I would like to implement a client-server architecture running on Linux using sockets and C/C++ language that is capable of sending and receiving files. Is there any library that makes this task easy? Could anyone please provide an example?
This question is related to
c++
c
linux
sockets
network-programming
Minimal runnable POSIX read
+ write
example
Usage:
get two computers on a LAN.
For example, this will work if both computers are connected to your home router in most cases, which is how I tested it.
On the server computer:
Find the server local IP with ifconfig
, e.g. 192.168.0.10
Run:
./server output.tmp 12345
On the client computer:
printf 'ab\ncd\n' > input.tmp
./client input.tmp 192.168.0.10 12345
Outcome: a file output.tmp
is created on the sever computer containing 'ab\ncd\n'
!
server.c
/*
Receive a file over a socket.
Saves it to output.tmp by default.
Interface:
./executable [<output_file> [<port>]]
Defaults:
- output_file: output.tmp
- port: 12345
*/
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <netdb.h> /* getprotobyname */
#include <netinet/in.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <unistd.h>
int main(int argc, char **argv) {
char *file_path = "output.tmp";
char buffer[BUFSIZ];
char protoname[] = "tcp";
int client_sockfd;
int enable = 1;
int filefd;
int i;
int server_sockfd;
socklen_t client_len;
ssize_t read_return;
struct protoent *protoent;
struct sockaddr_in client_address, server_address;
unsigned short server_port = 12345u;
if (argc > 1) {
file_path = argv[1];
if (argc > 2) {
server_port = strtol(argv[2], NULL, 10);
}
}
/* Create a socket and listen to it.. */
protoent = getprotobyname(protoname);
if (protoent == NULL) {
perror("getprotobyname");
exit(EXIT_FAILURE);
}
server_sockfd = socket(
AF_INET,
SOCK_STREAM,
protoent->p_proto
);
if (server_sockfd == -1) {
perror("socket");
exit(EXIT_FAILURE);
}
if (setsockopt(server_sockfd, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable)) < 0) {
perror("setsockopt(SO_REUSEADDR) failed");
exit(EXIT_FAILURE);
}
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
server_address.sin_port = htons(server_port);
if (bind(
server_sockfd,
(struct sockaddr*)&server_address,
sizeof(server_address)
) == -1
) {
perror("bind");
exit(EXIT_FAILURE);
}
if (listen(server_sockfd, 5) == -1) {
perror("listen");
exit(EXIT_FAILURE);
}
fprintf(stderr, "listening on port %d\n", server_port);
while (1) {
client_len = sizeof(client_address);
puts("waiting for client");
client_sockfd = accept(
server_sockfd,
(struct sockaddr*)&client_address,
&client_len
);
filefd = open(file_path,
O_WRONLY | O_CREAT | O_TRUNC,
S_IRUSR | S_IWUSR);
if (filefd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
do {
read_return = read(client_sockfd, buffer, BUFSIZ);
if (read_return == -1) {
perror("read");
exit(EXIT_FAILURE);
}
if (write(filefd, buffer, read_return) == -1) {
perror("write");
exit(EXIT_FAILURE);
}
} while (read_return > 0);
close(filefd);
close(client_sockfd);
}
return EXIT_SUCCESS;
}
client.c
/*
Send a file over a socket.
Interface:
./executable [<input_path> [<sever_hostname> [<port>]]]
Defaults:
- input_path: input.tmp
- server_hostname: 127.0.0.1
- port: 12345
*/
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <netdb.h> /* getprotobyname */
#include <netinet/in.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <unistd.h>
int main(int argc, char **argv) {
char protoname[] = "tcp";
struct protoent *protoent;
char *file_path = "input.tmp";
char *server_hostname = "127.0.0.1";
char *server_reply = NULL;
char *user_input = NULL;
char buffer[BUFSIZ];
in_addr_t in_addr;
in_addr_t server_addr;
int filefd;
int sockfd;
ssize_t i;
ssize_t read_return;
struct hostent *hostent;
struct sockaddr_in sockaddr_in;
unsigned short server_port = 12345;
if (argc > 1) {
file_path = argv[1];
if (argc > 2) {
server_hostname = argv[2];
if (argc > 3) {
server_port = strtol(argv[3], NULL, 10);
}
}
}
filefd = open(file_path, O_RDONLY);
if (filefd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
/* Get socket. */
protoent = getprotobyname(protoname);
if (protoent == NULL) {
perror("getprotobyname");
exit(EXIT_FAILURE);
}
sockfd = socket(AF_INET, SOCK_STREAM, protoent->p_proto);
if (sockfd == -1) {
perror("socket");
exit(EXIT_FAILURE);
}
/* Prepare sockaddr_in. */
hostent = gethostbyname(server_hostname);
if (hostent == NULL) {
fprintf(stderr, "error: gethostbyname(\"%s\")\n", server_hostname);
exit(EXIT_FAILURE);
}
in_addr = inet_addr(inet_ntoa(*(struct in_addr*)*(hostent->h_addr_list)));
if (in_addr == (in_addr_t)-1) {
fprintf(stderr, "error: inet_addr(\"%s\")\n", *(hostent->h_addr_list));
exit(EXIT_FAILURE);
}
sockaddr_in.sin_addr.s_addr = in_addr;
sockaddr_in.sin_family = AF_INET;
sockaddr_in.sin_port = htons(server_port);
/* Do the actual connection. */
if (connect(sockfd, (struct sockaddr*)&sockaddr_in, sizeof(sockaddr_in)) == -1) {
perror("connect");
return EXIT_FAILURE;
}
while (1) {
read_return = read(filefd, buffer, BUFSIZ);
if (read_return == 0)
break;
if (read_return == -1) {
perror("read");
exit(EXIT_FAILURE);
}
/* TODO use write loop: https://stackoverflow.com/questions/24259640/writing-a-full-buffer-using-write-system-call */
if (write(sockfd, buffer, read_return) == -1) {
perror("write");
exit(EXIT_FAILURE);
}
}
free(user_input);
free(server_reply);
close(filefd);
exit(EXIT_SUCCESS);
}
Further comments
Possible improvements:
Currently output.tmp
gets overwritten each time a send is done.
This begs for the creation of a simple protocol that allows to pass a filename so that multiple files can be uploaded, e.g.: filename up to the first newline character, max filename 256 chars, and the rest until socket closure are the contents. Of course, that would require sanitation to avoid a path transversal vulnerability.
Alternatively, we could make a server that hashes the files to find filenames, and keeps a map from original paths to hashes on disk (on a database).
Only one client can connect at a time.
This is specially harmful if there are slow clients whose connections last for a long time: the slow connection halts everyone down.
One way to work around that is to fork a process / thread for each accept
, start listening again immediately, and use file lock synchronization on the files.
Add timeouts, and close clients if they take too long. Or else it would be easy to do a DoS.
poll
or select
are some options: How to implement a timeout in read function call?
A simple HTTP wget
implementation is shown at: How to make an HTTP get request in C without libcurl?
Tested on Ubuntu 15.10.
This file will serve you as a good sendfile
example : http://tldp.org/LDP/LGNET/91/misc/tranter/server.c.txt
Do aman 2 sendfile
. You only need to open the source file on the client and destination file on the server, then call sendfile and the kernel will chop and move the data.
Source: Stackoverflow.com