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Blob Stat Protocol

This document describes the “batch stat” API end-point, for checking the size/existence of multiple blobs when the client and/or server do not support SPDY or HTTP/2.0. See blob-upload for more background.

Notably: the HTTP method may be GET or POST. GET is more correct but be aware that HTTP servers and proxies start to suck around the 2k and 4k URL lengths. If you’re stat’ing more than ~37 blobs, using POST would be safest.

The HTTP request path is $blobRoot/camli/stat. See blob-upload and discovery for background.

In either case, the request form values: (either in the URL for GET or application/x-www-form-urlencoded body for POST)

camliversion    required   Version of Perkeep and/or stat protocol;
                           reserved for future use.  Must be "1" for now.

blob<n>         optional/  Must start at 1 and go up, no gaps allowed, not
                repeated   zero-padded, etc.  Value is a blobref, e.g
                           "sha1-9b03f7aca1ac60d40b5e570c34f79a3e07c918e8"
                           There's no defined limit on how many you include here,
                           but servers may return a 400 Bad Request if you ask
                           for too many.  All servers should support <= 1000
                           though.

maxwaitsec      optional   The client may send this, an integer max number
                           of seconds the client is willing to wait
                           for the arrival of blobs.  If the server
                           supports long-polling (an optional
                           feature), then the server will return
                           immediately if all the requested blobs
                           or available, or wait up until this
                           amount of time for the blobs to become
                           available.  The server's reply must
                           include "canLongPoll" set to true if the
                           server supports this feature.  Even if
                           the server supports long polling, the
                           server may cap 'maxwaitsec' and wait for
                           less time than requested by the client.

Examples

GET /some-blob-root/camli/stat?camliversion=1&blob1=sha1-9b03f7aca1ac60d40b5e570c34f79a3e07c918e8 HTTP/1.1
Host: example.com

-or-

POST /some-blob-root/camli/stat HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: example.com

camliversion=1&
blob1=sha1-9b03f7aca1ac60d40b5e570c34f79a3e07c918e8&
blob2=sha1-abcdabcdabcdabcdabcdabcdabcdabcdabcdabcd&
blob3=sha1-deadbeefdeadbeefdeadbeefdeadbeefdeadbeef

Response:

HTTP/1.1 200 OK
Content-Length: ...
Content-Type: text/javascript

{
   "stat": [
      {"blobRef": "sha1-abcdabcdabcdabcdabcdabcdabcdabcdabcdabcd",
       "size": 12312}
   ],
   "canLongPoll": true
}

Response keys:

stat             required   Array of {"blobRef": BLOBREF, "size": INT_bytes}
                            for blobs that the system already has. Empty
                            list if no blobs are already present.

canLongPoll      optional   Set to true (type boolean) if the server supports
                            long polling.  If not true, the server ignores
                            the client's "maxwaitsec" parameter.
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