use explicit json content-type to avoid security issues with text/html

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

@@ -79,7 +79,7 @@ module.exports = HttpController =
 		logger.log {project_id, doc_id, from, to}, "getting diff"
 		DiffManager.getDiff project_id, doc_id, from, to, (error, diff) ->
 			return next(error) if error?
-			res.send JSON.stringify(diff: diff)
+			res.json {diff: diff}
 
 	getUpdates: (req, res, next = (error) ->) ->
 		project_id = req.params.project_id
@@ -91,9 +91,10 @@ module.exports = HttpController =
 
 		UpdatesManager.getSummarizedProjectUpdates project_id, before: before, min_count: min_count, (error, updates, nextBeforeTimestamp) ->
 			return next(error) if error?
-			res.send JSON.stringify
+			res.json {
 				updates: updates
 				nextBeforeTimestamp: nextBeforeTimestamp
+			}
 
 	restore: (req, res, next = (error) ->) ->
 		{doc_id, project_id, version} = req.params

services/track-changes/test/unit/coffee/HttpController/HttpControllerTests.coffee

@@ -71,7 +71,7 @@ describe "HttpController", ->
 					from: @from.toString()
 					to: @to.toString()
 			@res =
-				send: sinon.stub()
+				json: sinon.stub()
 			@diff = [ u: "mock-diff" ]
 			@DiffManager.getDiff = sinon.stub().callsArgWith(4, null, @diff)
 			@HttpController.getDiff @req, @res, @next
@@ -82,7 +82,7 @@ describe "HttpController", ->
 				.should.equal true
 
 		it "should return the diff", ->
-			@res.send.calledWith(JSON.stringify(diff: @diff)).should.equal true
+			@res.json.calledWith({diff: @diff}).should.equal true
 
 	describe "getUpdates", ->
 		beforeEach ->
@@ -96,7 +96,7 @@ describe "HttpController", ->
 					before:    @before.toString()
 					min_count: @min_count.toString()
 			@res =
-				send: sinon.stub()
+				json: sinon.stub()
 			@updates = ["mock-summarized-updates"]
 			@UpdatesManager.getSummarizedProjectUpdates = sinon.stub().callsArgWith(2, null, @updates, @nextBeforeTimestamp)
 			@HttpController.getUpdates @req, @res, @next
@@ -107,7 +107,7 @@ describe "HttpController", ->
 				.should.equal true
 
 		it "should return the formatted updates", ->
-			@res.send.calledWith(JSON.stringify(updates: @updates, nextBeforeTimestamp: @nextBeforeTimestamp)).should.equal true
+			@res.json.calledWith({updates: @updates, nextBeforeTimestamp: @nextBeforeTimestamp}).should.equal true
 
 	describe "RestoreManager", ->
 		beforeEach ->