node/lib/internal/streams/passthrough.js

// Copyright Joyent, Inc. and other Node contributors.
//
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// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
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// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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// a passthrough stream.
// basically just the most minimal sort of Transform stream.
// Every written chunk gets output as-is.

'use strict';

const {
  FunctionPrototypeCall,
  ObjectSetPrototypeOf,
} = primordials;

module.exports = PassThrough;

const Transform = require('internal/streams/transform');
ObjectSetPrototypeOf(PassThrough.prototype, Transform.prototype);
ObjectSetPrototypeOf(PassThrough, Transform);

function PassThrough(options) {
  if (!(this instanceof PassThrough))
    return new PassThrough(options);

  FunctionPrototypeCall(Transform, this, options);
}

PassThrough.prototype._transform = function(chunk, encoding, cb) {
  cb(null, chunk);
};