// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dart.io;

/**
 * The object containing the certificates to trust when making
 * a secure client connection, and the certificate chain and
 * private key to serve from a secure server.
 * 
 * The [SecureSocket]  and [SecureServer] classes take a SecurityContext
 * as an argument to their connect and bind methods.
 *
 * Certificates and keys can be added to a SecurityContext from PEM files
 * on the disk.  A PEM file contains one or more base-64 encoded DER-serialized
 * ASN1 objects, surrounded with delimiter strings like
 * "-----BEGIN CERTIFICATE -----" and "-----END CERTIFICATE-----".
 * Distinguished encoding rules (DER) is a canonical binary serialization
 * of ASN1 objects into an octet string.
 */
abstract class SecurityContext {
  external factory SecurityContext();
  external static SecurityContext get defaultContext;

  /**
   * Sets the private key for a server certificate or client certificate.
   * A secure connection using this SecurityContext will use this key with
   * the server or client certificate to sign and decrypt messages.
   * [keyFile] is a PEM file containing an encrypted
   * private key, encrypted with [password].  An unencrypted file can be
   * used, but this is not usual.
   */
  void usePrivateKey(String keyFile, {String password});

  /**
   * Sets the set of trusted X509 certificates used by [SecureSocket]
   * client connections, when connecting to a secure server.
   *
   * There are two ways to set a set of trusted certificates, with a single
   * PEM file, or with a directory containing individual PEM files for
   * certificates.
   *
   * [file] is an optional PEM file containing X509 certificates, usually
   * root certificates from certificate authorities.
   *
   * [directory] is an optional directory containing PEM files.  The directory
   * must also have filesystem links added, which link extra filenames based
   * on the hash of a certificate's distinguished name (DN) to the file
   * containing that certificate. OpenSSL contains a tool called c_rehash
   * to create these links in a directory.
   */
  void setTrustedCertificates({String file, String directory});

  /**
   * Sets the chain of X509 certificates served by [SecureServer]
   * when making secure connections, including the server certificate.
   * [file] is an PEM file containing X509 certificates, starting with
   * the root authority and intermediate authorities forming the signed
   * chain to the server certificate, and ending with the server certificate.
   * The private key for the server certificate is set by [usePrivateKey].
   */
  void useCertificateChain(String file);

  /**
   * Sets the list of authority names that a [SecureServer] will advertise
   * as accepted, when requesting a client certificate from a connecting
   * client.  [file] is a PEM file containing the accepted signing authority
   * certificates - the authority names are extracted from the certificates.
   */
  void setClientAuthorities(String file);

  /**
   * Sets the list of application-level protocols supported by a client
   * connection or server connection. The ALPN (application level protocol
   * negotiation) extension to TLS allows a client to send a list of
   * protocols in the TLS client hello message, and the server to pick
   * one and send the selected one back in its server hello message.
   *
   * Separate lists of protocols can be sent for client connections and
   * for server connections, using the same SecurityContext.  The [isServer]
   * boolean argument specifies whether to set the list for server connections
   * or client connections.
   */
   void setAlpnProtocols(List<String> protocols, bool isServer);

  /// Encodes a set of supported protocols for ALPN/NPN usage.
  ///
  /// The `protocols` list is expected to contain protocols in descending order
  /// of preference.
  ///
  /// See RFC 7301 (https://tools.ietf.org/html/rfc7301) for the encoding of
  /// `List<String> protocols`:
  ///     opaque ProtocolName<1..2^8-1>;
  ///
  ///     struct {
  ///         ProtocolName protocol_name_list<2..2^16-1>
  ///     } ProtocolNameList;
  ///
  /// The encoding of the opaque `ProtocolName<lower..upper>` vector is
  /// described in RFC 2246: 4.3 Vectors.
  ///
  /// Note: Even though this encoding scheme would allow a total
  /// `ProtocolNameList` length of 65535, this limit cannot be reached. Testing
  /// showed that more than ~ 2^14  bytes will fail to negotiate a protocol.
  /// We will be conservative and support only messages up to (1<<13)-1 bytes.
  static Uint8List _protocolsToLengthEncoding(List<String> protocols) {
    if (protocols == null || protocols.length == 0) {
      return new Uint8List(0);
    }
    int protocolsLength = protocols.length;

    // Calculate the number of bytes we will need if it is ASCII.
    int expectedLength = protocolsLength;
    for (int i = 0; i < protocolsLength; i++) {
      int length = protocols[i].length;
      if (length > 0 && length <= 255) {
        expectedLength += length;
      } else {
        throw new ArgumentError(
            'Length of protocol must be between 1 and 255 (was: $length).');
      }
    }

    if (expectedLength >= (1 << 13)) {
      throw new ArgumentError(
          'The maximum message length supported is 2^13-1.');
    }

    // Try encoding the `List<String> protocols` array using fast ASCII path.
    var bytes = new Uint8List(expectedLength);
    int bytesOffset = 0;
    for (int i = 0; i < protocolsLength; i++) {
      String proto = protocols[i];

      // Add length byte.
      bytes[bytesOffset++] = proto.length;
      int bits = 0;

      // Add protocol bytes.
      for (int j = 0; j < proto.length; j++) {
        var char = proto.codeUnitAt(j);
        bits |= char;
        bytes[bytesOffset++] = char & 0xff;
      }

      // Go slow case if we have encountered anything non-ascii.
      if (bits > 0x7f) {
        return _protocolsToLengthEncodingNonAsciiBailout(protocols);
      }
    }
    return bytes;
  }

  static Uint8List _protocolsToLengthEncodingNonAsciiBailout(
      List<String> protocols) {
    void addProtocol(List<int> outBytes, String protocol) {
      var protocolBytes = UTF8.encode(protocol);
      var len = protocolBytes.length;

      if (len > 255) {
        throw new ArgumentError(
            'Length of protocol must be between 1 and 255 (was: $len)');
      }
      // Add length byte.
      outBytes.add(len);

      // Add protocol bytes.
      outBytes.addAll(protocolBytes);
    }

    List<int> bytes = [];
    for (var i = 0; i < protocols.length; i++) {
      addProtocol(bytes, protocols[i]);
    }

    if (bytes.length >= (1 << 13)) {
      throw new ArgumentError(
          'The maximum message length supported is 2^13-1.');
    }

    return new Uint8List.fromList(bytes);
  }
}