I've found an odd bug / interaction between LWP and Device::SerialPort and/or Win32::SerialPort. I've also found a workaround, so the reason for the question is pure curiousity...and perhaps notifying the module owner of the issue if I can figure out what it is.

The issue, in short, is this:

If I take a scalar variable that was created using LWP::UserAgent's $req->decoded_content method, and pass it to Device::SerialPort as something to be written, I get:

• On Windows (Win32::SerialPort), a buffer overflow warning: "Win32::API::Call: parameter 2 had a buffer overflow at C:/Perl/site/lib/Win32API/CommPort.pm line 220"
• On Linux, no warnings, but the data going out the serial port is corrupted and/or truncated.

Here's the really odd part.

If I "disassociate" the variable that came from LWP before passing it to Win32::SerialPort or Device::SerialPort, everything works great. No warnings, no corrupted data:

my $data = $response->decoded_content;
# doing what should be a "no-op", below, makes the problem
# dissappear.
$data=substr($data,0);
[download]

Even more odd, other ways of "disassociating" the variable don't fix the problem.

# doesn't work
$data=~/^(.*)$/;
$data=$1;
[download]

# pass $newvar on instead of $data...doesn't work
my $newvar=$data
[download]

Aside from $data=substr($data,0), the only other method that fixed the problem was writing the data to a file, and reading it back into a fresh new variable to pass to Device::SerialPort (and/or Win32::SerialPort).

Other oddities:

• The bug shows itself on Windows, Debian, and Raspbian, on three different machines.
• It only occurs when $response->decoded_content is pulling from an https (ssl) url.

I did double-check myself by doing a hex dump of the contents in $data...nothing odd. Just a short text string like "THIS IS A TEST".

Any ideas on what this might be, and why $data=substr($data,0) would fix it when other methods don't?

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