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Debug Stream

Writable stream for debugging stream pipelines.

Installation

npm install @stdlib/streams-node-debug-sink

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var debugSinkStream = require( '@stdlib/streams-node-debug-sink' );

debugSinkStream( [options,] [clbk] )

Creates a writable stream for debugging stream pipelines.

var ENV = require( '@stdlib/process-env' );

// Set the `DEBUG` environment variable...
ENV.DEBUG = '*';

var stream = debugSinkStream({
    'name': 'my-stream'
});

stream.write( 'a' );
stream.write( 'b' );
stream.write( 'c' );
stream.end();

The function accepts the following options:

• name: debug namespace.
• objectMode: specifies whether a stream should operate in objectMode. Default: false.
• highWaterMark: specifies the Buffer level at which write() calls start returning false.
• decodeStrings: specifies whether to encode strings as Buffer objects before writing data to a returned stream. Default: true.
• defaultEncoding: default encoding when not explicitly specified when writing data. Default: 'utf8'.

To set stream options,

var opts = {
    'name': 'my-app',
    'objectMode': true,
    'highWaterMark': 64,
    'decodeStrings': false,
    'defaultEncoding': 'utf8'
};

var stream = debugSinkStream( opts );

By default, each chunk is logged as a JSON stringified string, along with the chunk index. For more control over logging behavior, provide a callback.

function logger( debug, chunk, idx ) {
    debug( 'Received a new chunk...' );
    debug( 'Beep: %s', chunk.beep );
    debug( 'Boop: %s', chunk.boop );
}

var opts = {
    'name': 'my-pipeline'
};

var stream = debugSinkStream( opts, logger );

debugSinkStream.factory( [options] )

Returns a function for creating streams which are identically configured according to provided options.

var opts = {
    'objectMode': true,
    'highWaterMark': 64
};

var factory = debugSinkStream.factory( opts );

This method accepts the same options as debugSinkStream(), except for name, which must be provided explicitly.

factory( name[, clbk] )

Creates a debug stream.

var factory = debugSinkStream.factory();

var streams = [];
var i;

// Assign each stream to a separate debug namespace...
for ( i = 0; i < 10; i++ ) {
    streams.push( factory( 'stream '+i ) );
}

debugSinkStream.objectMode( [options,] [clbk] )

This method is a convenience function to create streams which always operate in objectMode.

var stream = debugSinkStream.objectMode({
    'name': 'beep-boop'
});

stream.write({
    'value': 'a'
});
stream.write({
    'value': 'b'
});
stream.write({
    'value': 'c'
});
stream.end();

This method accepts the same options as debugSinkStream(); however, the method will always override the objectMode option in options.

Notes

• If the DEBUG environment variable is not set, no data is logged.
• Providing a name option is strongly encouraged, as the DEBUG environment variable can be used to filter debuggers.

Examples

var parseJSON = require( '@stdlib/utils-parse-json' );
var transformFactory = require( '@stdlib/streams-node-transform' ).factory;
var debug = require( '@stdlib/streams-node-debug-sink' ).objectMode;

function parse( chunk, enc, clbk ) {
    clbk( null, parseJSON( chunk ) );
}

function pluck( chunk, enc, clbk ) {
    clbk( null, chunk.value );
}

function square( chunk, enc, clbk ) {
    var v = +chunk;
    clbk( null, v*v );
}

function toStr( chunk, enc, clbk ) {
    clbk( null, chunk.toString() );
}

function join( chunk, enc, clbk ) {
    clbk( null, chunk+'\n' );
}

// Create a factory for generating streams running in `objectMode`:
var tStream = transformFactory({
    'objectMode': true
});

// Create streams for each transform:
var s1 = tStream( parse );
var s2 = tStream( pluck );
var s3 = tStream( square );
var s4 = tStream( toStr );
var s5 = tStream( join );

// Create a writable stream for debugging the result of the transformations:
var ds = debug({
    'name': 'debugger'
});

// Create the pipeline:
s1.pipe( s2 )
    .pipe( s3 )
    .pipe( s4 )
    .pipe( s5 )
    .pipe( ds );

// Write data to the pipeline...
var v;
var i;
for ( i = 0; i < 100; i++ ) {
    v = '{"value":'+i+'}';
    s1.write( v, 'utf8' );
}
s1.end();

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See Also

• @stdlib/streams-node/debug: transform stream for debugging stream pipelines.
• @stdlib/streams-node/inspect-sink: writable stream for inspecting streamed data.

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.