static _read()

in src/messages.js [169:216]
37 lines of code
10 McCabe index (conditional complexity)

  static _read(buf) {
    // The legacy_version field may indicate an earlier version of TLS
    // for backwards compatibility, but must not predate TLS 1.0!
    if (buf.readUint16() < VERSION_TLS_1_0) {
      throw new TLSError(ALERT_DESCRIPTION.PROTOCOL_VERSION);
    }
    // The random bytes provided by the peer.
    const random = buf.readBytes(32);
    // Read legacy_session_id, so the server can echo it.
    const sessionId = buf.readVectorBytes8();
    // We only support a single ciphersuite, but the peer may offer several.
    // Scan the list to confirm that the one we want is present.
    let found = false;
    buf.readVector16(buf => {
      const cipherSuite = buf.readUint16();
      if (cipherSuite === TLS_AES_128_GCM_SHA256) {
        found = true;
      }
    });
    if (! found) {
      throw new TLSError(ALERT_DESCRIPTION.HANDSHAKE_FAILURE);
    }
    // legacy_compression_methods must be a single zero byte for TLS1.3 ClientHellos.
    // It can be non-zero in previous versions of TLS, but we're not going to
    // make a successful handshake with such versions, so better to just bail out now.
    const legacyCompressionMethods = buf.readVectorBytes8();
    if (legacyCompressionMethods.byteLength !== 1) {
      throw new TLSError(ALERT_DESCRIPTION.ILLEGAL_PARAMETER);
    }
    if (legacyCompressionMethods[0] !== 0x00) {
      throw new TLSError(ALERT_DESCRIPTION.ILLEGAL_PARAMETER);
    }
    // Read and check the extensions.
    const extensions = this._readExtensions(HANDSHAKE_TYPE.CLIENT_HELLO, buf);
    if (! extensions.has(EXTENSION_TYPE.SUPPORTED_VERSIONS)) {
      throw new TLSError(ALERT_DESCRIPTION.MISSING_EXTENSION);
    }
    if (extensions.get(EXTENSION_TYPE.SUPPORTED_VERSIONS).versions.indexOf(VERSION_TLS_1_3) === -1) {
      throw new TLSError(ALERT_DESCRIPTION.PROTOCOL_VERSION);
    }
    // Was the PreSharedKey extension the last one?
    if (extensions.has(EXTENSION_TYPE.PRE_SHARED_KEY)) {
      if (extensions.lastSeenExtension !== EXTENSION_TYPE.PRE_SHARED_KEY) {
        throw new TLSError(ALERT_DESCRIPTION.ILLEGAL_PARAMETER);
      }
    }
    return new this(random, sessionId, extensions);
  }