HTTP Link Walking

Link walking (traversal) finds and returns objects by following links attached to them, starting from the object specified by the bucket and key portion. It is a special case of MapReduce, and can be expressed more verbosely as such. Read more about Links.

Request

GET /riak/bucket/key/[bucket],[tag],[keep]            # Old format
GET /buckets/bucket/keys/key/[bucket],[tag],[keep]    # New format

Link filters

A link filter within the request URL is made of three parts, separated by commas:

Bucket - a bucket name to limit the links to
Tag - a “riaktag” to limit the links to
Keep - 0 or 1, whether to return results from this phase

Any of the three parts may be replaced with _ (underscore), signifying that any value is valid. Multiple phases of links can be followed by adding additional path segments to the URL, separating the link filters by slashes. The final phase in the link-walking query implicitly returns its results.

Response

Normal status codes:

200 OK

Typical error codes:

400 Bad Request - if the format of the query in the URL is invalid
404 Not Found - if the origin object of the walk was missing

Important headers:

Content-Type - always multipart/mixed, with a boundary specified

Understanding the response body

The response body will always be multipart/mixed, with each chunk representing a single phase of the link-walking query. Each phase will also be encoded in multipart/mixed, with each chunk representing a single object that was found. If no objects were found or “keep” was not set on the phase, no chunks will be present in that phase. Objects inside phase results will include Location headers that can be used to determine bucket and key. In fact, you can treat each object-chunk similarly to a complete response from fetching the object, without the status code.

Example

$ curl -v http://127.0.0.1:8098/riak/test/doc3/test,_,1/_,next,1
* About to connect() to 127.0.0.1 port 8098 (#0)
*   Trying 127.0.0.1... connected
* Connected to 127.0.0.1 (127.0.0.1) port 8098 (#0)
> GET /riak/test/doc3/test,_,1/_,next,1 HTTP/1.1
> User-Agent: curl/7.19.4 (universal-apple-darwin10.0) libcurl/7.19.4 OpenSSL/0.9.8l zlib/1.2.3
> Host: 127.0.0.1:8098
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: MochiWeb/1.1 WebMachine/1.9.0 (participate in the frantic)
< Expires: Wed, 10 Mar 2010 20:24:49 GMT
< Date: Fri, 30 Sep 2011 15:24:35 GMT
< Content-Type: multipart/mixed; boundary=JZi8W8pB0Z3nO3odw11GUB4LQCN
< Content-Length: 970
<

--JZi8W8pB0Z3nO3odw11GUB4LQCN
Content-Type: multipart/mixed; boundary=OjZ8Km9J5vbsmxtcn1p48J91cJP

--OjZ8Km9J5vbsmxtcn1p48J91cJP
X-Riak-Vclock: a85hYGDgymDKBVIszMk55zKYEhnzWBlKIniO8kGF2TyvHYIKf0cIszUnMTBzHYVKbIhEUl+VK4spDFTPxhHzFyqhEoVQz7wkSAGLMGuz6FSocFIUijE3pt7HlGBhnqejARXmq0QyZnnxE6jwVJBwFgA=
Location: /riak/test/doc
Content-Type: application/json
Link: </riak/test>; rel="up", </riak/test/doc2>; riaktag="next"
Etag: 3pvmY35coyWPxh8mh4uBQC
Last-Modified: Wed, 10 Mar 2010 20:14:13 GMT

{"riak":"CAP"}
--OjZ8Km9J5vbsmxtcn1p48J91cJP--

--JZi8W8pB0Z3nO3odw11GUB4LQCN
Content-Type: multipart/mixed; boundary=RJKFlAs9PrdBNfd74HANycvbA8C

--RJKFlAs9PrdBNfd74HANycvbA8C
X-Riak-Vclock: a85hYGBgzGDKBVIsbLvm1WYwJTLmsTLcjeE5ypcFAA==
Location: /riak/test/doc2
Content-Type: application/json
Link: </riak/test>; rel="up"
Etag: 6dQBm9oYA1mxRSH0e96l5W
Last-Modified: Wed, 10 Mar 2010 18:11:41 GMT

{"foo":"bar"}
--RJKFlAs9PrdBNfd74HANycvbA8C--

--JZi8W8pB0Z3nO3odw11GUB4LQCN--
* Connection #0 to host 127.0.0.1 left intact
* Closing connection #0