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Inspect Stream

Transform stream for inspecting streamed data.

Installation

npm install @stdlib/streams-node-inspect

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 inspectStream = require( '@stdlib/streams-node-inspect' );

inspectStream( [options,] clbk )

Creates a transform stream for inspecting streamed data.

function log( chunk, idx ) {
    console.log( 'index: %d', idx );
    console.log( chunk );
}

var stream = inspectStream( log );

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

stream.end();
/* =>
'index: 0'
'a'
'index: 1'
'b'
'index: 2'
'c'
*/

The function accepts the following options:

• objectMode: specifies whether a stream should operate in objectMode. Default: false.
• highWaterMark: specifies the Buffer level at which write() calls start returning false.
• allowHalfOpen: specifies whether a stream should remain open even if one side ends. Default: false.
• readableObjectMode: specifies whether the readable side should be in objectMode. Default: false.

To set stream options,

function log( chunk, idx ) {
    console.log( 'index: %d', idx );
    console.log( chunk );
}

var opts = {
    'objectMode': true,
    'highWaterMark': 64,
    'allowHalfOpen': true,
    'readableObjectMode': false // overridden by `objectMode` option when `objectMode=true`
};

var stream = inspectStream( opts, log );

inspectStream.factory( [options] )

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

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

var factory = inspectStream.factory( opts );

This method accepts the same options as inspectStream().

factory( clbk )

Creates a transform stream for inspecting streamed data.

function log( chunk, idx ) {
    console.log( 'index: %d', idx );
    console.log( chunk );
}

var factory = inspectStream.factory();

// Create 10 identically configured streams...
var streams = [];
var i;
for ( i = 0; i < 10; i++ ) {
    streams.push( factory( log ) );
}

inspectStream.objectMode( [options,] clbk )

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

function log( chunk, idx ) {
    console.log( 'index: %d', idx );
    console.log( chunk );
}

var stream = inspectStream.objectMode( log );

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

stream.end();
/* =>
'index: 0'
{'value': 'a'}
'index: 1'
{'value': 'b'}
'index: 2'
{'value': 'c'}
*/

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

Examples

var parseJSON = require( '@stdlib/utils-parse-json' );
var stdout = require( '@stdlib/streams-node-stdout' );
var transformFactory = require( '@stdlib/streams-node-transform' ).factory;
var inspect = require( '@stdlib/streams-node-inspect' ).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' );
}

function logger( name ) {
    return log;

    function log( chunk, idx ) {
        console.log( 'name: %s', name );
        console.log( 'index: %d', idx );
        console.log( chunk );
    }
}

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

// Create streams for each transform:
var s1 = tStream( parse );
var i1 = inspect( logger( 'parse' ) );
var s2 = tStream( pluck );
var i2 = inspect( logger( 'pluck' ) );
var s3 = tStream( square );
var i3 = inspect( logger( 'square' ) );
var s4 = tStream( toStr );
var i4 = inspect( logger( 'toString' ) );
var s5 = tStream( join );
var i5 = inspect( logger( 'join' ) );

// Create the pipeline:
s1.pipe( i1 )
    .pipe( s2 )
    .pipe( i2 )
    .pipe( s3 )
    .pipe( i3 )
    .pipe( s4 )
    .pipe( i4 )
    .pipe( s5 )
    .pipe( i5 )
    .pipe( stdout );

// 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.

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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.