我正试图从客户端程序接收一条大消息,这两个程序都使用SOCK_STREAM套接字,因此,我不得不在recv调用上使用while循环。然而,它冻结了,并且似乎没有在循环中打印任何内容。
这是服务器的代码
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>
#define BUFSIZE 1024
extern int errno;
void error(char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
int sock, newsock, len, fromlen, n;
unsigned short port;
struct sockaddr_in server, from;
char buffer[BUFSIZE];
char *msg = "I Got your message";
if (argc < 2) {
fprintf(stderr,"usage %s portnumbern",argv[0]);
exit(0);
}
port = (unsigned short) atoi(argv[1]);
sock=socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) error("Opening socket");
server.sin_family=AF_INET;
server.sin_addr.s_addr=INADDR_ANY;
server.sin_port=htons(port);
len=sizeof(server);
if (bind(sock, (struct sockaddr *)&server, len) < 0)
error("binding socket");
fromlen=sizeof(from);
if (listen(sock,5) < 0)
error("listening");
// accept connections loop
while (1) {
newsock=accept(sock, (struct sockaddr *)&from, &fromlen);
if (newsock < 0) error("Accepting");
printf("A connection has been accepted from %sn",
inet_ntoa((struct in_addr)from.sin_addr));
// receive long messages loop
while ((n = recv(newsock,buffer,BUFSIZE-1,0)) > 0){
buffer[n] = ' ';
printf("n message: n%sn", buffer);
}
len = strlen(msg);
n = send(newsock,msg,len,0);
if (n < len) error("Error writing");
if (close(newsock) < 0) error("closing");
}
return 0; // we never get here
}
这是客户端的代码
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h> /* for atoi */
char *msg = "Very long message";
void error(char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
int sock, n;
unsigned short port;
struct sockaddr_in server;
struct hostent *hp;
char buffer[1024];
if (argc != 3) {
printf("Usage: %s server portn", argv[0]);
exit(1);
}
sock= socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) error("Opening socket");
server.sin_family = AF_INET;
hp = gethostbyname(argv[1]);
if (hp==NULL) error("Unknown host");
memcpy((char *)&server.sin_addr,(char *)hp->h_addr,
hp->h_length);
port = (unsigned short)atoi(argv[2]);
server.sin_port = htons(port);
if (connect(sock, (struct sockaddr *)&server, sizeof server) < 0)
error("Connecting");
n = send(sock, msg, strlen(msg),0);
printf("sent %d bytesn", n);
if (n < strlen(msg))
error("Writing to socket");
n = recv(sock, buffer, 1023,0);
if (n < 1) error("reading from socket");
buffer[n]=' ';
printf("The message from the server is %sn",buffer);
if (close(sock) < 0) error("closing");
printf("Client terminatingn");
return 0;
}
最终目标是在服务器端接收完整的消息,然后向客户端发回消息已收到的确认。
此条件:
(n = recv(newsock,buffer,BUFSIZE-1,0)) > 0
将始终为true,除非远程关闭套接字或系统调用返回错误。否则,如果没有从客户端发送数据,它将被阻止。
在STREAM套接字上,您必须期望一个字节流,而不需要假设它将如何在对recv()
的几个调用中分块。一种常见的解决方案是首先发送(和接收)长度信息,然后调用recv,直到总共接收到长度字节。
对于您的特殊情况,另一个选项("快速修复")可能是在发送大消息后关闭客户端中套接字的发送方向:
shutdown(fd, SHUT_WR);
之后,recv系统调用将返回0,服务器可以发送其确认。但是,客户端在调用shutdown()
之后将无法发送数据。