node_modules/union/examples/simple/middleware/gzip-encode.js

var spawn = require('child_process').spawn,
    util = require('util'),
    ResponseStream = require('../../lib').ResponseStream;
    
/**
 * Accepts a writable stream, i.e. fs.WriteStream, and returns a StreamStack
 * whose 'write()' calls are transparently sent to a 'gzip' process before
 * being written to the target stream.
 */
var GzipEncode = module.exports = function GzipEncode(options) {
  ResponseStream.call(this, options);

  if (compression) {
    process.assert(compression >= 1 && compression <= 9);
    this.compression = compression;
  }

  this.on('pipe', this.encode);
}

util.inherits(GzipEncode, ResponseStream);

GzipEncode.prototype.encode = function (source) {
  this.source = source;
};

GzipEncode.prototype.pipe = function (dest) {
  if (!this.source) {
    throw new Error('GzipEncode is only pipeable once it has been piped to');
  }
  
  this.encoder = spawn('gzip', ['-'+this.compression]);
  this.encoder.stdout.pipe(dest);
  this.encoder.stdin.pipe(this.source);
};

inherits(GzipEncoderStack, StreamStack);
exports.GzipEncoderStack = GzipEncoderStack;

GzipEncoderStack.prototype.compression = 6;