The /camli/enumerate-blobs endpoint enumerates all blobs that the
server knows about.

They're returned in sorted order, sorted by (digest_type,
digest_value).  That is, md5-acbd18db4cc2f85cedef654fccc4a4d8 sorts
before sha1-0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33 because "m" sorts
before "s", even though "0" sorts before "a".

GET /camli/enumerate-blobs?after=&limit= HTTP/1.1
Host: example.com

URL GET parameters:

     after     optional    If provided, only blobs GREATER THAN this
                           value are returned.

                           Can't be used in combination with 'maxwaitsec'

     limit     optional    Limit the number of returned blobrefs.  The
                           server may have its own lower limit, however,
                           so be sure to pay attention to the presence
                           of a "continueAfter" key in the JSON response.

     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 any blobs or available, else
                           it will wait for this number of seconds.
                           It is an error to send this option with a non-
                           zero value along with the 'after' option.
                           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.

                           Can't be used in combination with 'after'.


Response:

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

{
  "blobs": [
    {"blobRef": "md5-acbd18db4cc2f85cedef654fccc4a4d8",
     "size": 3},
    {"blobRef": "sha1-0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33",
     "size": 3},
  ],
  "continueAfter": "sha1-0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33",
  "canLongPoll": true,
}

Response keys:

   blobs          required   Array of {"blobRef": BLOBREF, "size": INT_bytes}
                             will be an empty list if no blobs are present.

   continueAfter  optional   If present, the result is truncated and there are
                             are more blobs after the provided blobref, which
                             should be passed to the next request's "after"
                             request parameter.

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