[PATCH] lib: cache configuration information from database

[David Bremner <david@tethera.net>]

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.
---
 lib/config.cc             | 45 +++++++++++++++++++++++++++++++++------
 lib/database-private.h    |  3 +++
 lib/notmuch-private.h     |  3 +++
 lib/open.cc               |  2 +-
 test/T562-lib-database.sh |  2 +-
 5 files changed, 47 insertions(+), 8 deletions(-)

diff --git a/lib/config.cc b/lib/config.cc
index 0b760dbc..7f97e528 100644
--- a/lib/config.cc
+++ b/lib/config.cc
@@ -84,17 +84,25 @@ 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 +209,28 @@ 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;
+}
diff --git a/lib/database-private.h b/lib/database-private.h
index c9bc712b..d83cf0d0 100644
--- a/lib/database-private.h
+++ b/lib/database-private.h
@@ -228,6 +228,9 @@ struct _notmuch_database {
      * here, but at least they are small */
     notmuch_string_map_t *user_prefix;
     notmuch_string_map_t *user_header;
+
+    /* Cached and possibly overridden configuration */
+    notmuch_string_map_t *config;
 };
 
 /* Prior to database version 3, features were implied by the database
diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index 57ec7f72..0f26b371 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -699,6 +699,9 @@ struct _notmuch_indexopts {
 
 #define EMPTY_STRING(s) ((s)[0] == '\0')
 
+/* config.cc */
+notmuch_status_t
+_notmuch_config_load_from_database (notmuch_database_t * db);
 NOTMUCH_END_DECLS
 
 #ifdef __cplusplus
diff --git a/lib/open.cc b/lib/open.cc
index 1b17e63a..c04e6f77 100644
--- a/lib/open.cc
+++ b/lib/open.cc
@@ -90,7 +90,7 @@ notmuch_database_open_verbose (const char *path,
     notmuch->exception_reported = false;
     notmuch->status_string = NULL;
     notmuch->path = talloc_strdup (notmuch, path);
-
+    notmuch->config = NULL;
     strip_trailing (notmuch->path, '/');
 
     notmuch->writable_xapian_db = NULL;
diff --git a/test/T562-lib-database.sh b/test/T562-lib-database.sh
index dd4f2566..37ca16ab 100755
--- a/test/T562-lib-database.sh
+++ b/test/T562-lib-database.sh
@@ -350,7 +350,7 @@ cat <<EOF > EXPECTED
 == stdout ==
 1
 == stderr ==
-Error: A Xapian exception occurred getting metadata: Database has been closed
+A Xapian exception occurred getting metadata iterator: Database has been closed.
 EOF
 test_expect_equal_file EXPECTED OUTPUT
 
-- 
2.29.2