations = [op]
     projectVersion = update.version
+  } else if (isHistoryOTEditOperationUpdate(update)) {
+    let { pathname } = update.meta
+    pathname = _convertPathname(pathname)
+    if (update.v != null) {
+      v2DocVersions[update.doc] = { pathname, v: update.v }
+    }
+    operations = update.op.map(op => {
+      // Turn EditOperation into EditFileOperation by adding the pathname field.
+      return { pathname, ...op }
+    })
   } else if (isTextUpdate(update)) {
     const docLength = update.meta.history_doc_length ?? update.meta.doc_length
     let pathname = update.meta.pathname
@@ -194,6 +204,22 @@ export function isTextUpdate(update) {
   )
 }
 
+/**
+ * @param {Update} update
+ * @returns {update is HistoryV1OTEditOperationUpdate}
+ */
+export function isHistoryOTEditOperationUpdate(update) {
+  return (
+    'doc' in update &&
+    update.doc != null &&
+    'op' in update &&
+    update.op != null &&
+    'pathname' in update.meta &&
+    update.meta.pathname != null &&
+    Core.EditOperationBuilder.isValid(update.op[0])
+  )
+}
+
 export function isProjectStructureUpdate(update) {
   return isAddUpdate(update) || _isRenameUpdate(update)
 }

services/project-history/app/js/types.ts

@@ -1,5 +1,9 @@
 import { HistoryRanges } from '../../../document-updater/app/js/types'
-import { LinkedFileData, RawOrigin } from 'overleaf-editor-core/lib/types'
+import {
+  LinkedFileData,
+  RawEditOperation,
+  RawOrigin,
+} from 'overleaf-editor-core/lib/types'
 
 export type Update =
   | TextUpdate
@@ -40,6 +44,15 @@ export type TextUpdate = {
   }
 }
 
+export type HistoryV1OTEditOperationUpdate = {
+  doc: string
+  op: RawEditOperation[]
+  v: number
+  meta: UpdateMeta & {
+    pathname: string
+  }
+}
+
 export type SetCommentStateUpdate = {
   pathname: string
   commentId: string

services/real-time/app/js/ConnectedUsersManager.js

@@ -29,6 +29,10 @@ function recordProjectNotEmptySinceMetric(res, status) {
 }
 
 module.exports = {
+  countConnectedClients(projectId, callback) {
+    rclient.scard(Keys.clientsInProject({ project_id: projectId }), callback)
+  },
+
   // Use the same method for when a user connects, and when a user sends a cursor
   // update. This way we don't care if the connected_user key has expired when
   // we receive a cursor update.

services/real-time/app/js/DocumentUpdaterManager.js

@@ -19,7 +19,7 @@ const Keys = settings.redis.documentupdater.key_schema
 const DocumentUpdaterManager = {
   getDocument(projectId, docId, fromVersion, callback) {
     const timer = new metrics.Timer('get-document')
-    const url = `${settings.apis.documentupdater.url}/project/${projectId}/doc/${docId}?fromVersion=${fromVersion}`
+    const url = `${settings.apis.documentupdater.url}/project/${projectId}/doc/${docId}?fromVersion=${fromVersion}&historyV1OTSupport=true`
     logger.debug(
       { projectId, docId, fromVersion },
       'getting doc from document updater'
@@ -48,7 +48,8 @@ const DocumentUpdaterManager = {
           body.version,
           body.ranges,
           body.ops,
-          body.ttlInS
+          body.ttlInS,
+          body.type
         )
       } else if (res.statusCode === 422 && body?.firstVersionInRedis) {
         callback(new ClientRequestedMissingOpsError(422, body))

services/real-time/app/js/HttpApiController.js

@@ -1,8 +1,23 @@
 const WebsocketLoadBalancer = require('./WebsocketLoadBalancer')
 const DrainManager = require('./DrainManager')
+const ConnectedUsersManager = require('./ConnectedUsersManager')
 const logger = require('@overleaf/logger')
 
 module.exports = {
+  countConnectedClients(req, res) {
+    const { projectId } = req.params
+    ConnectedUsersManager.countConnectedClients(
+      projectId,
+      (err, nConnectedClients) => {
+        if (err) {
+          logger.err({ err, projectId }, 'count connected clients failed')
+          return res.sendStatus(500)
+        }
+        res.json({ nConnectedClients })
+      }
+    )
+  },
+
   sendMessage(req, res) {
     logger.debug({ message: req.params.message }, 'sending message')
     if (Array.isArray(req.body)) {

services/real-time/app/js/Router.js

@@ -113,6 +113,10 @@ module.exports = Router = {
       bodyParser.json({ limit: '5mb' }),
       HttpApiController.sendMessage
     )
+    app.get(
+      '/project/:projectId/count-connected-clients',
+      HttpApiController.countConnectedClients
+    )
 
     app.post('/drain', HttpApiController.startDrain)
     app.post(

services/real-time/app/js/WebsocketController.js

@@ -8,6 +8,7 @@ const ConnectedUsersManager = require('./ConnectedUsersManager')
 const WebsocketLoadBalancer = require('./WebsocketLoadBalancer')
 const RoomManager = require('./RoomManager')
 const {
+  CodedError,
   JoinLeaveEpochMismatchError,
   NotAuthorizedError,
   NotJoinedError,
@@ -283,7 +284,7 @@ module.exports = WebsocketController = {
             projectId,
             docId,
             fromVersion,
-            function (error, lines, version, ranges, ops, ttlInS) {
+            function (error, lines, version, ranges, ops, ttlInS, type) {
               if (error) {
                 if (error instanceof ClientRequestedMissingOpsError) {
                   emitJoinDocCatchUpMetrics('missing', error.info)
@@ -307,36 +308,53 @@ module.exports = WebsocketController = {
               // See http://ecmanaut.blogspot.co.uk/2006/07/encoding-decoding-utf8-in-javascript.html
               const encodeForWebsockets = text =>
                 unescape(encodeURIComponent(text))
-              const escapedLines = []
-              for (let line of lines) {
-                try {
-                  line = encodeForWebsockets(line)
-                } catch (err) {
-                  OError.tag(err, 'error encoding line uri component', { line })
-                  return callback(err)
+              metrics.inc('client_supports_history_v1_ot', 1, {
+                status: options.supportsHistoryV1OT ? 'success' : 'failure',
+              })
+              let escapedLines
+              if (type === 'history-ot') {
+                if (!options.supportsHistoryV1OT) {
+                  RoomManager.leaveDoc(client, docId)
+                  // TODO(24596): ask the user to reload the editor page (via out-of-sync modal when there are pending ops).
+                  return callback(
+                    new CodedError('client does not support history-ot')
+                  )
                 }
-                escapedLines.push(line)
-              }
-              if (options.encodeRanges) {
-                try {
-                  for (const comment of (ranges && ranges.comments) || []) {
-                    if (comment.op.c) {
-                      comment.op.c = encodeForWebsockets(comment.op.c)
-                    }
+                escapedLines = lines
+              } else {
+                escapedLines = []
+                for (let line of lines) {
+                  try {
+                    line = encodeForWebsockets(line)
+                  } catch (err) {
+                    OError.tag(err, 'error encoding line uri component', {
+                      line,
+                    })
+                    return callback(err)
                   }
-                  for (const change of (ranges && ranges.changes) || []) {
-                    if (change.op.i) {
-                      change.op.i = encodeForWebsockets(change.op.i)
+                  escapedLines.push(line)
+                }
+                if (options.encodeRanges) {
+                  try {
+                    for (const comment of (ranges && ranges.comments) || []) {
+                      if (comment.op.c) {
+                        comment.op.c = encodeForWebsockets(comment.op.c)
+                      }
                     }
-                    if (change.op.d) {
-                      change.op.d = encodeForWebsockets(change.op.d)
+                    for (const change of (ranges && ranges.changes) || []) {
+                      if (change.op.i) {
+                        change.op.i = encodeForWebsockets(change.op.i)
+                      }
+                      if (change.op.d) {
+                        change.op.d = encodeForWebsockets(change.op.d)
+                      }
                     }
+                  } catch (err) {
+                    OError.tag(err, 'error encoding range uri component', {
+                      ranges,
+                    })
+                    return callback(err)
                   }
-                } catch (err) {
-                  OError.tag(err, 'error encoding range uri component', {
-                    ranges,
-                  })
-                  return callback(err)
                 }
               }
 
@@ -351,7 +369,7 @@ module.exports = WebsocketController = {
                 },
                 'client joined doc'
               )
-              callback(null, escapedLines, version, ops, ranges)
+              callback(null, escapedLines, version, ops, ranges, type)
             }
           )
         })

services/real-time/test/acceptance/js/ClientTrackingTests.js

@@ -19,6 +19,80 @@ const FixturesManager = require('./helpers/FixturesManager')
 const async = require('async')
 
 describe('clientTracking', function () {
+  describe('when another logged in user joins a project', function () {
+    before(function (done) {
+      return async.series(
+        [
+          cb => {
+            return FixturesManager.setUpProject(
+              {
+                privilegeLevel: 'owner',
+                project: { name: 'Test Project' },
+              },
+              (error, { user_id: userId, project_id: projectId }) => {
+                if (error) return done(error)
+                this.user_id = userId
+                this.project_id = projectId
+                return cb()
+              }
+            )
+          },
+
+          cb => {
+            return FixturesManager.setUpDoc(
+              this.project_id,
+              { lines: this.lines, version: this.version, ops: this.ops },
+              (e, { doc_id: docId }) => {
+                this.doc_id = docId
+                return cb(e)
+              }
+            )
+          },
+
+          cb => {
+            this.clientA = RealTimeClient.connect(this.project_id, cb)
+          },
+
+          cb => {
+            RealTimeClient.countConnectedClients(
+              this.project_id,
+              (err, body) => {
+                if (err) return cb(err)
+                expect(body).to.deep.equal({ nConnectedClients: 1 })
+                cb()
+              }
+            )
+          },
+
+          cb => {
+            this.clientB = RealTimeClient.connect(this.project_id, cb)
+          },
+        ],
+        done
+      )
+    })
+
+    it('should record the initial state in getConnectedUsers', function (done) {
+      this.clientA.emit('clientTracking.getConnectedUsers', (error, users) => {
+        if (error) return done(error)
+        for (const user of Array.from(users)) {
+          if (user.client_id === this.clientB.publicId) {
+            expect(user.cursorData).to.not.exist
+            return done()
+          }
+        }
+        throw new Error('other user was never found')
+      })
+    })
+    it('should list both clients via HTTP', function (done) {
+      RealTimeClient.countConnectedClients(this.project_id, (err, body) => {
+        if (err) return done(err)
+        expect(body).to.deep.equal({ nConnectedClients: 2 })
+        done()
+      })
+    })
+  })
+
   describe('when a client updates its cursor location', function () {
     before(function (done) {
       return async.series(

services/real-time/test/acceptance/js/JoinDocTests.js

@@ -89,6 +89,7 @@ describe('joinDoc', function () {
         this.version,
         this.ops,
         this.ranges,
+        'sharejs-text-ot',
       ])
     })
 
@@ -168,6 +169,7 @@ describe('joinDoc', function () {
         this.version,
         this.ops,
         this.ranges,
+        'sharejs-text-ot',
       ])
     })
 
@@ -247,6 +249,7 @@ describe('joinDoc', function () {
         this.version,
         this.ops,
         this.ranges,
+        'sharejs-text-ot',
       ])
     })
 
@@ -408,6 +411,7 @@ describe('joinDoc', function () {
         this.version,
         this.ops,
         this.ranges,
+        'sharejs-text-ot',
       ])
     })
 
@@ -489,6 +493,7 @@ describe('joinDoc', function () {
         this.version,
         this.ops,
         this.ranges,
+        'sharejs-text-ot',
       ])
     })
 
@@ -504,7 +509,7 @@ describe('joinDoc', function () {
     })
   })
 
-  return describe('with fromVersion and options', function () {
+  describe('with fromVersion and options', function () {
     before(function (done) {
       this.fromVersion = 36
       this.options = { encodeRanges: true }
@@ -572,6 +577,7 @@ describe('joinDoc', function () {
         this.version,
         this.ops,
         this.ranges,
+        'sharejs-text-ot',
       ])
     })
 
@@ -586,4 +592,139 @@ describe('joinDoc', function () {
       )
     })
   })
+
+  describe('with type=history-ot', function () {
+    before(function (done) {
+      async.series(
+        [
+          cb => {
+            FixturesManager.setUpProject(
+              { privilegeLevel: 'owner' },
+              (e, { project_id: projectId, user_id: userId }) => {
+                this.project_id = projectId
+                this.user_id = userId
+                cb(e)
+              }
+            )
+          },
+
+          cb => {
+            FixturesManager.setUpDoc(
+              this.project_id,
+              {
+                lines: this.lines,
+                version: this.version,
+                ops: this.ops,
+                ranges: this.ranges,
+                type: 'history-ot',
+              },
+              (e, { doc_id: docId }) => {
+                this.doc_id = docId
+                cb(e)
+              }
+            )
+          },
+        ],
+        done
+      )
+    })
+
+    describe('when support is indicated', function () {
+      before(function (done) {
+        MockDocUpdaterServer.getDocument.resetHistory()
+        async.series(
+          [
+            cb => {
+              this.client = RealTimeClient.connect(this.project_id, cb)
+            },
+            cb =>
+              this.client.emit(
+                'joinDoc',
+                this.doc_id,
+                { supportsHistoryV1OT: true },
+                (error, ...rest) => {
+                  ;[...this.returnedArgs] = Array.from(rest)
+                  cb(error)
+                }
+              ),
+          ],
+          done
+        )
+      })
+
+      it('should get the doc from the doc updater', function () {
+        MockDocUpdaterServer.getDocument
+          .calledWith(this.project_id, this.doc_id, -1)
+          .should.equal(true)
+      })
+
+      it('should return the doc lines, version, ranges and ops', function () {
+        this.returnedArgs.should.deep.equal([
+          this.lines,
+          this.version,
+          this.ops,
+          this.ranges,
+          'history-ot',
+        ])
+      })
+
+      it('should have joined the doc room', function (done) {
+        RealTimeClient.getConnectedClient(
+          this.client.socket.sessionid,
+          (error, client) => {
+            if (error) return done(error)
+            expect(client.rooms).to.deep.equal([this.project_id, this.doc_id])
+            done()
+          }
+        )
+      })
+    })
+
+    describe('when support is not indicated', function () {
+      before(function (done) {
+        MockDocUpdaterServer.getDocument.resetHistory()
+        async.series(
+          [
+            cb => {
+              this.client = RealTimeClient.connect(this.project_id, cb)
+            },
+            cb =>
+              this.client.emit('joinDoc', this.doc_id, (error, ...rest) => {
+                this.error = error
+                ;[...this.returnedArgs] = Array.from(rest)
+                cb()
+              }),
+          ],
+          done
+        )
+      })
+
+      it('should get the doc from the doc updater', function () {
+        MockDocUpdaterServer.getDocument
+          .calledWith(this.project_id, this.doc_id, -1)
+          .should.equal(true)
+      })
+
+      it('should return an error', function () {
+        expect(this.error).to.deep.equal({
+          message: 'client does not support history-ot',
+        })
+      })
+
+      it('should not return the doc lines, version, ranges and ops', function () {
+        this.returnedArgs.should.deep.equal([])
+      })
+
+      it('should leave the doc room again', function (done) {
+        RealTimeClient.getConnectedClient(
+          this.client.socket.sessionid,
+          (error, client) => {
+            if (error) return done(error)
+            expect(client.rooms).to.deep.equal([this.project_id])
+            done()
+          }
+        )
+      })
+    })
+  })
 })

services/real-time/test/acceptance/js/helpers/FixturesManager.js

@@ -108,13 +108,17 @@ module.exports = FixturesManager = {
     if (!options.ops) {
       options.ops = ['mock', 'ops']
     }
-    const { doc_id: docId, lines, version, ops, ranges } = options
+    if (!options.type) {
+      options.type = 'sharejs-text-ot'
+    }
+    const { doc_id: docId, lines, version, ops, ranges, type } = options
 
     MockDocUpdaterServer.createMockDoc(projectId, docId, {
       lines,
       version,
       ops,
       ranges,
+      type,
     })
     return MockDocUpdaterServer.run(error => {
       if (error != null) {

services/real-time/test/acceptance/js/helpers/RealTimeClient.js

@@ -123,6 +123,16 @@ module.exports = Client = {
     )
   },
 
+  countConnectedClients(projectId, callback) {
+    request.get(
+      {
+        url: `http://127.0.0.1:3026/project/${projectId}/count-connected-clients`,
+        json: true,
+      },
+      (error, response, data) => callback(error, data)
+    )
+  },
+
   getConnectedClient(clientId, callback) {
     if (callback == null) {
       callback = function () {}

services/real-time/test/unit/js/DocumentUpdaterManagerTests.js

@@ -79,7 +79,7 @@ describe('DocumentUpdaterManager', function () {
       })
 
       it('should get the document from the document updater', function () {
-        const url = `${this.settings.apis.documentupdater.url}/project/${this.project_id}/doc/${this.doc_id}?fromVersion=${this.fromVersion}`
+        const url = `${this.settings.apis.documentupdater.url}/project/${this.project_id}/doc/${this.doc_id}?fromVersion=${this.fromVersion}&historyV1OTSupport=true`
         return this.request.get.calledWith(url).should.equal(true)
       })
 

services/web/app/src/Features/Documents/DocumentController.mjs

@@ -52,6 +52,11 @@ async function getDocument(req, res) {
       'overleaf.history.rangesSupportEnabled',
       false
     )
+    const otMigrationStage = _.get(
+      project,
+      'overleaf.history.otMigrationStage',
+      0
+    )
 
     // all projects are now migrated to Full Project History, keeping the field
     // for API compatibility
@@ -65,6 +70,7 @@ async function getDocument(req, res) {
       projectHistoryId,
       projectHistoryType,
       historyRangesSupport,
+      otMigrationStage,
       resolvedCommentIds,
     })
   }

services/web/app/src/Features/Errors/Errors.js

@@ -300,6 +300,18 @@ class NonDeletableEntityError extends OError {
   }
 }
 
+class FoundConnectedClientsError extends OError {
+  constructor(nConnectedClients) {
+    super(`found ${nConnectedClients} remaining connected clients`)
+  }
+}
+
+class ConcurrentLoadingOfDocsDetectedError extends OError {
+  constructor() {
+    super('concurrent loading of docs detected')
+  }
+}
+
 module.exports = {
   OError,
   BackwardCompatibleError,
@@ -356,4 +368,6 @@ module.exports = {
   InvalidEmailError,
   InvalidInstitutionalEmailError,
   NonDeletableEntityError,
+  FoundConnectedClientsError,
+  ConcurrentLoadingOfDocsDetectedError,
 }

services/web/app/src/Features/History/HistoryOTMigration.mjs

@@ -0,0 +1,56 @@
+import ProjectGetter from '../Project/ProjectGetter.js'
+import DocumentUpdaterHandler from '../DocumentUpdater/DocumentUpdaterHandler.js'
+import HistoryManager from '../History/HistoryManager.js'
+import * as RealTimeHandler from '../References/RealTime/RealTimeHandler.mjs'
+import ProjectOptionsHandler from '../Project/ProjectOptionsHandler.js'
+import {
+  NotFoundError,
+  FoundConnectedClientsError,
+  ConcurrentLoadingOfDocsDetectedError,
+} from '../Errors/Errors.js'
+
+async function ensureNoConnectedClients(projectId) {
+  const n = await RealTimeHandler.countConnectedClients(projectId)
+  if (n > 0) throw new FoundConnectedClientsError(n)
+}
+
+/**
+ * @param {string} projectId
+ * @param {number} nextStage
+ * @return {Promise<{otMigrationStage: number}>}
+ */
+export async function advanceOTMigrationStage(projectId, nextStage) {
+  const project = await ProjectGetter.promises.getProject(projectId, {
+    overleaf: true,
+  })
+  if (!project) throw new NotFoundError()
+  const { otMigrationStage } = project?.overleaf?.history || {}
+  if (otMigrationStage >= nextStage) return { otMigrationStage }
+
+  // NOTE: For the single connected client case, we could emit a pub/sub event here asking any (inactive) client without pending edits to disconnect briefly.
+  // e.g. EditorRealTimeController.emitToRoom(projectId, 'attempt-history-ot-migration')
+
+  // Ensure we can perform the hard migration
+  await ensureNoConnectedClients(projectId)
+
+  // Flush ahead of migrating to keep the time under lock down.
+  await DocumentUpdaterHandler.promises.flushProjectToMongoAndDelete(projectId)
+  // Avoid mixing update types
+  await HistoryManager.promises.flushProject(projectId)
+
+  // Obtain lock
+  if (!(await DocumentUpdaterHandler.promises.blockProject(projectId))) {
+    throw new ConcurrentLoadingOfDocsDetectedError()
+  }
+
+  try {
+    // Perform the mongo update and tell caller about the latest stage.
+    return await ProjectOptionsHandler.promises.setOTMigrationStage(
+      projectId,
+      nextStage
+    )
+  } finally {
+    // Unlock again (The lock will expire after 30s otherwise)
+    await DocumentUpdaterHandler.promises.unblockProject(projectId)
+  }
+}

services/web/app/src/Features/Project/ProjectOptionsHandler.js

@@ -2,6 +2,8 @@ const { Project } = require('../../models/Project')
 const settings = require('@overleaf/settings')
 const { callbackify } = require('util')
 const { db, ObjectId } = require('../../infrastructure/mongodb')
+const Errors = require('../Errors/Errors')
+const { ReturnDocument } = require('mongodb-legacy')
 const safeCompilers = ['xelatex', 'pdflatex', 'latex', 'lualatex']
 
 const ProjectOptionsHandler = {
@@ -73,6 +75,21 @@ const ProjectOptionsHandler = {
     // because rangesSupportEnabled is not part of the schema?
     return db.projects.updateOne(conditions, update)
   },
+
+  async setOTMigrationStage(projectId, nextStage) {
+    const project = await db.projects.findOneAndUpdate(
+      { _id: new ObjectId(projectId) },
+      // Use $max to ensure that we never downgrade the migration stage.
+      { $max: { 'overleaf.history.otMigrationStage': nextStage } },
+      {
+        returnDocument: ReturnDocument.AFTER,
+        projection: { 'overleaf.history.otMigrationStage': 1 },
+      }
+    )
+    if (!project) throw new Errors.NotFoundError('project does not exist')
+    const { otMigrationStage } = project.overleaf.history
+    return { otMigrationStage }
+  },
 }
 
 module.exports = {

services/web/app/src/Features/References/RealTime/RealTimeHandler.mjs

@@ -0,0 +1,9 @@
+import Settings from '@overleaf/settings'
+import { fetchJson } from '@overleaf/fetch-utils'
+
+export async function countConnectedClients(projectId) {
+  const url = new URL(Settings.apis.realTime.url)
+  url.pathname = `/project/${projectId}/count-connected-clients`
+  const { nConnectedClients } = await fetchJson(url)
+  return nConnectedClients
+}

services/web/app/src/models/Project.js

@@ -99,6 +99,7 @@ const ProjectSchema = new Schema(
         allowDowngrade: { type: Boolean },
         zipFileArchivedInProject: { type: Boolean },
         rangesSupportEnabled: { type: Boolean },
+        otMigrationStage: { type: Number },
       },
     },
     collabratecUsers: [

services/web/frontend/js/features/ide-react/editor/document-container.ts

@@ -2,7 +2,7 @@
 // Migrated from services/web/frontend/js/ide/editor/Document.js
 
 import RangesTracker from '@overleaf/ranges-tracker'
-import { ShareJsDoc } from './share-js-doc'
+import { OTType, ShareJsDoc } from './share-js-doc'
 import { debugConsole } from '@/utils/debugging'
 import { Socket } from '@/features/ide-react/connection/types/socket'
 import { IdeEventEmitter } from '@/features/ide-react/create-ide-event-emitter'
@@ -28,6 +28,7 @@ import {
 } from '@/features/ide-react/editor/types/document'
 import { ThreadId } from '../../../../../types/review-panel/review-panel'
 import getMeta from '@/utils/meta'
+import OError from '@overleaf/o-error'
 
 const MAX_PENDING_OP_SIZE = 64
 
@@ -447,16 +448,36 @@ export class DocumentContainer extends EventEmitter {
         'joinDoc',
         this.doc_id,
         this.doc.getVersion(),
-        { encodeRanges: true, age: this.doc.getTimeSinceLastServerActivity() },
-        (error, docLines, version, updates, ranges) => {
+        {
+          encodeRanges: true,
+          age: this.doc.getTimeSinceLastServerActivity(),
+          supportsHistoryV1OT: true,
+        },
+        (
+          error,
+          docLines,
+          version,
+          updates,
+          ranges,
+          type = 'sharejs-text-ot'
+        ) => {
           if (error) {
             callback?.(error)
             return
           }
           this.joined = true
           this.doc?.catchUp(updates)
-          this.decodeRanges(ranges)
-          this.catchUpRanges(ranges?.changes, ranges?.comments)
+          if (this.doc?.getType() !== type) {
+            // TODO(24596): page reload after checking for pending ops?
+            throw new OError('ot type mismatch', {
+              got: type,
+              want: this.doc?.getType(),
+            })
+          }
+          if (type === 'sharejs-text-ot') {
+            this.decodeRanges(ranges)
+            this.catchUpRanges(ranges?.changes, ranges?.comments)
+          }
           callback?.()
         }
       )
@@ -464,8 +485,18 @@ export class DocumentContainer extends EventEmitter {
       this.socket.emit(
         'joinDoc',
         this.doc_id,
-        { encodeRanges: true },
-        (error, docLines, version, updates, ranges) => {
+        {
+          encodeRanges: true,
+          supportsHistoryV1OT: true,
+        },
+        (
+          error,
+          docLines,
+          version,
+          updates,
+          ranges,
+          type: OTType = 'sharejs-text-ot'
+        ) => {
           if (error) {
             callback?.(error)
             return
@@ -477,9 +508,12 @@ export class DocumentContainer extends EventEmitter {
             version,
             this.socket,
             this.globalEditorWatchdogManager,
-            this.ideEventEmitter
+            this.ideEventEmitter,
+            type
           )
-          this.decodeRanges(ranges)
+          if (type === 'sharejs-text-ot') {
+            this.decodeRanges(ranges)
+          }
           this.ranges = new RangesTracker(ranges?.changes, ranges?.comments)
           this.bindToShareJsDocEvents()
           callback?.()
@@ -580,7 +614,9 @@ export class DocumentContainer extends EventEmitter {
     this.doc.on(
       'change',
       (ops: AnyOperation[], oldSnapshot: any, msg: Message) => {
-        this.applyOpsToRanges(ops, msg)
+        if (this.getType() === 'sharejs-text-ot') {
+          this.applyOpsToRanges(ops, msg)
+        }
         if (docChangedTimeout) {
           window.clearTimeout(docChangedTimeout)
         }

services/web/frontend/js/features/ide-react/editor/share-js-doc.ts

@@ -2,7 +2,7 @@
 // Migrated from services/web/frontend/js/ide/editor/ShareJsDoc.js
 
 import EventEmitter from '../../../utils/EventEmitter'
-import { Doc } from '@/vendor/libs/sharejs'
+import sharejs, { Doc } from '@/vendor/libs/sharejs'
 import { Socket } from '@/features/ide-react/connection/types/socket'
 import { debugConsole } from '@/utils/debugging'
 import { decodeUtf8 } from '@/utils/decode-utf8'
@@ -12,11 +12,18 @@ import {
   Message,
   ShareJsConnectionState,
   ShareJsOperation,
+  ShareJsTextType,
   TrackChangesIdSeeds,
 } from '@/features/ide-react/editor/types/document'
 import { EditorFacade } from '@/features/source-editor/extensions/realtime'
 import { recordDocumentFirstChangeEvent } from '@/features/event-tracking/document-first-change-event'
 import getMeta from '@/utils/meta'
+import { HistoryOTType } from './share-js-history-ot-type'
+import { StringFileData } from 'overleaf-editor-core/index'
+import {
+  RawEditOperation,
+  StringFileRawData,
+} from 'overleaf-editor-core/lib/types'
 
 // All times below are in milliseconds
 const SINGLE_USER_FLUSH_DELAY = 2000
@@ -27,6 +34,7 @@ const FATAL_OP_TIMEOUT = 45000
 const RECENT_ACK_LIMIT = 2 * SINGLE_USER_FLUSH_DELAY
 
 type Update = Record<string, any>
+export type OTType = 'sharejs-text-ot' | 'history-ot'
 
 type Connection = {
   send: (update: Update) => void
@@ -35,7 +43,6 @@ type Connection = {
 }
 
 export class ShareJsDoc extends EventEmitter {
-  type: string
   track_changes = false
   track_changes_id_seeds: TrackChangesIdSeeds | null = null
   connection: Connection
@@ -57,12 +64,24 @@ export class ShareJsDoc extends EventEmitter {
     version: number,
     readonly socket: Socket,
     private readonly globalEditorWatchdogManager: EditorWatchdogManager,
-    private readonly eventEmitter: IdeEventEmitter
+    private readonly eventEmitter: IdeEventEmitter,
+    readonly type: OTType = 'sharejs-text-ot'
   ) {
     super()
-    this.type = 'text'
+    let sharejsType: ShareJsTextType = sharejs.types.text
     // Decode any binary bits of data
-    const snapshot = docLines.map(line => decodeUtf8(line)).join('\n')
+    let snapshot: string | StringFileData
+    if (this.type === 'history-ot') {
+      snapshot = StringFileData.fromRaw(
+        docLines as unknown as StringFileRawData
+      )
+      sharejsType = new HistoryOTType(snapshot) as ShareJsTextType<
+        StringFileData,
+        RawEditOperation[]
+      >
+    } else {
+      snapshot = docLines.map(line => decodeUtf8(line)).join('\n')
+    }
 
     this.connection = {
       send: (update: Update) => {
@@ -89,7 +108,7 @@ export class ShareJsDoc extends EventEmitter {
     }
 
     this._doc = new Doc(this.connection, this.doc_id, {
-      type: this.type,
+      type: sharejsType,
     })
     this._doc.setFlushDelay(SINGLE_USER_FLUSH_DELAY)
     this._doc.on('change', (...args: any[]) => {

services/web/frontend/js/features/ide-react/editor/share-js-history-ot-type.ts

@@ -0,0 +1,131 @@
+import EventEmitter from '@/utils/EventEmitter'
+import {
+  EditOperationBuilder,
+  InsertOp,
+  RemoveOp,
+  RetainOp,
+  StringFileData,
+  TextOperation,
+} from 'overleaf-editor-core'
+import { RawEditOperation } from 'overleaf-editor-core/lib/types'
+
+function loadTextOperation(raw: RawEditOperation): TextOperation {
+  const operation = EditOperationBuilder.fromJSON(raw)
+  if (!(operation instanceof TextOperation)) {
+    throw new Error(`operation not supported: ${operation.constructor.name}`)
+  }
+  return operation
+}
+
+export class HistoryOTType extends EventEmitter {
+  // stub interface, these are actually on the Doc
+  api: HistoryOTType
+  snapshot: StringFileData
+
+  constructor(snapshot: StringFileData) {
+    super()
+    this.api = this
+    this.snapshot = snapshot
+  }
+
+  transformX(raw1: RawEditOperation[], raw2: RawEditOperation[]) {
+    const [a, b] = TextOperation.transform(
+      loadTextOperation(raw1[0]),
+      loadTextOperation(raw2[0])
+    )
+    return [[a.toJSON()], [b.toJSON()]]
+  }
+
+  apply(snapshot: StringFileData, rawEditOperation: RawEditOperation[]) {
+    const operation = loadTextOperation(rawEditOperation[0])
+    const afterFile = StringFileData.fromRaw(snapshot.toRaw())
+    afterFile.edit(operation)
+    this.snapshot = afterFile
+    return afterFile
+  }
+
+  compose(op1: RawEditOperation[], op2: RawEditOperation[]) {
+    return [
+      loadTextOperation(op1[0]).compose(loadTextOperation(op2[0])).toJSON(),
+    ]
+  }
+
+  // Do not provide normalize, used by submitOp to fixup bad input.
+  // normalize(op: TextOperation) {}
+
+  // Do not provide invert, only needed for reverting a rejected update.
+  // We are displaying an out-of-sync modal when an op is rejected.
+  // invert(op: TextOperation) {}
+
+  // API
+  insert(pos: number, text: string, fromUndo: boolean) {
+    const old = this.getText()
+    const op = new TextOperation()
+    op.retain(pos)
+    op.insert(text)
+    op.retain(old.length - pos)
+    this.submitOp([op.toJSON()])
+  }
+
+  del(pos: number, length: number, fromUndo: boolean) {
+    const old = this.getText()
+    const op = new TextOperation()
+    op.retain(pos)
+    op.remove(length)
+    op.retain(old.length - pos - length)
+    this.submitOp([op.toJSON()])
+  }
+
+  getText() {
+    return this.snapshot.getContent({ filterTrackedDeletes: true })
+  }
+
+  getLength() {
+    return this.getText().length
+  }
+
+  _register() {
+    this.on(
+      'remoteop',
+      (rawEditOperation: RawEditOperation[], oldSnapshot: StringFileData) => {
+        const operation = loadTextOperation(rawEditOperation[0])
+        const str = oldSnapshot.getContent()
+        if (str.length !== operation.baseLength)
+          throw new TextOperation.ApplyError(
+            "The operation's base length must be equal to the string's length.",
+            operation,
+            str
+          )
+
+        let outputCursor = 0
+        let inputCursor = 0
+        for (const op of operation.ops) {
+          if (op instanceof RetainOp) {
+            inputCursor += op.length
+            outputCursor += op.length
+          } else if (op instanceof InsertOp) {
+            this.emit('insert', outputCursor, op.insertion, op.insertion.length)
+            outputCursor += op.insertion.length
+          } else if (op instanceof RemoveOp) {
+            this.emit(
+              'delete',
+              outputCursor,
+              str.slice(inputCursor, inputCursor + op.length)
+            )
+            inputCursor += op.length
+          }
+        }
+
+        if (inputCursor !== str.length)
+          throw new TextOperation.ApplyError(
+            "The operation didn't operate on the whole string.",
+            operation,
+            str
+          )
+      }
+    )
+  }
+
+  // stub-interface, provided by sharejs.Doc
+  submitOp(op: RawEditOperation[]) {}
+}

services/web/frontend/js/features/ide-react/editor/types/document.ts

@@ -1,3 +1,4 @@
+import { StringFileData } from 'overleaf-editor-core'
 import { AnyOperation } from '../../../../../../types/change'
 
 export type Version = number
@@ -8,6 +9,23 @@ export type ShareJsOperation = AnyOperation[]
 
 export type TrackChangesIdSeeds = { inflight: string; pending: string }
 
+export interface ShareJsTextType<Snapshot = any, Operation = any> {
+  transformX(op1: Operation, op2: Operation): Operation[]
+  apply(snapshot: Snapshot, op: Operation): Snapshot
+  compose(op1: Operation, op2: Operation): Operation
+
+  api: {
+    insert(pos: number, text: string, fromUndo: boolean): void
+    del(pos: number, length: number, fromUndo: boolean): void
+    getText(): string
+    getLength(): number
+    _register(): void
+  }
+
+  // stub-interface, provided by sharejs.Doc
+  submitOp(op: Operation): void
+}
+
 // TODO: check the properties of this type
 export type Message = {
   v: Version
@@ -16,5 +34,6 @@ export type Message = {
     type?: string
   }
   doc?: string
-  snapshot?: string
+  snapshot?: string | StringFileData
+  type?: ShareJsTextType
 }

services/web/test/unit/bootstrap.js

@@ -88,6 +88,7 @@ function getSandboxedModuleRequires() {
     'sshpk',
     'xml2js',
     'mongodb',
+    'mongodb-legacy',
   ]
   for (const modulePath of internalModules) {
     requires[Path.resolve(__dirname, modulePath)] = require(modulePath)

services/web/test/unit/src/Documents/DocumentControllerTests.mjs

@@ -126,6 +126,7 @@ describe('DocumentController', function () {
           projectHistoryType: 'project-history',
           resolvedCommentIds: ['comment2'],
           historyRangesSupport: false,
+          otMigrationStage: 0,
         })
       })
     })