mozilla-services/android-sync — comment on commit db2de0f8434be941663bbf5857bfbe7467200499
File: src/main/java/org/mozilla/gecko/sync/stage/SyncClientsEngineStage.java line 133
By rnewman:

Two problems here.

Firstly, the string you return should be acceptable to the server:

http://docs.services.mozilla.com/storage/apis-1.1.html#headers

That means — for API 1.1, at least — decimal seconds, not milliseconds.

(There's another bug that I just spotted elsewhere. Heh.)

Secondly, you need to handle whatever error will result if the X-Unmodified-Since header results in failure. Most likely you should loop, with a decrementing counter, fetching and processing commands until either a command causes an abort, or we get a clean reupload.