Unix/Linux socket 編程的一個問題？

01-05

服務端提供一個返回時間的服務，客戶端使用telnet去訪問
#include & #include & #include & #include & #include & #include & #include & #include & #include &
#define PORTNUM 13000 #define HOSTLEN 256 #define oops(msg) {perror(msg); exit(1);} int main() { struct sockaddr_in saddr; struct hostent *hp; char hostname[HOSTLEN]; int sock_id, sock_fd; FILE *sock_fp; char *ctime(); time_t thetime; sock_id = socket(PF_INET, SOCK_STREAM, 0); if( sock_id == -1 ) oops("scoket"); bzero((void*)saddr, sizeof(saddr)); gethostname(hostname, HOSTLEN); hp = gethostbyname(hostname); bcopy((void*)hp-&>h_addr, (void*)saddr.sin_addr, hp-&>h_length); saddr.sin_port = htons(PORTNUM); saddr.sin_family = AF_INET; if( bind(sock_id, (struct sockaddr*)saddr, sizeof(saddr)) != 0 ) oops("bind"); if( listen(sock_id, 1) != 0 ) oops("listen"); while(1) { sock_fd = accept(sock_id, NULL, NULL); printf("Wow! got a call "); if( sock_fd == -1 ) oops("accept"); sock_fp = fdopen(sock_id, "w"); if (sock_fp == NULL) oops("fdopen"); thetime = time(NULL);
fprintf(sock_fp, "The time here is..."); fprintf(sock_fp, "%s", ctime(thetime)); fclose(sock_fp); } }

運行結果如下：
deweixudeMBP:socket deweixu$ ./timeserv.out [1] 32999 deweixudeMBP:socket deweixu$ hostname deweixudeMBP.lan deweixudeMBP:socket deweixu$ telnet deweixudeMBP.lan 13000 Trying 192.168.199.205... Wow! got a call Connected to deweixudembp.lan. Escape character is "^]". Wow! got a call accept: Bad file descriptor Connection closed by foreign host. [1]+ Exit 1 ./timeserv.out deweixudeMBP:socket deweixu$
為什麼會 `accept: Bad file descriptor` ?

sock_fp = fdopen(sock_id, "w");

改成

sock_fp = fdopen(sock_fd, "w");

話說如果變數命名的時候Hamming距離大一點就不會犯這種錯誤了，比如 sock_id 改成 listening_fd。

fclose(sock_fp);

一般來說，bad file descriptor會有兩種情況。一個是用的時候被其他地方關閉了，另外一種是錯誤的值。

感覺代碼有點辣眼睛啊！

fdopen(sock_id) 只是返回了文件指針而已，並不會增加 socket 的引用計數，你後面 fclose 了 sock_fp 就相當於關閉了監聽 socket ，再 accept 肯定返回錯誤啊！