resolved: for a transaction, keep track where the answer data came from

Let's track where the data came from: from the network, the cache or the
local zone. This is not only useful for debugging purposes, but is also
useful when the zone probing wants to ensure it's not reusing
transactions that were answered from the cache or the zone itself.

3 files changed, 31 insertions, 4 deletions

diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index 20db1fbd81..6b496af412 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -661,7 +661,7 @@ DnsTransaction *dns_scope_find_transaction(DnsScope *scope, DnsResourceKey *key,
          * data instead of a real packet, if that's requested. */
         if (!cache_ok &&
             IN_SET(t->state, DNS_TRANSACTION_SUCCESS, DNS_TRANSACTION_FAILURE) &&
-            !t->received)
+            t->answer_source != DNS_TRANSACTION_NETWORK)
                 return NULL;
 
         return t;
diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index ef5097db39..519358ffb1 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -103,6 +103,7 @@ int dns_transaction_new(DnsTransaction **ret, DnsScope *s, DnsResourceKey *key)
                 return -ENOMEM;
 
         t->dns_udp_fd = -1;
+        t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
         t->key = dns_resource_key_ref(key);
 
         /* Find a fresh, unused transaction id */
@@ -197,11 +198,12 @@ void dns_transaction_complete(DnsTransaction *t, DnsTransactionState state) {
          * should hence not attempt to access the query or transaction
          * after calling this function. */
 
-        log_debug("Transaction on scope %s on %s/%s now complete with <%s>",
+        log_debug("Transaction on scope %s on %s/%s now complete with <%s> from %s",
                   dns_protocol_to_string(t->scope->protocol),
                   t->scope->link ? t->scope->link->name : "*",
                   t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family),
-                  dns_transaction_state_to_string(state));
+                  dns_transaction_state_to_string(state),
+                  t->answer_source < 0 ? "none" : dns_transaction_source_to_string(t->answer_source));
 
         t->state = state;
 
@@ -392,6 +394,8 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
                 t->received = dns_packet_ref(p);
         }
 
+        t->answer_source = DNS_TRANSACTION_NETWORK;
+
         if (p->ipproto == IPPROTO_TCP) {
                 if (DNS_PACKET_TC(p)) {
                         /* Truncated via TCP? Somebody must be fucking with us */
@@ -637,6 +641,7 @@ int dns_transaction_go(DnsTransaction *t) {
         t->received = dns_packet_unref(t->received);
         t->answer = dns_answer_unref(t->answer);
         t->answer_rcode = 0;
+        t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
 
         /* Check the zone, but obly if this transaction is not used
          * for probing or verifying a zone item. */
@@ -647,6 +652,7 @@ int dns_transaction_go(DnsTransaction *t) {
                         return r;
                 if (r > 0) {
                         t->answer_rcode = DNS_RCODE_SUCCESS;
+                        t->answer_source = DNS_TRANSACTION_ZONE;
                         dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                         return 0;
                 }
@@ -668,6 +674,7 @@ int dns_transaction_go(DnsTransaction *t) {
                 if (r < 0)
                         return r;
                 if (r > 0) {
+                        t->answer_source = DNS_TRANSACTION_CACHE;
                         if (t->answer_rcode == DNS_RCODE_SUCCESS)
                                 dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                         else
@@ -771,3 +778,10 @@ static const char* const dns_transaction_state_table[_DNS_TRANSACTION_STATE_MAX]
         [DNS_TRANSACTION_ABORTED] = "aborted",
 };
 DEFINE_STRING_TABLE_LOOKUP(dns_transaction_state, DnsTransactionState);
+
+static const char* const dns_transaction_source_table[_DNS_TRANSACTION_SOURCE_MAX] = {
+        [DNS_TRANSACTION_NETWORK] = "network",
+        [DNS_TRANSACTION_CACHE] = "cache",
+        [DNS_TRANSACTION_ZONE] = "zone",
+};
+DEFINE_STRING_TABLE_LOOKUP(dns_transaction_source, DnsTransactionSource);
diff --git a/src/resolve/resolved-dns-transaction.h b/src/resolve/resolved-dns-transaction.h
index a56bcdb6d6..ee80dcf5a9 100644
--- a/src/resolve/resolved-dns-transaction.h
+++ b/src/resolve/resolved-dns-transaction.h
@@ -23,6 +23,7 @@
 
 typedef struct DnsTransaction DnsTransaction;
 typedef enum DnsTransactionState DnsTransactionState;
+typedef enum DnsTransactionSource DnsTransactionSource;
 
 enum DnsTransactionState {
         DNS_TRANSACTION_NULL,
@@ -39,6 +40,14 @@ enum DnsTransactionState {
         _DNS_TRANSACTION_STATE_INVALID = -1
 };
 
+enum DnsTransactionSource {
+        DNS_TRANSACTION_NETWORK,
+        DNS_TRANSACTION_CACHE,
+        DNS_TRANSACTION_ZONE,
+        _DNS_TRANSACTION_SOURCE_MAX,
+        _DNS_TRANSACTION_SOURCE_INVALID = -1
+};
+
 #include "resolved-dns-answer.h"
 #include "resolved-dns-packet.h"
 #include "resolved-dns-question.h"
@@ -58,6 +67,7 @@ struct DnsTransaction {
 
         DnsAnswer *answer;
         int answer_rcode;
+        DnsTransactionSource answer_source;
 
         usec_t start_usec;
         sd_event_source *timeout_event_source;
@@ -98,6 +108,9 @@ void dns_transaction_complete(DnsTransaction *t, DnsTransactionState state);
 const char* dns_transaction_state_to_string(DnsTransactionState p) _const_;
 DnsTransactionState dns_transaction_state_from_string(const char *s) _pure_;
 
+const char* dns_transaction_source_to_string(DnsTransactionSource p) _const_;
+DnsTransactionSource dns_transaction_source_from_string(const char *s) _pure_;
+
 /* LLMNR Jitter interval, see RFC 4795 Section 7 */
 #define LLMNR_JITTER_INTERVAL_USEC (100 * USEC_PER_MSEC)
 
@@ -107,4 +120,4 @@ DnsTransactionState dns_transaction_state_from_string(const char *s) _pure_;
 /* Maximum attempts to send LLMNR requests, see RFC 4795 Section 2.7 */
 #define LLMNR_TRANSACTION_ATTEMPTS_MAX 3
 
-#define TRANSACTION_ATTEMPTS_MAX(p) (p == DNS_PROTOCOL_LLMNR ? LLMNR_TRANSACTION_ATTEMPTS_MAX : DNS_TRANSACTION_ATTEMPTS_MAX)
+#define TRANSACTION_ATTEMPTS_MAX(p) ((p) == DNS_PROTOCOL_LLMNR ? LLMNR_TRANSACTION_ATTEMPTS_MAX : DNS_TRANSACTION_ATTEMPTS_MAX)