gistfile1.pl

use Plack::Request;
use File::Slurp qw/write_file slurp/;

my $app = sub {
    my $req = Plack::Request->new(shift);

    my $input   = $req->body;    # `psgi.input` handle

    my $len    = 1024 * 8;
    my $offset = 0;
    my $buf;

    my $content = '';
    while (my $read = $input->read($buf, $len)) {
        print "read [$read] bytes\n";
    }

    my $res  = $req->new_response(200);
    $res->content_type('text/plain');
    $res->content(slurp 'misc/data');
    return $res->finalize;
};

gistfile2.pl

use strict;
use warnings;
use HTTP::Tiny;
use File::Slurp qw/slurp/;

my $http = HTTP::Tiny->new;

my $offset      = 0;
my $body        = slurp 'misc/data';
my $length      = length $body;
my $chunk_lenth = 1024 * 8;

my $res = $http->request(
    'POST',
    'http://localhost:5000/',
    {
        content => sub {
            return '' unless $offset < $length;

            my $chunk = substr $body, $offset, $chunk_lenth;
            $offset  += $chunk_lenth;

            return $chunk;
        }
    }
);

print "$res->{status}: $res->{reason}\n";

#!/bin/sh
curl -X POST --trace trace.out --header "Transfer-Encoding: chunked" --header "Content-Type: application/octet-stream" -d @misc/data "http://localhost:5000/upload/10" > content.out