一个可以把玩的针对WebSocket分段的处理方案
市场上各种高级语言的WebSocket Echo的测试方案不少，但找来找去，愣是没有一个现成的可以针对分段（fragmetation）处理的Echo服务端。分段处理在一些对实时性要求较高的场合非常重要，比如流媒体，实时监控等场景，不能等待所有数据都齐备了再发送回客户端。基于此，从零开始着手打造第一款针对分段需求的Echo服务端，提供各种测试所适用的场景需要。
服务端是基于IIS提供的WebSocket框架，这样可以专注于商业逻辑的开发。对于客户端，我也提供了二种不同的方案——同步和异步的客户端方案。同步和异步方案使用的都是WinHTTP提供的API，同步比较简单直接，适合基本应用。异步比较复杂，可以构建较为大型的商业应用，更符合直觉上的使用习惯。下面介绍一下同步方案的应用。
HINTERNET hConnectionHandle = NULL, hRequestHandle = NULL, hWebSocketHandle = NULL;
BYTE rgbBuffer[1024]{ }, rgbCommand[] = u8"How are you doing/你好吗/Cómo estás/お元気ですか/어떻게 지내세요", rgbClose[] = u8"Bye/再见/Adiós/さよなら/안녕";
BOOL fStatus = FALSE;
DWORD dwError = ERROR_SUCCESS;
SetConsoleOutputCP(CP_UTF8);
// Create session, connection and request handles.
HINTERNET hSessionHandle = WinHttpOpen(L"WebSocket sample", WINHTTP_ACCESS_TYPE_DEFAULT_PROXY, NULL, NULL, 0);
if (hSessionHandle == NULL)
{
dwError = GetLastError();
goto quit;
}
hConnectionHandle = WinHttpConnect(hSessionHandle, L"localhost", INTERNET_DEFAULT_HTTP_PORT, 0);
if (hConnectionHandle == NULL)
{
dwError = GetLastError();
goto quit;
}
hRequestHandle = WinHttpOpenRequest(hConnectionHandle, L"GET", L"/interactws/main.iws", NULL, NULL, NULL, 0);
if (hRequestHandle == NULL)
{
dwError = GetLastError();
goto quit;
}WebSocket的文本协议是基于UTF8的，和UNICODE比节省传输上的开销，所以在开头也定义了二个使用UTF8的字符串，一个是用于测试用的数据，一个是关闭连接时的状态内容。接下是命令行的输出方法，按UTF8格式输出。第一步是建立个新的会话session，然后是和服务端建立连接。有了连接后，访问特定的WebSocket应用所在的路径。
// Request protocol upgrade from http to websocket.
#pragma prefast(suppress:6387, "WINHTTP_OPTION_UPGRADE_TO_WEB_SOCKET does not take any arguments.")
fStatus = WinHttpSetOption(hRequestHandle, WINHTTP_OPTION_UPGRADE_TO_WEB_SOCKET, NULL, 0);
if (!fStatus)
{
dwError = GetLastError();
goto quit;
}
fStatus = WinHttpSendRequest(hRequestHandle, WINHTTP_NO_ADDITIONAL_HEADERS, 0, NULL, 0, 0, 0);
if (!fStatus)
{
dwError = GetLastError();
goto quit;
}
fStatus = WinHttpReceiveResponse(hRequestHandle, 0);
if (!fStatus)
{
dwError = GetLastError();
goto quit;
}
hWebSocketHandle = WinHttpWebSocketCompleteUpgrade(hRequestHandle, NULL);
if (hWebSocketHandle == NULL)
{
dwError = GetLastError();
goto quit;
}接着是准备更新协议，从HTTP更新到WebSocket，完成协议头的准备和发送，接受服务端的返回，最后完成这步协议更新。这里可以看到，对于WebSocket，不是说必须在浏览器下才能使用，任何普通的程序只要有支持HTTP的库，都可以使用WebSocket。
// Get connected message from server
receive(hWebSocketHandle, rgbBuffer);
printf("%s\n", rgbBuffer);
memset(rgbBuffer, NULL, sizeof rgbBuffer);
printf("\n***** Set server in Binary mode and use fragmentation with size 1 byte in response *****\n\n");
// Set server in Binary mode in response
dwError = WinHttpWebSocketSend(hWebSocketHandle, WINHTTP_WEB_SOCKET_BINARY_MESSAGE_BUFFER_TYPE, (PVOID)"Mode: Binary", (DWORD)strlen("Mode: Binary"));
if (dwError != ERROR_SUCCESS)
{
goto quit;
}
// Set server to use fragmentation in response
dwError = WinHttpWebSocketSend(hWebSocketHandle, WINHTTP_WEB_SOCKET_BINARY_MESSAGE_BUFFER_TYPE, (PVOID)"Fragment: 1", (DWORD)strlen("Fragment: 1"));
if (dwError != ERROR_SUCCESS)
{
goto quit;
}
Sleep(1000);
// Send data in Binary mode from client
dwError = WinHttpWebSocketSend(hWebSocketHandle, WINHTTP_WEB_SOCKET_BINARY_MESSAGE_BUFFER_TYPE, rgbCommand, sizeof rgbCommand);
if (dwError != ERROR_SUCCESS)
{
goto quit;
}
receive(hWebSocketHandle, rgbBuffer);
printf("%s\n", rgbBuffer);
memset(rgbBuffer, NULL, sizeof rgbBuffer);
和服务端连接成功后，服务端会返回一个连接成功的信息，客户端需要接收此信息，这是receive()承担的功能，具体在后分析。下面需要通知服务端，让它处于BINARY模式，同时采用分段返回，每次返回一个BYTE。这也是本方案的独特之处，可以动态地调整服务端，即可用BINARY模式，也可以使用UTF8模式，还可以进行分段返回。
printf("\n***** Set server in UTF8 mode and use configured fragmentation as before *****\n\n");
// Set server in UTF8 mode in response
dwError = WinHttpWebSocketSend(hWebSocketHandle, WINHTTP_WEB_SOCKET_UTF8_MESSAGE_BUFFER_TYPE, (PVOID)"Mode: UTF8", (DWORD)strlen("Mode: UTF8"));
if (dwError != ERROR_SUCCESS)
{
goto quit;
}
// Send data in Binary mode from client
dwError = WinHttpWebSocketSend(hWebSocketHandle, WINHTTP_WEB_SOCKET_BINARY_MESSAGE_BUFFER_TYPE, rgbCommand, sizeof rgbCommand);
if (dwError != ERROR_SUCCESS)
{
goto quit;
}
receive(hWebSocketHandle, rgbBuffer);
printf("%s\n", rgbBuffer);
memset(rgbBuffer, NULL, sizeof rgbBuffer);这段程序调整服务端进入UTF8模式，同时原来的分段设置还有效，所以接收的都是以UTF8模式返回的一个BYTE分段信息。
printf("\n***** Turn off fragmentation and use UTF8 as set before in server response *****\n\n");
// Turn off fragmentation in server response
dwError = WinHttpWebSocketSend(hWebSocketHandle, WINHTTP_WEB_SOCKET_BINARY_MESSAGE_BUFFER_TYPE, (PVOID)"Fragment: 0", (DWORD)strlen("Fragment: 0"));
if (dwError != ERROR_SUCCESS)
{
goto quit;
}
// Send data in UTF8 mode from client
dwError = WinHttpWebSocketSend(hWebSocketHandle, WINHTTP_WEB_SOCKET_UTF8_MESSAGE_BUFFER_TYPE, rgbCommand, sizeof rgbCommand);
if (dwError != ERROR_SUCCESS)
{
goto quit;
}
receive(hWebSocketHandle, rgbBuffer);
printf("%s\n", rgbBuffer);
memset(rgbBuffer, NULL, sizeof rgbBuffer);上面这段关闭了服务端的分段特性，返回的是以UTF8模式的完整文本，而不是一个BYTE的分段返回。
quit:
printf("\n***** Close connection with reason description *****\n\n");
// Gracefully close the connection.
WinHttpWebSocketClose(hWebSocketHandle, WINHTTP_WEB_SOCKET_SUCCESS_CLOSE_STATUS, rgbClose, sizeof rgbClose);
BYTE rgbCloseReasonBuffer[123]{};
DWORD dwCloseReasonLength = 0;
USHORT usStatus = 0;
WinHttpWebSocketQueryCloseStatus(hWebSocketHandle, &usStatus, rgbCloseReasonBuffer, ARRAYSIZE(rgbCloseReasonBuffer), &dwCloseReasonLength);
printf("The server closed the connection with status code: '%d' and reason: '%s'\n", (int)usStatus, rgbCloseReasonBuffer);
if (hRequestHandle != NULL)
{
WinHttpCloseHandle(hRequestHandle);
hRequestHandle = NULL;
}
if (hWebSocketHandle != NULL)
{
WinHttpCloseHandle(hWebSocketHandle);
hWebSocketHandle = NULL;
}
if (hConnectionHandle != NULL)
{
WinHttpCloseHandle(hConnectionHandle);
hConnectionHandle = NULL;
}
if (hSessionHandle != NULL)
{
WinHttpCloseHandle(hSessionHandle);
hSessionHandle = NULL;
}
return 0;最后是关闭连接，并从服务端获取客户端发送的关闭原因，清除相关的资源占用。下面看下文中用到的receive()函数，
VOID receive(HINTERNET hWebSocketHandle, BYTE* pbCurrentBufferPointer) {
BYTE* pbInitial = pbCurrentBufferPointer;
DWORD dwBytesTransferred = 0;
WINHTTP_WEB_SOCKET_BUFFER_TYPE bufferType;
DWORD dwBufferLength = 1024;;
do
{
DWORD dwError = WinHttpWebSocketReceive(hWebSocketHandle, pbCurrentBufferPointer, dwBufferLength, &dwBytesTransferred, &bufferType);
if (dwError != ERROR_SUCCESS)
{
return;
}
if (bufferType == WINHTTP_WEB_SOCKET_BINARY_FRAGMENT_BUFFER_TYPE || bufferType == WINHTTP_WEB_SOCKET_UTF8_FRAGMENT_BUFFER_TYPE)
printf("%c\n", *pbCurrentBufferPointer);
pbCurrentBufferPointer += dwBytesTransferred;
dwBufferLength -= dwBytesTransferred;
} while (bufferType == WINHTTP_WEB_SOCKET_BINARY_FRAGMENT_BUFFER_TYPE || bufferType == WINHTTP_WEB_SOCKET_UTF8_FRAGMENT_BUFFER_TYPE);
pbCurrentBufferPointer = pbInitial;
}这个是同步调用的核心，在一个大的循环中等待服务端的返回。如果返回的是分段信息，读完后移动指针到下一个等待位置，这样下个返回可以把读取的值正确复制到相应的位置。等返回是最后一个分段信息时，此时不满足while的条件因此循环跳出，把指针复原到原始位置，这样一个完整的分段信息就算重新组装完成了。运行以上程序的输出如下，
异步程序比较复杂，在此不再分析，直接上图，大家尽情把玩，
总之，有了这一套服务端和客户端，对于WebSocket的开发是如虎添翼。服务端和客户端可以联合使用，也可以分别使用，其它常用的第三方Echo服务端都支持。若觉得实用，好用，请到它的Github仓库加个星，本人也提供这方面的咨询服务，欢迎点赞评论和收藏！