Question

我正在尝试了解大学考试的C socket编程。我做了这个简单的例子：

socket_server.c

#include <sys/socket.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <arpa/inet.h>

#define SA struct sockaddr
#define MAX_MESS_LEN 16

int main(){
    struct sockaddr_in my_addr, cl_addr;
    int ret, len, sk, cn_sk;
    char cl_ip[INET_ADDRSTRLEN + 1], msg[MAX_MESS_LEN + 1];

    sk = socket(AF_INET, SOCK_STREAM, 0); //creo socket TCP/IPv4 listener
    printf("socket created! :)\n");
    memset(&my_addr, 0, sizeof(my_addr)); //azzero struttura my_addr
    my_addr.sin_family = AF_INET; //famiglia protocolli IPv4
    my_addr.sin_addr.s_addr = htonl(INADDR_ANY); //in ascolto su qualsiasi interfaccia
    my_addr.sin_port = htons(1234); //porta del socket

    ret = bind(sk, (SA *) &my_addr, sizeof(my_addr)); //lego il socket alla struttura   indirizzo
    printf("socket binded! :)\n");
    ret = listen(sk, 10); //mi pongo in ascolto sul socket con massimo 10 richieste pendenti
    printf("socket listening (on any interface with port 1234)! :)\n");
    len = sizeof(cl_addr);
    printf("socket is going to wait for a request... zzzzZZZ\n");
    cn_sk = accept(sk, (SA *) &cl_addr, &len); //creo il socket connected per la richiesta in cima alla lista
    printf("socket accepted request! :D\n");
    inet_ntop(AF_INET, &cl_addr.sin_addr, cl_ip, INET_ADDRSTRLEN); //converto indirizzo IPv4 cl_addr.sin_addr in stringa (cl_ip)
    printf("IP client: %s\n", cl_ip);

   ret = recv(sk, (void *) msg, MAX_MESS_LEN, MSG_WAITALL); //attendo la ricezione di tutti i caratteri della stringa inviata sul socket dal client
    msg[MAX_MESS_LEN + 1] = '\0';
    printf("received data (%d bytes): %s\n", ret, msg);
    if(ret == -1 || ret < MAX_MESS_LEN)
        printf("recv ERROR! :(\n");

    close(sk); //chiudo il server
}

socket_client.c

#include <sys/socket.h>
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#define SA struct sockaddr
#define MSG_LEN 17

int main(){
    struct sockaddr_in srv_addr;
    int ret, sk;
    char msg[MSG_LEN];

    sk = socket(AF_INET, SOCK_STREAM, 0);
    printf("Socket created! :)\n");
    memset(&srv_addr, 0, sizeof(srv_addr));
    srv_addr.sin_family = AF_INET;
    srv_addr.sin_port = htons(1234);
    ret = inet_pton(AF_INET, "192.168.1.132", &srv_addr.sin_addr);

    printf("Trying to establish a connection with 192.168.1.132 on port 1234...");  
    ret = connect(sk, (SA *) &srv_addr, sizeof(srv_addr)); //faccio una richiesta sul socket
    if(ret != -1) printf("Connection established! :D\n");
    else printf(" connection error :(\n");

    strcpy(msg, "something to send"); //scrivo messaggio in una stringa
    printf("sending message: %s\n", msg);
    ret = send(sk, (void *) msg, strlen(msg), 0); //invio il messaggio sul socket
    if(ret == -1 || ret < strlen(msg))
        printf("send ERROR! :(\n");

    close(sk);  
}

用以下内容编译：

gcc socket_client.c -o socket_client
gcc socket_server.c -o socket_server

也许这是一个愚蠢的问题，但服务器中的recv函数总是失败，有一个示例输出：

服务器：

socket created! :)
socket binded! :)
socket listening (on any interface with port 1234)! :)
socket is going to wait for a request... zzzzZZZ
socket accepted request! :D
IP client: 192.168.1.132
received data (-1 bytes): ����
recv ERROR! :(

客户端：

Socket created! :)
Trying to establish a connection with 192.168.1.132 on port 1234...Connection established! :D
sending message: something to send

有什么问题？我不明白！ :(我一步一步地跟着，老师的指导。

我正在运行arch linux 64位;）谢谢你的回复！

Answer 1

cn_sk = accept(sk, (SA *) &cl_addr, &len); //creo il socket connected per la richiesta in cima alla lista
...
ret = recv(sk, (void *) msg, MAX_MESS_LEN, MSG_WAITALL); //at

您不必在连接的套接字recv上cn_sk到客户端，而是在侦听器套接字sk上。如果您检查errno，您可能会看到ENOTCONN。

C套接字编程：recv总是失败

1 个答案: