concurrent-couch-follower

a couch follower wrapper that you can use to be sure you don't miss any documents even if you process them asynchronously.

``js
var changes = require('concurrent-couch-follower')
var someAction = require(.....)

var dataHandler = function(data, done) {
someAction(data, function() {
done()
})
}

var configOptions = {
db: 'https://url.to.couchdb/registry/_changes',
include_docs:true,
sequence:'.sequence',
now:false,
concurrency:5
}

changes(dataHandler, configOptions)
`

API
---

$3

- handler = function(change,done)
is a function that is called for every document
- change, the change from couchdb {seq:sequence,doc:the document,....}
- done, you must call this function when you are done processing the document.

- options
a config object as passed to changes-stream but including these additional properties.
- db, the connection string url pointing to the CouchDB registry to be followed.
- sequence, the name of the file to persist the sequence id, if this is a function this is passed as a persist function to concurrent-seq-file.
- concurrency, the maximum number of documents to process at a time.
- the changes-stream property since is populated by the value of the sequence file and cannot be set from outside except if now is set to true.
- now, if true, set the changes-stream property since to "now" (instead of 0) on the first start (before .sequence has been created)
- since only used, but is required, if you are using a custom backend to save the sequence ids. when you pass a function as sequence.

- stream = changes(handle,options)
- sream , return value is a readable object stream of data passed back with done(err,data)

- stream.sequence()
- returns current sequence id saved to disk. useful for logging.

- WARNING! stream.end()
- this calls destroy on the changes-stream and the through instead of properly ending them.
- this triggers a "premature close" error from changes-stream and is something that just has to be worked on. bind error or use end-of-stream


more examples
-------------

save the sequence ids in a database.

`js
var changes = require('concurrent-couch-follower')
var someAction = require(.....)

var dataHandler = function(data, done) {
someAction(data, function() {
done()
})
}

loadSequenceFromDB(function(err,sequence){
var configOptions = {
db: 'https://url.to.couchdb/registry/_changes',
include_docs:true,
sequence:function(seq,cb){
saveInDB(seq,cb)
},
since:sequence,
concurrency:5
}

changes(dataHandler, configOptions)
})
``