The /camli/preupload endpoint is used to begin uploading a blob.

A request to this endpoint will instruct the client where to actually upload the blob and what blobs are already present in the store.


Preupload request:

POST /camli/preupload HTTP/1.1
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

{
   "alreadyHave": [
      {"blobRef": "sha1-abcdabcdabcdabcdabcdabcdabcdabcdabcdabcd",
       "size": 12312}
   ],
   "maxUploadSize": 1048576,
   "uploadUrl": "http://upload-server.example.com/some/server-chosen/url",
   "uploadUrlExpirationSeconds": 7200,
}

Response keys:

   alreadyHave      required   Array of {"blobRef": BLOBREF, "size": INT_bytes}
                               for blobs that the system already has. Empty
                               list if no blobs are already present.
   maxUploadSize    required   Integer of max byte size for whole request
                               payload, which may be one or more blobs.
   uploadUrl        required   Next URL to use to upload any more blobs.
   uploadUrlExpirationSeconds
                    required   How long the upload URL will be valid for.


Upload request:

POST /some/server-chosen/url HTTP/1.1
Host: upload-server.example.com
Content-Type: multipart/form-data; boundary=randomboundaryXYZ

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

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

(binary blob data)
--randomboundaryXYZ--

Response (may be a 301/302/303 redirect to this data):

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

{
   "received": [
      {"blobRef": "sha1-9b03f7aca1ac60d40b5e570c34f79a3e07c918e8",
       "size": 12312},
      {"blobRef": "sha1-deadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
       "size": 29384933}
   ],
   "maxUploadSize": 1048576,
   "uploadUrl": "http://example.com/TheNextUploadUrlRandomString",
   "uploadUrlExpirationSeconds": 7200,
}

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.
   maxUploadSize    required   Integer of max byte size for whole request
                               payload, which may be one or more blobs.
   uploadUrl        required   Next URL to use to upload any more blobs.
   uploadUrlExpirationSeconds
                    required   How long the upload URL will be valid for.


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

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