Method ProcessReceivedPacketBytes

src/net.cpp:1212–1279

}

bool V2Transport::ProcessReceivedPacketBytes() noexcept
{
    AssertLockHeld(m_recv_mutex);
    Assume(m_recv_state == RecvState::VERSION || m_recv_state == RecvState::APP);

    // The maximum permitted contents length for a packet, consisting of:
    // - 0x00 byte: indicating long message type encoding
    // - 12 bytes of message type
    // - payload
    static constexpr size_t MAX_CONTENTS_LEN =
        1 + CMessageHeader::MESSAGE_TYPE_SIZE +
        std::min<size_t>(MAX_SIZE, MAX_PROTOCOL_MESSAGE_LENGTH);

    if (m_recv_buffer.size() == BIP324Cipher::LENGTH_LEN) {
        // Length descriptor received.
        m_recv_len = m_cipher.DecryptLength(MakeByteSpan(m_recv_buffer));
        if (m_recv_len > MAX_CONTENTS_LEN) {
            LogDebug(BCLog::NET, "V2 transport error: packet too large (%u bytes), peer=%d\n", m_recv_len, m_nodeid);
            return false;
        }
    } else if (m_recv_buffer.size() > BIP324Cipher::LENGTH_LEN && m_recv_buffer.size() == m_recv_len + BIP324Cipher::EXPANSION) {
        // Ciphertext received, decrypt it into m_recv_decode_buffer.
        // Note that it is impossible to reach this branch without hitting the branch above first,
        // as GetMaxBytesToProcess only allows up to LENGTH_LEN into the buffer before that point.
        m_recv_decode_buffer.resize(m_recv_len);
        bool ignore{false};
        bool ret = m_cipher.Decrypt(
            /*input=*/MakeByteSpan(m_recv_buffer).subspan(BIP324Cipher::LENGTH_LEN),
            /*aad=*/MakeByteSpan(m_recv_aad),
            /*ignore=*/ignore,
            /*contents=*/MakeWritableByteSpan(m_recv_decode_buffer));
        if (!ret) {
            LogDebug(BCLog::NET, "V2 transport error: packet decryption failure (%u bytes), peer=%d\n", m_recv_len, m_nodeid);
            return false;
        }
        // We have decrypted a valid packet with the AAD we expected, so clear the expected AAD.
        ClearShrink(m_recv_aad);
        // Feed the last 4 bytes of the Poly1305 authentication tag (and its timing) into our RNG.
        RandAddEvent(ReadLE32(m_recv_buffer.data() + m_recv_buffer.size() - 4));

        // At this point we have a valid packet decrypted into m_recv_decode_buffer. If it's not a
        // decoy, which we simply ignore, use the current state to decide what to do with it.
        if (!ignore) {
            switch (m_recv_state) {
            case RecvState::VERSION:
                // Version message received; transition to application phase. The contents is
                // ignored, but can be used for future extensions.
                SetReceiveState(RecvState::APP);
                break;
            case RecvState::APP:
                // Application message decrypted correctly. It can be extracted using GetMessage().
                SetReceiveState(RecvState::APP_READY);
                break;
            default:
                // Any other state is invalid (this function should not have been called).
                Assume(false);
            }
        }