hostip: cache negative name resolves

Hold them for half the normal lifetime. Helps when told to transfer N
URLs in quick succession that all use the same non-resolving hostname.

Done by storing a DNS entry with a NULL pointer for 'addr'.

Previously an attempt was made in #12406 by Björn Stenberg that was
ultimately never merged.

Closes #18157

tests/data/Makefile.am

@@ -252,7 +252,7 @@ test2064 test2065 test2066 test2067 test2068 test2069 test2070 test2071 \
 test2072 test2073 test2074 test2075 test2076 test2077 test2078 test2079 \
 test2080 test2081 test2082 test2083 test2084 test2085 test2086 test2087 \
 test2088 test2089 \
-test2100 test2101 test2102 test2103 \
+test2100 test2101 test2102 test2103 test2104 \
 \
 test2200 test2201 test2202 test2203 test2204 test2205 \
 \

tests/data/test2104

@@ -0,0 +1,49 @@
+<testcase>
+<info>
+<keywords>
+DNS cache
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<dns>
+</dns>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+dns
+</server>
+<features>
+override-dns
+</features>
+<name>
+Get three URLs with bad host name - cache
+</name>
+<setenv>
+CURL_DNS_SERVER=127.0.0.1:%DNSPORT
+</setenv>
+<command>
+http://examplehost.example/%TESTNUMBER http://examplehost.example/%TESTNUMBER http://examplehost.example/%TESTNUMBER
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+# curl: (6) Could not resolve host: examplehost.example
+<errorcode>
+6
+</errorcode>
+
+# Ignore HTTPS requests here
+<dns host="examplehost.example QTYPE A">
+QNAME examplehost.example QTYPE A
+QNAME examplehost.example QTYPE AAAA
+</dns>
+</verify>
+</testcase>

tests/data/test655

@@ -36,7 +36,7 @@ lib%TESTNUMBER
 resolver start callback
 </name>
 <command>
-http://%HOSTIP:%HTTPPORT/%TESTNUMBER
+http://failthis/%TESTNUMBER http://%HOSTIP:%HTTPPORT/%TESTNUMBER
 </command>
 </client>
 

tests/libtest/lib655.c

@@ -74,7 +74,7 @@ static CURLcode test_lib655(const char *URL)
     goto test_cleanup;
   }
 
-  /* First set the URL that is about to receive our request. */
+  /* Set the URL that is about to receive our first request. */
   test_setopt(curl, CURLOPT_URL, URL);
 
   test_setopt(curl, CURLOPT_RESOLVER_START_DATA, TEST_DATA_STRING);
@@ -91,6 +91,9 @@ static CURLcode test_lib655(const char *URL)
     goto test_cleanup;
   }
 
+  /* Set the URL that receives our second request. */
+  test_setopt(curl, CURLOPT_URL, libtest_arg2);
+
   test_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, resolver_alloc_cb_pass);
 
   /* this should succeed */

tests/runtests.pl

@@ -1674,6 +1674,29 @@ sub singletest_check {
         }
     }
 
+    my @dnsd = getpart("verify", "dns");
+    if(@dnsd) {
+        # we're supposed to verify a dynamically generated file!
+        my %hash = getpartattr("verify", "dns");
+        my $hostname=$hash{'host'};
+
+        # Verify the sent DNS requests
+        my @out = loadarray("$logdir/dnsd.input");
+        my @sverify = sort @dnsd;
+        my @sout = sort @out;
+
+        if($hostname) {
+            # when a hostname is set, we filter out requests to just this
+            # pattern
+            @sout = grep {/$hostname/} @sout;
+        }
+
+        $res = compare($runnerid, $testnum, $testname, "DNS", \@sout, \@sverify);
+        if($res) {
+            return -1;
+        }
+    }
+
     # accept multiple comma-separated error codes
     my @splerr = split(/ *, */, $errorcode);
     my $errok;

tests/server/dnsd.c

@@ -64,6 +64,19 @@ static int qname(const unsigned char **pkt, size_t *size)
 #define QTYPE_AAAA 28
 #define QTYPE_HTTPS 0x41
 
+static const char *type2string(unsigned short qtype)
+{
+  switch(qtype) {
+  case QTYPE_A:
+    return "A";
+  case QTYPE_AAAA:
+    return "AAAA";
+  case QTYPE_HTTPS:
+    return "HTTPS";
+  }
+  return "<unknown>";
+}
+
 /*
  * Handle initial connection protocol.
  *
@@ -125,8 +138,7 @@ static int store_incoming(const unsigned char *data, size_t size,
   fprintf(server, "Z: %x\n", (id & 0x70) >> 4);
   fprintf(server, "RCODE: %x\n", (id & 0x0f));
 #endif
-  qd = get16bit(&data, &size);
-  fprintf(server, "QDCOUNT: %04x\n", qd);
+  (void) get16bit(&data, &size);
 
   data += 6; /* skip ANCOUNT, NSCOUNT and ARCOUNT */
   size -= 6;
@@ -136,14 +148,13 @@ static int store_incoming(const unsigned char *data, size_t size,
   qptr = data;
 
   if(!qname(&data, &size)) {
-    fprintf(server, "QNAME: %s\n", name);
     qd = get16bit(&data, &size);
-    fprintf(server, "QTYPE: %04x\n", qd);
+    fprintf(server, "QNAME %s QTYPE %s\n", name, type2string(qd));
     *qtype = qd;
-    logmsg("Question for '%s' type %x", name, qd);
+    logmsg("Question for '%s' type %x / %s", name, qd,
+           type2string(qd));
 
-    qd = get16bit(&data, &size);
-    logmsg("QCLASS: %04x\n", qd);
+    (void) get16bit(&data, &size);
 
     *qlen = qsize - size; /* total size of the query */
     memcpy(qbuf, qptr, *qlen);
@@ -618,7 +629,7 @@ static int test_dnsd(int argc, char **argv)
       clear_advisor_read_lock(loglockfile);
     }
 
-    logmsg("end of one transfer");
+    /* logmsg("end of one transfer"); */
   }
 
 dnsd_cleanup: