stream-splicer

What is stream-splicer?

The stream-splicer npm package allows you to create a stream that can be dynamically spliced with other streams. This is particularly useful for building complex streaming pipelines where you need to insert, remove, or replace streams on the fly.

What are stream-splicer's main functionalities?

Dynamic Stream Splicing

This feature allows you to dynamically splice streams into a pipeline. In this example, a through stream is created that converts input to uppercase. The stream-splicer package is used to create a stream pipeline that can be dynamically modified.

const splicer = require('stream-splicer');
const through = require('through2');

const stream = splicer([
  through(function (chunk, enc, callback) {
    this.push(chunk.toString().toUpperCase());
    callback();
  })
]);

stream.write('hello');
stream.write('world');
stream.end();

stream.pipe(process.stdout);

Inserting Streams

This feature allows you to insert new streams into an existing pipeline. In this example, a new stream is inserted that reverses the input string.

const splicer = require('stream-splicer');
const through = require('through2');

const stream = splicer([
  through(function (chunk, enc, callback) {
    this.push(chunk.toString().toUpperCase());
    callback();
  })
]);

const newStream = through(function (chunk, enc, callback) {
  this.push(chunk.toString().split('').reverse().join(''));
  callback();
});

stream.splice(1, 0, newStream);

stream.write('hello');
stream.write('world');
stream.end();

stream.pipe(process.stdout);

Removing Streams

This feature allows you to remove streams from an existing pipeline. In this example, the second stream that reverses the input string is removed from the pipeline.

const splicer = require('stream-splicer');
const through = require('through2');

const stream = splicer([
  through(function (chunk, enc, callback) {
    this.push(chunk.toString().toUpperCase());
    callback();
  }),
  through(function (chunk, enc, callback) {
    this.push(chunk.toString().split('').reverse().join(''));
    callback();
  })
]);

stream.splice(1, 1);

stream.write('hello');
stream.write('world');
stream.end();

stream.pipe(process.stdout);

Other packages similar to stream-splicer

through2

The through2 package is a thin wrapper around Node.js streams.Transform. It simplifies the creation of transform streams. Unlike stream-splicer, through2 does not provide dynamic splicing capabilities but is often used in conjunction with other stream libraries to build pipelines.

multipipe

The multipipe package allows you to compose multiple streams into a single pipeline. It provides error handling and simplifies the process of connecting streams. However, it does not support dynamic splicing of streams like stream-splicer.

pumpify

The pumpify package combines multiple streams into a single duplex stream. It handles errors and ensures proper cleanup. While it is useful for creating complex pipelines, it does not offer the dynamic splicing capabilities of stream-splicer.

README

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('JSONStream');
var split = require('split');

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