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Winsock2，客户端-服务器通信——轮流发送/接收

[英]Winsock2, client-server communication - send/recv in turns

 原文  2020-06-19 16:49:47  8   2    c++/ winsock/ send/ winsock2/ recv

问题描述

我想编写一个客户端/服务器应用程序，客户端和服务器可以在其中交换消息。

Client site communication:

send
recv
send 
recv

Server site communication:

recv
send
recv
send

但是，我有一个问题，因为只有一条消息是发送/接收。 之后，套接字关闭，不再发送消息。 出了什么问题以及如何解决这个问题？ 谢谢你。

服务器代码：

#undef UNICODE

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#pragma comment (lib, "Ws2_32.lib")
#define DEFAULT_PORT "27501"
#define SIZE 1024

int SendAllToClient(SOCKET ClientSocket, char *buffer)
{
    int iSendResult;


    int total = 0, len = 1024;
    int bytesleft = 1024;

    while( total < len )
    {
        iSendResult = send( ClientSocket, buffer, 1024, NULL);

        if (iSendResult == SOCKET_ERROR)
        {
            printf("send failed with error: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        total += iSendResult;
        bytesleft -= iSendResult;
    }
    printf("Bytes sent: %d\n", iSendResult);

    return total<len?- 1: 1;
}

char *ReadFromClient(SOCKET ConnectSocket)
{
    int iResult;
    char *buffer = new char[1024];
    memset(buffer, 0, 1024);

    do
    {
        iResult = recv(ConnectSocket, buffer, 1024, 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());

    }
    while( iResult > 0 );
    return buffer;
}

int main(int argc , char *argv[])
{
    WSADATA wsaData;
    char *buffer;

    SOCKET ListenSocket = INVALID_SOCKET;
    SOCKET ClientSocket = INVALID_SOCKET;

    struct addrinfo *result = NULL;
    struct addrinfo hints;

    int sessionID;
    int iResult;

   // Datagram d1,d2,d3;

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0)
    {
        printf("WSAStartup failed with error: %d\n", iResult);
        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    // Resolve the server address and port
    iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
    if ( iResult != 0 )
    {
        printf("getaddrinfo failed with error: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // Create a SOCKET for connecting to server
    ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
    if (ListenSocket == INVALID_SOCKET)
    {
        printf("socket failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        WSACleanup();
        return 1;
    }

    // Setup the TCP listening socket
    iResult = bind( ListenSocket, result->ai_addr, (int)result->ai_addrlen);
    if (iResult == SOCKET_ERROR)
    {
        printf("bind failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    freeaddrinfo(result);

    iResult = listen(ListenSocket, SOMAXCONN);
    if (iResult == SOCKET_ERROR)
    {
        printf("listen failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    printf("Server is listening on localhost:%s ...\n", DEFAULT_PORT);

    // Accept a client socket
    SOCKADDR_IN addr;
    int addrlen = sizeof(addr);

    ClientSocket = accept(ListenSocket, (SOCKADDR*)&addr, &addrlen);
    if (ClientSocket == INVALID_SOCKET)
    {
        printf("accept failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    char *ip = inet_ntoa(addr.sin_addr);
    int port = addr.sin_port;
    printf("\nClient %s:%d connected to server\n", ip, port);

    // No longer need server socket
    closesocket(ListenSocket);

    // shutdown the connection since we're done
    iResult = shutdown(ClientSocket, SD_SEND);
    if (iResult == SOCKET_ERROR)
    {
        printf("shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }

    //read
    buffer = ReadFromClient(ClientSocket);
    printf("FROM CLIENT: %s\n", buffer);
    //send
    memset(buffer, 0, 1024);
    memcpy(buffer, "Hi client, how are you?", strlen("Hi client, how are you?"));
    SendAllToClient(ClientSocket, buffer);
    //read
    //send

    // cleanup
    closesocket(ClientSocket);
    WSACleanup();

    return 0;
}

客户端代码：

#undef UNICODE

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#pragma comment (lib, "Ws2_32.lib")
#define DEFAULT_PORT "27501"
#define SIZE 1024

int SendAllToServer(SOCKET ServerSocket, char *buffer)
{
    int iSendResult;

    int total = 0, len = 1024;
    int bytesleft = 1024;

    while( total < len )
    {
        iSendResult = send( ServerSocket, buffer, 1024, NULL);

        if (iSendResult == SOCKET_ERROR)
        {
            printf("send failed with error: %d\n", WSAGetLastError());
            closesocket(ServerSocket);
            WSACleanup();
            return 1;
        }
        total += iSendResult;
        bytesleft -= iSendResult;
    }
    printf("Bytes sent: %d\n", iSendResult);

    return total<len?- 1: 1;
}

char *ReadFromServer(SOCKET ConnectSocket)
{
    int iResult;
    char *buffer = new char[1024];
    memset(buffer, 0, 1024);

    do {
        iResult = recv(ConnectSocket, buffer, 1024, 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());

    } while( iResult > 0 );
    return buffer;
}

int main(int argc , char *argv[])
{
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct addrinfo *result = NULL,
                    *ptr = NULL,
                    hints;
    char* buffer;
    int sessionID;
    int iResult;
   // Datagram d1,d2;

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed with error: %d\n", 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);
    if ( iResult != 0 ) {
        printf("getaddrinfo failed with error: %d\n", 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
        ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype,
            ptr->ai_protocol);
        if (ConnectSocket == INVALID_SOCKET) {
            printf("socket failed with error: %d\n", WSAGetLastError());
            WSACleanup();
            return 1;
        }

        // Connect to server.
        iResult = connect( ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
        if (iResult == SOCKET_ERROR) {
            closesocket(ConnectSocket);
            ConnectSocket = INVALID_SOCKET;
            continue;
        }
        break;
    }

    freeaddrinfo(result);

    if (ConnectSocket == INVALID_SOCKET) {
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }

    //send
    buffer = new char[1024];
    memset(buffer, 0, 1024);
    memcpy(buffer, "Hi server", strlen("Hi server"));
    SendAllToServer(ConnectSocket, buffer);
    //read
    memset(buffer, 0, 1024);
    buffer = ReadFromServer(ConnectSocket);
    printf("FROM SERVER: %s\n", buffer);
    //send
    //read

    // cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

编辑

服务器

#include "data_types.h"
#undef UNICODE

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <string>
#include <iostream>
#pragma comment (lib, "Ws2_32.lib")
#define DEFAULT_PORT "27015"
#define SIZE 1024

int SendAllToClient(SOCKET ClientSocket)
{
    char *buffer = new char[SIZE];
    int iSendResult;
    memset(buffer, 0, SIZE);

    int total = 0, len = SIZE;
    int bytesleft = SIZE;

    while( total < len )
    {
        iSendResult = send( ClientSocket, buffer + total, bytesleft, NULL);

        if (iSendResult == SOCKET_ERROR)
        {
            printf("send failed with error: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        total += iSendResult;
        bytesleft -= iSendResult;
    }
    printf("Bytes sent: %d\n", iSendResult);
    delete buffer;

    return total<len?- 1: 1;
}

char* ReadFromClient(SOCKET ClientSocket)
{
    std::string data = "";
    char *all = NULL;
    char buffer[1];
    int total = 0, len = SIZE;
    int bytesleft = SIZE;
    int iResult;
    memset(buffer, 0, 1);

    while(total < len)
    {
        if ((iResult = recv(ClientSocket, buffer, 1, 0)) == 0)
        {
            if (errno != 0)
            {
                // cleanup
                closesocket(ClientSocket);
                WSACleanup();
                exit(1);
            }
        }
        data = data + std::string(buffer);
        total += iResult;
        bytesleft -= iResult;
        memset(buffer, 0, 1);
    }
    all = new char[data.length() + 1];
    strcpy(all, data.c_str());

    return all;
}

int main(int argc , char *argv[])
{
    WSADATA wsaData;
    char *buffer;

    SOCKET ListenSocket = INVALID_SOCKET;
    SOCKET ClientSocket = INVALID_SOCKET;

    struct addrinfo *result = NULL;
    struct addrinfo hints;

    int sessionID;
    int iResult;

   // Datagram d1,d2,d3;

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0)
    {
        printf("WSAStartup failed with error: %d\n", iResult);
        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    // Resolve the server address and port
    iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
    if ( iResult != 0 )
    {
        printf("getaddrinfo failed with error: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // Create a SOCKET for connecting to server
    ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
    if (ListenSocket == INVALID_SOCKET)
    {
        printf("socket failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        WSACleanup();
        return 1;
    }

    // Setup the TCP listening socket
    iResult = bind( ListenSocket, result->ai_addr, (int)result->ai_addrlen);
    if (iResult == SOCKET_ERROR)
    {
        printf("bind failed with error: %d\n", WSAGetLastError());
        freeaddrinfo(result);
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    freeaddrinfo(result);

    iResult = listen(ListenSocket, SOMAXCONN);
    if (iResult == SOCKET_ERROR)
    {
        printf("listen failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    printf("Server is listening on localhost:%s ...\n", DEFAULT_PORT);

    // Accept a client socket
    SOCKADDR_IN addr;
    int addrlen = sizeof(addr);

    ClientSocket = accept(ListenSocket, (SOCKADDR*)&addr, &addrlen);
    if (ClientSocket == INVALID_SOCKET)
    {
        printf("accept failed with error: %d\n", WSAGetLastError());
        closesocket(ListenSocket);
        WSACleanup();
        return 1;
    }

    char *ip = inet_ntoa(addr.sin_addr);
    int port = addr.sin_port;
    printf("\nClient %s:%d connected to server\n", ip, port);

    // No longer need server socket
    closesocket(ListenSocket);

    // shutdown the connection since we're done
    iResult = shutdown(ClientSocket, SD_SEND);
    if (iResult == SOCKET_ERROR)
    {
        printf("shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }

    //read
    buffer = new char[1024];
    memset(buffer, 0, 1024);
    buffer = ReadFromClient(ClientSocket);
    printf("FROM CLIENT: %s\n", buffer);

    //send
    memset(buffer, 0, 1024);
    memcpy(buffer, "Hi client, how are you?", strlen("Hi client, how are you?"));
    // Send an initial buffer
    iResult = send( ClientSocket, buffer, (int)strlen(buffer), 0 );
    if (iResult == SOCKET_ERROR) {
        wprintf(L"send failed with error: %d\n", WSAGetLastError());
        closesocket(ClientSocket);
        WSACleanup();
        return 1;
    }
    //read
    //send

    // cleanup
    closesocket(ClientSocket);
    WSACleanup();

    return 0;
}

客户

#include "data_types.h"
#undef UNICODE

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <string>
#include <iostream>
#pragma comment (lib, "Ws2_32.lib")
#define DEFAULT_PORT "27015"
#define SIZE 1024

int SendAllToServer(SOCKET ClientSocket)
{
    char *buffer = new char[SIZE];
    memset(buffer, 0, SIZE);

    int total = 0, len = SIZE;
    int bytesleft = SIZE, iSendResult;

    while( total < len )
    {
        iSendResult = send( ClientSocket, buffer + total, bytesleft, NULL);

        if (iSendResult == SOCKET_ERROR)
        {
            printf("send failed with error: %d\n", WSAGetLastError());
            closesocket(ClientSocket);
            WSACleanup();
            return 1;
        }
        total += iSendResult;
        bytesleft -= iSendResult;
    }
    printf("Bytes sent: %d\n", iSendResult);
    delete buffer;

    return total<len?- 1: 1;
}

char *ReadFromServer(SOCKET ClientSocket)
{
    std::string data = "";
    char *all = NULL;
    char buffer[1];
    int total = 0, len = SIZE;
    int bytesleft = SIZE;
    int iResult;
    memset(buffer, 0, 1);

    while(total < len)
    {
        if ((iResult = recv(ClientSocket, buffer, 1, 0)) == 0)
        {
            if (errno != 0)
            {
                // cleanup
                closesocket(ClientSocket);
                WSACleanup();
                exit(1);
            }
        }
        data = data + std::string(buffer);
        total += iResult;
        bytesleft -= iResult;
        memset(buffer, 0, 1);
    }
    all = new char[data.length() + 1];
    strcpy(all, data.c_str());

    return all;
}

int main(int argc , char *argv[])
{
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct addrinfo *result = NULL,
                    *ptr = NULL,
                    hints;
    char* buffer;
    int sessionID;
    int iResult;
   // Datagram d1,d2;

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed with error: %d\n", 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);
    if ( iResult != 0 ) {
        printf("getaddrinfo failed with error: %d\n", 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
        ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype,
            ptr->ai_protocol);
        if (ConnectSocket == INVALID_SOCKET) {
            printf("socket failed with error: %d\n", WSAGetLastError());
            WSACleanup();
            return 1;
        }

        // Connect to server.
        iResult = connect( ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
        if (iResult == SOCKET_ERROR) {
            closesocket(ConnectSocket);
            ConnectSocket = INVALID_SOCKET;
            continue;
        }
        break;
    }

    freeaddrinfo(result);

    if (ConnectSocket == INVALID_SOCKET) {
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }

    //send
    buffer = new char[1024];
    memset(buffer, 0, 1024);
    memcpy(buffer, "Hi server, how are you?", strlen("Hi server, how are you?"));
    // Send an initial buffer
    iResult = send( ConnectSocket, buffer, (int)strlen(buffer), 0 );
    if (iResult == SOCKET_ERROR) {
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }
    //read
    memset(buffer, 0, 1024);
    // Receive until the peer closes the connection
    do {

        iResult = recv(ConnectSocket, buffer, 1024, 0);
        if ( iResult > 0 )
            wprintf(L"Bytes received: %d\n", iResult);
        else if ( iResult == 0 )
            wprintf(L"Connection closed\n");
        else
            wprintf(L"recv failed with error: %d\n", WSAGetLastError());

    } while( iResult > 0 );
    printf("FROM SERVER: %s\n", buffer);
    //send
    //read

    // cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

2 个解决方案

解决方案1
 8  2020-06-21 19:47:20

首要问题：

    iSendResult = send( ClientSocket, buffer, 1024, NULL);

那 1024 应该是bytesleft 。 如果您已经读取了 512 个字节，那么您不想再读取 512 个字节。

该buffer应该是buffer + total 。 如果您已经发送了 512 个字节，您不想再次发送相同的 512 个字节，您想发送其他512 个字节。

第二题：

您的ReadFromServer function 完全损坏并且没有遵循正确的逻辑。 它只返回致命错误，甚至不尝试准确读取 1,024 个字节。 它最多只能读取 1,024 个字节，然后，无论它实际读取了多少字节，都会尝试再次读取 1,024 个字节——并在同一地址覆盖它已经读取的消息的任何部分！

它应该像发送 function 一样工作，首先尝试接收 1,024 字节，如果接收不到，则循环，直到它收到正好 1,024 字节或出现致命错误。

第三题：

    buffer = ReadFromServer(ConnectSocket);
    printf("FROM SERVER: %s\n", buffer);

不要这样做。 假设服务器是恶意的，向您发送了 1,024 个字节，这些字节不是合法的 C 样式字符串。 通过%s将其传递给printf可能会导致客户端崩溃或行为不端。 始终将从网络接收到的数据视为不受信任且可能具有恶意。 虽然你的代码不修复这个问题就可以工作，但有一天这样做会以某种可怕的方式咬你，这不是一个好习惯。

完成后，您还应该delete[]缓冲区。 但是你为什么要返回一个原始指针呢？ 您可以返回std::string 、 std::vector或许多其他更好的机制，以避免泄漏风险并使副本安全。

解决方案2
 3  2020-06-26 14:07:51

实际上，您正在关闭侦听套接字，因此一旦有接受的连接，它将不再接受：

ClientSocket = accept(ListenSocket, (SOCKADDR*)&addr, &addrlen);
if (ClientSocket == INVALID_SOCKET)
{
    printf("accept failed with error: %d\n", WSAGetLastError());
    closesocket(ListenSocket);
    WSACleanup();
    return 1;
}

char *ip = inet_ntoa(addr.sin_addr);
int port = addr.sin_port;
printf("\nClient %s:%d connected to server\n", ip, port);

// No longer need server socket
closesocket(ListenSocket);

关闭侦听器会阻止进一步的连接。 此外，您在处理之前关闭客户端套接字：

// shutdown the connection since we're done
iResult = shutdown(ClientSocket, SD_SEND);
if (iResult == SOCKET_ERROR)
{
    printf("shutdown failed with error: %d\n", WSAGetLastError());
    closesocket(ClientSocket);
    WSACleanup();
    return 1;
}

//read
buffer = new char[1024];
memset(buffer, 0, 1024);
buffer = ReadFromClient(ClientSocket);
printf("FROM CLIENT: %s\n", buffer);

//send
memset(buffer, 0, 1024);
memcpy(buffer, "Hi client, how are you?", strlen("Hi client, how are you?"));
// Send an initial buffer
iResult = send( ClientSocket, buffer, (int)strlen(buffer), 0 );

如果要多次发送和接收，则应循环读取/写入。 您只这样做了一次（并且做得不正确）：所以只有您在问题中描述的一条消息。

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