libnotmuch: Underlying support for doing partial-results searches.

The library interface now allows the caller to do incremental searches,
(such as one page of results at a time). Next we'll just need to hook
this up to "notmuch search" and the emacs interface.

lib/notmuch.h

@@ -313,6 +313,14 @@ notmuch_query_set_sort (notmuch_query_t *query, notmuch_sort_t sort);
  * object is owned by the query and as such, will only be valid until
  * notmuch_query_destroy.
  *
+ * The 'first' and 'max_threads' arguments can be used to obtain
+ * partial results from the search. For example, to get results 10 at
+ * a time, pass 'max_threads' as 10 and for 'first' pass the values 0,
+ * 10, 20, etc. As a special case, a value of -1 for 'max_threads'
+ * indicates that no limiting is to be performed. So a search with
+ * 'first' == 0 and 'max_threads' == -1 will return the complete
+ * results of the search.
+ *
  * Typical usage might be:
  *
  *     notmuch_query_t *query;
@@ -345,13 +353,22 @@ notmuch_query_set_sort (notmuch_query_t *query, notmuch_sort_t sort);
  * to call it if the query is about to be destroyed).
  */
 notmuch_threads_t *
-notmuch_query_search_threads (notmuch_query_t *query);
+notmuch_query_search_threads (notmuch_query_t *query,
+			      int first, int max_threads);
 
 /* Execute a query for messages, returning a notmuch_messages_t object
  * which can be used to iterate over the results. The returned
  * messages object is owned by the query and as such, will only be
  * valid until notmuch_query_destroy.
  *
+ * The 'first' and 'max_messages' arguments can be used to obtain
+ * partial results from the search. For example, to get results 10 at
+ * a time, pass 'max_messages' as 10 and for 'first' pass the values
+ * 0, 10, 20, etc. As a special case, a value of -1 for 'max_messages'
+ * indicates that no limiting is to be performed. So a search with
+ * 'first' == 0 and 'max_messages' == -1 will return the complete
+ * results of the search.
+ *
  * Typical usage might be:
  *
  *     notmuch_query_t *query;
@@ -384,7 +401,8 @@ notmuch_query_search_threads (notmuch_query_t *query);
  * reason to call it if the query is about to be destroyed).
  */
 notmuch_messages_t *
-notmuch_query_search_messages (notmuch_query_t *query);
+notmuch_query_search_messages (notmuch_query_t *query,
+			       int first, int max_messages);
 
 /* Destroy a notmuch_query_t along with any associated resources.
  *

lib/query.cc

@@ -88,7 +88,9 @@ _notmuch_messages_destructor (notmuch_messages_t *messages)
 }
 
 notmuch_messages_t *
-notmuch_query_search_messages (notmuch_query_t *query)
+notmuch_query_search_messages (notmuch_query_t *query,
+			       int first,
+			       int max_messages)
 {
     notmuch_database_t *notmuch = query->notmuch;
     const char *query_string = query->query_string;
@@ -138,7 +140,9 @@ notmuch_query_search_messages (notmuch_query_t *query)
 
 	enquire.set_query (final_query);
 
-	mset = enquire.get_mset (0, notmuch->xapian_db->get_doccount ());
+	if (max_messages == -1)
+	    max_messages = notmuch->xapian_db->get_doccount ();
+	mset = enquire.get_mset (first, max_messages);
 
 	messages->notmuch = notmuch;
 
@@ -171,7 +175,9 @@ _notmuch_threads_destructor (notmuch_threads_t *threads)
 }
 
 notmuch_threads_t *
-notmuch_query_search_threads (notmuch_query_t *query)
+notmuch_query_search_threads (notmuch_query_t *query,
+			      int first,
+			      int max_threads)
 {
     notmuch_threads_t *threads;
     notmuch_thread_t *thread;
@@ -179,6 +185,7 @@ notmuch_query_search_threads (notmuch_query_t *query)
     notmuch_messages_t *messages;
     notmuch_message_t *message;
     GHashTable *seen;
+    int messages_seen = 0, threads_seen = 0;
 
     threads = talloc (query, notmuch_threads_t);
     if (threads == NULL)
@@ -193,29 +200,48 @@ notmuch_query_search_threads (notmuch_query_t *query)
     seen = g_hash_table_new_full (g_str_hash, g_str_equal,
 				  free, NULL);
 
-    for (messages = notmuch_query_search_messages (query);
-	 notmuch_messages_has_more (messages);
-	 notmuch_messages_advance (messages))
+    while (threads_seen < first + max_threads)
     {
-	message = notmuch_messages_get (messages);
+	int messages_seen_previously = messages_seen;
 
-	thread_id = notmuch_message_get_thread_id (message);
-
-	if (! g_hash_table_lookup_extended (seen,
-					    thread_id, NULL,
-					    (void **) &thread))
+	for (messages = notmuch_query_search_messages (query,
+						       messages_seen,
+						       max_threads);
+	     notmuch_messages_has_more (messages);
+	     notmuch_messages_advance (messages))
 	{
-	    thread = _notmuch_thread_create (query, query->notmuch,
-					     thread_id);
+	    message = notmuch_messages_get (messages);
 
-	    g_hash_table_insert (seen, xstrdup (thread_id), thread);
+	    thread_id = notmuch_message_get_thread_id (message);
 
-	    g_ptr_array_add (threads->threads, thread);
+	    if (! g_hash_table_lookup_extended (seen,
+						thread_id, NULL,
+						(void **) &thread))
+	    {
+		if (threads_seen > first) {
+		    thread = _notmuch_thread_create (query, query->notmuch,
+						     thread_id);
+		    g_ptr_array_add (threads->threads, thread);
+		} else {
+		    thread = NULL;
+		}
+
+		g_hash_table_insert (seen, xstrdup (thread_id), thread);
+
+		threads_seen++;
+	    }
+
+	    if (thread)
+		_notmuch_thread_add_message (thread, message);
+
+	    notmuch_message_destroy (message);
+
+	    messages_seen++;
 	}
 
-	_notmuch_thread_add_message (thread, message);
-
-	notmuch_message_destroy (message);
+	/* Stop if we're not seeing any more messages. */
+	if (messages_seen == messages_seen_previously)
+	    break;
     }
 
     g_hash_table_unref (seen);

notmuch-dump.c

@@ -57,7 +57,7 @@ notmuch_dump_command (unused (void *ctx), int argc, char *argv[])
 	output = stdout;
     }
 
-    for (messages = notmuch_query_search_messages (query);
+    for (messages = notmuch_query_search_messages (query, 0, -1);
 	 notmuch_messages_has_more (messages);
 	 notmuch_messages_advance (messages))
     {

notmuch-reply.c

@@ -211,7 +211,7 @@ notmuch_reply_command (void *ctx, int argc, char *argv[])
 	return 1;
     }
 
-    for (messages = notmuch_query_search_messages (query);
+    for (messages = notmuch_query_search_messages (query, 0, -1);
 	 notmuch_messages_has_more (messages);
 	 notmuch_messages_advance (messages))
     {

notmuch-search.c

@@ -53,7 +53,7 @@ notmuch_search_command (void *ctx, int argc, char *argv[])
 	return 1;
     }
 
-    for (threads = notmuch_query_search_threads (query);
+    for (threads = notmuch_query_search_threads (query, 0, -1);
 	 notmuch_threads_has_more (threads);
 	 notmuch_threads_advance (threads))
     {

notmuch-show.c

@@ -153,7 +153,7 @@ notmuch_show_command (void *ctx, unused (int argc), unused (char *argv[]))
 	return 1;
     }
 
-    for (messages = notmuch_query_search_messages (query);
+    for (messages = notmuch_query_search_messages (query, 0, -1);
 	 notmuch_messages_has_more (messages);
 	 notmuch_messages_advance (messages))
     {

notmuch-tag.c

@@ -86,7 +86,7 @@ notmuch_tag_command (void *ctx, unused (int argc), unused (char *argv[]))
 	return 1;
     }
 
-    for (messages = notmuch_query_search_messages (query);
+    for (messages = notmuch_query_search_messages (query, 0, -1);
 	 notmuch_messages_has_more (messages);
 	 notmuch_messages_advance (messages))
     {