lib: cache configuration information from database

The main goal is to allow configuration information to be temporarily
overridden by a separate config file. That will require further
changes not in this commit.

The performance impact is unclear, and will depend on the balance
between number of queries and number of distinct metadata items read
on the first call to n_d_get_config.

1 files changed, 51 insertions, 7 deletions

diff --git a/lib/config.cc b/lib/config.cc
index 0b760dbc..c079d752 100644
--- a/lib/config.cc
+++ b/lib/config.cc
@@ -50,6 +50,11 @@ notmuch_database_set_config (notmuch_database_t *notmuch,
     if (status)
 	return status;
 
+    if (! notmuch->config) {
+	if ((status = _notmuch_config_load_from_database (notmuch)))
+	    return status;
+    }
+
     try {
 	notmuch->writable_xapian_db->set_metadata (CONFIG_PREFIX + key, value);
     } catch (const Xapian::Error &error) {
@@ -58,7 +63,13 @@ notmuch_database_set_config (notmuch_database_t *notmuch,
 	_notmuch_database_log (notmuch, "Error: A Xapian exception occurred setting metadata: %s\n",
 			       error.get_msg ().c_str ());
     }
-    return status;
+
+    if (status)
+	return status;
+
+    _notmuch_string_map_set (notmuch->config, key, value);
+
+    return NOTMUCH_STATUS_SUCCESS;
 }
 
 static notmuch_status_t
@@ -84,17 +95,25 @@ notmuch_database_get_config (notmuch_database_t *notmuch,
 			     const char *key,
 			     char **value)
 {
-    std::string strval;
+    const char* stored_val;
     notmuch_status_t status;
 
+    if (! notmuch->config) {
+	if ((status = _notmuch_config_load_from_database (notmuch)))
+	    return status;
+    }
+
     if (! value)
 	return NOTMUCH_STATUS_NULL_POINTER;
 
-    status = _metadata_value (notmuch, key, strval);
-    if (status)
-	return status;
-
-    *value = strdup (strval.c_str ());
+    stored_val = _notmuch_string_map_get (notmuch->config, key);
+    if (! stored_val) {
+	/* XXX in principle this API should be fixed so empty string
+	 * is distinguished from not found */
+	*value = strdup("");
+    } else {
+	*value = strdup (stored_val);
+    }
 
     return NOTMUCH_STATUS_SUCCESS;
 }
@@ -201,3 +220,28 @@ notmuch_config_list_destroy (notmuch_config_list_t *list)
 {
     talloc_free (list);
 }
+
+notmuch_status_t
+_notmuch_config_load_from_database (notmuch_database_t *notmuch)
+{
+    notmuch_status_t status = NOTMUCH_STATUS_SUCCESS;
+    notmuch_config_list_t *list;
+
+    if (notmuch->config == NULL)
+	notmuch->config = _notmuch_string_map_create (notmuch);
+
+    if (unlikely(notmuch->config == NULL))
+	return NOTMUCH_STATUS_OUT_OF_MEMORY;
+
+    status = notmuch_database_get_config_list (notmuch, "", &list);
+    if (status)
+	return status;
+
+    for (; notmuch_config_list_valid (list); notmuch_config_list_move_to_next (list)) {
+	_notmuch_string_map_append (notmuch->config,
+				    notmuch_config_list_key (list),
+				    notmuch_config_list_value (list));
+    }
+
+    return status;
+}