add range support for read.

src/monic.erl

@@ -14,7 +14,7 @@
 
 -module(monic).
 -export([start/0, stop/0]).
--export([write/2, read/2, read/3, delete/2]).
+-export([write/2, read/2, read/3, read/4, delete/2]).
 -include("monic.hrl").
 
 start() ->
@@ -34,6 +34,9 @@ read(Group, #handle{}=Handle) ->
 read(Group, #handle{}=Handle, Fun) when is_function(Fun) ->
     call(Group, {read, Handle, Fun}).
 
+read(Group, #handle{}=Handle, Ranges, Fun) when is_function(Fun) ->
+    call(Group, {read, Handle, Ranges, Fun}).
+
 delete(Group, #handle{}=Handle) ->
     call(Group, {delete, Handle}).
 

src/monic_file.erl

@@ -129,19 +129,34 @@ handle_call({read, #handle{location=Location,cookie=Cookie}}, _From, #state{fd=F
         Else ->
             {reply, {error, Else}, State}
     end;
-handle_call({read, #handle{location=Location,cookie=Cookie}, Fun}, _From, #state{fd=Fd}=State) ->
+handle_call({read, Handle, Fun}, From, State) ->
+    handle_call({read, Handle, [], Fun}, From, State);
+handle_call({read, #handle{location=Location,cookie=Cookie}, Ranges, Fun}, _From, #state{fd=Fd}=State) ->
     case read_item_header(Fd, Location) of
         {ok, #item_header{cookie=Cookie,len=Len}} ->
-            case stream_out(Fd, Fun, Location + ?ITEM_HEADER_SIZE, Len) of
-                {ok, CalculatedSha} ->
-                    case read_item_footer(Fd, Location + ?ITEM_HEADER_SIZE + Len) of
-                        {ok, #item_footer{sha=RecordedSha}} ->
-                            case RecordedSha of
-                                CalculatedSha -> Fun({checksum, valid});
-                                _ -> Fun({checksum, invalid})
-                            end,
-                            Fun(eof),
-                            {reply, ok, State};
+            Ranges1 = case Ranges of
+                          [] -> [{0, Len}];
+                          _ -> Ranges
+                      end,
+            case validate_ranges(Ranges1, Len) of
+                ok ->
+                    Start = Location + ?ITEM_HEADER_SIZE,
+                    case lists:foldl(fun({RangeOff, RangeLen}, _) ->
+                                             stream_out(Fd, Fun, Start + RangeOff, RangeLen)
+                                     end, fail, Ranges1) of
+                        {ok, CalculatedSha} ->
+                            case read_item_footer(Fd, Location + ?ITEM_HEADER_SIZE + Len) of
+                                {ok, #item_footer{sha=RecordedSha}} ->
+                                    case {Ranges1, RecordedSha} of
+                                        {[{0, Len}], CalculatedSha} -> Fun({checksum, valid});
+                                        {[{0, Len}], _OtherSha} -> Fun({checksum, invalid});
+                                        _ -> ok
+                                    end,
+                                    Fun(eof),
+                                    {reply, ok, State};
+                                Else ->
+                                    {reply, {error, Else}, State}
+                            end;
                         Else ->
                             {reply, {error, Else}, State}
                     end;
@@ -299,3 +314,13 @@ stream_out(Fd, Fun, Location, Remaining, Sha) when Remaining > 0 ->
         Else ->
             Else
     end.
+
+validate_ranges([], _MaxLen) ->
+    ok;
+validate_ranges([{From, Len}|T], MaxLen) ->
+    case From >= 0 andalso (From+Len) =< MaxLen of
+        true ->
+            validate_ranges(T, MaxLen);
+        false ->
+            {error, invalid_range}
+    end.

src/monic_group.erl

@@ -113,6 +113,8 @@ choose_worker({write, _}, [H|_]) ->
 choose_worker({read, #handle{uuid=UUID}}, Workers) ->
     choose_worker_by_uuid(UUID, Workers);
 choose_worker({read, #handle{uuid=UUID}, _}, Workers) ->
+    choose_worker_by_uuid(UUID, Workers);
+choose_worker({read, #handle{uuid=UUID}, _, _}, Workers) ->
     choose_worker_by_uuid(UUID, Workers).
 
 choose_worker_by_uuid(UUID, Workers) ->

test/monic_test.erl

@@ -24,6 +24,7 @@ all_test_() ->
       {timeout, 30, fun() -> write_bin() end},
       {timeout, 30, fun() -> write_fun() end},
       {timeout, 30, fun() -> read_fun() end},
+      {timeout, 30, fun() -> range_read() end},
       {timeout, 30, fun() -> unique_cookies() end},
       {timeout, 30, fun() -> unforgeable_cookie() end},
       {timeout, 30, fun() -> balanced_writers() end}
@@ -63,6 +64,18 @@ read_fun() ->
                   put(last, R) end,
     ok = monic:read("foo", Handle, Fun).
 
+range_read() ->
+    {ok, Handle} = monic:write("foo", <<"foobar">>),
+    Fun = fun(R) ->
+                  case get(last) of
+                      undefined ->
+                          ?assertEqual({ok, <<"ooba">>}, R);
+                      {ok, <<"ooba">>} ->
+                          ?assertEqual(eof, R)
+                  end,
+                  put(last, R) end,
+    ok = monic:read("foo", Handle, [{1, 4}], Fun).
+
 unique_cookies() ->
     Bin = <<"hello this is a quick test">>,
     {ok, Handle1} = monic:write("foo", Bin),