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Re: Missing data in IO::Socket::INET sysread/syswrite

by ikegami (Patriarch)
on Sep 10, 2009 at 15:35 UTC ( #794602=note: print w/replies, xml ) Need Help??


in reply to Missing data in IO::Socket::INET sysread/syswrite

So do a second read. Nothing guarantees you'll get the number of bytes you've requested.
use Carp qw( croak ); sub sysread_full my $fh = $_[0] our $buf; local *buf = \$_[1]; # alias my $to_read = $_[2] my $offset = $_[3] || 0; $offset += length($buf) if $offset < 0; croak("Offset outside string") if $offset < 0; my $tot_read = 0; while ($to_read > 0) { my $bytes_read = sysread($fh, $buf, $to_read, $offset+$tot_read); return undef if !defined($bytes_read); return $tot_read if !$bytes_read; $to_read -= $bytes_read; $tot_read += $bytes_read; } return $tot_read; } ... sysread_full $sock, $read_length, 20; sysread_full $sock, $buffer, $read_length; ...

The behaviour I've observed follows: If there are bytes available to be read, they will be returned immediately, even if there are fewer than requested. (Users of select rely on this.) If there no bytes available to read, it will block.

Update: Added code.
Update: sysread_full differed from sysread in its handling of the offset. Fixed.

Replies are listed 'Best First'.
Re^2: Missing data in IO::Socket::INET sysread/syswrite
by reasonablekeith (Deacon) on Sep 10, 2009 at 15:56 UTC
    d'oh. I'd ass-u-me d that it blocked for the full length of the read. I just hacked in this for the read subroutine...
    my $total_bytes_to_read; sysread $sock, $total_bytes_to_read, 20; my $total_bytes_read = 0; my $read_string = ''; while ($total_bytes_read < $total_bytes_to_read) { my $buffer; my $bytes_read = sysread $sock, $buffer, ($total_bytes_to_read + - $total_bytes_read); $total_bytes_read += $bytes_read; $read_string .= $buffer; } $total_bytes_to_read == $total_bytes_read or die("Tried to read $total_bytes_to_read bits but only got $to +tal_bytes_read bits\n"); return $read_string;
    and have been unable to reproduce the error. Thank you! ++

    PS: I will abstract the loop, as I realise the other sysread here could suffer the same problem

    Update: Just seen your code. I shall be nicking that :)

    Update2: Worked a treat with an extra curly bracket and two semi-colons :)

    ---
    my name's not Keith, and I'm not reasonable.
      sysread $sock, $total_bytes_to_read, 20; # could get less here too...

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