avoid compressing updates if the result would be too big

services/track-changes/app/coffee/UpdateCompressor.coffee

@@ -80,6 +80,7 @@ module.exports = UpdateCompressor =
 		return compressedUpdates
 
 	MAX_TIME_BETWEEN_UPDATES: oneMinute = 60 * 1000
+	MAX_UPDATE_SIZE: twoMegabytes = 2* 1024 * 1024
 
 	_concatTwoUpdates: (firstUpdate, secondUpdate) ->
 		firstUpdate =
@@ -105,8 +106,12 @@ module.exports = UpdateCompressor =
 
 		firstOp = firstUpdate.op
 		secondOp = secondUpdate.op
+
+		firstSize = firstOp.i?.length or firstOp.d?.length
+		secondSize = secondOp.i?.length or secondOp.d?.length
+
 		# Two inserts
-		if firstOp.i? and secondOp.i? and firstOp.p <= secondOp.p <= (firstOp.p + firstOp.i.length)
+		if firstOp.i? and secondOp.i? and firstOp.p <= secondOp.p <= (firstOp.p + firstOp.i.length) and firstSize + secondSize < UpdateCompressor.MAX_UPDATE_SIZE
 			return [
 				meta:
 					start_ts: firstUpdate.meta.start_ts
@@ -118,7 +123,7 @@ module.exports = UpdateCompressor =
 				v: secondUpdate.v
 			]
 		# Two deletes
-		else if firstOp.d? and secondOp.d? and secondOp.p <= firstOp.p <= (secondOp.p + secondOp.d.length)
+		else if firstOp.d? and secondOp.d? and secondOp.p <= firstOp.p <= (secondOp.p + secondOp.d.length) and firstSize + secondSize < UpdateCompressor.MAX_UPDATE_SIZE
 			return [
 				meta:
 					start_ts: firstUpdate.meta.start_ts

services/track-changes/test/unit/coffee/UpdateCompressor/UpdateCompressorTests.coffee

@@ -10,6 +10,8 @@ describe "UpdateCompressor", ->
 		@UpdateCompressor = SandboxedModule.require modulePath
 		@user_id = "user-id-1"
 		@other_user_id = "user-id-2"
+		@bigstring = ("a" for [0 .. 2*1024*1024]).join("")
+		@mediumstring = ("a" for [0 .. 1024*1024]).join("")
 		@ts1 = Date.now()
 		@ts2 = Date.now() + 1000
 
@@ -141,6 +143,67 @@ describe "UpdateCompressor", ->
 					v: 43
 				}]
 
+			it "should not append inserts that are too big (second op)", ->
+				expect(@UpdateCompressor.compressUpdates [{
+					op: { p: 3, i: "foo" }
+					meta: ts: @ts1, user_id: @user_id
+					v: 42
+				}, {
+					op: { p: 6, i: @bigstring }
+					meta: ts: @ts2, user_id: @user_id
+					v: 43
+				}])
+				.to.deep.equal [{
+					op: { p: 3, i: "foo" }
+					meta: start_ts: @ts1, end_ts: @ts1, user_id: @user_id
+					v: 42
+				}, {
+					op: { p: 6, i: @bigstring }
+					meta: start_ts: @ts2, end_ts: @ts2, user_id: @user_id
+					v: 43
+				}]
+
+			it "should not append inserts that are too big (first op)", ->
+				expect(@UpdateCompressor.compressUpdates [{
+					op: { p: 3, i: @bigstring }
+					meta: ts: @ts1, user_id: @user_id
+					v: 42
+				}, {
+					op: { p: 3 + @bigstring.length, i: "bar" }
+					meta: ts: @ts2, user_id: @user_id
+					v: 43
+				}])
+				.to.deep.equal [{
+					op: { p: 3, i: @bigstring }
+					meta: start_ts: @ts1, end_ts: @ts1, user_id: @user_id
+					v: 42
+				}, {
+					op: { p: 3 + @bigstring.length, i: "bar" }
+					meta: start_ts: @ts2, end_ts: @ts2, user_id: @user_id
+					v: 43
+				}]
+
+			it "should not append inserts that are too big (first and second op)", ->
+				expect(@UpdateCompressor.compressUpdates [{
+					op: { p: 3, i: @mediumstring }
+					meta: ts: @ts1, user_id: @user_id
+					v: 42
+				}, {
+					op: { p: 3 + @mediumstring.length, i: @mediumstring }
+					meta: ts: @ts2, user_id: @user_id
+					v: 43
+				}])
+				.to.deep.equal [{
+					op: { p: 3, i: @mediumstring }
+					meta: start_ts: @ts1, end_ts: @ts1, user_id: @user_id
+					v: 42
+				}, {
+					op: { p: 3 + @mediumstring.length, i: @mediumstring }
+					meta: start_ts: @ts2, end_ts: @ts2, user_id: @user_id
+					v: 43
+				}]
+
+
 		describe "delete - delete", ->
 			it "should append one delete to the other", ->
 				expect(@UpdateCompressor.compressUpdates [{