feat(error): add ICMP error utilities with tests

- Added `icmp_set_error`.
 - Added `icmp_strerror`.
 - Added unit tests.

includes/icmp.h

@@ -0,0 +1,47 @@
+#ifndef ICMP_H
+#define ICMP_H
+
+#include <stdint.h>
+#include <stddef.h>
+#include <netinet/in.h>
+#include <time.h>
+
+/* Opaque handle type */
+typedef struct icmp_handle icmp_handle_t;
+
+/* Reply structure passed to callback */
+typedef struct icmp_reply {
+	uint8_t type;
+	uint8_t code;
+	struct in_addr from;
+	uint8_t ttl;
+	struct timespec timestamp;
+	void *payload;
+	size_t payload_len;
+	void *ip_payload;
+	size_t ip_payload_len;
+} icmp_reply_t;
+
+/* Callback type for received packets */
+typedef void (*icmp_callback_t)(const icmp_reply_t *reply, void *userdata);
+
+/* Handle lifecycle */
+icmp_handle_t *icmp_create(void);
+void icmp_destroy(icmp_handle_t *h);
+int icmp_get_fd(const icmp_handle_t *h);
+
+/* Send functions */
+int icmp_send_raw(icmp_handle_t *h, uint8_t type, uint8_t code,
+					const void *payload, size_t len, struct in_addr dest,
+					uint8_t ttl);
+
+int icmp_send_echo(icmp_handle_t *h, struct in_addr dest, uint16_t id,
+					uint16_t seq, uint8_t ttl);
+
+/* Receive function */
+int icmp_process(icmp_handle_t *h, icmp_callback_t cb, void *userdata);
+
+/* Error handling */
+const char *icmp_strerror(const icmp_handle_t *h);
+
+#endif /* ICMP_H */

includes/internal/icmp_internal.h

@@ -0,0 +1,23 @@
+#ifndef ICMP_INTERNAL_H
+#define ICMP_INTERNAL_H
+
+/* Internal handle structure */
+struct icmp_handle {
+	int fd;
+	int last_error;
+	char error_msg[256];
+};
+
+/* Error codes */
+#define ICMP_OK				0
+#define ICMP_ERR_PERMISSION	-1
+#define ICMP_ERR_SOCKET		-2
+#define ICMP_ERR_SEND		-3
+#define ICMP_ERR_RECV		-4
+#define ICMP_ERR_INVALID	-5
+#define ICMP_ERR_ENOMEM		-6
+
+/* Internal error handling functions */
+void icmp_set_error(struct icmp_handle *h, int code, const char *msg);
+
+#endif

src/error/set_error.c

@@ -0,0 +1,13 @@
+#include "internal/icmp_internal.h"
+#include <stdio.h>
+
+void
+icmp_set_error(struct icmp_handle *h, int code, const char *msg)
+{
+	h->last_error = code;
+
+	if (NULL != msg)
+		snprintf(h->error_msg, sizeof(h->error_msg), "%s", msg);
+	else
+		h->error_msg[0] = '\0';
+}

src/error/strerror.c

@@ -0,0 +1,19 @@
+#include "icmp.h"
+#include "internal/icmp_internal.h"
+
+const char *
+icmp_strerror(const icmp_handle_t *h)
+{
+	const struct icmp_handle *handle = (const struct icmp_handle *)h;
+
+	if (NULL == handle)
+		return "Invalid handle";
+
+	if (ICMP_OK == handle->last_error)
+		return "No error";
+
+	if ('\0' == handle->error_msg[0])
+		return "Unknown error";
+
+	return handle->error_msg;
+}

tests/error/test_error.c

@@ -0,0 +1,58 @@
+#include <criterion/criterion.h>
+#include <string.h>
+#include "internal/icmp_internal.h"
+#include "icmp.h"
+
+/* Test 1: set_error sets code and message */
+Test(error, set_error_basic)
+{
+	struct icmp_handle h = {0};
+
+	icmp_set_error(&h, ICMP_ERR_SOCKET, "Test error message");
+
+	cr_assert_eq(h.last_error, ICMP_ERR_SOCKET);
+	cr_assert_str_eq(h.error_msg, "Test error message");
+}
+
+/* Test 3: set_error with NULL message clears error_msg */
+Test(error, set_error_null_message)
+{
+	struct icmp_handle h = {0};
+	strcpy(h.error_msg, "Old error");
+
+	icmp_set_error(&h, ICMP_ERR_SEND, NULL);
+
+	cr_assert_eq(h.last_error, ICMP_ERR_SEND);
+	cr_assert_eq(h.error_msg[0], '\0');
+}
+
+/* Test 4: strerror returns message from handle */
+Test(error, strerror_returns_message)
+{
+	struct icmp_handle h = {0};
+	h.last_error = ICMP_ERR_PERMISSION;
+	strcpy(h.error_msg, "Permission denied");
+
+	const char *msg = icmp_strerror((icmp_handle_t *)&h);
+
+	cr_assert_str_eq(msg, "Permission denied");
+}
+
+/* Test 5: strerror with NULL handle */
+Test(error, strerror_null_handle)
+{
+	const char *msg = icmp_strerror(NULL);
+
+	cr_assert_str_eq(msg, "Invalid handle");
+}
+
+/* Test 6: strerror with ICMP_OK */
+Test(error, strerror_no_error)
+{
+	struct icmp_handle h = {0};
+	h.last_error = ICMP_OK;
+
+	const char *msg = icmp_strerror((icmp_handle_t *)&h);
+
+	cr_assert_str_eq(msg, "No error");
+}