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Filename : byline.js
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// Copyright (C) 2011-2015 John Hewson
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit 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.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.

var stream = require('stream'),
    util = require('util'),
    timers = require('timers');

// convinience API
module.exports = function(readStream, options) {
  return module.exports.createStream(readStream, options);
};

// basic API
module.exports.createStream = function(readStream, options) {
  if (readStream) {
    return createLineStream(readStream, options);
  } else {
    return new LineStream(options);
  }
};

// deprecated API
module.exports.createLineStream = function(readStream) {
  console.log('WARNING: byline#createLineStream is deprecated and will be removed soon');
  return createLineStream(readStream);
};

function createLineStream(readStream, options) {
  if (!readStream) {
    throw new Error('expected readStream');
  }
  if (!readStream.readable) {
    throw new Error('readStream must be readable');
  }
  var ls = new LineStream(options);
  readStream.pipe(ls);
  return ls;
}

//
// using the new node v0.10 "streams2" API
//

module.exports.LineStream = LineStream;

function LineStream(options) {
  stream.Transform.call(this, options);
  options = options || {};

  // use objectMode to stop the output from being buffered
  // which re-concatanates the lines, just without newlines.
  this._readableState.objectMode = true;
  this._lineBuffer = [];
  this._keepEmptyLines = options.keepEmptyLines || false;
  this._lastChunkEndedWithCR = false;

  // take the source's encoding if we don't have one
  var self = this;
  this.on('pipe', function(src) {
    if (!self.encoding) {
      // but we can't do this for old-style streams
      if (src instanceof stream.Readable) {
        self.encoding = src._readableState.encoding;
      }
    }
  });
}
util.inherits(LineStream, stream.Transform);

LineStream.prototype._transform = function(chunk, encoding, done) {
  // decode binary chunks as UTF-8
  encoding = encoding || 'utf8';
  
  if (Buffer.isBuffer(chunk)) {
    if (encoding == 'buffer') {
      chunk = chunk.toString(); // utf8
      encoding = 'utf8';
    }
    else {
     chunk = chunk.toString(encoding);
    }
  }
  this._chunkEncoding = encoding;
  
  // see: http://www.unicode.org/reports/tr18/#Line_Boundaries
  var lines = chunk.split(/\r\n|[\n\v\f\r\x85\u2028\u2029]/g);
  
  // don't split CRLF which spans chunks
  if (this._lastChunkEndedWithCR && chunk[0] == '\n') {
    lines.shift();
  }
  
  if (this._lineBuffer.length > 0) {
    this._lineBuffer[this._lineBuffer.length - 1] += lines[0];
    lines.shift();
  }

  this._lastChunkEndedWithCR = chunk[chunk.length - 1] == '\r';
  this._lineBuffer = this._lineBuffer.concat(lines);
  this._pushBuffer(encoding, 1, done);
};

LineStream.prototype._pushBuffer = function(encoding, keep, done) {
  // always buffer the last (possibly partial) line
  while (this._lineBuffer.length > keep) {
    var line = this._lineBuffer.shift();
    // skip empty lines
    if (this._keepEmptyLines || line.length > 0 ) {
      if (!this.push(this._reencode(line, encoding))) {
        // when the high-water mark is reached, defer pushes until the next tick
        var self = this;
        timers.setImmediate(function() {
          self._pushBuffer(encoding, keep, done);
        });
        return;
      }
    }
  }
  done();
};

LineStream.prototype._flush = function(done) {
  this._pushBuffer(this._chunkEncoding, 0, done);
};

// see Readable::push
LineStream.prototype._reencode = function(line, chunkEncoding) {
  if (this.encoding && this.encoding != chunkEncoding) {
    return new Buffer(line, chunkEncoding).toString(this.encoding);
  }
  else if (this.encoding) {
    // this should be the most common case, i.e. we're using an encoded source stream
    return line;
  }
  else {
    return new Buffer(line, chunkEncoding);
  }
};