# Source: packet/one_pass_signature.js

    // GPG4Browsers - An OpenPGP implementation in javascript
    // Copyright (C) 2011 Recurity Labs GmbH
    //
    // This library is free software; you can redistribute it and/or
    // modify it under the terms of the GNU Lesser General Public
    // License as published by the Free Software Foundation; either
    // version 2.1 of the License, or (at your option) any later version.
    //
    // This library is distributed in the hope that it will be useful,
    // but WITHOUT ANY WARRANTY; without even the implied warranty of
    // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    // Lesser General Public License for more details.
    //
    // You should have received a copy of the GNU Lesser General Public
    // License along with this library; if not, write to the Free Software
    // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

    /** @module packet/one_pass_signature */

    var enums = require('../enums.js'),
      type_keyid = require('../type/keyid.js');

    /**
     * @class
     * @classdesc Implementation of the One-Pass Signature Packets (Tag 4)
     *
     * RFC4880 5.4:
     * The One-Pass Signature packet precedes the signed data and contains
     * enough information to allow the receiver to begin calculating any
     * hashes needed to verify the signature.  It allows the Signature
     * packet to be placed at the end of the message, so that the signer
     * can compute the entire signed message in one pass.
     */

    module.exports = function one_pass_signature() {
      this.version = null; // A one-octet version number.  The current version is 3.
      this.type = null; // A one-octet signature type.  Signature types are described in RFC4880 Section 5.2.1.
      this.hashAlgorithm = null; // A one-octet number describing the hash algorithm used. (See RFC4880 9.4)
      this.publicKeyAlgorithm = null; // A one-octet number describing the public-key algorithm used. (See RFC4880 9.1)
      this.signingKeyId = null; // An eight-octet number holding the Key ID of the signing key.
      this.flags = null; //  A one-octet number holding a flag showing whether the signature is nested.  A zero value indicates that the next packet is another One-Pass Signature packet that describes another signature to be applied to the same message data.

      /**
       * parsing function for a one-pass signature packet (tag 4).
       * @param {String} bytes payload of a tag 4 packet
       * @return {module:packet/one_pass_signature} object representation
       */
      this.read = function(bytes) {
        var mypos = 0;
        // A one-octet version number.  The current version is 3.
        this.version = bytes.charCodeAt(mypos++);

        // A one-octet signature type.  Signature types are described in
        //   Section 5.2.1.
        this.type = enums.read(enums.signature, bytes.charCodeAt(mypos++));

        // A one-octet number describing the hash algorithm used.
        this.hashAlgorithm = enums.read(enums.hash, bytes.charCodeAt(mypos++));

        // A one-octet number describing the public-key algorithm used.
        this.publicKeyAlgorithm = enums.read(enums.publicKey, bytes.charCodeAt(mypos++));

        // An eight-octet number holding the Key ID of the signing key.
        this.signingKeyId = new type_keyid();
        this.signingKeyId.read(bytes.substr(mypos));
        mypos += 8;

        // A one-octet number holding a flag showing whether the signature
        //   is nested.  A zero value indicates that the next packet is
        //   another One-Pass Signature packet that describes another
        //   signature to be applied to the same message data.
        this.flags = bytes.charCodeAt(mypos++);
        return this;
      }

      /**
       * creates a string representation of a one-pass signature packet
       * @return {String} a string representation of a one-pass signature packet
       */
      this.write = function() {
        var result = "";

        result += String.fromCharCode(3);
        result += String.fromCharCode(enums.write(enums.signature, this.type));
        result += String.fromCharCode(enums.write(enums.hash, this.hashAlgorithm));
        result += String.fromCharCode(enums.write(enums.publicKey, this.publicKeyAlgorithm));
        result += this.signingKeyId.write();
        result += String.fromCharCode(this.flags);

        return result;
      }
    };