[COUCHDB-800] Problem when writing larger than 4kb file headers

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.11
• Fix Version/s: 0.11.1
• Component/s: Database Core
• Assignee: Damien Katz
• Reporter: Damien Katz
• Created: 15/Jun/10 18:52
• Updated: 28/Dec/10 23:28
• Resolved: 15/Jun/10 19:13

Description

From Andrey Somov:

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