Perl LWP Post form-data with my boundary - perl

Question

I want to post data with content type multipart/form-data:
use strict;
use warnings;
use LWP::UserAgent;
my $ua = LWP::UserAgent->new;
$ua->post (
'http://127.0.0.1:12555',
'Content-Type' => 'form-data',
Content => {
'data1' => rand,
'data2' => rand,
}
);
And i tested the submitted data:
use strict;
use warnings;
use IO::Socket::INET;
use Socket qw ( inet_aton );
my $sock_listen = new IO::Socket::INET (
LocalHost => '127.0.0.1',
LocalPort => '12555',
Proto => 'tcp',
Listen => 3,
Reuse => 1,
);
$sock_listen->autoflush ();
my $sock;
while ( $sock = $sock_listen->accept ( ) )
{
my $data = '';
$sock->recv ( $data, 4096 );
print $data . "\n";
}
Test #1 result:
POST / HTTP/1.1
TE: deflate,gzip;q=0.3
Connection: TE, close
Host: 127.0.0.1:12555
User-Agent: libwww-perl/6.05
Content-Length: 162
Content-Type: multipart/form-data; boundary=xYzZY
--xYzZY
Content-Disposition: form-data; name="data2"
0.876556396484375
--xYzZY
Content-Disposition: form-data; name="data1"
0.62921142578125
--xYzZY--
Test #2 result:
POST / HTTP/1.1
TE: deflate,gzip;q=0.3
Connection: TE, close
Host: 127.0.0.1:12555
User-Agent: libwww-perl/6.05
Content-Length: 163
Content-Type: multipart/form-data; boundary=xYzZY
--xYzZY
Content-Disposition: form-data; name="data2"
0.896942138671875
--xYzZY
Content-Disposition: form-data; name="data1"
0.041656494140625
--xYzZY--
I added a data:
'data3' => '--xYzZY'
and got:
POST / HTTP/1.1
TE: deflate,gzip;q=0.3
Connection: TE, close
Host: 127.0.0.1:12555
User-Agent: libwww-perl/6.05
Content-Length: 221
Content-Type: multipart/form-data; boundary=Tegj
--Tegj
Content-Disposition: form-data; name="data2"
0.34613037109375
--Tegj
Content-Disposition: form-data; name="data3"
--xYzZY
--Tegj
Content-Disposition: form-data; name="data1"
0.678955078125
--Tegj--
The question is how i can set the boundary manually to 32 chars string like browser's ----WebKitFormBoundary[...] using LWP?
Or can just use IO::Socket?

Answer 1

LWP allows you set the boundary manually when you do multipart/form-data requests. This feature is unfortunately not documented at all.
However, you have to do multipart explicitly. You can set your own boundary by appending the boundary as an additional field of the Content-Type. It will be converted to a header appropriately by HTTP::Request::Common.
my $ua = LWP::UserAgent->new;
$ua->post(
'http://127.0.0.1:12555',
'Content-Type' =>
'multipart/form-data;boundary=Nobody-has-the-intention-to-erect-a-wall',
# ^^^^^^^ ^^^^^^^^
Content => {
data1 => rand,
data2 => rand,
},
);
With your listener, this result in the following output.
POST / HTTP/1.1
TE: deflate,gzip;q=0.3
Connection: TE, close
Host: 127.0.0.1:12555
User-Agent: libwww-perl/6.15
Content-Length: 269
Content-Type: multipart/form-data; boundary=Nobody-has-the-intention-to-erect-a-wall
--Nobody-has-the-intention-to-erect-a-wall
Content-Disposition: form-data; name="data2"
0.0575856828104122
--Nobody-has-the-intention-to-erect-a-wall
Content-Disposition: form-data; name="data1"
0.677908250902878
--Nobody-has-the-intention-to-erect-a-wall--
Note that HTTP::Request::Common will replace your boundary with a random string if it finds the boundary string in the body of any of the parts. It will not just add a number to your boundary.

Answer 2

The sole purpose of the boundary is to separate the message parts and the only requirement on it is that it doesn't appear anywhere in the message. I don't see a good reason to attempt to set it to be "the same" as anything else. Besides, no tool guarantees that it will always use the same one.
More importantly, setting it to a fixed string (without regard for the message) is dangerous: how does anyone know that such a string may not be in a message?
Finally, I don't think it is possible to do so, precisely because the boundary must be checked to ensure that it indeed isn't in the message; so no tool should provide a way to set it to a predefined string.
Have a look at HTTP::Request::Common's source. See how the sub boundary() badly mangles the string to return, and how much work goes into the boundary elsewhere. Then CHECK_BOUNDARY: block changes it further if it isn't good enough. This is clearly not meant to be set outside.
The post method of LWP::UserAgent exists as a shortcut for this module's one.
Note that simbabque found a way to set the boundary, which then also undergoes the checks.