networkd: rework Domains= setting

Previously, .network files only knew a vaguely defined "Domains=" concept, for which the documentation declared it was
the "DNS domain" for the network connection, without specifying what that means.

With this the Domains setting is reworked, so that there are now "routing" domains and "search" domains. The former are
to be used by resolved to route DNS request to specific network interfaces, the latter is to be used for searching
single-label hostnames with (in addition to being used for routing). Both settings are configured in the "Domains="
setting. Normal domain names listed in it are now considered search domains (for compatibility with existing setups),
while those prefixed with "~" are considered routing domains only. To route all lookups to a specific interface the
routing domain "." may be used, referring to the root domain. An alternative syntax for this is the "*", as was already
implemented before using the "wildcard" domain concept.

This commit adds proper parsers for this new logic, and exposes this via the sd-network API. This information is not
used by resolved yet, this will be added in a later commit.

1 files changed, 76 insertions, 36 deletions

diff --git a/src/network/networkd-network.c b/src/network/networkd-network.c
index c11cb3dcb3..1e520062f4 100644
--- a/src/network/networkd-network.c
+++ b/src/network/networkd-network.c
@@ -233,7 +233,8 @@ void network_free(Network *network) {
 
         strv_free(network->ntp);
         strv_free(network->dns);
-        strv_free(network->domains);
+        strv_free(network->search_domains);
+        strv_free(network->route_domains);
         strv_free(network->bind_carrier);
 
         netdev_unref(network->bridge);
@@ -384,7 +385,10 @@ int network_apply(Manager *manager, Network *network, Link *link) {
                 route->protocol = RTPROT_STATIC;
         }
 
-        if (network->dns || network->ntp || network->domains) {
+        if (!strv_isempty(network->dns) ||
+            !strv_isempty(network->ntp) ||
+            !strv_isempty(network->search_domains) ||
+            !strv_isempty(network->route_domains)) {
                 manager_dirty(manager);
                 link_dirty(link);
         }
@@ -469,49 +473,85 @@ int config_parse_netdev(const char *unit,
         return 0;
 }
 
-int config_parse_domains(const char *unit,
-                         const char *filename,
-                         unsigned line,
-                         const char *section,
-                         unsigned section_line,
-                         const char *lvalue,
-                         int ltype,
-                         const char *rvalue,
-                         void *data,
-                         void *userdata) {
-        Network *network = userdata;
-        char ***domains = data;
-        char **domain;
+int config_parse_domains(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        const char *p;
+        Network *n = data;
         int r;
 
-        r = config_parse_strv(unit, filename, line, section, section_line,
-                              lvalue, ltype, rvalue, domains, userdata);
-        if (r < 0)
-                return r;
+        assert(n);
+        assert(lvalue);
+        assert(rvalue);
 
-        strv_uniq(*domains);
-        network->wildcard_domain = !!strv_find(*domains, "*");
+        if (isempty(rvalue)) {
+                n->search_domains = strv_free(n->search_domains);
+                n->route_domains = strv_free(n->route_domains);
+                return 0;
+        }
 
-        STRV_FOREACH(domain, *domains) {
-                if (is_localhost(*domain))
-                        log_syntax(unit, LOG_ERR, filename, line, 0, "'localhost' domain names may not be configured, ignoring assignment: %s", *domain);
-                else {
-                        r = dns_name_is_valid(*domain);
-                        if (r <= 0 && !streq(*domain, "*")) {
-                                if (r < 0)
-                                        log_error_errno(r, "Failed to validate domain name: %s: %m", *domain);
-                                if (r == 0)
-                                        log_warning("Domain name is not valid, ignoring assignment: %s", *domain);
-                        } else
+        p = rvalue;
+        for (;;) {
+                _cleanup_free_ char *w = NULL, *normalized = NULL;
+                const char *domain;
+                bool is_route;
+
+                r = extract_first_word(&p, &w, NULL, 0);
+                if (r < 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, r, "Failed to extract search or route domain, ignoring: %s", rvalue);
+                        break;
+                }
+                if (r == 0)
+                        break;
+
+                is_route = w[0] == '~';
+                domain = is_route ? w + 1 : w;
+
+                if (dns_name_is_root(domain) || streq(domain, "*")) {
+                        /* If the root domain appears as is, or the special token "*" is found, we'll consider this as
+                         * routing domain, unconditionally. */
+                        is_route = true;
+                        domain = "."; /* make sure we don't allow empty strings, thus write the root domain as "." */
+
+                } else {
+                        r = dns_name_normalize(domain, &normalized);
+                        if (r < 0) {
+                                log_syntax(unit, LOG_ERR, filename, line, r, "'%s' is not a valid domain name, ignoring.", domain);
+                                continue;
+                        }
+
+                        domain = normalized;
+
+                        if (is_localhost(domain)) {
+                                log_syntax(unit, LOG_ERR, filename, line, 0, "'localhost' domain names may not be configure as search or route domains, ignoring assignment: %s", domain);
                                 continue;
+                        }
                 }
 
-                strv_remove(*domains, *domain);
+                if (is_route) {
+                        r = strv_extend(&n->route_domains, domain);
+                        if (r < 0)
+                                return log_oom();
 
-                /* We removed one entry, make sure we don't skip the next one */
-                domain--;
+                } else {
+                        r = strv_extend(&n->search_domains, domain);
+                        if (r < 0)
+                                return log_oom();
+                }
         }
 
+        strv_uniq(n->route_domains);
+        strv_uniq(n->search_domains);
+
         return 0;
 }
 
@@ -930,7 +970,7 @@ int config_parse_dnssec_negative_trust_anchors(
         Network *n = data;
         int r;
 
-        assert(filename);
+        assert(n);
         assert(lvalue);
         assert(rvalue);