don't assume that a block has more data than what is being written to…

… that block bz://497

Otherwise the binary-match fails, and the put_stream process dies, losing the new data.

src/luwak_io.erl

@@ -111,8 +111,14 @@ write_blocks(Riak, File, undefined, Start, Data, BlockSize, Written)
                                  byte_size(Data)}|
                                 Written])};
         {ok, Block} ->
-            <<_:DataSize/binary, Tail/binary>> = luwak_block:data(Block),
-            BlockData = <<Data/binary, Tail/binary>>,
+            BlockData = case luwak_block:data(Block) of
+                            <<_:DataSize/binary, Tail/binary>> ->
+                                <<Data/binary, Tail/binary>>;
+                            _ ->
+                                %% block usage is less than the new
+                                %% data for the block
+                                Data
+                        end,
             {ok, NewBlock} = luwak_block:create(Riak, BlockData),
             {ok, lists:reverse([{luwak_block:name(NewBlock),
                                  byte_size(BlockData)}|

test/luwak_io_tests.erl

@@ -81,4 +81,29 @@ sub_block_partial_write_test() ->
       Blocks = luwak_io:get_range(Riak, File3, 0, 66),
       ?debugFmt("blocks ~p~n", [Blocks]),
       ?assertEqual(<<B1/binary, B2/binary>>, iolist_to_binary(Blocks))
-    end).
+    end).
+
+%% overwrite a file with more data than the file already had, but not
+%% enough to touch the next block boundary
+overwrite_nonfull_block_test() ->
+    test_helper:riak_test(fun(Riak) ->
+        {ok, F0} = luwak_file:create(Riak,
+                                     <<"basho1">>,
+                                     [{block_size, 4}],
+                                     dict:new()),
+        S0 = luwak_put_stream:start_link(Riak, F0, 0, 1000),
+        luwak_put_stream:send(S0, <<"a">>),
+        luwak_put_stream:close(S0),
+        timer:sleep(100),
+
+        {ok, F1} = luwak_file:get(Riak, <<"basho1">>),
+        S1 = luwak_put_stream:start_link(Riak, F1, 0, 1000),
+        luwak_put_stream:send(S1, <<"aa">>),
+        luwak_put_sream:close(S1),
+        timer:sleep(100),
+
+        {ok, F2} = luwak_file:get(Riak, <<"basho1">>),
+        Blocks = luwak_io:get_range(Riak, F2, 0, 4),
+        ?debugFmt("blocks ~p~n", [Blocks]),
+        ?assertEqual(<<"aa">>, iolist_to_binary(Blocks))
+      end).