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Bug #17673

closed

sysseek(0) and '1A' in header return "EOFError (end of file reached)"

Added by stiuna (Juan Gregorio) over 3 years ago. Updated over 3 years ago.

Status:
Closed
Assignee:
-
Target version:
-
ruby -v:
ruby 3.0.0p0 (2020-12-25 revision 95aff21468)
[ruby-core:102751]

Description

The first byte of my file starts with the value '1A' .

Then:

descriptor = IO.sysopen(filePath)
file2Read = IO.new(descriptor)
file2Read.sysseek(0)
p file2Read.sysread(2).unpack('H*')
#=> "EOFError (end of file reached)"

But when I change the first byte of my file to 'AA' for example.
Then:

#=> "aa45"

Is it a bug or am I missing something? I thought sysseek only changed the cursor and nothing else.

This error only occurs with byte '1A' I did the test with the rest of the bytes [00..FF] and there is no problem except with '1A' .

Actions #1

Updated by stiuna (Juan Gregorio) over 3 years ago

  • Description updated (diff)
Actions #2

Updated by stiuna (Juan Gregorio) over 3 years ago

  • Description updated (diff)

Updated by jeremyevans0 (Jeremy Evans) over 3 years ago

  • Status changed from Open to Feedback

I tried your example and was unable to reproduce your problem:

filePath = 'test.txt'
File.binwrite(filePath, "\x1A\x45")
descriptor = IO.sysopen(filePath)
file2Read = IO.new(descriptor)
file2Read.sysseek(0)
p file2Read.sysread(2).unpack('H*')
# => ["1a45"]

Can you try on a different machine to check if this is a local problem?

Updated by stiuna (Juan Gregorio) over 3 years ago

Can you try on a different machine to check if this is a local problem?

Unfortunately I don't have another computer to test the bug with, what version of ruby do you use?

Updated by stiuna (Juan Gregorio) over 3 years ago

Aaah! I don't know if it matters but I use Windows, did you run it on Linux all of a sudden?

Updated by jeremyevans0 (Jeremy Evans) over 3 years ago

  • Status changed from Feedback to Closed

I tried on Windows and I was able to reproduce the issue:

C:\Users\jeremye>c:\Ruby30-x64\bin\ruby

filePath = 'test.txt'
File.binwrite(filePath, "\x1A\x45")
descriptor = IO.sysopen(filePath)
file2Read = IO.new(descriptor)
file2Read.sysseek(0)
p file2Read.sysread(2).unpack('H*')
__END__
-:7:in `sysread': end of file reached (EOFError)
        from -:7:in `<main>'

From some brief research, this is expected behavior on Windows for text files. You need to put the file in binary mode (IO#binmode):

:\Users\jeremye>c:\Ruby30-x64\bin\ruby
filePath = 'test.txt'
File.binwrite(filePath, "\x1A\x45")
descriptor = IO.sysopen(filePath)
file2Read = IO.new(descriptor)
file2Read.binmode
file2Read.sysseek(0)
p file2Read.sysread(2).unpack('H*')
__END__
["1a45"]

Updated by stiuna (Juan Gregorio) over 3 years ago

Right, that solved it, the Ruby documentation should specify that. Ok, thanks.

Updated by nobu (Nobuyoshi Nakada) over 3 years ago

This is not specific to Ruby, but the very (in)famous text mode spec of Windows (and other dosish systems).

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