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Blob Upload Protocol

Uploading a single blob is done in two parts:

  1. Optional: see if the server already has it with a HEAD request to its blob URL, or do a multi-stat request with a single blob. If the server has it, you’re done. Blobs are content-addressable and have no metadata or version, so if the server has it, it has the right version.

  2. PUT that blob to its blob URL (or do a multipart batch put of a single blob)

When uploading multiple blobs (the common case), the fastest option depends on whether or not you’re using a modern HTTP transport (e.g. SPDY). If your client and server don’t support SPDY, you want to use the batch stat and batch upload endpoints, which hopefully can die when the future finishes arriving.

If you have SPDY, uploading 100 blobs is just like uploading 100 single blobs, but all at once. Send all your 100 HEAD requests at once, wait 1 RTT for all 100 replies, and then send then the <= 100 PUT requests with the blobs that the server didn’t have.

If you DON’T have SPDY on both sides, you want to use the batch stat and batch upload endpoints, described below.

Preupload request:

see blob-stat

Batch upload request:

Things to note about the request:

Some of these requirements may be relaxed in the future.


Host: upload-server.example.com
Content-Type: multipart/form-data; boundary=randomboundaryXYZ

Content-Disposition: form-data; name="sha1-9b03f7aca1ac60d40b5e570c34f79a3e07c918e8"; filename="blob1"
Content-Type: application/octet-stream

(binary or text blob data)
Content-Disposition: form-data; name="sha1-deadbeefdeadbeefdeadbeefdeadbeefdeadbeef"; filename="blob2"
Content-Type: application/octet-stream

(binary or text blob data)

Response (status may be a 200 or a 303 to this data):

HTTP/1.1 200 OK
Content-Type: text/plain

   "received": [
      {"blobRef": "sha1-9b03f7aca1ac60d40b5e570c34f79a3e07c918e8",
       "size": 12312},
      {"blobRef": "sha1-deadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
       "size": 29384933}

Response keys:

received         required   Array of {"blobRef": BLOBREF, "size": INT_bytes}
                            for blobs that were successfully saved. Empty
                            list in the case nothing was received.
errorText        optional   String error message for protocol errors
                            not relating to a particular blob.
                            Mostly for debugging clients.

If connection drops during a POST to an upload URL, you should re-do a stat request to verify which objects were received by the server and which were not. Also, the URL you received from stat before might no longer work, so stat is required to a get a valid upload URL.

For information on resuming truncated uploads, read blob-upload-resume.

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