I have been trying to learn sockets programming, and came across this website: http://beej.us/guide/bgnet/output/html/multipage/index.html which is really good. I was able to understand, but after writing a test program myself I ended up with a problem which I cannot figure after 3 hours. Have very limited time, so thought asking experts help here.
This is my server program:
/**
* Program showing how sockets can be used
*/
#include <stdio.h> // For printf
#include <strings.h> // For bzero, memset
#include <stdlib.h> // For exit, atoi
#include <unistd.h> // For close
#include <sys/socket.h> // For socket
#include <sys/types.h> // For types
#include <arpa/inet.h> // For inet_addr
#include <netdb.h> // Import module network database
#include <errno.h> // To access the global errno that holds last system call error
#include <assert.h> // For asserting
#define ADDRESSINFO_GET_SUCCESS 0
const int kSuccess = 0;
const char *kMyPort = "3490"; // Can be either port num or name of the service
const int kMaxListenConn = 10; // How many connections queue will hold
// Utility function to get socket address, IPv4 or IPv6:
void* getSocketAddress(const struct sockaddr *sa)
{
// Cast socketaddr to sockaddr_in to get address and port values from data
if (sa->sa_family == PF_INET) {
return &(((struct sockaddr_in *)sa)->sin_addr);
}
return &(((struct sockaddr_in6 *)sa)->sin6_addr);
}
// Utility function to get socket address string
void getSocketAddressString(const struct sockaddr *sd, char *ipAddr)
{
inet_ntop(sd->sa_family, getSocketAddress(sd), ipAddr, INET6_ADDRSTRLEN);
}
int createAndBindSocket(const struct addrinfo *addrList)
{
int status = -1; // Invalid status
int socketFileDesc = -1; // Invalid descriptor
const struct addrinfo *addrIt;
/*
* STEP 2.1: Loop through all the addrinfo nodes and bind to the one we can
*/
for (addrIt = addrList; addrIt != NULL; addrIt = addrIt->ai_next)
{
char ipAddr[INET6_ADDRSTRLEN];
inet_ntop(addrIt->ai_family, getSocketAddress(addrIt->ai_addr), ipAddr, sizeof ipAddr);
printf("IP: %s\n", ipAddr);
/*
* STEP 2.2: Crete the socket file descriptor for our IP address
*/
socketFileDesc = socket(addrIt->ai_family, addrIt->ai_socktype, addrIt->ai_protocol);
if (socketFileDesc == -1) {
fprintf(stderr, "Failed to create socket with error: %d\n", errno);
perror("socket"); // Get error desc
continue; // Try next address
}
/*
* STEP 2.3: Set socket behaviour by making ip address to be re-used if used already
*/
int yes=1;
if (setsockopt(socketFileDesc, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
{
perror("setsockopt");
exit(1);
}
printf("Port %d\n",((struct sockaddr_in *)addrIt->ai_addr)->sin_port);
/*
* STEP 2.4: Bind our socket with ip address and port number to listen
*/
status = bind(socketFileDesc, addrIt->ai_addr, addrIt->ai_addrlen);
if (status != kSuccess) {
fprintf(stderr, "Failed to bind socket with error:%d\n", errno);
perror("bind"); // Get error desc
// Clear socket
close(socketFileDesc);
socketFileDesc = -1;
continue; // Try next address
}
}
return socketFileDesc;
}
int main()
{
int status = -1; // Status is invalid
struct addrinfo hints; // Holds our hints to get address info
struct addrinfo *addrList; // Contains our address info
/*
* STEP 1: Setup service details
*/
// Make sure struct is empty
bzero(&hints, sizeof hints); // memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_UNSPEC; // Don't care IPv4 or v6
hints.ai_socktype = SOCK_STREAM; // Use TCP stream sockets
hints.ai_flags = AI_PASSIVE; // Use my local IPs or you igore this and provide IP manually in first arg
status = getaddrinfo(NULL, kMyPort, &hints, &addrList);
if (status != kSuccess) {
fprintf(stderr, "Failed to get address info with error: %s\n", gai_strerror(status));
exit(1);
}
/*
* STEP 2: Create a socket and bind it
*/
int socketFileDesc;
socketFileDesc = createAndBindSocket(addrList);
freeaddrinfo(addrList); // Done with list
if (socketFileDesc == -1) {
exit(1);
}
/*
* STEP 3: Listen to the port for incoming connections
*/
status = listen(socketFileDesc, kMaxListenConn); // Second arg is number of incoming connections in queue
if (status != kSuccess) {
fprintf(stderr, "Failed to listen to the port\n");
perror("listen");
goto exit;
}
printf("Server is listening at the port %s\n", kMyPort);
struct sockaddr_storage inConnAddr; // Big enough to hold both IPv4 and v6
socklen_t inConnAddrLen = sizeof inConnAddr;
const size_t kMaxBufferSize = 50;
char buff[kMaxBufferSize] = {0};
long bytesReceived = -1;
long bytesSent = 0;
int clientSockfd;
while (1) {
/*
* STEP 4: Accept incoming connections
*/
inConnAddrLen = sizeof inConnAddr;
clientSockfd = accept(socketFileDesc, (struct sockaddr *)&inConnAddr, &inConnAddrLen);
// Got new connection ?
if (clientSockfd == -1) {
perror("accept"); // Print error description
continue; // Continue to look for new connections
}
//
// Got connection, create child process to handle request
//
if (!fork()) {
close(socketFileDesc); // No need with child
char ipAddr[INET6_ADDRSTRLEN];
getSocketAddressString((struct sockaddr *)&inConnAddr, ipAddr);
printf("Child process created for hanlding request from %s\n", ipAddr);
/*
* STEP 5: Receive and Send data to requests
*/
bytesReceived = recv(clientSockfd, &buff, kMaxBufferSize - 1, 0);
if (bytesReceived > 0)
{
printf("Data from client %s\n", buff);
while (bytesSent < bytesReceived) {
bytesSent = send(clientSockfd, buff, bytesReceived, 0);
printf("Bytes sent %ld\n", bytesSent);
}
}
if (bytesReceived < 0) {
perror("recv");
}
else if (bytesReceived == 0) {
printf("Connection closed by server\n");
}
close(clientSockfd); // Close socket
exit(0);
}
}
exit:
/*
* STEP 5: Close the socket
*/
close(socketFileDesc);
return 0;
}
This is my client program:
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#include <netdb.h>
#include <strings.h>
#include <arpa/inet.h>
const char kSuccess = 0;
// Utility function to get socket address
void* getSocketAddress(const struct sockaddr *sa)
{
if (sa->sa_family == AF_INET) {
return &( ((struct sockaddr_in *)sa)->sin_addr );
}
return &( ((struct sockaddr_in6 *)sa)->sin6_addr );
}
// Utility function to get socket address string
void getSocketAddressString(const struct sockaddr *sd, char *ipAddr)
{
inet_ntop(sd->sa_family, getSocketAddress(sd), ipAddr, INET6_ADDRSTRLEN);
}
int createAndConnectSocket(const struct addrinfo *addrList)
{
int socketFileDesc = -1; // Invalid descriptor
const struct addrinfo *addrIt;
/*
* STEP 2.1: Loop through all the addrinfo nodes and bind to the one we can
*/
for (addrIt = addrList; addrIt != NULL; addrIt = addrIt->ai_next)
{
/*
* STEP 2.2: Crete the socket file descriptor for our IP address
*/
socketFileDesc = socket(addrIt->ai_family, addrIt->ai_socktype, addrIt->ai_protocol);
if (socketFileDesc == -1) {
fprintf(stderr, "Failed to create socket with error: %d\n", errno);
perror("socket"); // Get error desc
continue; // Try next address
}
/*
* STEP 2.3: Set socket behaviour by making ip address to be re-used if used already
*/
int yes=1;
if (setsockopt(socketFileDesc, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
{
perror("setsockopt");
exit(1);
}
char ipAdd[INET6_ADDRSTRLEN];
getSocketAddressString(addrIt->ai_addr, ipAdd);
((struct sockaddr_in *)addrIt->ai_addr)->sin_port = atoi("3490");
printf("IP is %s::%d\n", ipAdd,((struct sockaddr_in *)addrIt->ai_addr)->sin_port);
// Connect to the socket
int status;
status = connect(socketFileDesc, addrIt->ai_addr, addrIt->ai_addrlen);
if (status != kSuccess) {
perror("connect");
close(socketFileDesc);
socketFileDesc = -1;
continue;
}
}
return socketFileDesc;
}
int main(int argc, char* argv[])
{
// Check we have data from arguments
if (argc < 3 || argc > 3) {
perror("Invalid command");
printf("Usage: %s hostname portnumber\n", argv[0]);
printf(" %s 192.168.1.2 3490\n", argv[0]);
}
// Setup server address info
struct addrinfo *serverInfo;
struct addrinfo hints;
int status = -1;
memset(&hints, 0, sizeof hints); // Make sure it is empty
hints.ai_family = AF_INET; // IPv4
hints.ai_socktype = SOCK_STREAM; // Use socket stream
((struct sockaddr_in *)&hints.ai_addr)->sin_port = atoi(argv[2]);
status = getaddrinfo(argv[1], "3490", &hints, &serverInfo);
if (status != kSuccess) {
fprintf(stderr, "Failed to get address info %s\n", gai_strerror(status));
exit(1);
}
printf("Connecting to %s::%s...\n", argv[1], argv[2]);
// Create and bind socket
int sockfd = createAndConnectSocket(serverInfo);
freeaddrinfo(serverInfo); // We are done with serverinfo
if (sockfd == -1) {
exit(1);
}
// Send and receive data from server
long bytesReceived = -1;
long bytesSent = 0;
const size_t kMaxBufferSize = 50;
char buff[kMaxBufferSize];
const char *msg = "Hi! I am client!";
size_t msgLen = strlen(msg);
printf("Connected to server\n");
// Loop to send and receive data
while (1) {
while (bytesSent < msgLen) {
bytesSent = send(sockfd, msg, msgLen, 0);
printf("Bytes sent %ld\n", bytesSent);
}
bytesReceived = recv(sockfd, &buff, kMaxBufferSize - 1, 0);
if (bytesReceived > 0)
{
printf("Data received from server: %s\n", buff);
}
else if (bytesReceived < 0) {
perror("Read error");
break;
}
else if (bytesReceived == 0) {
printf("Connection closed by server\n");
break;
}
}
// Close socket
close(sockfd);
return 0;
}
My problem is: Even though I have set the port and IP in getaddrinfo() call, but when it is binding or connecting the port number found in sockaddr struct is wrong as it is different value. I do know what is happing here, and I get connection refused message when I do that because of that. Can anyone please take a look at my program and tell me why I am getting connection refused ? I would really appreciate if someone can suggest any improvements in my code.
Thanks
