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, 13 insertions, 0 deletions

diff --git a/src/resolve-host/resolve-host.c b/src/resolve-host/resolve-host.c
index 2c17ad6ede..f68751a2e5 100644
--- a/src/resolve-host/resolve-host.c
+++ b/src/resolve-host/resolve-host.c
@@ -680,6 +680,7 @@ static void help(void) {
                "     --service-address=BOOL Do [not] resolve address for services\n"
                "     --service-txt=BOOL     Do [not] resolve TXT records for services\n"
                "     --cname=BOOL           Do [not] follow CNAME redirects\n"
+               "     --search=BOOL          Do [not] use search domains\n"
                "     --legend=BOOL          Do [not] print column headers\n"
                , program_invocation_short_name, program_invocation_short_name);
 }
@@ -692,6 +693,7 @@ static int parse_argv(int argc, char *argv[]) {
                 ARG_CNAME,
                 ARG_SERVICE_ADDRESS,
                 ARG_SERVICE_TXT,
+                ARG_SEARCH,
         };
 
         static const struct option options[] = {
@@ -705,6 +707,7 @@ static int parse_argv(int argc, char *argv[]) {
                 { "service",         no_argument,       NULL, ARG_SERVICE         },
                 { "service-address", required_argument, NULL, ARG_SERVICE_ADDRESS },
                 { "service-txt",     required_argument, NULL, ARG_SERVICE_TXT     },
+                { "search",          required_argument, NULL, ARG_SEARCH          },
                 {}
         };
 
@@ -834,6 +837,16 @@ static int parse_argv(int argc, char *argv[]) {
                                 arg_flags &= ~SD_RESOLVED_NO_TXT;
                         break;
 
+                case ARG_SEARCH:
+                        r = parse_boolean(optarg);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to parse --search argument.");
+                        if (r == 0)
+                                arg_flags |= SD_RESOLVED_NO_SEARCH;
+                        else
+                                arg_flags &= ~SD_RESOLVED_NO_SEARCH;
+                        break;
+
                 case '?':
                         return -EINVAL;