How do I do a chunked transfer-encoding upload with WWW:Mechanize? - perl

Question

I'm attempting to use a particular web service, and I can successfully perform the upload with the following command:
curl -X POST --header "Transfer-Encoding: chunked" -d #Downloads/file.pdf https://some.webservice/upload
I get back a json response indicate success.
However, I'm unable to figure out how to do the same with WWW::Mechanize.
$mech->post("https://" . $server . "/upload", Content_Type => 'multipart/form-data', Content => [upID => $upid, name => $dlfile, userID => 0, userK => 0, file_0 => [$dlfile]]);
This receives a similar json response with a big fat error message in it.
Do I need to explicitly set the Transfer-Encoding header first? Is there some other trick to it? Google's not shedding much light on this, Perlmonks neither, and the documentation's a little obtuse.

Answer 1

You can do it using HTTP::Request::StreamingUpload
my $starttime = time();
my $req = HTTP::Request::StreamingUpload->new(
POST => $url,
path => $file,
headers => HTTP::Headers->new(
'Transfer-Encoding' => 'chunked'
),
);
my $gen = $req->content;
die unless ref($gen) eq "CODE";
my $total = 0;
$req->content(sub {
my $chunk = &$gen();
$total += length($chunk);
print "\r$total / $size bytes ("
. int($total/$size*100)
. "%) sent, "
. int($total/1000/(time()-$starttime+1))
. " k / sec ";
return $chunk;
});
my $resp = $ua->request($req);
print "\n";
unless ($resp->is_success) {
die "Failed uploading the file: ", $resp->status_line;
}
my $con = $resp->content;
return $con;

Answer 2

Do you really need WWW::Mechanize? It is a subclass of LWP::UserAgent with additional functionality that gives browser-like functionality like filling in and submitting forms, clicking links, a page history with a "back" operation etc. If you don't need all of that then you may as well use LWP::UserAgent directly
Either way, the post method is inherited unchanged from LWP::UserAgent, and it's fine to use it directly as you have done
The way to send a chunked POST is to set the Content to a reference to a subroutine. The subroutine must return the next chunk of data each time it is called, and finally ann empty string or undef when there is no more to send
Is the data supposed to be a JSON string?
It's easiest to write a factory subroutine that returns a closure, like this
sub make_callback {
my ($data) = shift;
sub { substr($data, 0, 512, "") }
}
Then you can call post like this
my $payload = to_json(...);
$mech->post(
"https://$server/upload",
Content_Type => 'multipart/form-data',
Content => make_callback($payload)
);
Please be aware that all of this is untested