2 byte frame with payload length of 0 throws "Incomplete Frame Received" exception #490
Description
Appweb server sends a PING frame to a C++/Poco client which throws the following exception:
Exception Type: WebSocket Exception
Exception Message: Incomplete frame received
A two byte frame with palyload length of zero is valid as it has all the information needed, but the current Poco implementation requires a frame larger than 2 bytes else it throws an "Invalid frame exception".
In the following I have added the code within
///////////////////////////////////SATYA SIDHU: BUG FIXED//////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
that ensures that a two byte frame with a payload length of zero is valid as is with other libraries such as C#, JavaScript and Python etc. I am returning -1 because it is a control frame and also to prevent changes in my client code, but a return value of zero would also be fine.
int WebSocketImpl::receiveBytes(void* buffer, int length, int)
{
char header[MAX_HEADER_LENGTH];
int n = receiveNBytes(header, 2);
if (n <= 0)
{
_frameFlags = 0;
return n;
}
poco_assert (n == 2);
Poco::UInt8 lengthByte = static_cast<Poco::UInt8>(header[1]);
int maskOffset = 0;
if (lengthByte & FRAME_FLAG_MASK) maskOffset += 4;
lengthByte &= 0x7f;
if (lengthByte + 2 + maskOffset < MAX_HEADER_LENGTH)
{
n = receiveNBytes(header + 2, lengthByte + maskOffset);
}
else
{
n = receiveNBytes(header + 2, MAX_HEADER_LENGTH - 2);
}
/////////////////////////////SATYA SIDHU: BUG FIXED////////////////////////////////////
if ((0 == n) && (0 == lengthByte))
{
Poco::MemoryInputStream istr(header, 2); // 2 bytes have been recieved so parse them only.
Poco::BinaryReader reader(istr, Poco::BinaryReader::NETWORK_BYTE_ORDER);
Poco::UInt8 flags;
char mask[4];
reader >> flags >> lengthByte;
_frameFlags = flags;
return -1;
}
//////////////////////////////////////////////////////////////////////////////////////
if (n <= 0) throw WebSocketException("Incomplete frame received", WebSocket::WS_ERR_INCOMPLETE_FRAME);
n += 2;
Poco::MemoryInputStream istr(header, n);
Poco::BinaryReader reader(istr, Poco::BinaryReader::NETWORK_BYTE_ORDER);
Poco::UInt8 flags;
char mask[4];
reader >> flags >> lengthByte;
_frameFlags = flags;
int payloadLength = 0;
int payloadOffset = 2;
if ((lengthByte & 0x7f) == 127)
{
Poco::UInt64 l;
reader >> l;
if (l > length) throw WebSocketException(Poco::format("Insufficient buffer for payload size %Lu", l), WebSocket::WS_ERR_PAYLOAD_TOO_BIG);
payloadLength = static_cast<int>(l);
payloadOffset += 8;
}
else if ((lengthByte & 0x7f) == 126)
{
Poco::UInt16 l;
reader >> l;
if (l > length) throw WebSocketException(Poco::format("Insufficient buffer for payload size %hu", l), WebSocket::WS_ERR_PAYLOAD_TOO_BIG);
payloadLength = static_cast<int>(l);
payloadOffset += 2;
}
else
{
Poco::UInt8 l = lengthByte & 0x7f;
if (l > length) throw WebSocketException(Poco::format("Insufficient buffer for payload size %u", unsigned(l)), WebSocket::WS_ERR_PAYLOAD_TOO_BIG);
payloadLength = static_cast<int>(l);
}
if (lengthByte & FRAME_FLAG_MASK)
{
reader.readRaw(mask, 4);
payloadOffset += 4;
}
int received = 0;
if (payloadOffset < n)
{
std::memcpy(buffer, header + payloadOffset, n - payloadOffset);
received = n - payloadOffset;
}
if (received < payloadLength)
{
n = receiveNBytes(reinterpret_cast<char*>(buffer) + received, payloadLength - received);
if (n <= 0) throw WebSocketException("Incomplete frame received", WebSocket::WS_ERR_INCOMPLETE_FRAME);
received += n;
}
if (lengthByte & FRAME_FLAG_MASK)
{
char* p = reinterpret_cast<char*>(buffer);
for (int i = 0; i < received; i++)
{
p[i] ^= mask[i % 4];
}
}
return received;
}
Websocket frame information obtained from the following link:
http://chimera.labs.oreilly.com/books/1230000000545/ch17.html#_websocket_protocol