add LastModified header, allow I/O free caching.

TODO

@@ -1,7 +1,6 @@
 * compaction
 * parallel reads
 * round-robin writing
-* LastModified instead of Version
 * DELETE support
 * efficient range requests
 * remember Content-Type

src/monic_file.erl

@@ -102,7 +102,7 @@ init(Path) ->
 handle_call({start_writing, Key, Cookie, Size}, _From,
             #state{main_fd=MainFd, write_pos=Pos, writer=nil}=State) ->
     Ref = make_ref(),
-    LastModified = now(),
+    LastModified = erlang:universaltime(),
     Header = #header{cookie=Cookie, key=Key, size=Size, last_modified=LastModified},
     Index = #index{cookie=Cookie, key=Key, location=Pos, size=Size, last_modified=LastModified},
     case monic_utils:pwrite_term(MainFd, Pos, Header) of

src/monic_item_resource.erl

@@ -17,6 +17,7 @@
     allowed_methods/2,
     content_types_accepted/2,
     content_types_provided/2,
+    last_modified/2,
     resource_exists/2,
     valid_entity_length/2]).
 -export([get_item/2, put_item/2]).
@@ -38,6 +39,22 @@ content_types_provided(ReqData, Context) ->
 content_types_accepted(ReqData, Context) ->
     {[{?ITEM_MIME_TYPE, put_item}], ReqData, Context}.
 
+last_modified(ReqData, Context) ->
+    Key = wrq:path_info(key, ReqData),
+    Cookie = list_to_integer(wrq:path_info(cookie, ReqData)),
+    LastModified1 = case monic_utils:open(ReqData, Context) of
+        {ok, Pid} ->
+            case monic_file:info(Pid, Key, Cookie) of
+                {ok, {_, _, LastModified}} ->
+                    LastModified;
+                {error, not_found} ->
+                    undefined
+            end;
+        _ ->
+            undefined
+    end,
+    {LastModified1, ReqData, Context}.
+
 resource_exists(ReqData, Context) ->
     Key = wrq:path_info(key, ReqData),
     Cookie = list_to_integer(wrq:path_info(cookie, ReqData)),