
Blob Support
************

Crate includes support to store binary large objects. By utilizing
Crate's cluster features the files can be replicated and sharded just
like regular data.

Any index can hold blobs if enabled. To enable blobs on an index the
"blobs.enabled" flag needs to be set to true like this:

   sh$ curl -sSX PUT 'localhost:9200/myblobs?pretty' -d '{
   ... "number_of_shards": 3,
   ... "number_of_replicas": 1,
   ... "blobs.enabled": true}'
   {
     "ok" : true,
     "acknowledged" : true
   }

Now crate is configured to allow blobs to be management under the
index's "_blobs" endpoint.


Uploading
=========

To upload a blob the sha1 hash of the blob has to be known upfront
since this has to be used as the id of the new blob. For this example
we use a fancy python one-liner to compute the shasum:

   sh$ python -c 'import hashlib;print(hashlib.sha1("contents".encode("utf-8")).hexdigest())'
   4a756ca07e9487f482465a99e8286abc86ba4dc7

The blob can now be uploaded by issuing a PUT request:

   sh$ curl -isSX PUT 'localhost:9200/myblobs/_blobs/4a756ca07e9487f482465a99e8286abc86ba4dc7' -d 'contents'
   HTTP/1.1 201 Created
   Content-Length: 0

If a blob already exists with the given hash a 409 Conflict is
returned:

   sh$ curl -isSX PUT 'localhost:9200/myblobs/_blobs/4a756ca07e9487f482465a99e8286abc86ba4dc7' -d 'contents'
   HTTP/1.1 409 Conflict
   Content-Length: 0


Download
========

To download a blob simply use a GET request:

   sh$ curl -sS 'localhost:9200/myblobs/_blobs/4a756ca07e9487f482465a99e8286abc86ba4dc7'
   contents

Note: Since the blobs are sharded throughout the cluster not every node
  has all the blobs. In case that the GET request has been sent to a
  node that doesn't contain the requested file it will respond with a
  307 Temporary Redirect which will lead to a node that does contain
  the file.

If the blob doesn't exist a 404 Not Found error is returned:

   sh$ curl -isS 'localhost:9200/myblobs/_blobs/e5fa44f2b31c1fb553b6021e7360d07d5d91ff5e'
   HTTP/1.1 404 Not Found
   Content-Length: 0

To determine if a blob exists without downloading it, a HEAD request
can be used:

   sh$ curl -sS -I 'localhost:9200/myblobs/_blobs/4a756ca07e9487f482465a99e8286abc86ba4dc7'
   HTTP/1.1 200 OK
   Content-Length: 8
   Accept-Ranges: bytes
   Expires: Thu, 31 Dec 2037 23:59:59 GMT
   Cache-Control: max-age=315360000

Note: The cache headers for blobs are static and basically allows clients
  to cache the response forever since the blob is immutable.


Delete
======

To delete a blob simply use a DELETE request:

   sh$ curl -isS -XDELETE 'localhost:9200/myblobs/_blobs/4a756ca07e9487f482465a99e8286abc86ba4dc7'
   HTTP/1.1 204 No Content
   Content-Length: 0

If the blob doesn't exist a 404 Not Found error is returned:

   sh$ curl -isS -XDELETE 'localhost:9200/myblobs/_blobs/4a756ca07e9487f482465a99e8286abc86ba4dc7'
   HTTP/1.1 404 Not Found
   Content-Length: 0
