CDRIVER-5739 do not warn if TXT authSource is ignored (#1741)

* only trace if `authSource` is ignored from TXT record

Author: kevinAlbs

src/libmongoc/src/mongoc/mongoc-uri.c

@@ -36,6 +36,7 @@
 #include "mongoc-write-concern-private.h"
 #include "mongoc-compression-private.h"
 #include "utlist.h"
+#include "mongoc-trace-private.h"
 
 #include <bson-dsl.h>
 
@@ -897,7 +898,15 @@ mongoc_uri_split_option (mongoc_uri_t *uri, bson_t *options, const char *str, bo
        * through TXT records." So, do NOT override existing options with TXT
        * options. */
       if (from_dns) {
-         MONGOC_WARNING ("Cannot override URI option \"%s\" from TXT record \"%s\"", key, str);
+         if (0 == strcmp (lkey, MONGOC_URI_AUTHSOURCE)) {
+            // Treat `authSource` as a special case. A server may support authentication with multiple mechanisms.
+            // MONGODB-X509 requires authSource=$external. SCRAM-SHA-256 requires authSource=admin.
+            // Only log a trace message since this may be expected.
+            TRACE ("Ignoring URI option \"%s\" from TXT record \"%s\". Option is already present in URI", key, str);
+         } else {
+            MONGOC_WARNING (
+               "Ignoring URI option \"%s\" from TXT record \"%s\". Option is already present in URI", key, str);
+         }
          ret = true;
          goto CLEANUP;
       }

src/libmongoc/tests/test-mongoc-uri.c

@@ -1847,14 +1847,24 @@ test_mongoc_uri_dns_options (void)
    mongoc_uri_destroy (uri);
    uri = mongoc_uri_new ("mongodb+srv://[email protected]/?authSource=db1&replicaSet=rs1");
 
-   capture_logs (true);
-   /* parse_options returns true, but logs warnings */
-   BSON_ASSERT (mongoc_uri_parse_options (uri, "authSource=db2&replicaSet=db2", true, NULL));
-   ASSERT_CAPTURED_LOG ("parsing TXT record", MONGOC_LOG_LEVEL_WARNING, "Cannot override URI option \"authSource\"");
-   ASSERT_CAPTURED_LOG ("parsing TXT record", MONGOC_LOG_LEVEL_WARNING, "Cannot override URI option \"replicaSet\"");
-   capture_logs (false);
-   ASSERT_MATCH (mongoc_uri_get_credentials (uri), "{'authsource': 'db1'}");
-   ASSERT_MATCH (mongoc_uri_get_options (uri), "{'replicaset': 'rs1'}");
+   // test that parsing warns if replicaSet is ignored from TXT records.
+   {
+      capture_logs (true);
+      ASSERT (mongoc_uri_parse_options (uri, "replicaSet=db2", true, NULL));
+      ASSERT_CAPTURED_LOG (
+         "parsing replicaSet from TXT", MONGOC_LOG_LEVEL_WARNING, "Ignoring URI option \"replicaSet\"");
+      capture_logs (false);
+      ASSERT_MATCH (mongoc_uri_get_options (uri), "{'replicaset': 'rs1'}");
+   }
+
+   // test that parsing does not warn if authSource is ignored from TXT records.
+   {
+      capture_logs (true);
+      ASSERT (mongoc_uri_parse_options (uri, "authSource=db2", true, NULL));
+      ASSERT_NO_CAPTURED_LOGS ("parsing authSource from TXT");
+      capture_logs (false);
+      ASSERT_MATCH (mongoc_uri_get_credentials (uri), "{'authsource': 'db1'}");
+   }
 
    mongoc_uri_destroy (uri);
 }