rethinkdbdash/lib/stream.js

A Node.js driver for RethinkDB with promises and a connection pool

var Readable = require('stream').Readable;
var Cursor = require(__dirname+'/cursor.js');
var util = require('util');

// Experimental, but should work fine.
function ReadableStream(options, cursor) {
  if (cursor) this._cursor = cursor;
  this._pending = 0; // How many time we called _read while no cursor was available
  this._index = 0;
  this._maxRecursion = 1000; // Hardcoded
  this._highWaterMark = options.highWaterMark;
  this._closed = false;

  Readable.call(this, {
    objectMode: true,
    highWaterMark: this._highWaterMark
  });
};
util.inherits(ReadableStream, Readable);


ReadableStream.prototype._setCursor = function(cursor) {
  if (cursor instanceof Cursor === false) {
    this.emit('error', new Error('Cannot create a stream on a single value.'));
    this.push(null);
    return this;
  }
  this._cursor = cursor;
  this._fetchAndDecrement();
}
ReadableStream.prototype._read = function(size) {
  this._count++;
  if (this._cursor === undefined) {
    this._pending++;
    return;
  }

  this._recursion = 0;
  this._fetch();
}

//TODO: Refactor with _fetch?
ReadableStream.prototype._fetchAndDecrement = function() {
  var self = this;
  self._pending--;
  if (self._pending < 0 || self._closed === true) {
    return;
  }

  if (self._cursor._closed === true) {
    self.push(null);
  }
  else {
    self._cursor._next().then(function(data) {
      // Silently drop null values for now
      if (data === null) {
        if (self._recursion++ === self._maxRecursion) {
          //Avoid maximum call stack errors
          process.nextTick(function() {
            self._fetchAndDecrement();
          });
        }
        else {
          self._fetchAndDecrement();
        }
      }
      else {
        if (self.push(data) !== false) {
          if (self._recursion++ === self._maxRecursion) {
            process.nextTick(function() {
              self._fetchAndDecrement();
            });
          }
          else {
            self._fetchAndDecrement();
          }
        }
      }
      return null;
    }).error(function(error) {
      if (error.message.match(/No more rows in the/)) {
        self.push(null);
      }
      else if (error.message === 'You cannot retrieve data from a cursor that is closed.') {
        // if the user call `close`, the cursor may reject pending requests. We just
        // ignore them here.
      }
      else {
        self.emit('error', error);
        self.push(null);
      }
    });
  }
}

ReadableStream.prototype._fetch = function() {
  var self = this;
  if (self._closed === true) {
    return;
  }
  if (self._cursor._closed === true) {
    self.push(null);
  }
  else {
    self._cursor._next().then(function(data) {
      if (self._closed === true) {
        return;
      }
      // Silently drop null values for now
      if (data === null) {
        if (self._recursion++ === self._maxRecursion) {
          process.nextTick(function() {
            self._fetch();
          });
        }
        else {
          self._fetch();
        }
      }
      else {
        if (self.push(data) !== false) {
          if (self._recursion++ === self._maxRecursion) {
            process.nextTick(function() {
              self._fetch();
            });
          }
          else {
            self._fetch();
          }
        }
      }
      return null;
    }).error(function(error) {
      if (error.message.match(/No more rows in the/)) {
        self.push(null);
      }
      else if (error.message === 'You cannot retrieve data from a cursor that is closed.') {
        // if the user call `close`, the cursor may reject pending requests. We just
        // ignore them here.
      }
      else {
        self.emit('error', error);
        self.push(null);
      }
    });
  }
}


ReadableStream.prototype.close = function() {
  this._closed = true;
  this.push(null);
  return this._cursor.close();
}

module.exports = ReadableStream;