feat(socket): add raw socket utilities with tests

- Added `socket_create`.
 - Added `socket_configure`.
 - Added socket error utilities
 - Added unit tests.

includes/internal/icmp_socket.h

@@ -0,0 +1,16 @@
+#ifndef ICMP_SOCKET_H
+#define ICMP_SOCKET_H
+
+#include "internal/icmp_internal.h"
+
+/* Create raw ICMP socket */
+int socket_create(struct icmp_handle *h);
+
+/* Configure socket (non-blocking, buffer size) */
+int socket_configure(struct icmp_handle *h);
+
+/* Internal helpers for error handling */
+void socket_clear_error(struct icmp_handle *h);
+void socket_set_error(struct icmp_handle *h, int code, const char *fmt, ...);
+
+#endif

src/socket/configure.c

@@ -0,0 +1,42 @@
+#include "internal/icmp_internal.h"
+#include "internal/icmp_socket.h"
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+
+/* Forward declarations */
+static void handle_configure_error(struct icmp_handle *h, const char *func);
+/* -------------------- */
+
+int
+socket_configure(struct icmp_handle *h)
+{
+	int flags;
+
+	/* Get current file status flags */
+	flags = fcntl(h->fd, F_GETFL, 0);
+	if (-1 == flags)
+	{
+		handle_configure_error(h, "fcntl(F_GETFL)");
+		return -1;
+	}
+
+	/* Set non-blocking flag */
+	if (-1 == fcntl(h->fd, F_SETFL, flags | O_NONBLOCK))
+	{
+		handle_configure_error(h, "fcntl(F_SETFL)");
+		return -1;
+	}
+
+	/* Clear error state on success */
+	socket_clear_error(h);
+
+	return 0;
+}
+
+static void
+handle_configure_error(struct icmp_handle *h, const char *func)
+{
+	socket_set_error(h, ICMP_ERR_SOCKET,
+			"%s failed: %s", func, strerror(errno));
+}

src/socket/create.c

@@ -0,0 +1,48 @@
+#include "internal/icmp_internal.h"
+#include "internal/icmp_socket.h"
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <errno.h>
+#include <string.h>
+
+/* Forward declarations */
+static void handle_socket_error(struct icmp_handle *h, int err);
+/* -------------------- */
+
+int
+socket_create(struct icmp_handle *h)
+{
+	int fd;
+
+	/* Create raw ICMP socket */
+	fd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
+
+	if (fd < 0)
+	{
+		handle_socket_error(h, errno);
+		return -1;
+	}
+
+	/* Store file descriptor in handle */
+	h->fd = fd;
+
+	/* Clear error state on success */
+	socket_clear_error(h);
+
+	return 0;
+}
+
+static void
+handle_socket_error(struct icmp_handle *h, int err)
+{
+	if (EPERM == err)
+	{
+		socket_set_error(h, ICMP_ERR_PERMISSION,
+				"Raw socket requires CAP_NET_RAW or root");
+	}
+	else
+	{
+		socket_set_error(h, ICMP_ERR_SOCKET,
+				"socket() failed: %s", strerror(err));
+	}
+}

src/socket/utils.c

@@ -0,0 +1,22 @@
+#include "internal/icmp_internal.h"
+#include <stdarg.h>
+#include <stdio.h>
+
+void
+socket_clear_error(struct icmp_handle *h)
+{
+	h->last_error = ICMP_OK;
+	h->error_msg[0] = '\0';
+}
+
+void
+socket_set_error(struct icmp_handle *h, int code, const char *fmt, ...)
+{
+	va_list args;
+
+	h->last_error = code;
+
+	va_start(args, fmt);
+	vsnprintf(h->error_msg, sizeof(h->error_msg), fmt, args);
+	va_end(args);
+}

tests/socket/test_socket.c

@@ -0,0 +1,96 @@
+#include <criterion/criterion.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "internal/icmp_internal.h"
+#include "internal/icmp_socket.h"
+
+/* Helper: check if we have CAP_NET_RAW capability */
+static int
+has_net_raw_capability(void)
+{
+	struct icmp_handle h = {0};
+	int ret = socket_create(&h);
+
+	if (0 == ret)
+	{
+		close(h.fd);
+		return 1;
+	}
+
+	if (ICMP_ERR_PERMISSION == h.last_error)
+		return 0;
+
+	return -1;
+}
+
+/* Test 1: socket_create() success (skip without privileges) */
+Test(socket, create_success)
+{
+	struct icmp_handle h = {0};
+	int ret = socket_create(&h);
+
+	if (-1 == ret && ICMP_ERR_PERMISSION == h.last_error)
+	{
+		cr_skip("Test requires CAP_NET_RAW or root privileges");
+	}
+
+	cr_assert_eq(ret, 0, "socket_create() failed: %s", h.error_msg);
+	cr_assert_geq(h.fd, 0, "Expected valid file descriptor");
+	cr_assert_eq(h.last_error, ICMP_OK, "Expected no error");
+
+	close(h.fd);
+}
+
+/* Test 2: socket_create() sets error message on failure */
+Test(socket, create_error_message)
+{
+	struct icmp_handle h = {0};
+	int ret = socket_create(&h);
+
+	if (0 == ret)
+	{
+		/* We have privileges - can't test error case */
+		close(h.fd);
+		cr_skip("Test requires missing CAP_NET_RAW");
+	}
+
+	/* Without privileges, should get ICMP_ERR_PERMISSION */
+	cr_assert_eq(h.last_error, ICMP_ERR_PERMISSION);
+	cr_assert_neq(h.error_msg[0], '\0', "Error message should not be empty");
+}
+
+/* Test 3: socket_configure() success (skip without privileges) */
+Test(socket, configure_success)
+{
+	if (0 == has_net_raw_capability())
+	{
+		cr_skip("Test requires CAP_NET_RAW or root privileges");
+	}
+
+	struct icmp_handle h = {0};
+	socket_create(&h);
+
+	int ret = socket_configure(&h);
+
+	cr_assert_eq(ret, 0, "socket_configure() failed: %s", h.error_msg);
+	cr_assert_eq(h.last_error, ICMP_OK, "Expected no error");
+
+	/* Verify O_NONBLOCK flag is set */
+	int flags = fcntl(h.fd, F_GETFL, 0);
+	cr_assert(flags & O_NONBLOCK, "O_NONBLOCK flag not set");
+
+	close(h.fd);
+}
+
+/* Test 4: socket_configure() with invalid fd (always runnable) */
+Test(socket, configure_invalid_fd)
+{
+	struct icmp_handle h = {0};
+	h.fd = -1;
+
+	int ret = socket_configure(&h);
+
+	cr_assert_eq(ret, -1, "Expected -1 for invalid fd");
+	cr_assert_eq(h.last_error, ICMP_ERR_SOCKET, "Expected ICMP_ERR_SOCKET");
+	cr_assert_neq(h.error_msg[0], '\0', "Error message should not be empty");
+}