resolved: fully support DNS search domains

This adds support for searching single-label hostnames in a set of
configured search domains.

A new object DnsQueryCandidate is added that links queries to scopes.
It keeps track of the search domain last used for a query on a specific
link. Whenever a host name was unsuccessfuly resolved on a scope all its
transactions are flushed out and replaced by a new set, with the next
search domain appended.

This also adds a new flag SD_RESOLVED_NO_SEARCH to disable search domain
behaviour. The "systemd-resolve-host" tool is updated to make this
configurable via --search=.

Fixes #1697

1 files changed, 10 insertions, 2 deletions

diff --git a/src/resolve/resolved-dns-question.h b/src/resolve/resolved-dns-question.h
index d728b9bed2..e77116c03a 100644
--- a/src/resolve/resolved-dns-question.h
+++ b/src/resolve/resolved-dns-question.h
@@ -43,8 +43,8 @@ int dns_question_new_service(DnsQuestion **ret, const char *name, bool with_txt)
 
 int dns_question_add(DnsQuestion *q, DnsResourceKey *key);
 
-int dns_question_matches_rr(DnsQuestion *q, DnsResourceRecord *rr);
-int dns_question_matches_cname(DnsQuestion *q, DnsResourceRecord *rr);
+int dns_question_matches_rr(DnsQuestion *q, DnsResourceRecord *rr, const char *search_domain);
+int dns_question_matches_cname(DnsQuestion *q, DnsResourceRecord *rr, const char* search_domain);
 int dns_question_is_valid_for_query(DnsQuestion *q);
 int dns_question_contains(DnsQuestion *a, DnsResourceKey *k);
 int dns_question_is_equal(DnsQuestion *a, DnsQuestion *b);
@@ -54,3 +54,11 @@ int dns_question_cname_redirect(DnsQuestion *q, const DnsResourceRecord *cname,
 const char *dns_question_first_name(DnsQuestion *q);
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsQuestion*, dns_question_unref);
+
+#define DNS_QUESTION_FOREACH(key, q)                                    \
+        for (unsigned _i = ({                                           \
+                                (key) = ((q) && (q)->n_keys > 0) ? (q)->keys[0] : NULL; \
+                                0;                                      \
+                        });                                             \
+             (q) && ((_i) < (q)->n_keys);                               \
+             _i++, (key) = (_i < (q)->n_keys ? (q)->keys[_i] : NULL))