So i’ve made a concurrent server that transferes files with socket programming by using fork(), and made a client to connect to a known localhost and ask for a txt. that is in a file. Then the server sends the file to the client that will be then saved locally. This is for a project at college and i’ve been getting feedback that my fork() function in my server isn’t correct and it shouldn’t work, but for me it works just fine? Please have a look.
Server:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#define SIZE 1024
void send_file(FILE *fp, int sockfd){
int n;
char data(SIZE) = {0};
while(fgets(data, SIZE, fp) != NULL) {
if (send(sockfd, data, sizeof(data), 0) < 0) {
perror("(-)Error in sending file.");
exit(1);
}
bzero(data, SIZE);
}
return;
}
int main(){
// ip address and port
char *ip = "127.0.0.1";
int port = 8888;
// variables and structures
int e;
int sockfd, new_sock;
struct sockaddr_in server_addr, new_addr;
socklen_t addr_size;
char buffer(SIZE);
pid_t childpid;
FILE *fp;
char *filepath;
// 1. creating the socket
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0){
perror("(-)Error in socket");
exit(1);
}
printf("(+)Server socket created.n");
// 2. writing the data in the structure
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(ip);
server_addr.sin_port = port;
// 3. binding the ip address with the port
addr_size = sizeof(server_addr);
e = bind(sockfd, (struct sockaddr*)&server_addr, addr_size);
if (e < 0){
perror("(-)Error in bind");
exit(1);
}
printf("(+)Binding successfull.n");
// 4. listening to the clients
e = listen(sockfd, 10);
if (e < 0) {
perror("(-)Error in listen");
exit(1);
}
printf("(+)Listening...n");
// 5. accepting the client connection.
while (1){
addr_size = sizeof(new_addr);
new_sock = accept(sockfd, (struct sockaddr*)&new_addr, &addr_size);
if (new_sock < 0){
perror("(-)Error in accpet");
exit(1);
}
printf("Connection accepted from %s:%dn", inet_ntoa(new_addr.sin_addr), ntohs(new_addr.sin_port));
childpid = fork();
if (childpid == 0){
close(sockfd);
while(1){
recv(new_sock, buffer, SIZE, 0);
if (strcmp(buffer, "LIST") == 0){
// send the list of filenames.
bzero(buffer, SIZE);
strcpy(buffer, "data.txtnhello.txt");
send(new_sock, buffer, SIZE, 0);
bzero(buffer, SIZE);
}
else if (strcmp(buffer, "QUIT") == 0){
// connection disconnected.
printf("Connection disconnected from %s:%dn", inet_ntoa(new_addr.sin_addr), ntohs(new_addr.sin_port));
break;
}
else {
// received the filename, send the file data.
if (strcmp(buffer, "data.txt") == 0){
filepath = "server_files/data.txt";
fp = fopen(filepath, "r");
send_file(fp, new_sock);
}
else if (strcmp(buffer, "hello.txt") == 0) {
filepath = "server_files/hello.txt";
fp = fopen(filepath, "r");
send_file(fp, new_sock);
}
bzero(buffer, SIZE);
send(new_sock, " ", 1, 0);
bzero(buffer, SIZE);
}
}
}
}
}
Client:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#define SIZE 1024
void remove_char(char *s, int c){
/* This function is used to remove a character from the character array. */
int j, n = strlen(s);
for (int i=j=0; i<n; i++)
if (s(i) != c){
s(j++) = s(i);
}
s(j) = ' ';
}
void write_file(char *filepath, int sockfd){
int n;
FILE *fp;
char buffer(SIZE);
fp = fopen(filepath, "w");
if (fp == NULL) {
perror("(-)Error in creating file");
exit(1);
}
while (1) {
n = recv(sockfd, buffer, SIZE, 0);
if (n == 1) {
break;
return;
}
fprintf(fp, "%s", buffer);
fflush(fp);
bzero(buffer, SIZE);
}
return;
}
int main(){
// ip address and port
char *ip = "127.0.0.1";
int port = 8888;
// variables and structures,
int e;
int sockfd;
struct sockaddr_in server_addr;
char buffer(SIZE);
char *filepath;
// 1. creating the socket
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0){
perror("(-)Error in socket");
exit(1);
}
printf("(+)Client socket created.n");
// 2. writing the data in the structure
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(ip);
server_addr.sin_port = port;
// 3. connect to the server
e = connect(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr));
if(sockfd < 0){
perror("(-)Error in connect");
exit(1);
}
printf("(+)Connected to the servern");
printf("n");
printf("List of the commands.n");
printf("LIST - list all the files.n");
printf("LOAD - download the file.n");
printf(" LOAD <path>n");
printf("QUIT - disconnect from the server.n");
while(1){
fflush(stdout);
printf("> ");
fgets(buffer, SIZE, stdin);
if (strlen(buffer) > 1){
char *token1 = strtok(buffer, " ");
char *token2 = strtok(NULL, " ");
remove_char(token1, 'n');
if (strcmp(token1, "LIST") == 0) {
// list all the file of the server.
send(sockfd, buffer, SIZE, 0);
recv(sockfd, buffer, SIZE, 0);
printf("%sn", buffer);
}
else if (strcmp(token1, "LOAD") == 0) {
if (token2 == NULL) {
printf("(-)Specify the correct filename.n");
} else {
// save the data of the file received from the server.
remove_char(token2, 'n');
send(sockfd, token2, SIZE, 0);
if (strcmp(token2, "data.txt") == 0){
filepath = "client_files/data.txt";
write_file(filepath, sockfd);
printf("(+)File saved.n");
}
else if (strcmp(token2, "hello.txt") == 0) {
filepath = "client_files/hello.txt";
write_file(filepath, sockfd);
printf("(+)File saved.n");
}
else {
printf("Incorrect pathn");
}
}
}
else if (strcmp(token1, "QUIT") == 0) {
// disconnect from the server.
printf("(+)Disconnected from the server.n");
send(sockfd, token1, SIZE, 0);
break;
}
else {
printf("(-)Invalid commandn");
}
}
bzero(buffer, SIZE);
}
}
