dcpl: lightweight DCP proxy


BUILDING

    git clone git@github.com:couchbaselabs/dcpl.git ~/dcpl-gopath/src/dcpl
    export GOPATH=~/dcpl-gopath
    cd $GOPATH/src/dcpl
    go get                  # fetch all dependencies
    go build                # produce binary

    $ ./dcpl --help
    Usage of ./dcpl:
      -address string
                interface and port to bind the server (default "localhost:12345")
      -batch-size int
                the maximum size of websockets frame (default 16384)
      -cluster-uri string
                URI of Couchbase cluster (default "couchbase://localhost/")
      -debug
                export pprof and expvars
      -filter-script string
                .ank script to filter values (bypass all event by default)
      -repl
                run REPL to test and debug .ank scripts


USAGE

    ./dcpl --cluster-uri="couchbase://127.0.0.1/" --batch-size=SIZE_IN_BYTES

where SIZE_IN_BYTES is the maximum size of websocket frame, which will be sent to the client.
The server will try to buffer the DCP messages together to optimize bandwidth.

During websocket connection initialization, it looks at two HTTP headers:

'Authorization': which should hold encoded basic authorization, where username will be used
as a bucket and password for its password.

'X-Partition-Range': can be one of:

* "1,2,3,4-10,11" etc., where each number partition (vbucket)

* "auto:N": where N is index of node in cluster. The dcpl will look into the
  cluster config, fetch all vbuckets for the server with this index, and select these
  vbuckets to listen.

The server by default registers two endpoints for different protocols: Websockets and HTTP.
The following commands do the same thing: fetch all documents from the unprotected bucket
'beer-sample':

    curl -v -N -u'beer-sample:' http://localhost:12345/ws/ \
               -H "Connection: Upgrade" \
               -H "Upgrade: websocket" \
               -H "Sec-Websocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
               -H "Sec-Websocket-Version: 13"

    curl -v -N -u'beer-sample:' -N http://localhost:12345/http/

The server also supports several modes in regard of stream boundaries through 'X-Direction'
header. It could accept three values:

* 'everything' -- start from the beginning, and listen forever (default)
* 'from_now'   -- start from current state, and listen forever
* 'till_now'   -- start from the beginning, and listen until current state

So if you want to dump through websocket all new breweries (in terms of one of the sample
buckets of Couchbase Server), you would need to start server like this:

    ./dcpl --filter-script examples/breweries.ank

and for client use this curl incantation:

    curl -v -N -u'beer-sample:' http://localhost:12345/ws/ \
               -H "Connection: Upgrade" \
               -H "Upgrade: websocket" \
               -H "Sec-Websocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
               -H "Sec-Websocket-Version: 13"
               -H "X-Direction: from_now"

after that try to create new brewery, for example with cbc:

    cbc create test -V '{"name":"Test","type":"brewery"}'


ANKO scripting

The server has embedded scripting language Anko (https://github.com/mattn/anko).
It used to supply user-defined algorithms. For example to filter incoming events.
To run interactive ANKO console, use switch --repl.