How to assign hostname and portnumber that client connected from? - c

Question

I have this ftserver.c program which is implementing a file transfer server which listens for a client and then responds to the clients request over a data connection. Right now it works but I have the hostname and port number for the data connection hardcoded. The portnumber has been provided by the client and the server should be able to get the hostname from the client's control connection.
References:http://beej.us/guide/bgnet/output/html/multipage/getaddrinfoman.html
How can I assign the hostname and portnumber dynamically? Thank you.
void error(const char *msg)
{
perror(msg);
exit(1);
}
void startup(int portNumber);
void setupData(char* portNum);
int sockfd, newsockfd, datasock, portno;
char buffer[256]; socklen_t clilen;
struct sockaddr_in serv_addr, cli_addr, port_addr;
struct addrinfo hints, *servinfo, *p;
char ipstr[1000];
struct in_addr ipAddr;
struct sockaddr_in *s;
int main(int argc, char *argv[]){
int n; char* dataport; char * token; char filename[100];
if (argc < 2) {
fprintf(stderr,"ERROR, no port provided\n");
exit(1);
}
portno = atoi(argv[1]);
startup(portno);
n = read(newsockfd,buffer,255);
if (n < 0) error("ERROR reading from socket");
printf("Here is the message: %s\n",buffer);
token = strtok(buffer, " ");
//if client requested a list, setup data connection and send it
if (strcmp(token, "-l") == 0){
token = strtok(NULL, " ");
printf("the token is %s\n", token);
//dataport = atoi(token);
dataport = token;
setupData(dataport);
//sendList(dataport);
}
//if client requested a file, setup data connection and send it
else if (strcmp(token, "-g") == 0){
token = strtok(NULL, " ");
//filename = *token;
token = strtok(NULL, " ");
//dataport = atoi(token);
printf("the data port is %d\n", dataport);
//setupData(dataport);
//sendFile(filename, dataport);
}
else {
n = write(newsockfd,"not a valid command",19);
if (n < 0) error("ERROR writing to socket");
}
//close sockets for connection P
close(datasock);
close(newsockfd);
close(sockfd);
return 0;
}
void startup(int portNumber)
{
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portNumber);
if (bind(sockfd, (struct sockaddr *) &serv_addr,
sizeof(serv_addr)) < 0)
error("ERROR on binding");
listen(sockfd,5);
clilen = sizeof(cli_addr);
newsockfd = accept(sockfd,
(struct sockaddr *) &cli_addr,
&clilen);
if (newsockfd < 0)
error("ERROR on accept");
bzero(buffer,256);
}
void setupData(char* portNum){
int rv;
const char* name = "localhost";
char s[1000];
memset(&hints, 0, sizeof (hints));
hints.ai_family = AF_UNSPEC; // use AF_INET6 to force IPv6
hints.ai_socktype = SOCK_STREAM;
if ((rv = getaddrinfo(name, "30024", &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
exit(1);
}
// loop through all the results and connect to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((datasock = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("socket");
continue;
}
if (connect(datasock, p->ai_addr, p->ai_addrlen) == -1) {
perror("connect");
close(sockfd);
continue;
}
break; // if we get here, we must have connected successfully
}
if (p == NULL) {
// looped off the end of the list with no connection
fprintf(stderr, "failed to connect\n");
exit(2);
}
printf("data connection setup successful\n");
}

Answer 1

I have resolved this. By using a simplified version of setting up the data conection, not using getaddrinfo() and using a hostname_to_ip conversion function. Reference: http://www.linuxhowtos.org/data/6/client.c
int setupData(char* hostname, char* portNum){
int sock_fd; char ip[100];
struct sockaddr_in srv_addr;
memset(&srv_addr, 0, sizeof(srv_addr)); /* zero-fill srv_addr structure*/
/* create a client socket */
sock_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
srv_addr.sin_family = AF_INET; /* internet address family */
/* convert command line argument to numeric IP */
hostname_to_ip(hostname, ip);
printf("%s resolved to %s" , hostname , ip);
if ( inet_pton(AF_INET, ip, &(srv_addr.sin_addr)) < 1 )
{
printf("Invalid IP address\n");
exit(EXIT_FAILURE);
}
srv_addr.sin_port = htons(atoi(portNum));
if( connect(sock_fd, (struct sockaddr*) &srv_addr, sizeof(srv_addr)) < 0 )
{
perror("connect error");
exit(EXIT_FAILURE);
}
return sockfd;
}