From e504e84b3c22735ec3ef97ecf33c12ebc535a5c8 Mon Sep 17 00:00:00 2001
From: Aadhavan <aadhavanlenin@gmail.com>
Date: Tue, 30 Apr 2024 17:01:08 +0530
Subject: [PATCH] xps_utils

---
 docs/guides/references/xps_utils.md | 128 ++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)

diff --git a/docs/guides/references/xps_utils.md b/docs/guides/references/xps_utils.md
index 93e9062..972845c 100644
--- a/docs/guides/references/xps_utils.md
+++ b/docs/guides/references/xps_utils.md
@@ -1 +1,129 @@
 # 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`.
+
+::: details **expserver/src/utils/xps_utils.h**
+
+```c
+#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).
+
+```c
+bool is_valid_port(u_int port) { return port >= 0 && port <= 65535; }
+```
+
+### `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.
+
+```c
+int make_socket_non_blocking(u_int sock_fd) {
+  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;
+  }
+
+  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;
+}
+```
+
+### `xps_getaddrinfo()`
+
+Resolves the given host and port to an IPv4 address using `[getaddrinfo()](https://man7.org/linux/man-pages/man3/getaddrinfo.3.html)`, and returns a pointer to the resulting `addrinfo` structure.
+
+The `getaddrinfo()` function provided by the [<netdb.h>](https://pubs.opengroup.org/onlinepubs/7908799/xns/netdb.h.html) header used to perform [DNS](https://en.wikipedia.org/wiki/Domain_Name_System) lookup to resolve a hostname and service name to a set of socket addresses.
+
+```c
+struct addrinfo *xps_getaddrinfo(const char *host, u_int port) {
+  assert(host != NULL);
+
+  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;
+}
+```
+
+### `get_remote_ip()`
+
+Retrieves the IP address of the remote peer connected to the given socket file descriptor `sock_fd`. It uses `[getpeername()](https://man7.org/linux/man-pages/man2/getpeername.2.html)` to get the peer's address, then converts it from binary to text using `[inet_ntop()](https://man7.org/linux/man-pages/man3/inet_ntop.3.html)`.
+
+```c
+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;
+}
+
+```