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From Andrey Somov <py4...@gmail.com>
Subject error in handle_call({write_header, Bin}
Date Tue, 15 Jun 2010 16:10:17 GMT
Hi,
while reading the CouchDB source I found a question in couch_file.erl,
I am not sure whether it is a bug or not.

Lines 297-311:

handle_call({write_header, Bin}, _From, #file{fd=Fd, eof=Pos}=File) ->
    BinSize = size(Bin),
    case Pos rem ?SIZE_BLOCK of
    0 ->
        Padding = <<>>;
    BlockOffset ->
        Padding = <<0:(8*(?SIZE_BLOCK-BlockOffset))>>
    end,
    FinalBin = [Padding, <<1, BinSize:32/integer>> | make_blocks(1, [Bin])],
    case file:write(Fd, FinalBin) of
    ok ->
        {reply, ok, File#file{eof=Pos+iolist_size(FinalBin)}};
    Error ->
        {reply, Error, File}
    end;


Because <<1, BinSize:32/integer>> occupies 5 bytes make_blocks() shall
use offset=5, but the offset is only 1.
(it should be make_blocks(5, [Bin]))

Since the header is smaller then 4k there is no difference and it
works (the tests succeed with both 1 and 5). But it makes it more
difficult to understand the code for those who study the source to
understand how it works.

-
Thank you,
Andrey

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