Why am I receiving more bytes than I am sending C? - c

Question

I am receiving more bytes than I am sending on server side, and the file I receive has some garbage characters at the start of my file.
client code
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <dirent.h>
#include <time.h>
int main() {
int serverPort, clientPort, clientSock, serverSock;
scanf("%d", &clientPort);
struct sockaddr_in cadd, sadd1, sadd2, clen, slen;
cadd.sin_family = AF_INET;
cadd.sin_addr.s_addr = inet_addr("127.0.0.1");
cadd.sin_port = htons(clientPort);
clientSock = socket(AF_INET, SOCK_STREAM, 0);
if(clientSock == -1)
fprintf(stderr, "unable to create socket: %s\n", strerror(errno));
int result = connect(clientSock, (struct sockaddr *)&cadd, sizeof(cadd) );
if(result == -1) {
fprintf(stderr, "unable to create socket: %s\n", strerror(errno));
return -1;
}
while(1) {
struct stat stat_buf;
off_t offset = 0;;
int choice = 1;
int fd = open("myList.txt", O_RDONLY);
if (fd == -1) {
fprintf(stderr, "unable to open %s", strerror(errno));
exit(1);
}
fstat(fd, &stat_buf);
offset = 0;
int size = (int)stat_buf.st_size;
printf("File size: %d\n", size);
send(clientSock, &size, sizeof(stat_buf.st_size), 0);
int sent = sendfile(clientSock, fd, &offset, stat_buf.st_size);
if(sent == -1) {
fprintf(stderr, "error sendfile: %s\n", strerror(errno));
exit(1);
}
if(sent != stat_buf.st_size) {
fprintf(stderr, "error sendfile %d of %d bytes\n", sent, (int)stat_buf.st_size);
exit(1);
}
printf("sendfile succesfull %d\n", sent);
break;
}
}
server code
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <dirent.h>
#include <time.h>
int main() {
int serverPort, sock;
printf("Enter port number: ");
scanf("%d", &serverPort);
struct sockaddr_in server1, server2;
int addrlen = sizeof(server2);
sock = socket(AF_INET, SOCK_STREAM, 0);
if(sock == -1) {
fprintf(stderr, "unable to create socket: %s\n", strerror(errno));
exit(1);
}
server1.sin_family = AF_INET;
server1.sin_port = htons(serverPort);
int rc = bind(sock, (struct sockaddr *) &server1, sizeof(server1));
if(rc == -1) {
fprintf(stderr, "bind error: %s\n", strerror(errno));
close(rc);
exit(1);
}
rc = listen(sock, 1);
if(rc == -1) {
fprintf(stderr, "listen failed: %s\n", strerror(errno));
exit(1);
}
while(1) {
int con = accept(sock, (struct sockaddr *) &server2, &addrlen);
int crt = creat("please.txt", S_IRWXU), size, count = 0;
recv(con, &size, sizeof(size), 0);
while(1) {
char mssg[100];
memset(mssg, '\0', sizeof(mssg));
int n = recv(con, mssg, sizeof(mssg), 0);
int wrt = write(crt, mssg, n);
count = count + wrt;
printf("Count: %d\n", count);
if(count >= size)
break;
}
printf("Write successful\n");
}
}
Attaching the screen-shots
client send =>
[server recv] =>

Answer 1

In the client you do this:
send(clientSock, &size, sizeof(stat_buf.st_size), 0);
But in the server you do:
recv(con, &size, sizeof(size), 0);
size is an int, which is 4 bytes. But st_size is off_t, which is presumably 8 bytes. So you're only reading the first 4 bytes of the the size, and leaving the rest to be copied into the file. That's why you end up with 4 extra bytes on the server.
Declare size with the same data type as st_size, rather than int, and your problem should be solved.