resolved: split out function to determine the local llmnr hostname

1 files changed, 84 insertions, 0 deletions

diff --git a/src/resolve/resolved-util.c b/src/resolve/resolved-util.c
new file mode 100644
index 0000000000..00abada426
--- /dev/null
+++ b/src/resolve/resolved-util.c
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "dns-def.h"
+#include "dns-domain.h"
+#include "hostname-util.h"
+#include "idn-util.h"
+#include "resolved-util.h"
+#include "utf8.h"
+
+int resolve_system_hostname(char **full_hostname, char **first_label) {
+        _cleanup_free_ char *h = NULL, *n = NULL;
+#if HAVE_LIBIDN2
+        _cleanup_free_ char *utf8 = NULL;
+#elif HAVE_LIBIDN
+        int k;
+#endif
+        char label[DNS_LABEL_MAX];
+        const char *p, *decoded;
+        int r;
+
+        /* Return the full hostname in *full_hostname, if nonnull.
+         *
+         * Extract and normalize the first label of the locally configured hostname, check it's not
+         * "localhost", and return it in *first_label, if nonnull. */
+
+        r = gethostname_strict(&h);
+        if (r < 0)
+                return log_debug_errno(r, "Can't determine system hostname: %m");
+
+        p = h;
+        r = dns_label_unescape(&p, label, sizeof label, 0);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to unescape hostname: %m");
+        if (r == 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "Couldn't find a single label in hostname.");
+
+#if HAVE_LIBIDN || HAVE_LIBIDN2
+        r = dlopen_idn();
+        if (r < 0) {
+                log_debug_errno(r, "Failed to initialize IDN support, ignoring: %m");
+                decoded = label; /* no decoding */
+        } else
+#endif
+        {
+#if HAVE_LIBIDN2
+                r = sym_idn2_to_unicode_8z8z(label, &utf8, 0);
+                if (r != IDN2_OK)
+                        return log_debug_errno(SYNTHETIC_ERRNO(EUCLEAN),
+                                               "Failed to undo IDNA: %s", sym_idn2_strerror(r));
+                assert(utf8_is_valid(utf8));
+
+                r = strlen(utf8);
+                decoded = utf8;
+#elif HAVE_LIBIDN
+                k = dns_label_undo_idna(label, r, label, sizeof label);
+                if (k < 0)
+                        return log_debug_errno(k, "Failed to undo IDNA: %m");
+                if (k > 0)
+                        r = k;
+
+                if (!utf8_is_valid(label))
+                        return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
+                                               "System hostname is not UTF-8 clean.");
+                decoded = label;
+#else
+                decoded = label; /* no decoding */
+#endif
+        }
+
+        r = dns_label_escape_new(decoded, r, &n);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to escape hostname: %m");
+
+        if (is_localhost(n))
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "System hostname is 'localhost', ignoring.");
+
+        if (full_hostname)
+                *full_hostname = TAKE_PTR(h);
+        if (first_label)
+                *first_label = TAKE_PTR(n);
+        return 0;
+}