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// Copyright Epic Games, Inc. All Rights Reserved.
#include "wsframecodec.h"
#include <zencore/base64.h>
#include <zencore/sha1.h>
#include <cstring>
#include <random>
namespace zen {
//////////////////////////////////////////////////////////////////////////
//
// Frame parsing
//
WsFrameParseResult
WsFrameCodec::TryParseFrame(const uint8_t* Data, size_t Size)
{
// Minimum frame: 2 bytes header (unmasked server frames) or 6 bytes (masked client frames)
if (Size < 2)
{
return {};
}
const bool Fin = (Data[0] & 0x80) != 0;
const uint8_t OpcodeRaw = Data[0] & 0x0F;
const bool Masked = (Data[1] & 0x80) != 0;
uint64_t PayloadLen = Data[1] & 0x7F;
size_t HeaderSize = 2;
if (PayloadLen == 126)
{
if (Size < 4)
{
return {};
}
PayloadLen = (uint64_t(Data[2]) << 8) | uint64_t(Data[3]);
HeaderSize = 4;
}
else if (PayloadLen == 127)
{
if (Size < 10)
{
return {};
}
PayloadLen = (uint64_t(Data[2]) << 56) | (uint64_t(Data[3]) << 48) | (uint64_t(Data[4]) << 40) | (uint64_t(Data[5]) << 32) |
(uint64_t(Data[6]) << 24) | (uint64_t(Data[7]) << 16) | (uint64_t(Data[8]) << 8) | uint64_t(Data[9]);
HeaderSize = 10;
}
const size_t MaskSize = Masked ? 4 : 0;
const size_t TotalFrame = HeaderSize + MaskSize + PayloadLen;
if (Size < TotalFrame)
{
return {};
}
const uint8_t* MaskKey = Masked ? (Data + HeaderSize) : nullptr;
const uint8_t* PayloadData = Data + HeaderSize + MaskSize;
WsFrameParseResult Result;
Result.IsValid = true;
Result.BytesConsumed = TotalFrame;
Result.Opcode = static_cast<WebSocketOpcode>(OpcodeRaw);
Result.Fin = Fin;
Result.Payload.resize(static_cast<size_t>(PayloadLen));
if (PayloadLen > 0)
{
std::memcpy(Result.Payload.data(), PayloadData, static_cast<size_t>(PayloadLen));
if (Masked)
{
for (size_t i = 0; i < Result.Payload.size(); ++i)
{
Result.Payload[i] ^= MaskKey[i & 3];
}
}
}
return Result;
}
//////////////////////////////////////////////////////////////////////////
//
// Frame building (server-to-client, no masking)
//
std::vector<uint8_t>
WsFrameCodec::BuildFrame(WebSocketOpcode Opcode, std::span<const uint8_t> Payload)
{
std::vector<uint8_t> Frame;
const size_t PayloadLen = Payload.size();
// FIN + opcode
Frame.push_back(0x80 | static_cast<uint8_t>(Opcode));
// Payload length (no mask bit for server frames)
if (PayloadLen < 126)
{
Frame.push_back(static_cast<uint8_t>(PayloadLen));
}
else if (PayloadLen <= 0xFFFF)
{
Frame.push_back(126);
Frame.push_back(static_cast<uint8_t>((PayloadLen >> 8) & 0xFF));
Frame.push_back(static_cast<uint8_t>(PayloadLen & 0xFF));
}
else
{
Frame.push_back(127);
for (int i = 7; i >= 0; --i)
{
Frame.push_back(static_cast<uint8_t>((PayloadLen >> (i * 8)) & 0xFF));
}
}
Frame.insert(Frame.end(), Payload.begin(), Payload.end());
return Frame;
}
std::vector<uint8_t>
WsFrameCodec::BuildCloseFrame(uint16_t Code, std::string_view Reason)
{
std::vector<uint8_t> Payload;
Payload.push_back(static_cast<uint8_t>((Code >> 8) & 0xFF));
Payload.push_back(static_cast<uint8_t>(Code & 0xFF));
Payload.insert(Payload.end(), Reason.begin(), Reason.end());
return BuildFrame(WebSocketOpcode::kClose, Payload);
}
//////////////////////////////////////////////////////////////////////////
//
// Frame building (client-to-server, with masking)
//
std::vector<uint8_t>
WsFrameCodec::BuildMaskedFrame(WebSocketOpcode Opcode, std::span<const uint8_t> Payload)
{
std::vector<uint8_t> Frame;
const size_t PayloadLen = Payload.size();
// FIN + opcode
Frame.push_back(0x80 | static_cast<uint8_t>(Opcode));
// Payload length with mask bit set
if (PayloadLen < 126)
{
Frame.push_back(0x80 | static_cast<uint8_t>(PayloadLen));
}
else if (PayloadLen <= 0xFFFF)
{
Frame.push_back(0x80 | 126);
Frame.push_back(static_cast<uint8_t>((PayloadLen >> 8) & 0xFF));
Frame.push_back(static_cast<uint8_t>(PayloadLen & 0xFF));
}
else
{
Frame.push_back(0x80 | 127);
for (int i = 7; i >= 0; --i)
{
Frame.push_back(static_cast<uint8_t>((PayloadLen >> (i * 8)) & 0xFF));
}
}
// Generate random 4-byte mask key
static thread_local std::mt19937 s_Rng(std::random_device{}());
uint32_t MaskValue = s_Rng();
uint8_t MaskKey[4];
std::memcpy(MaskKey, &MaskValue, 4);
Frame.insert(Frame.end(), MaskKey, MaskKey + 4);
// Masked payload
for (size_t i = 0; i < PayloadLen; ++i)
{
Frame.push_back(Payload[i] ^ MaskKey[i & 3]);
}
return Frame;
}
std::vector<uint8_t>
WsFrameCodec::BuildMaskedCloseFrame(uint16_t Code, std::string_view Reason)
{
std::vector<uint8_t> Payload;
Payload.push_back(static_cast<uint8_t>((Code >> 8) & 0xFF));
Payload.push_back(static_cast<uint8_t>(Code & 0xFF));
Payload.insert(Payload.end(), Reason.begin(), Reason.end());
return BuildMaskedFrame(WebSocketOpcode::kClose, Payload);
}
//////////////////////////////////////////////////////////////////////////
//
// Sec-WebSocket-Accept key computation (RFC 6455 section 4.2.2)
//
static constexpr std::string_view kWebSocketMagicGuid = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
std::string
WsFrameCodec::ComputeAcceptKey(std::string_view ClientKey)
{
// Concatenate client key with the magic GUID
std::string Combined;
Combined.reserve(ClientKey.size() + kWebSocketMagicGuid.size());
Combined.append(ClientKey);
Combined.append(kWebSocketMagicGuid);
// SHA1 hash
SHA1 Hash = SHA1::HashMemory(Combined.data(), Combined.size());
// Base64 encode the 20-byte hash
char Base64Buf[Base64::GetEncodedDataSize(20) + 1];
uint32_t EncodedLen = Base64::Encode(Hash.Hash, 20, Base64Buf);
Base64Buf[EncodedLen] = '\0';
return std::string(Base64Buf, EncodedLen);
}
} // namespace zen
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