rebaseline_server: extend returned JSON dict to allow for result-editing in coming CL

gm/rebaseline_server/server.py

Index: gm/rebaseline_server/server.py
===================================================================
--- gm/rebaseline_server/server.py	(revision 11659)
+++ gm/rebaseline_server/server.py	(working copy)
@@ -79,6 +79,11 @@
     self._port = port
     self._export = export
 
+  def is_exported(self):
+    """ Returns true iff HTTP clients on other hosts are allowed to access
+    this server. """
+    return self._export
+
   def fetch_results(self):
     """ Create self.results, based on the expectations in
     self._expectations_dir and the latest actuals from skia-autogen.
@@ -150,8 +155,24 @@
     TODO(epoger): Unless we start making use of result_type, remove that
     parameter."""
     print 'do_GET_results: sending results of type "%s"' % result_type
+    # TODO(epoger): Cache response_dict rather than the results object, to save
+    # time on subsequent fetches (no need to regenerate the header, etc.)
     response_dict = _SERVER.results.GetAll()
     if response_dict:
+      response_dict["header"] = {
+        # Hash of testData, which the client must return with any edits--
+        # this ensures that the edits were made to a particular dataset.
+        "data-hash": str(hash(repr(response_dict["testData"]))),
+
+        # Whether the server will accept edits back.
+        # TODO(epoger): Not yet implemented, so hardcoding to False;
+        # once we implement the "browseonly" mode discussed in
+        # https://codereview.chromium.org/24274003/#msg6 , this value will vary.
+        "is-editable": False,
+
+        # Whether the service is accessible from other hosts.
+        "is-exported": _SERVER.is_exported(),
+      }
       self.send_json_dict(response_dict)
     else:
       self.send_error(404)