QDnsLookup: add TimeoutError for timeouts

We were getting InvalidReplyError because it was simply unknown, which
is not very useful. Previously, the Unix code used res_nquery(), which
does not return timeouts as a condition. It returns -1 if a timeout did
happen, but the content in errno could be a left-over from a previous
timeout (see the "Not a typewriter"[1] problem).

With the rewrite to using res_nmkquery() and res_nsend() from the
previous commits, we can rely on errno being set properly by
res_nsend().

$ $objdir/tests/manual/qdnslookup/qdnslookup @0.0.0.1
; <<>> QDnsLookup 6.6.0 <<>> qdnslookup @0.0.0.1
;; status: TimeoutError (Request timed out)
;; QUESTION:
;qt-project.org                 IN A

;; Query time: 10008 ms
;; SERVER: 0.0.0.1#53

Tested on FreeBSD, Linux, macOS, and Windows.

[1] https://en.wikipedia.org/wiki/Not_a_typewriter

Change-Id: I3e3bfef633af4130a03afffd175e31958247f9b1
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/network/kernel/qdnslookup.cpp

@@ -187,6 +187,9 @@ static void qt_qdnsservicerecord_sort(QList<QDnsServiceRecord> &records)
 
     \value NotFoundError        the requested domain name does not exist
     (NXDOMAIN).
+
+    \value TimeoutError         the server was not reached or did not reply
+    in time (since 6.6).
 */
 
 /*!
@@ -1079,6 +1082,7 @@ void QDnsLookupRunnable::run()
     case QDnsLookup::NotFoundError:
     case QDnsLookup::ServerFailureError:
     case QDnsLookup::ServerRefusedError:
+    case QDnsLookup::TimeoutError:
         break;      // no warning for these
 
     case QDnsLookup::ResolverError:

src/network/kernel/qdnslookup.h

@@ -159,7 +159,8 @@ public:
         InvalidReplyError,
         ServerFailureError,
         ServerRefusedError,
-        NotFoundError
+        NotFoundError,
+        TimeoutError,
     };
     Q_ENUM(Error)
 

src/network/kernel/qdnslookup_p.h

@@ -65,6 +65,12 @@ public:
         setError(QDnsLookup::ResolverError, qt_error_string(code));
     }
 
+    void makeTimeoutError()
+    {
+        Q_ASSERT(allAreEmpty());
+        setError(QDnsLookup::TimeoutError, QDnsLookup::tr("Request timed out"));
+    }
+
     void makeDnsRcodeError(quint8 rcode)
     {
         Q_ASSERT(allAreEmpty());

src/network/kernel/qdnslookup_unix.cpp

@@ -174,7 +174,10 @@ void QDnsLookupRunnable::query(QDnsLookupReply *reply)
         int responseLength = res_nsend(&state, qbuffer.data(), queryLength, buffer.data(), buffer.size());
         if (responseLength < 0) {
             // network error of some sort
-            reply->makeResolverSystemError();
+            if (errno == ETIMEDOUT)
+                reply->makeTimeoutError();
+            else
+                reply->makeResolverSystemError();
         }
         return responseLength;
     };

src/network/kernel/qdnslookup_win.cpp

@@ -91,6 +91,8 @@ void QDnsLookupRunnable::query(QDnsLookupReply *reply)
     const DNS_STATUS status = DnsQueryEx(&request, &results, nullptr);
     if (status >= DNS_ERROR_RCODE_FORMAT_ERROR && status <= DNS_ERROR_RCODE_LAST)
         return reply->makeDnsRcodeError(status - DNS_ERROR_RCODE_FORMAT_ERROR + 1);
+    else if (status == ERROR_TIMEOUT)
+        return reply->makeTimeoutError();
     else if (status != ERROR_SUCCESS)
         return reply->makeResolverSystemError(status);
 

tests/auto/network/kernel/qdnslookup/tst_qdnslookup.cpp

@@ -328,7 +328,8 @@ void tst_QDnsLookup::lookup()
     };
 
     if (!dnsServersMustWork && (lookup.error() == QDnsLookup::ServerFailureError
-                                || lookup.error() == QDnsLookup::ServerRefusedError)) {
+                                || lookup.error() == QDnsLookup::ServerRefusedError
+                                || lookup.error() == QDnsLookup::TimeoutError)) {
         // It's not a QDnsLookup problem if the server refuses to answer the query.
         // This happens for queries of type ANY through Dnsmasq, for example.
         qWarning("Server refused or was unable to answer query; %s", extraErrorMsg().constData());