Creating a file transfer application using UDP in C - c

Question

I am trying to implement a server-client application in which the client sends the name of file to server. The server looks for the file and if the file exist it sends the file to the client back and this goes on . Here is the code i have written but the problem is that the server does not send the content of file back to client I had the same problem earlier ,then i re-wrote the code .
Here is the code :-
Server Side
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <string.h>
int main() {
char buff[20];
char content[200];
int sd, connfd, len, bytes_read;
struct sockaddr_in servaddr, cliaddr;
sd = socket(AF_INET, SOCK_DGRAM, 0);
if (sd == -1) {
puts("socket not created in server");
return 1;
} else {
puts("socket created in server");
}
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(7802);
if (bind(sd, (struct sockaddr *)&servaddr, sizeof(servaddr)) != 0) {
puts("Not binded");
return 1;
} else {
puts("Binded");
}
len = sizeof(cliaddr);
recvfrom(sd, buff, 1024, 0, (struct sockaddr *)&cliaddr, &len);
printf("%s\n", buff);
FILE *fp = fopen(buff, "r");
if (fp == NULL) {
printf("File does not exist \n");
return 1;
}
while (1) {
bytes_read = read(fp, content, sizeof(content));
if (bytes_read == 0)
break;
sendto(sd, content, sizeof(content), 0, (struct sockaddr*)&cliaddr, len);
bzero(content, 200);
}
strcpy(content, "end");
sendto(sd, content, sizeof(content), 0, (struct sockaddr*)&cliaddr, len);
return 0;
}
Client side:
#include <stdio.h>
#include <errno.h>
#include <sys/socket.h>
#include <resolv.h>
#include <netinet/in.h>
#include <sys/types.h>
int main() {
int count = 0;
char buff[20], output[20];
char file_buffer[200];
int sockfd, connfd, len;
struct sockaddr_in servaddr, cliaddr;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd == -1) {
puts("socket not created in client");
return 1;
} else {
puts("socket created in client");
}
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = INADDR_ANY; // ANY address or use specific address
servaddr.sin_port = htons(7802); // Port address
puts("Type your UDP client message");
scanf("%s", buff);
puts("enter the name of new file to be saved");
scanf("%s", output);
// send msg to server
sendto(sockfd, buff, strlen(buff) + 1, 0,
(struct sockaddr *)&servaddr, sizeof(struct sockaddr));
count++;
printf("%d\n", count);
FILE *fp = fopen(output, "a");
if (fp == NULL) {
puts("error in file handling");
return 1;
}
recvfrom(sockfd, file_buffer, sizeof(file_buffer), 0, NULL, NULL);
while (1) {
if (strcmp(file_buffer, "end") == 0)
break;
printf("%s", file_buffer);
write(fp, file_buffer, strlen(file_buffer));
bzero(file_buffer, 200);
recvfrom(sockfd, file_buffer, sizeof(file_buffer), 0, NULL, NULL);
}
puts("completed");
return 0;
}

Answer 1

Probably you should use the fread() function instead of read() on server side.
Functions fopen() and read() are parts of different interfaces:
Family read() -> open, close, read, write, ioctl (system calls)
Family fread() -> fopen, fclose, fread, fwrite, fcntl (standard library)
I can suppose that file descriptor given by fopen() is not exactly the same as read() expects.
The same on client side. You use the fopen() to open file and write() to write. Please use the fwrite()