core: add nm_utils_shorten_hostname()

Add a function to shorten a overlong hostname, truncating it to the
first dot or 64 characters.

src/core/nm-core-utils.c

@@ -30,6 +30,7 @@
 #include "libnm-glib-aux/nm-secret-utils.h"
 #include "libnm-glib-aux/nm-time-utils.h"
 #include "libnm-glib-aux/nm-str-buf.h"
+#include "libnm-systemd-shared/nm-sd-utils-shared.h"
 #include "nm-utils.h"
 #include "libnm-core-intern/nm-core-internal.h"
 #include "nm-setting-connection.h"
@@ -5201,3 +5202,50 @@ again:
 
     return g;
 }
+
+/*****************************************************************************/
+
+/**
+ * nm_utils_shorten_hostname:
+ * @hostname: the input hostname
+ * @shortened: (out) (transfer full): on return, the shortened hostname
+ *
+ * Checks whether the input hostname is valid. If not, tries to shorten it
+ * to HOST_NAME_MAX or to the first dot, whatever comes earlier.
+ * The new hostname is returned in @shortened.
+ *
+ * Returns: %TRUE if the input hostname was already valid or if was shortened
+ * successfully; %FALSE otherwise
+ */
+gboolean
+nm_utils_shorten_hostname(const char *hostname, char **shortened)
+{
+    gs_free char *s = NULL;
+    const char   *dot;
+    gsize         l;
+
+    nm_assert(hostname);
+    nm_assert(shortened);
+
+    if (nm_sd_hostname_is_valid(hostname, FALSE)) {
+        *shortened = NULL;
+        return TRUE;
+    }
+
+    dot = strchr(hostname, '.');
+    if (dot)
+        l = (dot - hostname);
+    else
+        l = strlen(hostname);
+    l = MIN(l, (gsize) HOST_NAME_MAX);
+
+    s = g_strndup(hostname, l);
+
+    if (!nm_sd_hostname_is_valid(s, FALSE)) {
+        *shortened = NULL;
+        return FALSE;
+    }
+
+    *shortened = g_steal_pointer(&s);
+    return TRUE;
+}

src/core/nm-core-utils.h

@@ -233,6 +233,7 @@ void nm_utils_log_connection_diff(NMConnection *connection,
                                   const char   *dbus_path);
 
 gboolean nm_utils_is_specific_hostname(const char *name);
+gboolean nm_utils_shorten_hostname(const char *hostname, char **shortened);
 
 struct _NMUuid;
 

src/core/tests/test-utils.c

@@ -212,6 +212,62 @@ test_hw_addr_gen_stable_eth(void)
                     "04:0D:CD:0C:9E:2C");
 }
 
+static void
+test_shorten_hostname(void)
+{
+    gboolean res;
+    char    *shortened = NULL;
+
+    res = nm_utils_shorten_hostname("name1", &shortened);
+    g_assert_cmpint(res, ==, TRUE);
+    g_assert_cmpstr(shortened, ==, NULL);
+    nm_clear_g_free(&shortened);
+
+    res = nm_utils_shorten_hostname("name1.example.com", &shortened);
+    g_assert_cmpint(res, ==, TRUE);
+    g_assert_cmpstr(shortened, ==, NULL);
+    nm_clear_g_free(&shortened);
+
+    res = nm_utils_shorten_hostname(
+        "123456789-123456789-123456789-123456789-123456789-123456789-1234",
+        &shortened);
+    g_assert_cmpint(res, ==, TRUE);
+    g_assert_cmpstr(shortened, ==, NULL);
+    nm_clear_g_free(&shortened);
+
+    res = nm_utils_shorten_hostname(
+        "123456789-123456789-123456789-123456789-123456789-123456789-12345",
+        &shortened);
+    g_assert_cmpint(res, ==, TRUE);
+    g_assert_cmpstr(shortened,
+                    ==,
+                    "123456789-123456789-123456789-123456789-123456789-123456789-1234");
+    nm_clear_g_free(&shortened);
+
+    res = nm_utils_shorten_hostname(
+        "name1.test-dhcp-this-one-here-is-a-very-very-long-domain.example.com",
+        &shortened);
+    g_assert_cmpint(res, ==, TRUE);
+    g_assert_cmpstr(shortened, ==, "name1");
+    nm_clear_g_free(&shortened);
+
+    res = nm_utils_shorten_hostname(
+        "test-dhcp-this-one-here-is-a-very-very-long-hostname-without-domainname",
+        &shortened);
+    g_assert_cmpint(res, ==, TRUE);
+    g_assert_cmpstr(shortened,
+                    ==,
+                    "test-dhcp-this-one-here-is-a-very-very-long-hostname-without-dom");
+    nm_clear_g_free(&shortened);
+
+    res = nm_utils_shorten_hostname(
+        ".test-dhcp-this-one-here-is-a-very-very-long-hostname.example.com",
+        &shortened);
+    g_assert_cmpint(res, ==, FALSE);
+    g_assert_cmpstr(shortened, ==, NULL);
+    nm_clear_g_free(&shortened);
+}
+
 /*****************************************************************************/
 
 NMTST_DEFINE();
@@ -223,6 +279,7 @@ main(int argc, char **argv)
 
     g_test_add_func("/utils/stable_privacy", test_stable_privacy);
     g_test_add_func("/utils/hw_addr_gen_stable_eth", test_hw_addr_gen_stable_eth);
+    g_test_add_func("/utils/shorten-hostname", test_shorten_hostname);
 
     return g_test_run();
 }