windows 套接字编程 C/C++ - recv 函数在服务器中挂起
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Socket Programming C/C++ - recv function hangs in Server
提问by hemanth
I am having problem in usage of recv function
我在使用recv 函数时遇到问题
I have an application that send some data from client, these data are received by the server & send a responses based on data.
我有一个从客户端发送一些数据的应用程序，这些数据由服务器接收并根据数据发送响应。
The implementation works fine when I send less than ~16 requests. But when I send more than 16 request (one after the other) from the client, the response are fine from the server until 16th request but after this the server hangs. I could see that the data are transmitted from client but are not received by server. I am using the function recv
当我发送少于 16 个请求时，实现工作正常。但是当我从客户端发送超过 16 个请求（一个接一个）时，从服务器到第 16 个请求的响应都很好，但在此之后服务器挂起。我可以看到数据是从客户端传输的，但没有被服务器接收。我正在使用函数recv
The reception is happening in a loop which is exited only when termination request is received from the client.
接收发生在循环中，只有在从客户端收到终止请求时才会退出。
Server Code:
服务器代码：
// Request Winsock version 2.2
fprintf(stderr,"Performing WSAStartup\n");
if ((retval = WSAStartup(0x202, &wsaData)) != 0)
{
fprintf(stderr,"FAILED with error %d\n", retval);
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
if (port == 0)
{
Usage(argv[0]);
}
/* open socket connection */
printf("Opening socket\n");
local.sin_family = AF_INET;
local.sin_addr.s_addr = (!ip_address) ? INADDR_ANY:inet_addr(ip_address);
/* Port MUST be in Network Byte Order */
local.sin_port = htons(port);
// TCP socket
listen_socket = socket(AF_INET, socket_type,0);
if (listen_socket == INVALID_SOCKET){
fprintf(stderr,"socket() failed with error %d\n", WSAGetLastError());
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
// bind() associates a local address and port combination with the socket just created.
// This is most useful when the application is a
// server that has a well-known port that clients know about in advance.
printf("Bind address and port to socket\n");
if (bind(listen_socket, (struct sockaddr*)&local, sizeof(local)) == SOCKET_ERROR)
{
fprintf(stderr,"bind() failed with error %d\n", WSAGetLastError());
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
// So far, everything we did was applicable to TCP as well as UDP.
// However, there are certain steps that do not work when the server is
// using UDP. We cannot listen() on a UDP socket.
if (socket_type != SOCK_DGRAM)
{
printf("TCP: listening on socket\n");
if (listen(listen_socket,5) == SOCKET_ERROR)
{
fprintf(stderr,"listen() failed with error %d\n", WSAGetLastError());
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
}
//Perform Applcation task
//initisations
printf("Server is listening and waiting for a connection\non port %d, protocol %s\n",port, (socket_type == SOCK_STREAM)?"TCP":"UDP");
executeServer = 1;
while(executeServer == 1)
{
fromlen =sizeof(from);
// accept() doesn't make sense on UDP, since we do not listen()
if (socket_type != SOCK_DGRAM)
{
printf("TCP: Waiting for connection (accept())\n");
msgsock = accept(listen_socket, (struct sockaddr*)&from, &fromlen);
if (msgsock == INVALID_SOCKET)
{
fprintf(stderr,"accept() error %d\n", WSAGetLastError());
WSACleanup();
return -1;
}
else
{
printf("OK\n");
printf("accepted connection from %s, port %d\n", inet_ntoa(from.sin_addr), htons(from.sin_port)) ;
}
}
else
{
msgsock = listen_socket;
}
// In the case of SOCK_STREAM, the server can do recv() and send() on
// the accepted socket and then close it.
// However, for SOCK_DGRAM (UDP), the server will do recvfrom() and sendto() in a loop.
printf("Receiving data");
if (socket_type != SOCK_DGRAM)
{
retval = recv(msgsock, Buffer, sizeof(Buffer), 0);
}
else
{
retval = recvfrom(msgsock,Buffer, sizeof(Buffer), 0, (struct sockaddr *)&from, &fromlen);
printf("Received datagram from %s\n", inet_ntoa(from.sin_addr));
}
if (retval == SOCKET_ERROR)
{
fprintf(stderr,"recv() failed: error %d\n", WSAGetLastError());
closesocket(msgsock);
return -2;
}
else
{
printf("OK\n");
}
if (retval == 0)
{
printf("Client closed connection.\n");
closesocket(msgsock);
}
else
{
printf("Received %d bytes, data \"%s\" from client\n", retval, Buffer);
}
printf("Processing Data\n");
if (!stricmp(Buffer, "exit"))
{
wsprintf(AckBuffer,"ACK");
executeServer = 0;
}
else
{
// Perform use task here based on recieved data
}
printf("Sending answer to client\n");
if (socket_type != SOCK_DGRAM)
{
retval = send(msgsock, AckBuffer, sizeof(AckBuffer), 0);
}
else
{
retval = sendto(msgsock, AckBuffer, sizeof(AckBuffer), 0, (struct sockaddr *)&from, fromlen);
}
if (retval == SOCKET_ERROR)
{
fprintf(stderr,"send() failed: error %d\n", WSAGetLastError());
}
else
{
printf("OK\n");
}
/* close TCP connection */
if (socket_type != SOCK_DGRAM)
{
closesocket(msgsock);
}
}
printf("terminating server\n");
closesocket(msgsock);
WSACleanup();
Client Code:
客户代码：
fprintf(stderr,"Performing WSAStartup");
if ((retval = WSAStartup(0x202, &wsaData)) != 0)
{
fprintf(stderr,"WSAStartup() failed with error %d\n", retval);
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
if (port == 0)
{
Usage(argv[0]);
}
// Attempt to detect if we should call gethostbyname() or gethostbyaddr()
printf("Translate hastname to address -> gethostbyaddr()\n");
if (isalpha(server_name[0]))
{ // server address is a name
hp = gethostbyname(server_name);
}
else
{ // Convert nnn.nnn address to a usable one
addr = inet_addr(server_name);
hp = gethostbyaddr((char *)&addr, 4, AF_INET);
}
if (hp == NULL )
{
fprintf(stderr,"Cannot resolve address \"%s\": Error %d\n", server_name, WSAGetLastError());
WSACleanup();
exit(1);
}
else
{
printf("OK\n");
}
// Copy the resolved information into the sockaddr_in structure
printf("Opening socket\n");
memset(&server, 0, sizeof(server));
memcpy(&(server.sin_addr), hp->h_addr, hp->h_length);
server.sin_family = hp->h_addrtype;
server.sin_port = htons(port);
conn_socket = socket(AF_INET, socket_type, 0); /* Open a socket */
if (conn_socket <0 )
{
fprintf(stderr,"Error Opening socket: Error %d\n", WSAGetLastError());
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
// Notice that nothing in this code is specific to whether we
// are using UDP or TCP.
// We achieve this by using a simple trick.
// When connect() is called on a datagram socket, it does not
// actually establish the connection as a stream (TCP) socket
// would. Instead, TCP/IP establishes the remote half of the
// (LocalIPAddress, LocalPort, RemoteIP, RemotePort) mapping.
// This enables us to use send() and recv() on datagram sockets,
// instead of recvfrom() and sendto()
printf("Client connecting to: %s.\n", hp->h_name);
if (connect(conn_socket, (struct sockaddr*)&server, sizeof(server)) == SOCKET_ERROR)
{
fprintf(stderr,"connect() failed: %d\n", WSAGetLastError());
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
/* copy options string to buffer */
strcpy(Buffer,Options);
printf("Sending Data \"%s\"\n", Buffer);
retval = send(conn_socket, Buffer, sizeof(Buffer), 0);
if (retval == SOCKET_ERROR)
{
fprintf(stderr,"send() failed: error %d.\n", WSAGetLastError());
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
printf("Receiving status from server\n");
retval = recv(conn_socket, Buffer, sizeof(Buffer), 0);
if (retval == SOCKET_ERROR)
{
fprintf(stderr,"recv() failed: error %d.\n", WSAGetLastError());
closesocket(conn_socket);
WSACleanup();
return -1;
}
else
{
printf("OK\n");
}
// We are not likely to see this with UDP, since there is no
// 'connection' established.
if (retval == 0)
{
printf("Client: Server closed connection.\n");
closesocket(conn_socket);
WSACleanup();
return -1;
}
printf("Received %d bytes, data \"%s\" from server.\n", retval, Buffer);
closesocket(conn_socket);
WSACleanup();
回答by young
If you use recvwithout making your socket non-blocking mode, your recvis doing a right thing. It blocks until it has something to read.
如果您在recv没有使套接字非阻塞模式的情况下使用，那么您recv正在做正确的事情。它阻塞，直到它有东西要读。
[UPDATE]
[更新]
From the code, you are indeed using blocking socket. I recommend you use non-blocking socket at least for your server. I believe you can easily google how to make non-blocking socket and handle async IO in Windows. Good Luck!
从代码中，您确实使用了阻塞套接字。我建议您至少为您的服务器使用非阻塞套接字。我相信你可以很容易地谷歌搜索如何在 Windows 中制作非阻塞套接字和处理异步 IO。祝你好运！
[UPDATE2]
[更新2]
First of all, your server code seems to close connection once recvreads something. Since TCP does not care data boundary, you can't just close the connection. Remember one sendcall in client may require multiple recvcalls in server with TCP or vice versa.
首先，一旦recv读取某些内容，您的服务器代码似乎就会关闭连接。由于 TCP 不关心数据边界，因此您不能只是关闭连接。请记住send，客户端中的一次调用可能需要recv使用 TCP 在服务器中进行多次调用，反之亦然。
For your specific problem, I'm pretty sure there is nothing to read and that's why recvis blocking your program. Make it sure that your client really sends something successfully.
对于您的具体问题，我很确定没有什么可阅读的，这recv就是阻止您的程序的原因。确保您的客户真的成功发送了一些东西。
