In C, how to indicate EOF after writing data without close/shutdown a socket? -


i new c socket programming. learned after sending data through socket, 1 should either close or shutdown socket descriptor, triggers eof sent other end. without eof, read/recv keeps blocking.

now wondering if possible @ keep socket open further data transfer. read, seems people when establish keep-alive http connection. not figure out how achieved.

the following code shows scenario, stuck after client's write.

#include <stdio.h> #include <string.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <netdb.h>  #define thread_printf(...) printf("[pid %d] ", getpid()); printf(__va_args__);  int create_socket() {   int socket_fd;   socket_fd = socket(af_inet, sock_stream, 0);   if (socket_fd < 0)     perror("error opening socket");   return socket_fd; }  int listen_port(int portno) {   int socket_fd;   struct sockaddr_in server_addr;    socket_fd = create_socket();    memset((void *) &server_addr, 0, sizeof(server_addr));   server_addr.sin_family = af_inet;   server_addr.sin_port = htons(portno);   server_addr.sin_addr.s_addr = inaddr_any;    if (bind(socket_fd, (struct sockaddr *) &server_addr, sizeof(server_addr)) < 0)     perror("error on binding");    listen(socket_fd, 5);   return socket_fd; }  int connect_port(const char *host, int portno) {   int socket_fd;   struct sockaddr_in proxy_addr;   struct hostent *proxy;    socket_fd = create_socket();    proxy = gethostbyname(host);   if (proxy == null)     perror("error no such host");    proxy_addr.sin_family = af_inet;   proxy_addr.sin_port = htons(portno);   memcpy((void *) &proxy_addr.sin_addr.s_addr, (void *) proxy->h_addr, proxy->h_length);    if (connect(socket_fd, (struct sockaddr *) &proxy_addr, sizeof(proxy_addr)) < 0)     perror("error connecting");    return socket_fd; }  int read_socket(int fd, char *buf, int bufsize) {   thread_printf("read_socket\n");   int m = 0;                    /* total number of bytes received */   int n = 0;                    /* number of bytes received in single read */    while (m < bufsize - 1)   {     n = read(fd, buf + m, bufsize - m - 1);     if (n == -1)                /* socket read error */     {       perror("error reading socket");       break;     }     if (n == 0)                 /* socket closed */       break;     m += n;   }    if (m >= bufsize)     perror("error buffer overflow");    buf[m] = '\0';   return m; }  int write_socket(int fd, char *buf, int len) {   thread_printf("write_socket\n");   int m = 0;   int n = 0;    while (m < len)   {     n = write(fd, buf + m, len - m);     if (n == -1) {       perror("error socket send");       break;     }     if (n == 0)                 /* socket closed */       break;     m += n;   }   thread_printf("m = %d, len = %d\n", m, len);   return m; }  int main() {   int socket_fd = listen_port(3129);   if (fork() == 0)              /* client */   {     close(socket_fd);     int client_socket_fd = connect_port("127.0.0.1", 3129);     int n;     char *msg = "this client request\n";     char buf[1024];     memset((void *) buf, 0, 1024);     n = write_socket(client_socket_fd, msg, strlen(msg));     thread_printf("client sent: %s\n", msg);     n = read_socket(client_socket_fd, buf, 1024);     thread_printf("client received: %s\n", buf);     close(client_socket_fd);   }   else                          /* server */   {     struct sockaddr_in client_addr;     int client_len;     client_len = sizeof(client_addr);     int client_socket_fd = accept(socket_fd, (struct sockaddr *) &client_addr, &client_len);     int n;     char *msg = "this server response\n";     char buf[1024];     n = read_socket(client_socket_fd, buf, 1024);     thread_printf("server received: %s\n", buf);     n = write_socket(client_socket_fd, msg, strlen(msg));     thread_printf("server sent: %s\n", msg);     close(client_socket_fd);   }    return 0; }

in server code waits read 1024 bytes in client sending 26 bytes strlen(msg), server never return read_socket

as socket client-server application, need define own protocol client , server when conclude data has been read, either deciding fixed length packets or including length of data part of data itself

e.g. can decide data include, first 2 bytes length of data followed actual data


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