fix(downloads): Wait for download file stream to finalize before resolving and rendering inline attachments. Fixes T1210

Test Plan: No new tests, need to figure out how to prevent regression here.

Reviewers: evan

Reviewed By: evan

Maniphest Tasks: T1210

Differential Revision: https://phab.nylas.com/D1558

src/flux/nylas-api.coffee

@@ -112,11 +112,13 @@ class NylasAPI
     return console.log('Cannot make Nylas request without auth token.') unless @APIToken
     options.method ?= 'GET'
     options.url ?= "#{@APIRoot}#{options.path}" if options.path
-    options.body ?= {} unless options.formData
     options.json ?= true
     options.auth = {'user': @APIToken, 'pass': '', sendImmediately: true}
     options.error ?= @_defaultErrorCallback
 
+    unless options.method is 'GET' or options.formData
+      options.body ?= {}
+
     request options, (error, response, body) =>
       PriorityUICoordinator.settle.then =>
         Actions.didMakeAPIRequest({request: options, response: response})

src/flux/stores/file-download-store.coffee

@@ -37,19 +37,49 @@ class Download
       return reject(new Error("Must pass a fileID to download")) unless @fileId?
       return reject(new Error("Must have a target path to download")) unless @targetPath?
 
-      # Does the file already exist on disk? If so, just resolve immediately.
       fs.exists @targetPath, (exists) =>
+        # Does the file already exist on disk? If so, just resolve immediately.
         return resolve(@) if exists
+
+        stream = fs.createWriteStream(@targetPath)
+        finished = false
+        finishedAction = null
+
+        # We need to watch the request for `success` or `error`, but not fire
+        # a callback until the stream has ended. These helper functions ensure
+        # that resolve or reject is only fired once regardless of the order
+        # these two events (stream end and `success`) happen in.
+        streamEnded = ->
+          finished = true
+          if finishedAction
+            finishedAction(@)
+
+        onStreamEnded = (action) ->
+          if finished
+            action(@)
+          else
+            finishedAction = action
+
         @request = NylasAPI.makeRequest
+          json: false
           path: "/n/#{namespace}/files/#{@fileId}/download"
-          success: => resolve(@)
-          error: => reject(@)
+          success: =>
+            # At this point, the file stream has not finished writing to disk.
+            # Don't resolve yet, or the browser will load only part of the image.
+            onStreamEnded(resolve)
+          error: =>
+            onStreamEnded(reject)
 
         progress(@request, {throtte: 250})
         .on("progress", (progress) =>
           @percent = progress.percent
           @progressCallback()
-        ).pipe(fs.createWriteStream(@targetPath))
+        )
+        .on("end", =>
+          # Wait for the file stream to finish writing before we resolve or reject
+          stream.end(streamEnded)
+        )
+        .pipe(stream)
 
   abort: ->
     @request?.abort()

src/flux/tasks/file-upload-task.coffee

@@ -30,7 +30,6 @@ class FileUploadTask extends Task
         path: "/n/#{@_namespaceId()}/files"
         method: "POST"
         json: false
-        returnsModel: true
         formData: @_formData()
         error: reject
         success: (rawResponseString) =>