@stdlib/streams
Version:
Streams.
266 lines (235 loc) • 7.58 kB
JavaScript
/**
* @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 Readable = require( 'readable-stream' ).Readable;
var hasOwnProp = require( '@stdlib/assert/has-own-property' );
var isIteratorLike = require( '@stdlib/assert/is-iterator-like' );
var isError = require( '@stdlib/assert/is-error' );
var isBuffer = require( '@stdlib/assert/is-buffer' );
var assign = require( '@stdlib/object/assign' );
var inherit = require( '@stdlib/utils/inherit' );
var setNonEnumerable = require( '@stdlib/utils/define-nonenumerable-property' );
var setNonEnumerableReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
var string2buffer = require( '@stdlib/buffer/from-string' );
var Buffer = require( '@stdlib/buffer/ctor' ); // TODO: replace Buffer.concat usage with stdlib pkg
var nextTick = require( '@stdlib/utils/next-tick' );
var format = require( '@stdlib/string/format' );
var DEFAULTS = require( './defaults.json' );
var validate = require( './validate.js' );
var debug = require( './debug.js' );
// FUNCTIONS //
/**
* Implements the `_read` method.
*
* @private
* @param {number} size - number (of bytes) to read
* @returns {void}
*/
function read() {
/* eslint-disable no-invalid-this */
var FLG;
var err;
var v;
if ( this._destroyed ) {
return;
}
FLG = true;
while ( FLG ) {
v = this._iterator.next();
this._i += 1;
if ( v.done ) {
if ( hasOwnProp( v, 'value' ) ) {
v = v.value;
debug( 'Value: %s. Iter: %d.', JSON.stringify( v ), this._i );
if ( this._objectMode === false ) {
v = this._serialize( v );
if ( typeof v === 'string' ) {
if ( this._i === 1 ) { // eslint-disable-line max-depth
v = string2buffer( v );
} else {
v = string2buffer( this._sep+v );
}
this.push( v );
} else if ( isBuffer( v ) ) {
if ( this._i > 1 ) { // eslint-disable-line max-depth
v = Buffer.concat( [ string2buffer( this._sep ), v ] ); // eslint-disable-line max-len
}
this.push( v );
} else {
err = new Error( format( 'invalid operation. Serialization function must return a string or Buffer. Value: `%s`.', v ) );
this.emit( 'error', err );
}
}
}
debug( 'Finished iteration.' );
return this.push( null );
}
v = v.value;
debug( 'Value: %s. Iter: %d.', JSON.stringify( v ), this._i );
if ( this._objectMode === false ) {
v = this._serialize( v );
if ( typeof v === 'string' ) {
if ( this._i === 1 ) {
v = string2buffer( v );
} else {
v = string2buffer( this._sep+v );
}
} else if ( isBuffer( v ) ) {
if ( this._i > 1 ) {
v = Buffer.concat( [ string2buffer( this._sep ), v ] );
}
} else {
err = new Error( format( 'invalid operation. Serialization function must return a string or Buffer. Value: `%s`.', v ) );
this.emit( 'error', err );
continue;
}
}
FLG = this.push( v );
}
/* eslint-enable no-invalid-this */
}
/**
* Gracefully destroys a stream, providing backward compatibility.
*
* @private
* @param {(string|Object|Error)} [error] - error
* @returns {IteratorStream} Stream instance
*/
function destroy( error ) {
/* eslint-disable no-invalid-this */
var self;
if ( this._destroyed ) {
debug( 'Attempted to destroy an already destroyed stream.' );
return this;
}
self = this;
this._destroyed = true;
nextTick( close );
return this;
/**
* Closes a stream.
*
* @private
*/
function close() {
if ( error ) {
debug( 'Stream was destroyed due to an error. Error: %s.', ( isError( error ) ) ? error.message : JSON.stringify( error ) );
self.emit( 'error', error );
}
debug( 'Closing the stream...' );
self.emit( 'close' );
}
/* eslint-enable no-invalid-this */
}
// MAIN //
/**
* Stream constructor for generating a readable stream from an iterator.
*
* @constructor
* @param {Iterator} iterator - source iterator
* @param {Options} [options] - stream options
* @param {boolean} [options.objectMode=false] - specifies whether the 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 maximum number of bytes to store in an internal buffer before pausing iteration
* @param {string} [options.sep='\n'] - separator used to join streamed data
* @param {Function} [options.serialize] - custom serialization function
* @throws {TypeError} first argument must be an iterator
* @throws {TypeError} options argument must be an object
* @throws {TypeError} must provide valid options
* @returns {IteratorStream} Stream instance
*
* @example
* var inspectStream = require( '@stdlib/streams/node/inspect-sink' );
* var randu = require( '@stdlib/random/iter/randu' );
*
* function log( chunk ) {
* console.log( chunk.toString() );
* }
*
* var opts = {
* 'iter': 10
* };
*
* var stream = new IteratorStream( randu( opts ) );
*
* stream.pipe( inspectStream( log ) );
*/
function IteratorStream( iterator, options ) {
var opts;
var err;
if ( !( this instanceof IteratorStream ) ) {
if ( arguments.length > 1 ) {
return new IteratorStream( iterator, options );
}
return new IteratorStream( iterator );
}
if ( !isIteratorLike( iterator ) ) {
throw new TypeError( format( 'invalid argument. First argument must be an iterator. Value: `%s`.', iterator ) );
}
opts = assign( {}, DEFAULTS );
if ( arguments.length > 1 ) {
err = validate( opts, options );
if ( err ) {
throw err;
}
}
// Make the stream a readable stream:
debug( 'Creating a readable stream configured with the following options: %s.', JSON.stringify( opts ) );
Readable.call( this, opts );
// Destruction state:
setNonEnumerable( this, '_destroyed', false );
// Cache whether the stream is operating in object mode:
setNonEnumerableReadOnly( this, '_objectMode', opts.objectMode );
// Cache the separator:
setNonEnumerableReadOnly( this, '_sep', opts.sep );
// Define the serialization function:
setNonEnumerableReadOnly( this, '_serialize', opts.serialize || JSON.stringify );
// Cache the iterator:
setNonEnumerableReadOnly( this, '_iterator', iterator );
// Initialize an iteration counter:
setNonEnumerable( this, '_i', 0 );
return this;
}
/*
* Inherit from the `Readable` prototype.
*/
inherit( IteratorStream, Readable );
/**
* Implements the `_read` method.
*
* @private
* @name _read
* @memberof IteratorStream.prototype
* @type {Function}
* @param {number} size - number (of bytes) to read
* @returns {void}
*/
setNonEnumerableReadOnly( IteratorStream.prototype, '_read', read );
/**
* Gracefully destroys a stream, providing backward compatibility.
*
* @name destroy
* @memberof IteratorStream.prototype
* @type {Function}
* @param {(string|Object|Error)} [error] - error
* @returns {IteratorStream} Stream instance
*/
setNonEnumerableReadOnly( IteratorStream.prototype, 'destroy', destroy );
// EXPORTS //
module.exports = IteratorStream;