resolved: add new accessor dns_stream_take_read_packet() for taking read packet from stream

This ensures the packet is complete when it is taken out, and resets
n_read so that we can start reading the next one.

src/resolve/resolved-dns-stream.c

@@ -533,3 +533,19 @@ int dns_stream_write_packet(DnsStream *s, DnsPacket *p) {
 
         return dns_stream_update_io(s);
 }
+
+DnsPacket *dns_stream_take_read_packet(DnsStream *s) {
+        assert(s);
+
+        if (!s->read_packet)
+                return NULL;
+
+        if (s->n_read < sizeof(s->read_size))
+                return NULL;
+
+        if (s->n_read < sizeof(s->read_size) + be16toh(s->read_size))
+                return NULL;
+
+        s->n_read = 0;
+        return TAKE_PTR(s->read_packet);
+}

src/resolve/resolved-dns-stream.h

@@ -87,3 +87,5 @@ static inline bool DNS_STREAM_QUEUED(DnsStream *s) {
 
         return !!s->write_packet;
 }
+
+DnsPacket *dns_stream_take_read_packet(DnsStream *s);

src/resolve/resolved-dns-stub.c

@@ -437,13 +437,17 @@ static int manager_dns_stub_udp_fd(Manager *m) {
 }
 
 static int on_dns_stub_stream_packet(DnsStream *s) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+
         assert(s);
-        assert(s->read_packet);
 
-        if (dns_packet_validate_query(s->read_packet) > 0) {
-                log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
+        p = dns_stream_take_read_packet(s);
+        assert(p);
 
-                dns_stub_process_query(s->manager, s, s->read_packet);
+        if (dns_packet_validate_query(p) > 0) {
+                log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
+
+                dns_stub_process_query(s->manager, s, p);
         } else
                 log_debug("Invalid DNS stub TCP packet, ignoring.");
 

src/resolve/resolved-dns-transaction.c

@@ -532,27 +532,25 @@ static int on_stream_complete(DnsStream *s, int error) {
 
 static int dns_stream_on_packet(DnsStream *s) {
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
-        int r = 0;
         DnsTransaction *t;
 
+        assert(s);
+
         /* Take ownership of packet to be able to receive new packets */
-        p = TAKE_PTR(s->read_packet);
-        s->n_read = 0;
+        p = dns_stream_take_read_packet(s);
+        assert(p);
 
         t = hashmap_get(s->manager->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
+        if (t)
+                return dns_transaction_on_stream_packet(t, p);
 
         /* Ignore incorrect transaction id as transaction can have been canceled */
-        if (t)
-                r = dns_transaction_on_stream_packet(t, p);
-        else {
-                if (dns_packet_validate_reply(p) <= 0) {
-                        log_debug("Invalid TCP reply packet.");
-                        on_stream_complete(s, 0);
-                }
-                return 0;
+        if (dns_packet_validate_reply(p) <= 0) {
+                log_debug("Invalid TCP reply packet.");
+                on_stream_complete(s, 0);
         }
 
-        return r;
+        return 0;
 }
 
 static int dns_transaction_emit_tcp(DnsTransaction *t) {

src/resolve/resolved-llmnr.c

@@ -260,18 +260,21 @@ int manager_llmnr_ipv6_udp_fd(Manager *m) {
 }
 
 static int on_llmnr_stream_packet(DnsStream *s) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
         DnsScope *scope;
 
         assert(s);
-        assert(s->read_packet);
 
-        scope = manager_find_scope(s->manager, s->read_packet);
+        p = dns_stream_take_read_packet(s);
+        assert(p);
+
+        scope = manager_find_scope(s->manager, p);
         if (!scope)
                 log_debug("Got LLMNR TCP packet on unknown scope. Ignoring.");
-        else if (dns_packet_validate_query(s->read_packet) > 0) {
-                log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
+        else if (dns_packet_validate_query(p) > 0) {
+                log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(p));
 
-                dns_scope_process_query(scope, s, s->read_packet);
+                dns_scope_process_query(scope, s, p);
         } else
                 log_debug("Invalid LLMNR TCP packet, ignoring.");