feat(sockutls): Add support for gethostname()

Closes https://github.com/espressif/esp-idf/issues/14849

components/sock_utils/src/gethostname.c

@@ -0,0 +1,46 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <string.h>
+#include "gethostname.h"
+#include "esp_netif.h"
+#include "errno.h"
+#include "esp_log.h"
+
+
+static bool highest_prio_netif(esp_netif_t *netif, void *ctx)
+{
+    esp_netif_t **highest_so_far = ctx;
+    if (esp_netif_get_route_prio(netif) > esp_netif_get_route_prio(*highest_so_far)) {
+        *highest_so_far = netif;
+    }
+    return false;   // go over the entire list to find the netif with the highest route-prio
+}
+
+int gethostname(char *name, size_t len)
+{
+    if (name == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+    const char *netif_hostname = CONFIG_LWIP_LOCAL_HOSTNAME;    // default value from Kconfig
+
+    // Find the default netif
+    esp_netif_t *default_netif = esp_netif_get_default_netif();
+    if (default_netif == NULL) {    // if no netif is active/up -> find the highest prio netif
+        esp_netif_find_if(highest_prio_netif, &default_netif);
+    }
+    // now the `default_netif` could be NULL and/or the esp_netif_get_hostname() could fail
+    // but we ignore the return code, as if it fails, the `netif_hostname` still holds the default value
+    esp_netif_get_hostname(default_netif, &netif_hostname);
+
+    size_t hostname_len;
+    if (netif_hostname == NULL || len < (hostname_len = strlen(netif_hostname) + 1)) { // including the NULL terminator
+        errno = EINVAL;
+        return -1;
+    }
+    memcpy(name, netif_hostname, hostname_len);
+    return 0;
+}