CDRIVER-4614 Include topology description in error messages (#1527)

Author: adriandole

src/libmongoc/src/mongoc/mongoc-error-private.h

@@ -89,4 +89,8 @@ _mongoc_error_is_server (const bson_error_t *error);
 bool
 _mongoc_error_is_auth (const bson_error_t *error);
 
+/* Try to append `s` to `error`. Truncates `s` if `error` is out of space. */
+void
+_mongoc_error_append (bson_error_t *error, const char *s);
+
 BSON_END_DECLS

src/libmongoc/src/mongoc/mongoc-error.c

@@ -311,3 +311,12 @@ _mongoc_error_is_auth (const bson_error_t *error)
 
    return error->domain == MONGOC_ERROR_CLIENT && error->code == MONGOC_ERROR_CLIENT_AUTHENTICATE;
 }
+
+void
+_mongoc_error_append (bson_error_t *error, const char *s)
+{
+   BSON_ASSERT (error);
+   const size_t error_len = strlen (error->message);
+   const size_t remaining = sizeof (error->message) - error_len;
+   bson_strncpy (error->message + error_len, s, remaining);
+}

src/libmongoc/src/mongoc/mongoc-topology.c

@@ -1098,6 +1098,9 @@ mongoc_topology_select_server_id (mongoc_topology_t *topology,
    uint32_t server_id;
    mc_shared_tpld td = mc_tpld_take_ref (topology);
 
+   bson_string_t *topology_type = bson_string_new (". Topology type: ");
+   bson_string_append (topology_type, mongoc_topology_description_type (td.ptr));
+
    /* These names come from the Server Selection Spec pseudocode */
    int64_t loop_start;  /* when we entered this function */
    int64_t loop_end;    /* when we last completed a loop (single-threaded) */
@@ -1153,10 +1156,7 @@ mongoc_topology_select_server_id (mongoc_topology_t *topology,
 
             if (scan_ready > expire_at && !try_once) {
                /* selection timeout will expire before min heartbeat passes */
-               _mongoc_server_selection_error ("No suitable servers found: "
-                                               "`serverselectiontimeoutms` timed out",
-                                               &scanner_error,
-                                               error);
+               _mongoc_server_selection_error (timeout_msg, &scanner_error, error);
 
                server_id = 0;
                goto done;
@@ -1301,6 +1301,10 @@ mongoc_topology_select_server_id (mongoc_topology_t *topology,
    }
 
 done:
+   if (error) {
+      _mongoc_error_append (error, topology_type->str);
+   }
+   bson_string_free (topology_type, true);
    mc_tpld_drop_ref (&td);
    return server_id;
 }

src/libmongoc/tests/test-mongoc-server-selection-errors.c

@@ -81,7 +81,8 @@ test_server_selection_error_dns_direct_single (void)
 {
    server_selection_error_dns ("mongodb://example-localhost.invalid:27017/",
                                "No suitable servers found (`serverSelectionTryOnce` set): "
-                               "[Fake error for 'example-localhost.invalid']",
+                               "[Fake error for 'example-localhost.invalid']"
+                               ". Topology type: Single",
                                false,
                                false);
 }
@@ -93,7 +94,8 @@ test_server_selection_error_dns_direct_pooled (void *ctx)
 
    server_selection_error_dns ("mongodb://example-localhost.invalid:27017/",
                                "No suitable servers found: `serverSelectionTimeoutMS` expired: "
-                               "[Fake error for 'example-localhost.invalid']",
+                               "[Fake error for 'example-localhost.invalid']"
+                               ". Topology type: Single",
                                false,
                                true);
 }
@@ -105,7 +107,8 @@ test_server_selection_error_dns_multi_fail_single (void)
                                "example-localhost.invalid:27017,other-example-localhost.invalid:27017/",
                                "No suitable servers found (`serverSelectionTryOnce` set):"
                                " [Fake error for 'example-localhost.invalid']"
-                               " [Fake error for 'other-example-localhost.invalid']",
+                               " [Fake error for 'other-example-localhost.invalid']"
+                               ". Topology type: Unknown",
                                false,
                                false);
 }
@@ -119,7 +122,8 @@ test_server_selection_error_dns_multi_fail_pooled (void *ctx)
                                "example-localhost.invalid:27017,other-example-localhost.invalid:27017/",
                                "No suitable servers found: `serverSelectionTimeoutMS` expired:"
                                " [Fake error for 'example-localhost.invalid']"
-                               " [Fake error for 'other-example-localhost.invalid']",
+                               " [Fake error for 'other-example-localhost.invalid']"
+                               ". Topology type: Unknown",
                                false,
                                true);
 }