mod_mam: Simplify querying the archive

Now that the Mnesia tables are no longer queried in transaction context,
the code can be simplified a bit.  The behavior should remain unchanged.

mod_mam/src/mod_mam.erl

@@ -633,14 +633,12 @@ handle_form_request(IQ) ->
 
 handle_archive_request(#jid{luser = U, lserver = S} = JID,
 		       #iq{sub_el = SubEl} = IQ) ->
-    Query1 = parse_request(S, SubEl),
+    Query = parse_request(S, SubEl),
-    Query2 = Query1#mam_query{mam_jid = {U, S}},
+    case query_archive(Query#mam_query{mam_jid = {U, S}}) of
-    DBType = gen_mod:db_type(S, ?MODULE),
-    case query_archive(Query2, DBType) of
       #mam_result{messages = Msgs} = Result ->
 	  ?DEBUG("MAM archive query for ~s successful",
 		 [jlib:jid_to_string(JID)]),
-	  QueryID = Query2#mam_query.query_id,
+	  QueryID = Query#mam_query.query_id,
 	  send_iq_result(JID, IQ),
 	  send_mam_messages(JID, QueryID, Msgs),
 	  send_fin_message(JID, QueryID, Result),
@@ -926,47 +924,28 @@ send_fin_message(#jid{lserver = Host} = JID, QueryID,
 %% Query MAM archive.
 %%--------------------------------------------------------------------
 
--spec query_archive(mam_query(), db_type()) -> mam_result() | {error, _}.
+-spec query_archive(mam_query()) -> mam_result() | {error, _}.
 
-query_archive(Query, mnesia) ->
+query_archive(#mam_query{mam_jid = {U, S}, max = Max} = Query) ->
-    mnesia:sync_dirty(fun() -> collect_messages(Query, mnesia) end),
-
--spec read_meta(mam_jid(), db_type()) -> mam_meta().
-
-read_meta(US, mnesia) ->
-    case mnesia:read(mam_meta, US) of
-      [M] ->
-	  M;
-      [] ->
-	  M = #mam_meta{mam_jid = US, mam_type = user},
-	  mnesia:write(M), % Initialize MAM for this user.
-	  M
-    end.
-
--spec collect_messages(mam_query(), db_type())
-      -> mam_result() | {error, _}.
-
-collect_messages(#mam_query{mam_jid = {U, S}, max = Max} = Query, DBType) ->
     case check_request(Query) of
       ok ->
+	  DBType = gen_mod:db_type(S, ?MODULE),
 	  Meta = read_meta({U, S}, DBType),
 	  StartID = get_start_id(Query, Meta),
-	  collect_messages(Query, #mam_query_state{current = StartID,
+	  query_archive(Query, #mam_query_state{current = StartID,
 						n_remaining = Max},
 			   Meta, DBType);
       {error, Error} ->
 	  {error, Error}
     end.
 
--spec collect_messages(mam_query(), mam_query_state(), mam_meta(), db_type())
+-spec query_archive(mam_query(), mam_query_state(), mam_meta(), db_type())
       -> mam_result().
 
-collect_messages(Query,
+query_archive(Query,
-		 #mam_query_state{n_remaining = Remaining,
+	      #mam_query_state{n_remaining = ToDo, current = ID} = QueryState,
-				  current = ID} = QueryState,
+	      #mam_meta{first_id = FirstID, last_id = LastID} = Meta, DBType)
-		 #mam_meta{first_id = FirstID,
+    when ToDo =:= 0;
-			   last_id = LastID} = Meta,
-		 DBType) when Remaining =:= 0;
 	 ID =:= undefined;
 	 ID < FirstID;
 	 ID > LastID -> % We're done!
@@ -977,8 +956,7 @@ collect_messages(Query,
 		last = resulting_last(Query, QueryState),
 		is_complete = result_is_complete(Query, QueryState, Meta,
 						 DBType)};
-collect_messages(#mam_query{mam_jid = {U, S},
+query_archive(#mam_query{mam_jid = {U, S}, filter = Filter} = Query,
-			    filter = Filter} = Query,
 	      #mam_query_state{messages = Msgs,
 			       current = ID,
 			       n_remaining = N} = QueryState,
@@ -995,33 +973,45 @@ collect_messages(#mam_query{mam_jid = {U, S},
 		QueryState#mam_query_state{last = ID,
 					   messages = [Msg | Msgs]}
 	  end,
-	  collect_next(Query, NewQueryState, Meta, N - 1, DBType);
+	  query_next(Query, NewQueryState, Meta, N - 1, DBType);
       filtered ->
-	  collect_next(Query, QueryState, Meta, N, DBType);
+	  query_next(Query, QueryState, Meta, N, DBType);
       not_found ->
 	  ?DEBUG("MAM message ~B of ~s@~s not found", [ID, U, S]),
-	  collect_next(Query, QueryState, Meta, N - 1, DBType)
+	  query_next(Query, QueryState, Meta, N - 1, DBType)
     end.
 
--spec collect_next(mam_query(), mam_query_state(), mam_meta(),
+-spec query_next(mam_query(), mam_query_state(), mam_meta(),
 		   non_neg_integer(), db_type()) -> mam_result().
 
-collect_next(#mam_query{direction = before} = Query,
+query_next(#mam_query{direction = before} = Query,
 	   #mam_query_state{current = ID} = QueryState, Meta, N, DBType) ->
-    collect_messages(Query, QueryState#mam_query_state{current = ID - 1,
+    query_archive(Query, QueryState#mam_query_state{current = ID - 1,
 						    n_remaining = N},
 		  Meta, DBType);
-collect_next(#mam_query{direction = aft} = Query,
+query_next(#mam_query{direction = aft} = Query,
 	   #mam_query_state{current = ID} = QueryState, Meta, N, DBType) ->
-    collect_messages(Query, QueryState#mam_query_state{current = ID + 1,
+    query_archive(Query, QueryState#mam_query_state{current = ID + 1,
 						    n_remaining = N},
 		  Meta, DBType).
 
+-spec read_meta(mam_jid(), db_type()) -> mam_meta().
+
+read_meta(US, mnesia) ->
+    case mnesia:dirty_read(mam_meta, US) of
+      [M] ->
+	  M;
+      [] ->
+	  M = #mam_meta{mam_jid = US, mam_type = user},
+	  mnesia:dirty_write(M), % Initialize MAM for this user.
+	  M
+    end.
+
 -spec read_message(mam_msg_key(), mam_filter(), db_type())
       -> mam_msg() | filtered | not_found.
 
 read_message(Key, Filter, mnesia) ->
-    ReadMsg = fun() -> mnesia:read(mam_msg, Key) end,
+    ReadMsg = fun() -> mnesia:dirty_read(mam_msg, Key) end,
     case mnesia:activity(sync_dirty, ReadMsg, [], mnesia_frag) of
       [#mam_msg{} = Msg] ->
 	  case filter_message(Msg, Filter) of
@@ -1139,7 +1129,7 @@ another_message_exists(#mam_query{mam_jid = {U, S},
     end.
 
 %%--------------------------------------------------------------------
-%% Extract collect_messages/4 results.
+%% Extract query_archive/4 results.
 %%--------------------------------------------------------------------
 
 -spec resulting_messages(mam_query(), mam_query_state()) -> [mam_msg()].