[英]C++/Winsock TCP send/recv issue between client/server
當我連續發送並且之后在客戶端上接收時,我與通過套接字進行客戶端/服務器通信有關。 例:
情況A:
Client Server
send(...);----------->While(recv(...)>0){
send(...);-----------> print(message);
send(...);----------->}
recv(...);----------->Send(...);
服務器收到3條消息並發送最后一個答案,但是客戶端上的recv失敗,SOCKET_ERROR的WSAGetLastError()值為10060。使這種情況起作用的唯一方法是當我添加shutdown(...,SD_SEND)時在最后一個發送客戶端之后。
為什么案例A有這種行為? 為什么只有當我添加shutdown()命令時它才能工作?
但是如果我這樣做:
情況B:
Client Server
send(...);----------->While(recv(...)>0){
recv(...);-----------> send(...);
send(...);-----------> ...
recv(...);-----------> ...
send(...);-----------> ...
recv(...);----------->}
它工作正常,服務器/客戶端接收並發送每條消息。
這是案例A的代碼:客戶:
#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
// Need to link with Ws2_32.lib, Mswsock.lib, and Advapi32.lib
#pragma comment (lib, "Ws2_32.lib")
#pragma comment (lib, "Mswsock.lib")
#pragma comment (lib, "AdvApi32.lib")
#define DEFAULT_BUFLEN 1024
#define DEFAULT_PORT "27015"
int main() {
WSADATA wsaData;
SOCKET ConnectSocket = INVALID_SOCKET;
ADDRINFOA *ptr = NULL, *result = NULL, hints;
char *ans, *sendbuf = "message\0";
char recvbuf[1024];
int iResult;
int recvbuflen = DEFAULT_BUFLEN;
ans=new char[1024];
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
printf("--> Initializing Winsock...\n*** Version: %s\n", wsaData.szDescription);
if (iResult != 0) {
printf("*** Could not initialize Socket.\n*** Error code: %d", iResult);
return 1;
}
ZeroMemory( &hints, sizeof(hints) );
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
// Resolve the server address and port
iResult = getaddrinfo("127.0.0.1", DEFAULT_PORT, &hints, &result);
printf("--> Setting server address...\n");
printf("--> local ip: 127.0.0.1 at port: %s...\n",DEFAULT_PORT);
if ( iResult != 0 ) {
printf("*** Error in setting server address.\n*** Error code: %d", iResult);
WSACleanup();
return 1;
}
// Attempt to connect to an address until one succeeds
for(ptr=result; ptr != NULL ;ptr=ptr->ai_next) {
// Create a SOCKET for connecting to server
printf("--> Creating client socket object...\n");
ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype, ptr->ai_protocol);
if (ConnectSocket == INVALID_SOCKET) {
printf("*** Error creating socket.\n*** Error code: %d\n",WSAGetLastError());
freeaddrinfo(result);
WSACleanup();
return 1;
}
if(setsockopt(ConnectSocket, SOL_SOCKET, SO_RCVTIMEO, (char *)new int(1000), sizeof(int))){
WSACleanup();
//strcpy(recvbuf, "EX_95");
return -5; // Error setting recv timeout.
}
// Connect to server.
iResult = connect( ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
if (iResult == SOCKET_ERROR) {
closesocket(ConnectSocket);
ConnectSocket = INVALID_SOCKET;
continue;
}
printf("*** Client ready *** \n\n");
break;
}
freeaddrinfo(result);
if (ConnectSocket == INVALID_SOCKET) {
printf("*** Unable to connect to server!\n");
WSACleanup();
return 1;
}
// Send an initial buffer
iResult = send( ConnectSocket, sendbuf, (int)strlen(sendbuf), 0 );
if (iResult == SOCKET_ERROR) {
printf("*** Send failed: %d\n", WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}
printf("<-- Bytes Sent: %ld\n", iResult);
iResult = send( ConnectSocket, sendbuf, (int)strlen(sendbuf), 0 );
if (iResult == SOCKET_ERROR) {
printf("*** Send failed: %d\n", WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}
printf("<-- Bytes Sent: %ld\n", iResult);
iResult = send( ConnectSocket, sendbuf, (int)strlen(sendbuf), 0 );
if (iResult == SOCKET_ERROR) {
printf("*** Send failed: %d\n", WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}
printf("<-- Bytes Sent: %ld\n", iResult);
// shutdown the connection since no more data will be sent
/*iResult = shutdown(ConnectSocket, SD_SEND);
if (iResult == SOCKET_ERROR) {
printf("shutdown failed with error: %d\n", WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}*/
iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
if ( iResult > 0 )
printf("Bytes received: %d\n", iResult);
else if ( iResult == 0 )
printf("Connection closed\n");
else
printf("recv failed with error: %d\n", WSAGetLastError());
// cleanup
closesocket(ConnectSocket);
WSACleanup();
system("pause");
return 0;
}
服務器:
// Need to link with Ws2_32.lib, Mswsock.lib, and Advapi32.lib
#include <iostream>
#include <Winsock2.h>
#include <Ws2tcpip.h>
#include <string>
#pragma comment (lib, "Ws2_32.lib")
#pragma comment (lib, "Mswsock.lib")
#pragma comment (lib, "AdvApi32.lib")
const char* DEFAULT_PORT = "27015";
const int DEFAULT_BUFLEN = 1024;
using namespace std;
int main(){
//Connection Variables.
WSADATA wsaData;
ADDRINFOA *result = NULL, hints;
SOCKADDR *clientInfo = NULL;
int iResult;
//Receive Variables.
char recvBuff[DEFAULT_BUFLEN];
int recvBuffLen = DEFAULT_BUFLEN;
int iSendResult;
//Server/Client sockets.
SOCKET ListenSocket = INVALID_SOCKET; //SOCKET for the server to listen for client connections.
SOCKET ClientSocket = INVALID_SOCKET;
//Initialize Winsock
iResult = WSAStartup( MAKEWORD( 2, 2 ), &wsaData );
printf("--> Initializing Winsock...\n*** Version: %s\n", wsaData.szDescription);
if ( iResult != 0 ){
printf("*** Could not initialize Socket.\n*** Error code: %d", iResult);
return 1;
}
//Initialize hints allocated memory.
ZeroMemory( &hints, sizeof( hints ) );
hints.ai_family = AF_INET; //AF_INET is used to specify the IPv4 address family.
hints.ai_socktype = SOCK_STREAM; //SOCK_STREAM is used to specify a stream socket.
hints.ai_protocol = IPPROTO_TCP; //IPPROTO_TCP is used to specify the TCP protocol.
hints.ai_flags = AI_PASSIVE; //AI_PASSIVE The socket address will be used in a call to the bind function.
printf("--> Getting address info from server...\n");
iResult = getaddrinfo( NULL, DEFAULT_PORT, &hints, &result );
if( iResult != 0 ){
printf("*** Error in getting address info from server.\n*** Error code: %d", iResult);
WSACleanup();
return 2;
}
printf("--> Creating server socket object...\n");
//printf("Create socket to ip: %s at port: %s\n", inet_ntoa(((SOCKADDR_IN*)(result->ai_addr))->sin_addr),DEFAULT_PORT);
ListenSocket = socket( result->ai_family, result->ai_socktype, result->ai_protocol );
if( ListenSocket == INVALID_SOCKET ){
printf("*** Error creating socket.\n*** Error code: %d\n",WSAGetLastError());
freeaddrinfo( result );
WSACleanup();
return 3;
}
//BIND()->Associates a local address to a socket.
printf("--> Bind listen object to local ip: 127.0.0.1 at port: %s...\n",DEFAULT_PORT);
iResult = bind( ListenSocket, result->ai_addr, result->ai_addrlen );
if( iResult == SOCKET_ERROR ){
printf("*** Binding failed.\n*** Error code: %d\n", WSAGetLastError());
closesocket( ListenSocket );
freeaddrinfo( result );
WSACleanup();
return 4;
}
freeaddrinfo(result);
printf("*** Server ONLINE: Listening...\n\n");
iResult = listen( ListenSocket, SOMAXCONN );
if( iResult == SOCKET_ERROR ){
printf("*** Failed start listening.\n*** Error code: %d\n",WSAGetLastError());
closesocket( ListenSocket );
freeaddrinfo( result );
WSACleanup();
return 5;
}
for(;1;){
ClientSocket = accept( ListenSocket,clientInfo, NULL );
if( ClientSocket == INVALID_SOCKET ){
printf("*** Failed accepting connection from client.\n*** Error code: %d\n",WSAGetLastError());
continue;
}
else{
printf("--> Connection accepted from client.\n");
iResult=1;
while(iResult > 0){
iResult = recv( ClientSocket, recvBuff, recvBuffLen, 0 );
if( iResult > 0 ){
printf("--> Message received: %s\n--> Total: %d\n", recvBuff, iResult);
}
}
iSendResult = send( ClientSocket, "Answer\0", DEFAULT_BUFLEN, 0 );
if( iSendResult == SOCKET_ERROR ){
printf("*** Sending data failed.\n*** Error code: %d\n",WSAGetLastError());
continue;
}
else{
printf("--> Sent: %d bytes\n", iSendResult);
}
printf("*** Closing connection... \n\n");
iResult = shutdown( ClientSocket, SD_BOTH );
if( iResult == SOCKET_ERROR ){
printf("*** Shutdown client failed.\nError code: %d\n",WSAGetLastError());
closesocket( ClientSocket );
WSACleanup();
return 9;
}
}
}
closesocket( ClientSocket );
WSACleanup();
system("pause");
return 0;
}
提前致謝!!!! 尼古拉斯·米蘭達(Nicolas Miranda S.)
當客戶端等待響應時,服務器無法在recv調用中被阻塞,因此無法發送任何內容。 您的接收器超時為1秒,因此1秒鍾后客戶端會生成超時錯誤(WSAETIMEDOUT == 10060)。
執行關閉操作時,僅指定SD_SEND,因此連接不會關閉,但是會導致服務器退出recv,因此能夠發送響應。
注意:recv將阻塞,直到收到流套接字(SOCK_STREAM)的內容為止。 您應該查看select()函數,以了解如何在調用recv之前“窺視”是否有可用數據。
這是使用select的示例:
fd_set fds;
timeval tv;
tv.tv_sec = 5000;
fds.fd_count = 1;
fds.fd_array[0] = ClientSocket;
int select_result = select(1, &fds, NULL, NULL, &tv);
如果select_result == 0,則存在超時。 否則,fd_set中的套接字之一已准備好數據。 這里只有一個,它在select調用中被指定為readfds。
您需要重新安排應用程序,以使導致服務器發送響應的某些事件(例如,接收到第三條消息,或者超時而沒有收到任何消息,或者消息本身中有一些東西)。 您可以使用第二個線程進行響應,但這超出了我簡短回答中的范圍。
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