xps_utils

xps_utils is a module containing a collection of utility functions that will be utilized throughout the project. Additional utility functions will be implemented as needed according to the project roadmap.

Usage

Utility code and functions are defined inside xps_utils.c and xps_utils.h placed in expserver/src/utils.

expserver/src/utils/xps_utils.h

#ifndef XPS_UTILS_H
#define XPS_UTILS_H

#include "../xps.h"

// Sockets
bool is_valid_port(u_int port);
int make_socket_non_blocking(u_int sock_fd);
struct addrinfo *xps_getaddrinfo(const char *host, u_int port);
char *get_remote_ip(u_int sock_fd);

// Other functions

#endif

Functions

is_valid_port()

Checks if a port number is within the valid range of 0 to 65535 (inclusive).

bool is_valid_port(u_int port) { return port >= 0 && port <= 65535; }

xps_getaddrinfo()

Resolves the given host and port to an IPv4 address using getaddrinfo(), and returns a pointer to the resulting addrinfo structure.

The getaddrinfo() function provided by the <netdb.h> header used to perform DNS lookup to resolve a hostname and service name to a set of socket addresses.

struct addrinfo {
  int              ai_flags;
  int              ai_family;
  int              ai_socktype;
  int              ai_protocol;
  socklen_t        ai_addrlen;
  struct sockaddr *ai_addr;
  char            *ai_canonname;
  struct addrinfo *ai_next;
};

Given above is the definintion for struct addrinfo. A call to getaddrinfo(host, port_str, &hints, &result) will return a linked list of all the resolved addresses. A given host and port combination could have multiple addresses. For example, the host google.com could resolve to multiple IP addresses.

We are only interested in the ai_addr field as it is taken by bind() system call to bind to the particular addresss.

inet_ntop() provided by <arpa/inet.h> converts the IPv4 address in binary form to text form.

The memory for struct addrinfo * is dynamically allocated by getaddrinfo(). Hence a corresponding free funciton, freeaddrinfo() is used to free the memory.

struct addrinfo *xps_getaddrinfo(const char *host, u_int port) {
  assert(host != NULL);
  assert(is_valid_port(port));

  struct addrinfo hints, *result;
  memset(&hints, 0, sizeof(struct addrinfo));
  hints.ai_family = AF_INET;
  hints.ai_socktype = SOCK_STREAM;

  char port_str[20];
  sprintf(port_str, "%u", port);

  int err = getaddrinfo(host, port_str, &hints, &result);
  if (err != 0) {
    logger(LOG_ERROR, "xps_getaddrinfo()", "getaddrinfo() error");
    return NULL;
  }

  char ip_str[30];
  struct sockaddr_in *ipv4 = (struct sockaddr_in *)result->ai_addr;
  if (inet_ntop(result->ai_family, &(ipv4->sin_addr), ip_str, sizeof(ip_str)) == NULL) {
    logger(LOG_ERROR, "xps_getaddrinfo()", "inet_ntop() failed");
    perror("Error message");
    freeaddrinfo(result);
    return NULL;
  }

  logger(LOG_DEBUG, "xps_getaddrinfo()", "host: %s, port: %u, resolved ip: %s", host, port, ip_str);

  return result;
}

make_socket_non_blocking()

Makes a socket non-blocking by modifying its file descriptor flags using the fcntl system call. It returns an error code if unsuccessful.

int make_socket_non_blocking(u_int sock_fd) {
  // Get the current socket flags
  int flags = fcntl(sock_fd, F_GETFL, 0);
  if (flags < 0) {
    logger(LOG_ERROR, "make_socket_non_blocking()", "failed to get flags");
    perror("Error message");
    return E_FAIL;
  }

  // Set flags with O_NONBLOCK
  if (fcntl(sock_fd, F_SETFL, flags | O_NONBLOCK) < 0) {
    logger(LOG_ERROR, "make_socket_non_blocking()", "failed to set flags");
    perror("Error message");
    return E_FAIL;
  }

  return OK;
}

get_remote_ip()

Retrieves the IP address of the remote peer connected to the given socket file descriptor sock_fd. It uses getpeername() to get the peer's address, then converts it from binary to text using inet_ntop().

char *get_remote_ip(u_int sock_fd) {
  struct sockaddr_in addr;
  socklen_t addr_len = sizeof(addr);
  char ipstr[INET_ADDRSTRLEN];

  if (getpeername(sock_fd, (struct sockaddr *)&addr, &addr_len) != 0) {
    logger(LOG_ERROR, "get_remote_ip()", "getpeername() failed");
    perror("Error message");
    return NULL;
  }

  char *ip_str = malloc(INET_ADDRSTRLEN);
  if (ip_str == NULL) {
    logger(LOG_ERROR, "get_remote_ip()", "malloc() failed for 'ip_str");
    return NULL;
  }

  inet_ntop(AF_INET, &addr.sin_addr, ip_str, INET_ADDRSTRLEN);

  return ip_str;
}