lib/messages.c: Make message searches stream as well.

Xapian provides an interator-based interface to all search results.
So it was natural to make notmuch_messages_t be iterator-based as
well. Which we did originally.

But we ran into a problem when we added two APIs, (_get_replies and
_get_toplevel_messages), that want to return a messages iterator
that's *not* based on a Xapian search result. My original compromise
was to use notmuch_message_list_t as the basis for all returned
messages iterators in the public interface.

This had the problem of introducing extra latency at the beginning
of a search for messages, (the call would block while iterating over
all results from Xapian, converting to a message list).

In this commit, we remove that initial conversion and instead provide
two alternate implementations of notmuch_messages_t (one on top of a
Xapian iterator and one on top of a message list).

With this change, I tested a "notmuch search" returning *many* results
as previously taking about 7 seconds before results started appearing,
and now taking only 2 seconds.

1 files changed, 20 insertions, 0 deletions

diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index 2b4bf319..d3f9a4c4 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -290,6 +290,15 @@ typedef struct _notmuch_message_list {
     notmuch_message_node_t **tail;
 } notmuch_message_list_t;
 
+/* There's a rumor that there's an alternate struct _notmuch_messages
+ * somewhere with some nasty C++ objects in it. We'll try to maintain
+ * ignorance of that here. (See notmuch_mset_messages_t in query.cc)
+ */
+struct _notmuch_messages {
+    notmuch_bool_t is_of_list_type;
+    notmuch_message_node_t *iterator;
+};
+
 notmuch_message_list_t *
 _notmuch_message_list_create (const void *ctx);
 
@@ -304,6 +313,17 @@ _notmuch_message_list_add_message (notmuch_message_list_t *list,
 notmuch_messages_t *
 _notmuch_messages_create (notmuch_message_list_t *list);
 
+/* query.cc */
+
+notmuch_bool_t
+_notmuch_mset_messages_has_more (notmuch_messages_t *messages);
+
+notmuch_message_t *
+_notmuch_mset_messages_get (notmuch_messages_t *messages);
+
+void
+_notmuch_mset_messages_advance (notmuch_messages_t *messages);
+
 /* message.cc */
 
 void