C file server and client hanging on recv - c

Question

So I am trying to work on this toy client file server problem.
The iterative version works fine, but when I attempt to fork each new connection in the server code, the client code hangs on the recv call.
I am fairly sure the issue is with the peer_socket, but I have been unable to find my mistake.
It completes just fine if I hit the server with a Ctrl-c though.
CLIENT CODE:
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netinet/in.h>
#define PORT_NUMBER 5108
#define SERVER_ADDRESS "localhost"
//#define FILENAME "test.txt"
int main(int argc, char **argv)
{
int client_socket;
ssize_t len;
struct sockaddr_in remote_addr;
char buffer[BUFSIZ];
char filename[256];
char local_filename[256];
int file_size;
FILE *received_file;
int remain_data = 0;
/* Zeroing remote_addr struct */
memset(&remote_addr, 0, sizeof(remote_addr));
memset(local_filename, 0, sizeof(local_filename));
if(argc >1){
strncpy(local_filename, argv[1], 256);
}
/* Construct remote_addr struct */
remote_addr.sin_family = AF_INET;
inet_pton(AF_INET, SERVER_ADDRESS, &(remote_addr.sin_addr));
remote_addr.sin_port = htons(PORT_NUMBER);
/* Create client socket */
client_socket = socket(AF_INET, SOCK_STREAM, 0);
if (client_socket == -1)
{
fprintf(stderr, "Error creating socket --> %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
//Prompt for file to retrieve
printf("Enter file name: ");
fgets(filename,sizeof(filename),stdin);
printf("Getting file %s", filename);
/* Connect to the server */
if (connect(client_socket, (struct sockaddr *)&remote_addr, sizeof(struct sockaddr)) == -1)
{
fprintf(stderr, "Error on connect --> %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
//Send filename to server
/*if(!send(client_socket,filename, sizeof(filename))) {
printf("Error sending filename\n");
exit(EXIT_FAILURE);
}*/
send(client_socket,filename, sizeof(filename),0);
printf("success\n");
/* Receiving file size */
memset(&buffer, 0, sizeof(buffer));
recv(client_socket, buffer, sizeof(buffer), 0);
file_size = atoi(buffer);
fprintf(stdout, "\nFile size : %d\n", file_size);
if(!local_filename[0]) {
received_file = fopen("test2.txt", "w");
}else{
received_file = fopen(local_filename, "w");
}
if (received_file == NULL)
{
fprintf(stderr, "Failed to open file foo --> %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
remain_data = file_size;
//THIS IS THE LOOP THAT HANGS!
while (((len = recv(client_socket, buffer, BUFSIZ, 0)) > 0) && (remain_data > 0))
{
fwrite(buffer, sizeof(char), len, received_file);
remain_data -= len;
fprintf(stdout, "Receive %d bytes and we hope :- %d bytes\n", len, remain_data);
}
printf("did we reach here in the code?\n");
fclose(received_file);
printf("did we reach here in the code?\n");
close(client_socket);
return 0;
}
SERVER CODE:
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <signal.h>
#define PORT_NUMBER 5108
#define SERVER_ADDRESS "localhost"
//#define FILE_TO_SEND "hello.c"
int main(int argc, char **argv)
{
int server_socket;
socklen_t global_sock_len;
struct sockaddr_in server_addr;
struct sockaddr_in peer_addr;
/* Create server socket */
server_socket = socket(AF_INET, SOCK_STREAM, 0);
if (server_socket == -1)
{
fprintf(stderr, "Error creating socket --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Zeroing server_addr struct */
memset(&server_addr, 0, sizeof(server_addr));
/* Construct server_addr struct */
server_addr.sin_family = AF_INET;
inet_pton(AF_INET, SERVER_ADDRESS, &(server_addr.sin_addr));
server_addr.sin_port = htons(PORT_NUMBER);
/* Bind */
if ((bind(server_socket, (struct sockaddr *)&server_addr, sizeof(struct sockaddr))) == -1)
{
fprintf(stderr, "Error on bind --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Listening to incoming connections */
if ((listen(server_socket, 5)) == -1)
{
fprintf(stderr, "Error on listen --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
//attempt multiple connections via fork
int peer_socket;
int fid;
while(1) {
bool servexit = false;
printf("did we reach HERE in the code?%d\n",getpid());
peer_socket = accept(server_socket, (struct sockaddr *) &peer_addr, &global_sock_len);
//printf("did we reach HERE in the code?\n");
if (peer_socket == -1) {
fprintf(stderr, "Error on accept --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
if((fid = fork()) == -1) {
printf("error\n");
close(peer_socket);
//continue;
}else if(fid > 0){
printf("parent\n");
close(peer_socket);
//continue;
}else if(fid == 0) {
printf("child\n");
socklen_t sock_len;
ssize_t len;
int fd;
int sent_bytes = 0;
char FILE_TO_SEND[256];
char file_size[256];
struct stat file_stat;
off_t offset;
int remain_data;
//int peer_socket = peer_socket;
recv(peer_socket, FILE_TO_SEND, sizeof(FILE_TO_SEND), 0);
printf("Client requested %s", FILE_TO_SEND);
if (strlen(FILE_TO_SEND) > 1) {
strtok(FILE_TO_SEND, "\n");
}
//check for server close command from client
if(strcmp(FILE_TO_SEND,"quit") == 0){
servexit = true;
printf("Quiting server\n");
close(server_socket);
close(peer_socket);
pid_t pid = getppid();
kill(pid, SIGKILL);
exit(0);
}else {
fd = open(FILE_TO_SEND, O_RDONLY);
if (fd == -1) {
fprintf(stderr, "Error opening file --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Get file stats */
if (fstat(fd, &file_stat) < 0) {
fprintf(stderr, "Error fstat --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(stdout, "File Size: \n%d bytes\n", file_stat.st_size);
sock_len = sizeof(struct sockaddr_in);
fprintf(stdout, "Accept peer --> %s\n", inet_ntoa(peer_addr.sin_addr));
sprintf(file_size, "%d", file_stat.st_size);
/* Sending file size */
len = send(peer_socket, file_size, sizeof(file_size), 0);
if (len < 0) {
fprintf(stderr, "Error on sending greetings --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(stdout, "Server sent %d bytes for the size\n", len);
//fflush((FILE*)peer_socket);
offset = 0;
remain_data = file_stat.st_size;
/* Sending file data */
while (((sent_bytes = sendfile(peer_socket, fd, &offset, BUFSIZ)) > 0) && (remain_data > 0)) {
fprintf(stdout,
"1. Server sent %d bytes from file's data, offset is now : %d and remaining data = %d\n",
sent_bytes, offset, remain_data);
remain_data -= sent_bytes;
fprintf(stdout,
"2. Server sent %d bytes from file's data, offset is now : %d and remaining data = %d\n",
sent_bytes, offset, remain_data);
}
}
break;
}
}
return 0;
}

Answer 1

Ok, so, it turns out that sendfile() doesn't play as nicely as send() in this situation. I found two fixes.
1.) Use send() instead of sendfile()
2.) Retry in both sendfile() (Server) and recv() (client) if either returns -1 (error)