我想编写一个简单的客户端/服务器应用程序，其中我将有固定长度的消息(BUFFER_SIZE)。我想确定，我发送/接收所有数据。
由于send_all效果很好，所以我对recv_all有问题。当我测试程序时，当客户端向服务器发送消息时，它没有得到响应。怎么了？谢谢。
客户端.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#define BUFFER_SIZE 1024
void hostname_to_ip(char *hostname, char *ip)
{
int sockfd;
struct addrinfo hints, *servinfo;
struct sockaddr_in *h;
int rv;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if ( (rv = getaddrinfo(hostname, NULL, &hints, &servinfo)) != 0)
{
fprintf(stderr, "getaddrinfo: %sn", gai_strerror(rv));
exit(1);
}
h = (struct sockaddr_in *) servinfo->ai_addr;
strcpy(ip, inet_ntoa( h->sin_addr ));
freeaddrinfo(servinfo);
}
ssize_t send_all(int sockfd, const char *buf)
{
ssize_t total_bytes = 0;
ssize_t bytes = 0;
size_t len = BUFFER_SIZE;
while (len > 0)
{
bytes = send(sockfd, buf + total_bytes, len, 0);
if (bytes == -1)
break;
total_bytes += bytes;
len -= bytes;
}
return total_bytes;
}
int recv_all(int sockfd, char *buf)
{
size_t len = BUFFER_SIZE;
char *p = buf;
ssize_t n, total_bytes = 0;
while (len > 0 && (n = recv(sockfd, p, len, 0)) > 0)
{
p += n;
len =- (size_t)n;
total_bytes += n;
}
if ( len > 0 || n < 0 )
{
return -1;
}
return total_bytes;
}
int main(int argc, char **argv)
{
char *hostname = "127.0.0.1";
char ip_addr[BUFFER_SIZE];
char buffer[BUFFER_SIZE+1];
int port = 6666;
char msg[BUFFER_SIZE];
int sockfd, recv_size, err;
struct sockaddr_in server_addr;
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("socket");
exit(1);
}
hostname_to_ip(hostname, ip_addr);
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
inet_aton(ip_addr, &server_addr.sin_addr);
if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
{
perror("connect");
exit(1);
}
while (1)
{
memset(buffer, BUFFER_SIZE+1, ' ');
printf("> ");
fgets (msg, BUFFER_SIZE-1, stdin);
err = send_all(sockfd, msg);
if (err == 0)
{
perror("send");
return 1;
}
if ((recv_size = recv(sockfd, buffer, BUFFER_SIZE, 0)) == 0)
{
close(sockfd);
if (errno != 0)
{
perror("recv");
exit(1);
}
}
buffer[recv_size] = ' ';
printf("FROM SERVER: %sn", buffer);
}
close(sockfd);
return 0;
}
服务器.c
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <string.h>
#define BUFFER_SIZE 1024
ssize_t send_all(int sockfd, const char *buf)
{
ssize_t total_bytes = 0;
ssize_t bytes = 0;
size_t len = BUFFER_SIZE;
while (len > 0)
{
bytes = send(sockfd, buf + total_bytes, len, 0);
if (bytes == -1)
break;
total_bytes += bytes;
len -= bytes;
}
return total_bytes;
}
ssize_t recv_all(int sockfd, char * buf)
{
size_t len = BUFFER_SIZE;
char *p = buf;
ssize_t total_bytes = 0, bytes = 0;
while (len > 0 && (bytes = recv(sockfd, p, len, 0)) > 0)
{
p += bytes;
len =- (size_t)bytes;
total_bytes += bytes;
}
if ( len > 0 || bytes < 0 )
{
return -1;
}
return total_bytes;
}
int main()
{
int port = 6666;
int server_fd, client_fd, err, res;
struct sockaddr_in server, client;
char buffer[BUFFER_SIZE];
memset(buffer, BUFFER_SIZE, ' ');
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd < 0)
{
printf("Could not create socketn");
perror("socket");
return 1;
}
int optval = 1;
setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, (const void *)&optval, sizeof(int));
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = htonl(INADDR_ANY);
err = bind(server_fd, (struct sockaddr *) &server, sizeof(server));
if (err < 0)
{
printf("Could not bind socketn");
perror("socket");
return 1;
}
err = listen(server_fd, 128);
if (err < 0)
{
printf("Could not listen on socketn");
perror("socket");
return 1;
}
printf("Server TCP is listening on port %d ... n", port);
socklen_t client_len = sizeof(client);
client_fd = accept(server_fd, (struct sockaddr *) &client, &client_len);
if (client_fd < 0)
{
printf("Could not establish new connectionn");
perror("socket");
return 1;
}
while(1)
{
char IP[255];
int remote_port;
struct sockaddr_in *s = (struct sockaddr_in *)&client;
remote_port = ntohs(s->sin_port);
inet_ntop(AF_INET, &s->sin_addr, IP, sizeof(IP));
printf("Client IP address: %s, port %dn", IP, remote_port);
int read;
memset(buffer, BUFFER_SIZE, ' ');
read = recv_all(client_fd, buffer);
if (read < 0)
{
printf("Client read failedn");
perror("socket");
return 1;
}
err = send_all(client_fd, buffer);
if (err == 0)
{
printf("Client write failedn");
perror("socket");
return 1;
}
}
close(server_fd);
close(client_fd);
return 0;
}
两边的recv_all()都有一个拼写错误，你倒着输入-=运算符：
-
客户：
len =- (size_t)n;需要len -= (size_t)n; -
服务器：需要
len =- (size_t)bytes;len -= (size_t)bytes;
您将len设置为n/bytes的负数，并且由于size_t是无符号类型，这会导致len变成一个非常大的数字，因此if (len > 0)总是为真，使recv()等待更多永远不会到达的数据。
我还看到了许多其他问题。
双方：
-
最好让
send_all()和recv_all()对BUFFER_SIZE一无所知. 改为将所需的len作为输入参数传递，并让调用方决定发送/读取多少字节。 这也将允许您简化他们的逻辑。 -
未正确验证
send_all()的返回值。 该代码假定只有返回值0是错误，但send_all()可以在失败时返回任何< BUFFER_SIZE值。
在客户端：
-
hostname_to_ip()假定返回的 IP(并且忽略了可能存在多个输出 IP 的事实)始终是AF_INET地址，但它对查询使用AF_UNSPEC，因此返回的 IP 可以是AF_INET6地址，这不适用于AF_INET套接字。 -
将
sockaddr_in转换为char[]只是为了将其转换回sockaddr_in是没有意义的。使用getaddrinfo()返回的原始sockaddr_in数据。 -
recv_all()根本没有被使用。客户端不处理recv()可能失败的情况，返回值< 0。
话虽如此，请尝试更多类似的东西：
客户端.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#define BUFFER_SIZE 1024
socklen_t hostname_to_ip_port(char *hostname, int port, struct sockaddr_storage *addr)
{
int sockfd;
struct addrinfo hints, *servinfo;
int rv;
char service[20];
sprintf(service, "%d", port);
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // <-- if you really want only IPv4, this should be AF_INET !
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
if ( (rv = getaddrinfo(hostname, service, &hints, &servinfo)) != 0)
{
fprintf(stderr, "getaddrinfo: %sn", gai_strerror(rv));
return 0;
}
socklen_t addrlen = servinfo->ai_addrlen;
memcpy(addr, servinfo->ai_addr, addrlen);
freeaddrinfo(servinfo);
return addrlen;
}
int send_all(int sockfd, const char *buf, size_t len)
{
ssize_t n;
while (len > 0)
{
n = send(sockfd, buf, len, 0);
if (n < 0)
return -1;
buf += n;
len -= n;
}
return 0;
}
int recv_all(int sockfd, char *buf, int len)
{
ssize_t n;
while (len > 0)
{
n = recv(sockfd, buf, len, 0);
if (n <= 0)
return n;
buf += n;
len -= n;
}
return 1;
}
int main(int argc, char **argv)
{
char *hostname = "127.0.0.1";
int port = 6666;
char buffer[BUFFER_SIZE];
int sockfd, err;
struct sockaddr_storage server_addr;
socklen_t server_addr_len;
server_addr_len = hostname_to_ip_port(hostname, port, &server_addr);
if (server_addr_len == 0)
return 1;
sockfd = socket(server_addr.ss_family, SOCK_STREAM, IPPROTO_TCP);
if (sockfd < 0)
{
perror("Could not create socket");
return 1;
}
if (connect(sockfd, (struct sockaddr *)&server_addr, server_addr_len) < 0)
{
perror("Could not connect socket");
return 1;
}
while (1)
{
printf("> ");
if (!fgets(buffer, BUFFER_SIZE, stdin))
break;
if (send_all(sockfd, buffer, BUFFER_SIZE) < 0)
{
perror("Could not send message");
close(sockfd);
return 1;
}
err = recv_all(sockfd, buffer, BUFFER_SIZE);
if (err <= 0)
{
if (err < 0)
perror("Could not read message");
else
printf("Server disconnectedn");
break;
}
printf("FROM SERVER: %.*sn", BUFFER_SIZE, buffer);
}
close(sockfd);
return 0;
}
服务器.c
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <string.h>
#define BUFFER_SIZE 1024
int send_all(int sockfd, const char *buf, int len)
{
ssize_t n;
while (len > 0)
{
n = send(sockfd, buf, len, 0);
if (n < 0)
return -1;
buf += n;
len -= n;
}
return 0;
}
int recv_all(int sockfd, char * buf, int len)
{
ssize_t n;
while (len > 0)
{
n = recv(sockfd, buf, len, 0);
if (n <= 0)
return n;
buf += n;
len -= n;
}
return 1;
}
int main()
{
int port = 6666;
int server_fd, client_fd, read;
struct sockaddr_in server, client;
char buffer[BUFFER_SIZE];
char remote_ip[16];
int remote_port;
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd < 0)
{
perror("Could not create socket");
return 1;
}
int optval = 1;
setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, (const void *)&optval, sizeof(int));
memset(&server, ' ', sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(server_fd, (struct sockaddr *) &server, sizeof(server)) < 0)
{
perror("Could not bind socket");
close(server_fd);
return 1;
}
if (listen(server_fd, 1) < 0)
{
perror("Could not listen on socket");
close(server_fd);
return 1;
}
printf("Server TCP is listening on port %d ... n", port);
socklen_t client_len = sizeof(client);
client_fd = accept(server_fd, (struct sockaddr *) &client, &client_len);
if (client_fd < 0)
{
perror("Could not establish new connection");
close(server_fd);
return 1;
}
remote_port = ntohs(client.sin_port);
inet_ntop(AF_INET, &client.sin_addr, remote_ip, sizeof(remote_ip));
printf("Client IP address: %s, port %dn", remote_ip, remote_port);
while (1)
{
read = recv_all(client_fd, buffer, BUFFER_SIZE);
if (read <= 0)
{
if (read < 0)
perror("Client read failed");
else
printf("Client disconnectedn");
break;
}
printf("FROM CLIENT: %.*sn", BUFFER_SIZE, buffer);
if (send_all(client_fd, buffer, BUFFER_SIZE) < 0)
{
perror("Client write failed");
break;
}
}
close(client_fd);
close(server_fd);
return 0;
}