streaming

A few stream helpers, built for Node.js 0.10+ streams ("Streams2").

npm install streaming

streaming.Filter

new Filter(predicate) inherits stream.Readable

• _readableState.objectMode: true

streaming.json.Stringifier

new Stringifier(replacer, space) inherits streaming.Splitter

• objectMode: false
  • _writableState.objectMode: false
  • _readableState.objectMode: true

streaming.json.Parser

new Parser() inherits streaming.Splitter

• objectMode: true

streaming.Mapper

new Mapper(fn) inherits stream.Transform

• _writableState.objectMode: true
• _readableState.objectMode: true

streaming.Queue

new Queue(concurrency, worker) inherits streaming.Mapper

• _writableState.objectMode: true
• _readableState.objectMode: true

Example:

var streaming = require('streaming');

var lazy_worker = function(task, callback) {
  setTimeout(function() {
    var json = JSON.stringify(task);
    callback(null, json.length + ' after 1s\n');
  }, 1000);
};

process.stdin
.pipe(new streaming.Splitter())
.pipe(new streaming.Mapper(JSON.parse))
.pipe(new streaming.Queue(5, lazy_worker))
.pipe(process.stdout);

streaming.Splitter

What used to be streaming.Line and Rechunker have been folder into this more generic, more flexible class.

new Splitter(split, opts) inherits stream.Transform

streaming.Timeout

new Timeout(seconds, opts) inherits stream.Transform

streaming.Walk

new Walk(root) inherits stream.Readable

A streaming.Walk will emit data that are streaming.Walk.Node objects. A Node has two fields, .path, which is relative to the given root, and .stats, which is a fs.Stats object. node.toString() will return node.path.

It recurses the filesystem structure depth-first. If the given root is not a directory, it will only ever emit that file. Otherwise, if root is a directory, it will be emitted as a data point (just like all other directories under root as it comes to them). The directory entry itself will always immediately precede its children. The order of children is taken exactly as they produced by fs.readdir, which seems to be undefined or maybe by creation date (newest first).

fs.Stats has helper functions .isFile() and .isDirectory(), so we can print the paths only files (ignoring directories) like this:

var streaming = require('streaming');

var walk = new streaming.Walk('/usr/local');
walk.on('error', function(err) {
  console.error('error', err);
  if (err.code == 'EACCES') {
    // if the error is just "access denied", ignore both the error and the file.
    // call resume() to carry on as if nothing had happened
    walk.resume();
  }
  else {
    console.error('Critical error; not resuming.');
  }
});
walk.on('data', function(node) {
  // just skip over directories:
  if (node.stats.isFile()) {
    console.log(node.toString());
  }
});

stream.Transform(opts) results:

| opts. decodeStrings | opts. objectMode | _writableState. decodeStrings | _writableState. objectMode | _readableState. objectMode | |:----|:----|:----|:----|:----| | true | true | true | true | true | | false | true | false | true | true | | undefined | true | true | true | true | | true | false | true | false | false | | false | false | false | false | false | | undefined | false | true | false | false | | true | undefined | true | false | false | | false | undefined | false | false | false | | undefined | undefined | true | false | false |

(Only _writableState has a decodeStrings field.)

License

Copyright 2013-2015 Christopher Brown. MIT Licensed.