asyn-thrdd: retry link-local ipv6 if missing scope id

When the threaded resolver gets AAAA results that carry a link-local
address without scope-id, it now re-queues a query with AF_UNSPEC and
strips ipv4 addresses from that result. Whatever the resulting addresses
and scope-ids are, this becomes the result of the resolve.

Fixes #22330
Reported-by: Bartel Sielski
Closes #22368

tests/http/test_21_resolve.py

@@ -26,6 +26,7 @@
 #
 import logging
 import os
+import re
 from datetime import timedelta
 from typing import Generator
 
@@ -283,6 +284,30 @@ class TestResolve:
         r.check_stats(count=1, http_status=0, exitcode=6)
         assert r.duration < timedelta(seconds=20), f'{r}'
 
+    # dnsd with one answer for AAAA, delayed one for A
+    @pytest.mark.skipif(condition=not Env.curl_override_dns(), reason="no DNS override")
+    @pytest.mark.skipif(condition=not Env.curl_has_feature('IPv6'), reason="no IPv6")
+    @pytest.mark.skipif(condition=not Env.curl_resolv_threaded(), reason="no threaded resolver")
+    def test_21_16_dnsd_link_local(self, env: Env, httpd, dnsd):
+        dnsd.set_answers(addr_aaaa=['[fe80::1]'])
+        run_env = os.environ.copy()
+        run_env['CURL_DNS_SERVER'] = f'127.0.0.1:{dnsd.port}'
+        run_env['CURL_QUICK_EXIT'] = '1'
+        run_env['CURL_DEBUG'] = 'dns'
+        curl = CurlClient(env=env, run_env=run_env, force_resolv=False)
+        url = f'https://{env.authority_for(env.domain1, "http/1.1")}/data.json'
+        r = curl.http_download(urls=[url], with_stats=True, extra_args=[
+            '--connect-timeout', '1'
+        ])
+        # should fail with CURLE_OPERATION_TIMEOUT or COULDNT_CONNECT
+        assert r.exit_code in (7, 28), f'{r.dump_logs()}'
+        af_unspec_resolves = [line for line in r.trace_lines if
+            re.match(r'.* \[DNS] re-queueing query .+ for AF_UNSPEC resolve', line)]
+        assert len(af_unspec_resolves) == 1, f'{r.dump_logs()}'
+        aaaa_resolves = [line for line in r.trace_lines if
+            re.match(r'.* \* IPv6: fe80::1', line)]
+        assert len(aaaa_resolves) == 1, f'{r.dump_logs()}'
+
     def _clean_files(self, files):
         for file in files:
             if os.path.exists(file):

tests/unit/unit3301.c

@@ -88,7 +88,7 @@ static CURLcode test_unit3301(const char *arg)
 
   /* create and teardown queue */
   memset(&ctx, 0, sizeof(ctx));
-  result = Curl_thrdq_create(&tqueue, "unit3301-a", 0, 0, 2, 1,
+  result = Curl_thrdq_create(&tqueue, "unit3301-a", 0, 2, 1,
                              unit3301_item_free, unit3301_process,
                              unit3301_event, &ctx);
   fail_unless(!result, "queue-a create");
@@ -99,7 +99,7 @@ static CURLcode test_unit3301(const char *arg)
   /* create queue, have it process `count` items */
   count = 10;
   memset(&ctx, 0, sizeof(ctx));
-  result = Curl_thrdq_create(&tqueue, "unit3301-b", 0, 0, 2, 1,
+  result = Curl_thrdq_create(&tqueue, "unit3301-b", 0, 2, 1,
                              unit3301_item_free, unit3301_process,
                              unit3301_event, &ctx);
   fail_unless(!result, "queue-b create");

tests/unit/unit3306.c

@@ -76,7 +76,7 @@ static CURLcode test_unit3306(const char *arg)
   fail_unless(getenv("CURL_DBG_THRDPOOL_FAIL_STARTS"),
               "CURL_DBG_THRDPOOL_FAIL_STARTS must be set for this test");
 
-  result = Curl_thrdq_create(&tqueue, "unit3306", 0, 0, 2, 1,
+  result = Curl_thrdq_create(&tqueue, "unit3306", 0, 2, 1,
                              unit3306_item_free, unit3306_process,
                              NULL, NULL);
   fail_unless(!result, "queue create");