mysql2/lib/packets/column_definition.js

fast mysql driver. Implements core protocol, prepared statements, ssl and compression in native JS

var Buffer = require('safe-buffer').Buffer;
var Packet = require('../packets/packet');
var StringParser = require('../parsers/string');
var CharsetToEncoding = require('../constants/charset_encodings.js');

// creating JS string is relatively expensive (compared to
// reading few bytes from buffer) because all string properties
// except for name are unlikely to be used we postpone
// string conversion until property access
//
// TODO: watch for integration benchmarks (one with real network buffer)
// there could be bad side effect as keeping reference to a buffer makes it
// sit in the memory longer (usually until final .query() callback)
// Latest v8 perform much better in regard to bufferer -> string conversion,
// at some point of time this optimisation might become unnecessary
// see https://github.com/sidorares/node-mysql2/pull/137
//
function ColumnDefinition(packet, clientEncoding) {
  this._buf = packet.buffer;
  this._clientEncoding = clientEncoding;

  this._catalogLength = packet.readLengthCodedNumber();
  this._catalogStart = packet.offset;
  packet.offset += this._catalogLength;

  this._schemaLength = packet.readLengthCodedNumber();
  this._schemaStart = packet.offset;
  packet.offset += this._schemaLength;

  this._tableLength = packet.readLengthCodedNumber();
  this._tableStart = packet.offset;
  packet.offset += this._tableLength;

  this._orgTableLength = packet.readLengthCodedNumber();
  this._orgTableStart = packet.offset;
  packet.offset += this._orgTableLength;

  // name is always used, don't make it lazy
  var _nameLength = packet.readLengthCodedNumber();
  var _nameStart = packet.offset;
  packet.offset += _nameLength;

  this._orgNameLength = packet.readLengthCodedNumber();
  this._orgNameStart = packet.offset;
  packet.offset += this._orgNameLength;

  packet.skip(1); //  length of the following fields (always 0x0c)
  this.characterSet = packet.readInt16();
  this.encoding = CharsetToEncoding[this.characterSet];

  this.name = StringParser.decode(
    this._buf.slice(_nameStart, _nameStart + _nameLength),
    this.encoding === 'binary' ? this._clientEncoding : this.encoding
  );

  this.columnLength = packet.readInt32();
  this.columnType = packet.readInt8();
  this.flags = packet.readInt16();
  this.decimals = packet.readInt8();
}

var addString = function(name) {
  Object.defineProperty(ColumnDefinition.prototype, name, {
    get: function() {
      var start = this['_' + name + 'Start'];
      var end = start + this['_' + name + 'Length'];
      return StringParser.decode(
        this._buf.slice(start, end),
        this.encoding === 'binary' ? this._clientEncoding : this.encoding
      );
    }
  });
};

addString('catalog');
addString('schema');
addString('table');
addString('orgTable');
addString('orgName');

// node-mysql compatibility: alias "db" to "schema"
Object.defineProperty(ColumnDefinition.prototype, 'db', {
  get: function() {
    var start = this._schemaStart;
    var end = start._shemaLength;
    return this._buf.utf8Slice(start, end);
  }
});

ColumnDefinition.prototype.inspect = function() {
  return {
    catalog: this.catalog,
    schema: this.schema,
    name: this.name,
    orgName: this.orgName,
    table: this.table,
    orgTable: this.orgTable,
    characterSet: this.characterSet,
    columnLength: this.columnLength,
    columnType: this.columnType,
    flags: this.flags,
    decimals: this.decimals
  };
};

var fields = ['catalog', 'schema', 'table', 'orgTable', 'name', 'orgName'];

ColumnDefinition.toPacket = function(column, sequenceId) {
  var length = 17; // = 4 padding + 1 + 12 for the rest
  fields.forEach(function(field) {
    length += Packet.lengthCodedStringLength(
      column[field],
      CharsetToEncoding[column.characterSet]
    );
  });

  var buffer = Buffer.allocUnsafe(length);

  function writeField(name) {
    packet.writeLengthCodedString(
      column[name],
      CharsetToEncoding[column.characterSet]
    );
  }
  var packet = new Packet(sequenceId, buffer, 0, length);
  packet.offset = 4;
  fields.forEach(writeField);
  packet.writeInt8(0x0c);
  packet.writeInt16(column.characterSet);
  packet.writeInt32(column.columnLength);
  packet.writeInt8(column.columnType);
  packet.writeInt16(column.flags);
  packet.writeInt8(column.decimals);
  packet.writeInt16(0); // filler
  return packet;
};

module.exports = ColumnDefinition;