In C, I am trying to connect to a server using the following function:
int clientConnect() {
//1. Set up connection address and port
char *ipAddress = SMSA_DEFAULT_IP;
int port = SMSA_DEFAULT_PORT;
//1a. Set up a sockaddr_in struct as described in lecture
struct sockaddr_in caddr;
caddr.sin_family = AF_INET;
caddr.sin_addr.s_addr = htonl(SMSA_DEFAULT_IP);
caddr.sin_port = htons( port );
//2. Create a socket
server_socket = socket(PF_INET, SOCK_STREAM, 0);
if(server_socket == -1)
{
logMessage(1, "There was an error creating a socket in clientConnect()");
return -1;
}
//3. Connect
if( connect(server_socket, (const struct sockaddr *)&caddr, sizeof(struct sockaddr) ) == -1)
{
logMessage(1, "There was an error connecting in clientConnect()");\
return -1;
}
logMessage(2, "The connection was made!");
return 0;}
When this function is called, I get a message in my log There was an error connecting in clientConnect(). This is my first time doing network programming with C so I suspect I am missing something.
The last argument to connect should be sizeof caddr:
connect(server_socket, (const struct sockaddr *)&caddr, sizeof caddr);
Related
I am exploring network programming in C.The code is supposed to connect to a server on port 80 send an http request and from the response print on what server is the web page running on, but it runs into Invalid Argument error. The error occurs with error message "[ERR] connecting to target server: Invalid argument" so the error should be somewhere in the connect() function.
rec = connect(sockfd, (struct sockaddr *)&target_addr, sizeof(struct sockaddr) == -1);
if(rec == -1)
fail("[ERR] connecting to target server");
Although I have seen a lot of similar issues, none of the fixes neither worked or applied to this case, strangely this code works as a standalone program when parsing argc[1] instead of char *name, regardless of what the exact string literal is(ip or hostname, experimented with multiple for both). The only difference between the two being that the entire web server function is written in main and passed command-line arguments(working example) while here it is written as a standalone function and called in main where it was tested on a few web page names and IP addresses.
Any help would be appreciated as I feel this might be some simple mistake I overlooked or something I don't understand well enough. Thanks!
int web_server(char *name){
int sockfd, rec;
struct hostent *host_info;
//struct in_addr *address;
struct sockaddr_in target_addr;
unsigned char buffer[4096];
if(is_ip(name)){
target_addr.sin_addr.s_addr = inet_addr(name);
} else if(host_info = gethostbyname(name)){
if(host_info == NULL){
fail("[ERR] looking up hostname!");
}else{
target_addr.sin_addr = *((struct in_addr *) host_info -> h_addr);
}
} else{
fail("[ERR] getting address");
}
target_addr.sin_family = AF_INET;
target_addr.sin_port = htons(80);
memset(&(target_addr.sin_zero), 0, 8);
sockfd = socket(PF_INET, SOCK_STREAM, 0);
if(sockfd == -1){
fail("[ERR] in socket");
}
rec = connect(sockfd, (struct sockaddr *)&target_addr, sizeof(struct sockaddr) == -1);
if(rec == -1)
fail("[ERR] connecting to target server");
send_string(sockfd, "HEAD / HTTP/1.0\r\n\r\n");
while(recv_line(sockfd, buffer)){
if(strncasecmp(buffer, "Server: ", 7) == 0){
printf("The web server for %s is %s\n", name, buffer+8);
}
}
close(sockfd);
printf("Server line not found\n");
exit(1);
}
int main(){
web_server("127.0.0.1");//doesn't work with hostnames either
}
For a school project I have to use sockets to create a server, I think I managed to do it but I am supposed to use Telnet to test it, and whenever I try I get
telnet: connect to address 0.0.0.0: Connection refused
So i guess it is with the IP that I'm wrong.
The simplified version of my code that should still work for one connection is
int main(int argc , char *argv[])
{
int sock;
int fd = 0;
int err = 0;
struct sockaddr_in sock_data;
socklen_t addr_size;
char *path;
path = get_current_dir_name();
if (argc == 2)
printf("%s", Usage);
sock = socket(AF_INET , SOCK_STREAM , 0);
if (sock == -1) {
printf("Could not create socket");
return (84);
}
memset(&sock_data, 0, sizeof(struct sockaddr_in));
sock_data.sin_family = AF_INET;
sock_data.sin_port = htons(5133);
sock_data.sin_addr.s_addr = htonl(INADDR_ANY);
printf("%s, %s, %s\n", path, sock_data.sin_addr, inet_ntoa(sock_data.sin_addr));
if (bind(sock, (const struct sockaddr *) &sock_data, sizeof(sock_data)) == -1)
printf("Error with binding\n");
if (listen(sock, LISTEN_BACKLOG) == -1)
printf("Error with listen");
addr_size = sizeof(struct sockaddr_in);
err = accept(sock, (struct sockaddr *) &sock_data, &addr_size);
while ((sock = accept(sock, NULL, NULL)) < 0)
err = 0;
return 84;
}
I saw this link: TCP sockets in c
that was quite clear but I still don't get how I am supposed to test my program
And the more I work on it the more I am convinced that I must have made a stupid mistake.
So do you know where I went wrong?
In your Telnet command you missed a port. The commamd should be like a
telnet system_ip port
For example
telnet 192.168.1.1 5631
I am currently coding a small chat application in C for learning network.
I develop using the Transmission Control Protocol with socket in C. I was able to connect to my server with a client not coded by myself (on local network). Now telnet succeed to connect to my chat server(so with server and telnet client on the same computer) and I can send and receive message BUT my very simple client cannot connect to it.
Since the begining I use port 9002 and right now I am trying to connect with IPv6 address ::1.
Here the "accept client" code of my server:
int main(void)
{
//Create the socket
int sock = socket(AF_INET6, SOCK_STREAM, 0);
printf("Socket créer\n");
//Set up the socket interface
struct sockaddr_in6 sin6 = { 0 };
sin6.sin6_family = AF_INET6;
sin6.sin6_port = htons(PORT);
sin6.sin6_addr = in6addr_any;
//Bind the socket on the port
if(bind(sock, (struct sockaddr *) &sin6, sizeof(struct sockaddr_in6)) == SO_ERROR)
{
perror("bind()");
errx(EXIT_FAILURE, "Fail to bind");
}
//Make the sockey listen the port
if(listen(sock, MAX_CLIENT) == SO_ERROR)
{
perror("listen()");
errx(EXIT_FAILURE, "Fail to listen");
}
printf("Socket listening\n");
int csock;
size_t clientID = 0;
--snip--
while(1)
{
struct sockaddr_in6 csin6;
memset(&csin6, 0, sizeof(struct sockaddr_in6));
int sin6size = sizeof(struct sockaddr_in6);
//Accept a communication
printf("Wait for communication\n");
csock = accept(sock, (struct sockaddr *) &csin6, &sin6size);
printf("Connection accepted\n");
char msg[16];
sprintf(msg, "CONNECTED - %zu\n", clientID);
send(csock, msg, sizeof(msg), 0);
printf("Client %zu connected\n", clientID);
//Handle client
--snip--
}
So this is a basic connection with socket using connected communication. The server handle several client in the while loop thanks to threading.
Here the code of the client:
void *sender(void *arg)
{
int socket = (int)(long)arg;
char buffer[BUFF_SIZE];
while(1)
{
scanf("%s", buffer);
send(socket, buffer, strlen(buffer), 0);
bzero(buffer, BUFF_SIZE);
}
}
int main(int argc, char *argv[])
{
if(argc < 2)
errx(EXIT_FAILURE, "Usage: ./client <server ip>\n");
//Create the socket
int sock = socket(AF_INET6, SOCK_STREAM, 0);
struct hostent *hostinfo = NULL;
hostinfo = gethostbyname2(argv[1], AF_INET6);
if(hostinfo == NULL)
errx(EXIT_FAILURE, "Can't connect to the server\n");
//Set up the socket interface
struct sockaddr_in6 sin6 = { 0 };
sin6.sin6_family = AF_INET6;
sin6.sin6_port = htons(PORT);
sin6.sin6_addr = *(struct in6_addr *)hostinfo->h_addr;
if(connect(sock, (struct sockaddr *) &sin6, sizeof(struct sockaddr)) == SO_ERROR)
{
perror("connect()");
errx(EXIT_FAILURE, "Fail to connect");
}
printf("Connection established\n");
pthread_t sending;
if(pthread_create(&sending, NULL, sender, (void *)(long)sock) != 0)
printf("Fail to create a thread\n");
//Handle reception
char buffer[BUFF_SIZE];
int n;
while((n = recv(sock, buffer, BUFF_SIZE - 1, 0)) >= 0)
{
buffer[n] = '\0';
printf("%s", buffer);
}
printf("Erreur: %d\nConnection broken\n", n);
pthread_cancel(sending);
close(sock);
return EXIT_SUCCESS;
}
So I start the client with:
~ ./client ::1
The output is the following:
Connection established
Error: -1
Connection broken
While the server is still "Waiting for communication". This means that the server do not accept the connection but the client succeed to connect.
Thank you for you help.
It is probably already the connect(), which fails here:
if(connect(sock, (struct sockaddr *) &sin6, sizeof(struct sockaddr)) == SO_ERROR)
SO_ERROR is not meant to be used here, but as a socket option when retrieving the error when an asynchronous connect fails. A (synchronous) connect() returns -1 on error and sets errno, so do
if(connect(sock, (struct sockaddr *) &sin6, sizeof(struct sockaddr)) == -1) {
...
Later, the recv here:
while((n = recv(sock, buffer, BUFF_SIZE - 1, 0)) >= 0)
fails with errno ENOTCONN, since the connection failed beforehand.
The same SO_ERROR mistake is present at various locations in your server code; it is possible, that already the bind() there fails! The call to listen() will then autobind it to a free ephemereal port, so the call as well as the call to accept() will succeed.
Why can the call to bind() fail? You might have to set the socket option SO_REUSEADDR when (re-)starting the server, otherwise it might refuse to use a recently bound port if connections are still in TIME_WAIT state. Place this directly before the bind() call:
int one = 1;
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
This might help.
I'm working on a project that involves sending various requests to a server through UDP. However, I seem to be setting up the socket entirely wrong, as the server does not respond to any of my requests. We were provided with a server binary to test against, and the code below ellicits no response. Am I setting up the UDP socket correctly? If so, am I somehow using sendto wrong? I have confirmed that I am sending the correct number of bits.
The input for the program is: ./client [URL] [port] [username], and I always test with ./client localhost 8080 user. Here is the struct I am sending and the code.
struct request_login {
int req_type; /* = REQ_LOGIN */
char req_username[32];
} packed;
Code:
struct sockaddr_in sa;
int sockfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
if(sockfd == -1){
printf("Could not create socket.");
exit(EXIT_FAILURE);
}
// Prepare the socket address
memset(&sa, 0, sizeof sa);
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = inet_addr(argv[1]);
// Convert to network order
sa.sin_port = htonl(atoi(argv[2]));
// Assemble and send login request
struct request_login * reqlogin = (struct request_login *) malloc(sizeof(struct request_login));
reqlogin->req_type = REQ_LOGIN;
strcpy(reqlogin->req_username, argv[3]);
int res = sendto(sockfd, reqlogin, sizeof (struct request_login), 0, (struct sockaddr*)&sa, sizeof sa);
free(reqlogin)
Huh?
This:
sa.sin_addr.s_addr = inet_addr(argv[1]);
certainly won't do the right thing if, as you say, argv[1] is typically "localhost". You need to look up the host name, so that you get an IP address. You can only use inet_addr() if the input is a dotted IP address, not a host name.
Look at getaddrinfo().
After re-reading your code a couple of times, I think I know what one cause of the error may be:
sa.sin_port = htonl(atoi(argv[2]));
The port number is a short so you should use htons instead. It's very small and easy to miss.
try this instead:
struct addrinfo hint;
memset(&chk,0,sizeof(chk));
hint.ai_family = AF_INET;
hint.ai_socktype = SOCK_DGRAM;
hint.ai_protocol = IPPROTO_UDP;
struct addrinfo* servAddr = NULL;
int ret = getaddrinfo(argv[1],atoi(argv[2]),&hint,&servAddr);
if (-1 == ret)
{
perror("getaddrinfo failed");
exit(EXIT_FAILURE);
}
int sockfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
if(sockfd == -1){
printf("Could not create socket.");
exit(EXIT_FAILURE);
}
// Assemble and send login request
struct request_login reqlogin;
reqlogin.req_type = REQ_LOGIN;
strcpy(reqlogin.req_username, argv[3]);
int res = sendto(sockfd, &reqlogin, sizeof (struct request_login), 0, servAddr->ai_addr, servAddr->ai_addrlen);
I have written the following code as an intermediate to connect two programs. There is a server program running and a client program on two different systems. This code is expected to act as an intermediate between these two programs.
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
//Connect with program on server side
char * serv_con(char app_data[50])
{
int sock, bytes_recieved;
char send_data[1024];
char *recv_data = malloc(1024);
struct hostent *host;
struct sockaddr_in server_addr;
host = gethostbyname("10.47.3.249");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("Socket");
exit(1);
}
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(3128);
server_addr.sin_addr = *((struct in_addr *)host->h_addr);
bzero(&(server_addr.sin_zero),8);
if (connect(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
{
perror("Connect");
exit(1);
}
bytes_recieved=recv(sock,recv_data,1024,0);
recv_data[bytes_recieved] = '\0';
send(sock, app_data, 50, 0);
return recv_data;
//close(sock);
}
//Connect with client app
char * cli_con(char ser_data[50])
{
int sock, connected, bytes_recieved , true = 1;
char send_data [1024];
char *recv_data = malloc(1024);
struct sockaddr_in server_addr,client_addr;
int sin_size;
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("Socket");
exit(1);
}
if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&true,sizeof(int)) == -1)
{
perror("Setsockopt");
exit(1);
}
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(5000);
server_addr.sin_addr.s_addr = INADDR_ANY;
bzero(&(server_addr.sin_zero),8);
if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
{
perror("Unable to bind1");
exit(1);
}
if (listen(sock, 5) == -1)
{
perror("Listen");
exit(1);
}
sin_size = sizeof(struct sockaddr_in);
connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size1);
printf("\n I got a connection from (%s , %d)",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));
bytes_recieved = recv(connected,recv_data,1024,0);
recv_data[bytes_recieved] = '\0';
send(connected, ser_data,50, 0);
//close(sock);
}
int main()
{
char *ser_data, *app_data;
int pid = fork();
while(1)
{
if(pid == 0)
app_data = serv_con(ser_data);
else
ser_data = cli_con(app_data);
}
}
It works fine until the client side app runs. But as soon as the client side app runs, the code exit giving the error:
Unable to bind: Address already in use
I got a connection from (192.168.0.3 , 45691)
What modification should I make in the code to rectify this error? I am working on linux. Thanks in advance.
EDIT:
I have removved the comment from close(sock)and added close(connect) in the function cli_con. The code on the client side is given below:
int sock, bytes_recieved;
char send_data[1024],recv_data[1024];
struct hostent *host;
struct sockaddr_in server_addr;
host = gethostbyname("192.168.0.2");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("Socket");
exit(1);
}
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(5555);
server_addr.sin_addr = *((struct in_addr *)host->h_addr);
bzero(&(server_addr.sin_zero),8);
if (connect(sock, (struct sockaddr *)&server_addr,
sizeof(struct sockaddr)) == -1)
{
perror("Connect");
exit(1);
}
while(1)
{
//necessary codes
if (connect(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
{
close(sock);
goto connct;
}
}
But now on running, the first program doesnot exit but doesnot even print
I got a connection from (192.168.0.3 , 45691)
But just keeps on running without printing ANY messages. But on the other hand, the client exits showing the error:
Connect: Connection reset by peer
What should I do now?
When a client disconnects you create a new server socket and bind it to the same port. If the server side socket was not closed the port is still in use, so bind fails.
Usually the server side of a socket program has a loop around accept to allow it process connections from many clients. This way bind and listen are called only once.
while (connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size1)) {
printf("\n I got a connection from (%s , %d)",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));
bytes_recieved = recv(connected,recv_data,1024,0);
recv_data[bytes_recieved] = '\0';
send(connected, ser_data,50, 0);
close(connected);
}
It means you're trying to listen on port 5000, but there is already a program listening on that port (possibly an earlier version of your program which didn't close the port properly.) Change the port number to another value, or close any application listening on the port.
Since you're under Linux, you can use "netstat -nlp" as root to see what programs have which ports open.
One pointer for you is that, you should close both the listen socket and the socket which you obtain from the accept call.
close(connected);
close(sock);
Also, the socket takes sometime to be freed by the OS after it's usage and so, it might fail with an "Address already in use" error. You can check again properly in your code if your SO_REUSEADDR part of the code is executing properly.
Also, since you can try to add the listen socket creation code in your main function itself and pass it as an argument to cli_con function. Commonly followed mechanism is to create one listen socket and use it to accept multiple connections from client.
I hope in your original code you have proper memory allocation, initialization etc for ser_data & app_data.