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在以非阻塞方式 connect() 时,返回的结果如果是 -1 ,并且错误号为 EINPROGRESS ,那么表示连接还在进行并处理中(IN PROGRESS),而不是真的发生了错误。
下面用一个实例来演示如何观察到返回 EINPROGRESS 的情况。
服务器端代码:
[C++] 纯文本查看 复制代码 #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
void str_echo(int sockfd)
{
int error;
ssize_t n;
char buf[1024];
again:
while ( (n = read(sockfd, buf, 1024)) > 0)
write(sockfd, buf, n); /* Dend back to client */
if (n < 0 && errno == EINTR)
goto again;
else if (n < 0) {
fprintf (stderr, "Read error");
exit (EXIT_FAILURE);
}
}
int main(int argc, char **argv)
{
int listenfd, connfd;
int clilen;
pid_t childpid;
struct sockaddr_in servaddr, cliaddr;
listenfd = socket(AF_INET, SOCK_STREAM, 0);
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(2013);
inet_aton("192.168.1.106", &servaddr.sin_addr);
bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
listen(listenfd, 1);
for (; ;) {
clilen = sizeof(cliaddr);
connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
if ( (childpid = fork()) == 0) {
close(listenfd);
str_echo(connfd);
exit(0);
}
close(connfd); /* parent closes connected socket */
}
}
服务器端监绑定在 192.168.1.106,并监听在 2013 端口,当客户端连接上时,读取客户算发来的信息,然后回射(echo)给客户端。
客户端代码:
[C++] 纯文本查看 复制代码 #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#define MAXLINE 1024
static int read_cnt;
static char *read_ptr;
static char read_buf[MAXLINE];
static ssize_t
my_read(int fd, char *ptr)
{
if (read_cnt <= 0) {
again:
if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {
if (errno == EINTR)
goto again;
return(-1);
} else if (read_cnt == 0)
return(0);
read_ptr = read_buf;
}
read_cnt--;
*ptr = *read_ptr++;
return(1);
}
ssize_t
readline(int fd, void *vptr, size_t maxlen)
{
ssize_t n, rc;
char c, *ptr;
ptr = vptr;
for (n = 1; n < maxlen; n++) {
if ( (rc = my_read(fd, &c)) == 1) {
*ptr++ = c;
if (c == '\n')
break; /* newline is stored, like fgets() */
} else if (rc == 0) {
*ptr = 0;
return(n - 1); /* EOF, n - 1 bytes were read */
} else
return(-1); /* error, errno set by read() */
}
*ptr = 0; /* null terminate like fgets() */
return(n);
}
ssize_t
readlinebuf(void **vptrptr)
{
if (read_cnt)
*vptrptr = read_ptr;
return(read_cnt);
}
/* end readline */
ssize_t
Readline(int fd, void *ptr, size_t maxlen)
{
ssize_t n;
if ( (n = readline(fd, ptr, maxlen)) < 0) {
printf("readline error");
exit(EXIT_FAILURE);
}
return(n);
}
void
Fputs(const char *ptr, FILE *stream)
{
if (fputs(ptr, stream) == EOF) {
perror("fputs error");
exit(EXIT_FAILURE);
}
}
void str_cli(FILE *fp, int sockfd)
{
char sendline[MAXLINE], recvline[MAXLINE];
while (fgets(sendline, MAXLINE, fp) != NULL) {
write(sockfd, sendline, strlen(sendline));
if (Readline(sockfd, recvline, MAXLINE) == 0) {
printf ("str_cli: server terminated prematurely");
exit(EXIT_FAILURE);
}
Fputs(recvline, stdout);
}
}
int main(int argc, char **argv)
{
int sockfd;
struct sockaddr_in servaddr;
if (argc != 2) {
printf ("usage: tcpcli <IP>");
exit(EXIT_FAILURE);
}
sockfd = socket(AF_INET, SOCK_STREAM, 0);
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
inet_pton(AF_INET, argv[1], &servaddr.sin_addr);
servaddr.sin_port = htons(2013);
int arg;
if ( (arg = fcntl(sockfd, F_GETFL, NULL)) < 0) {
fprintf(stderr, "Error fcntl(..., F_GETFL) (%S)\n", strerror(errno));
exit(EXIT_FAILURE);
}
arg |= O_NONBLOCK; /*设置为非阻塞模式*/
if (fcntl(sockfd, F_SETFL, arg) < 0) {
fprintf(stderr, "Error fcntl(..., F_SETFL) (%S)\n", strerror(errno));
exit(EXIT_FAILURE);
}
int conret;
fd_set myset;
struct timeval tv;
int valopt;
int len;
conret = connect(sockfd+1, (struct sockaddr *)&servaddr, sizeof(servaddr));
if (conret < 0) {
if (errno == EINPROGRESS) {
fprintf(stderr, "EINPROGRESS in connect() - selecting\n");
do {
tv.tv_sec = 15; /* 15 秒等待*/
tv.tv_usec = 0;
FD_ZERO(&myset);
FD_SET(sockfd, &myset);
conret = select(sockfd+1, NULL, &myset, NULL, &tv);
if (conret < 0 && errno != EINTR) {
fprintf(stderr, "Error connecting %d - %s\n", errno, strerror(errno));
exit(0);
}
else if (conret > 0) {
// Socket selected for write
len = sizeof(int);
if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, (void*)(&valopt), &len) < 0) {
fprintf(stderr, "Error in getsockopt() %d - %s\n", errno, strerror(errno));
exit(0);
}
// Check the value returned...
if (valopt) {
fprintf(stderr, "Error in delayed connection() %d - %s\n", valopt, strerror(valopt));
exit(0);
}
break;
}
else {
fprintf(stderr, "Timeout in select() - Cancelling!\n");
exit(0);
}
} while(1);
}
else {
fprintf(stderr, "Error connecting %d - %s\n", errno, strerror(errno));
exit(0);
}
}
// Set to blocking mode again...
if( (arg = fcntl(sockfd, F_GETFL, NULL)) < 0) {
fprintf(stderr, "Error fcntl(..., F_GETFL) (%s)\n", strerror(errno));
exit(0);
}
/*再次设置为阻塞模式*/
arg &= (~O_NONBLOCK);
if( fcntl(sockfd, F_SETFL, arg) < 0) {
fprintf(stderr, "Error fcntl(..., F_SETFL) (%s)\n", strerror(errno));
exit(0);
}
str_cli(stdin, sockfd);
exit(0);
}
当使用该客户端连接服务器后,由于客户端设置了非阻塞模式,因此在调用 connect() 时,它会马上返回(此时三次握手还在进行中,也就是连接还在处理(IN PROGRESS)),并且返回的错误号为 EINPROGRESS 。
实际上,连接客户端的代码并不需要像上面那样复杂,关键点就是为客户端设置非阻塞模式。 |
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