stream-splicer

streaming pipeline with a mutable configuration

This module is similar to stream-combiner, but with a pipeline configuration that can be changed at runtime.

example

This example begins with an HTTP header parser that waits for an empty line to signify the end of the header. At that point, it switches to a streaming json parser to operate on the HTTP body.

var splicer = require('stream-splicer');
var through = require('through2');
var jsonStream = require('jsonstream2');
var split = require('split2');
 
var headerData = {};
var headers = through.obj(function (buf, enc, next) {
    var line = buf.toString('utf8');
    if (line === '') {
        this.push(headerData);
        pipeline.splice(1, 1, jsonStream.parse([ 'rows', true ]));
    }
    else {
        var m = /^(\S+):(.+)/.exec(line);
        var key = m && m[1].trim();
        var value = m && m[2].trim();
        if (m) headerData[key] = value;
    }
    next();
});
var pipeline = splicer([ split(), headers, jsonStream.stringify() ]);
process.stdin.pipe(pipeline).pipe(process.stdout);

intput:

GET / HTTP/1.1
Host: substack.net
User-Agent: echo

{"rows":["beep","boop"]}

output:

$ echo -ne 'GET / HTTP/1.1\nHost: substack.net\nUser-Agent: echo\n\n{"rows":["beep","boop"]}\n' | node example/header.js
[
{"Host":"substack.net","User-Agent":"echo"}
,
"beep"
,
"boop"
]

methods

var splicer = require('stream-splicer')

var pipeline = splicer(streams, opts)

Create a pipeline duplex stream given an array of streams. Each stream will be piped to the next. Writes to pipeline get written to the first stream and data for reads from pipeline come from the last stream.

For example, for streams [ a, b, c, d ], this pipeline is constructed internally:

a.pipe(b).pipe(c).pipe(d)

Input will get written into a. Output will be read from d.

If any of the elements in streams are arrays, they will be converted into nested pipelines. This is useful if you want to expose a hookable pipeline with grouped insertion points.

var pipeline = splicer.obj(streams, opts)

Create a pipeline with opts.objectMode set to true for convenience.

var removed = pipeline.splice(index, howMany, stream, ...)

Splice the pipeline starting at index, removing howMany streams and replacing them with each additional stream argument provided.

The streams that were removed from the splice and returned.

pipeline.push(stream, ...)

Push one or more streams to the end of the pipeline.

var stream = pipeline.pop()

Pop a stream from the end of the pipeline.

pipeline.unshift(stream, ...)

Unshift one or more streams to the begining of the pipeline.

var stream = pipeline.shift()

Shift a stream from the begining of the pipeline.

var stream = pipeline.get(index, ...)

Return the stream at index index, .... Indexes can be negative.

Multiple indexes will traverse into nested pipelines.

attributes

pipeline.length

The number of streams in the pipeline

install

With npm do:

npm install stream-splicer

license

MIT