Centralize file format version tag.

src/hanoidb.hrl

@@ -27,6 +27,7 @@
 -define(TOP_LEVEL, 8).
 -define(BTREE_SIZE(Level), (1 bsl (Level))).
 -define(FIRST_BLOCK_POS, 4).
+-define(FILE_FORMAT, <<"HAN1">>).
 
 -define(TOMBSTONE, 'deleted').
 

src/hanoidb_reader.erl

@@ -68,7 +68,7 @@ open(Name, Config) ->
             {ok, FileInfo} = file:read_file_info(Name),
 
             %% read and validate magic tag
-            {ok, <<"HAN1">>} = file:pread(File, 0, 4),
+            {ok, ?FILE_FORMAT} = file:pread(File, 0, 4),
 
             %% read root position
             {ok, <<RootPos:64/unsigned>>} = file:pread(File, FileInfo#file_info.size-8, 8),

src/hanoidb_writer.erl

@@ -94,7 +94,7 @@ init([Name,Options]) ->
 %    io:format("got name: ~p~n", [Name]),
     case do_open(Name, Options, [exclusive]) of
         {ok, IdxFile} ->
-            file:write(IdxFile, <<"HAN1">>),
+            file:write(IdxFile, ?FILE_FORMAT),
             {ok, BloomFilter} = ebloom:new(erlang:min(Size,16#ffffffff), 0.01, 123),
             BlockSize = hanoidb:get_opt(block_size, Options, ?NODE_SIZE),
             {ok, #state{ name=Name,