@stdlib/streams/node/transform/lib/factory.js

Streams.

/**
* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

'use strict';

// MODULES //

var isObject = require( '@stdlib/assert/is-plain-object' );
var format = require( '@stdlib/string/format' );
var assign = require( '@stdlib/object/assign' );
var Stream = require( './main.js' );


// MAIN //

/**
* Creates a reusable transform stream factory.
*
* @param {Options} [options] - stream options
* @param {boolean} [options.objectMode=false] - specifies whether a stream should operate in object mode
* @param {(string|null)} [options.encoding=null] - specifies how `Buffer` objects should be decoded to `strings`
* @param {NonNegativeNumber} [options.highWaterMark] - specifies the `Buffer` level for when `write()` starts returning `false`
* @param {boolean} [options.allowHalfOpen=false] - specifies whether the stream should remain open even if one side ends
* @param {boolean} [options.decodeStrings=true] - specifies whether to decode `strings` into `Buffer` objects when writing
* @throws {TypeError} options argument must be an object
* @returns {Function} transform stream factory
*
* @example
* function transform( chunk, enc, clbk ) {
*     clbk( null, chunk.toString()+'\n' );
* }
*
* var opts = {
*     'objectMode': true,
*     'encoding': 'utf8',
*     'highWaterMark': 64,
*     'decodeStrings': false
* };
*
* var factory = streamFactory( opts );
*
* // Create 10 identically configured streams...
* var streams = [];
* var i;
* for ( i = 0; i < 10; i++ ) {
*     streams.push( factory( transform ) );
* }
*/
function streamFactory( options ) {
	var opts;
	if ( arguments.length ) {
		if ( !isObject( options ) ) {
			throw new TypeError( format( 'invalid argument. Options argument must be an object. Value: `%s`.', options ) );
		}
		opts = assign( {}, options );
	} else {
		opts = {};
	}
	return createStream;

	/**
	* Creates a transform stream.
	*
	* @private
	* @param {Function} transform - callback to invoke upon receiving a new chunk
	* @param {Function} [flush] - callback to invoke after receiving all chunks and prior to the stream closing
	* @throws {TypeError} must provide valid options
	* @throws {TypeError} transform callback must be a function
	* @throws {TypeError} flush callback must be a function
	* @returns {TransformStream} transform stream
	*/
	function createStream( transform, flush ) {
		opts.transform = transform;
		if ( arguments.length > 1 ) {
			opts.flush = flush;
		} else {
			delete opts.flush; // clear any previous `flush`
		}
		return new Stream( opts );
	}
}


// EXPORTS //

module.exports = streamFactory;