couchdb-global-changes

couchdb-global-changes

Does what it says on the tin: emit a db-change event for each document change in each db of a couchdb instance. Can also persist its progress (sequence id-wise) to a file or in the monitored databases.

Installation

npm install couchdb-global-changes

Simple usage

var couchdb_changes = require('couchdb-global-changes')
var feed = couchdb_changes('http://user:pass@127.0.0.1:5984')

feed.on('db-change', function(details) {
    console.log('document changed: %s / %s', details.db_name, details.change.id)
})
feed.on('error', function(err) {
    console.error('something is wrong:', err)
    process.exit()
})

Advanced usage

var couchdb_changes = require('couchdb-global-changes')
var twilio = require('twilio')('ACCOUNT_SID', 'AUTH_TOKEN')

var options = 
    {   couch: 'http://user:pass@127.0.0.1:5984'
    ,   include: '^userdb-'
    ,   persist: '_local'
    ,   namespace: 'sms-daemon'
    ,   include_docs: true
    }

var feed = couchdb_changes(options)

feed.on('db-change', function(details) {

    var doc = details.change.doc
    if(!doc.type == 'sms-message')
        return

    twilio.sendMessage(
            {   to: doc.recipient
            ,   from: doc.sender
            ,   body: doc.message
            }
        ,   function(err, responseData) {
                if (!err)
                    console.log('Successfully sent an sms from %s to %s', doc.sender, doc.recipient)
                else
                    console.error('Could not send sms from %s to %s:\n', doc.sender, doc.recipient, err)
        }
    )
})

feed.on('db-persist', function(details) {
    // after this, we can be sure the update sequence has been saved.
    // when this script is started again, it will pick up just where
    // it left off and not process any document a second time.
    console.log("%s processed all documents in the database %s (up to update-sequence %s)", feed.namespace, details.db_name, details.persist.seq)
})

Details

Options

• if options is a string, it is interpreted as the url to a couchdb instance

options.couch

• the root url of the couchdb instance
• defaults to http://127.0.0.1:5984

options.include

• if provided, will be evaluated as a regular expression
• each db's name must then match that regular expression

options.exclude

• if provided, will be evaluated as a regular expression
• each db's name must then not match that regular expression

options.since can be one of

• 'now' or an integer sequence id: all feeds will use this same value
• { db1: 'now', db2: 1234 }: provide a value for each db's name individually (good for managing resuming operations)
• defaults to 0 for every feed

options.include_docs can be one of

• true or false: all feeds will use this same value
• { db1: true, db2: false }: provide a value for each db's name individually
• defaults to false for every feed

options.persist can be

• a string containg the path to a JSON file, where the db's sequences can be stored and later retrieved
• '_local', which will persist the db's sequence ids to {db}/_local/couchdb-global-changes:{namespace}
• nothing else right now

options.persist_debounce

• to avoid hammering the filesystem or the db with write queries, the actual call to persist sequence ids is debounced by this amount of milliseconds
• defaults to 200

options.namespace (mandatory if options.persist is provided)

• this allows the persistence layer to save sequence ids individually for every script that invokes the couchdb-global-changes module.

Functions

• feed.total_dbs() returns the number of dbs that are being followed
• feed.caught_up_dbs() returns the number of dbs have emitted the catchup event

Events

progress | function(details)

• calculated global progress during the catchup-phase.
• details.progress goes from 0 to 1
• details.caught_up_dbs the number of caught up dbs
• details.total_dbs the number of dbs being followed

catchup | function()

• all followed dbs have caught up

db-catchup | function(details)

• the db details.db_name has caught up to sequence id details.seq (which is an alias to details.catchup)

db-progress | function(details)

• calculated progress of a single db during the catchup-phase.
• details.progress goes from 0 to 1
• details.db_name the name of the db

db-removed | function(details)

• the db details.db_name has been removed from the feed, probably due to deletion of the db

db-* | function(details)

• each of iriscouch's follow events is forwarded with a db- prefix
• the originating db's name is passed as details.db_name
• arguments are passed as details.<eventname>
• Example: the db-change event gets passed { db_name: 'foo', change: <change-obj> }

Tests

The tests are quite incomplete, as this still is a work in progress.

# *nix
export COUCH=http://admin:passw0rd@127.0.0.1:5984
# windows
set COUCH=http://admin:passw0rd@127.0.0.1:5984

# the tests will create a few dbs prefixed with 'cgc-tests-'
# these can be removed afterwards

cd node_modules/couchdb-global-changes
npm install
npm test

Changes

3.0.0

• removed caught_up_dbs and total_dbs info from the db-catchup event
• extended the progress event's parameter to an object with progress and caught_up_dbs and total_dbs

2.0.0

• renamed options.filter to options.include (and add accordingly options.exclude)
• added "_local" as an option to options.persist
• added options.namespace (needed for namespacing in the persistence layer)
• added event db-persist which gets emitted after the current sequence id has been persisted to disk/db.
• added options.persist_debounce
• added caught_up_dbs and total_dbs info to the db-catchup event's details
• (internal) persistence layers are now async