How to set connection keep-alive with LWP::UserAgent in Perl?

To set connection keep-alive using LWP::UserAgent in Perl, you instruct the client to send the Connection: keep-alive header. This hints that the TCP connection should persist for multiple requests. However, actual connection reuse depends on the server and network conditions, not only on client headers.

The original example targets http://httpbin.org, which requires network access and will fail in a sandboxed environment without network or filesystem access. To provide a runnable example here, we simulate the usage without real HTTP requests by showing how to set headers and construct requests but skip actual network calls.

Key Points About Keep-Alive in LWP::UserAgent

• HTTP/1.1 assumes keep-alive by default; adding Connection: keep-alive explicitly is mostly needed for HTTP/1.0 or special cases.
• default_header method sets headers globally for all requests.
• LWP::UserAgent manages connections internally and reuses sockets if the server agrees.
• Connection persistence can't be verified without real HTTP interactions or debug output.

Runnable Example Without External HTTP Calls

This example demonstrates creating a user agent, setting the Connection: keep-alive header globally, and preparing HTTP::Request objects. It then prints the full raw requests to STDOUT. No actual network activity or external dependencies run, so it works safely in a restricted sandbox environment.

use strict;
use warnings;
use LWP::UserAgent;
use HTTP::Request;

# Create UserAgent
my $ua = LWP::UserAgent->new;

# Set Connection: keep-alive header globally
$ua->default_header( 'Connection' => 'keep-alive' );

# Prepare two sample HTTP::Request objects targeting the same host
my $url = 'http://example.com/path';

my $req1 = HTTP::Request->new(GET => $url);
my $req2 = HTTP::Request->new(GET => $url);

# Since we set default_header, these requests will include Connection: keep-alive
# Print the requests as strings (raw HTTP format) to demonstrate headers included

print "First HTTP request:\n";
print $req1->as_string, "\n";

print "Second HTTP request:\n";
print $req2->as_string, "\n";

# Note: Actual $ua->request($req) call is omitted to avoid network usage.
# In a normal environment, you would run:
# my $res1 = $ua->request($req1);
# my $res2 = $ua->request($req2);
# and check $res1->status_line, content, etc.

# Important Perl concepts demonstrated:
# - Sigils: $ua is a scalar holding a UserAgent object
# - method calls with arrow -> syntax
# - TMTOWTDI ("There's more than one way to do it"), e.g. headers can be set per request or globally.

Explanation

• The default_header method sets headers on every request made by $ua automatically, so Connection: keep-alive will be sent.
• The example builds two requests to the same URL, mimicking repeated calls that may reuse connections in real HTTP usage.
• We print the HTTP request as a raw HTTP string to illustrate inclusion of the keep-alive header without making network calls.
• Real connection reuse requires the server to honor the header and keep the connection open.

Common Pitfalls

• Simply setting Connection: keep-alive doesn’t guarantee reuse; the server controls connection persistence.
• HTTP/1.1 defaults to persistent connections, so explicitly setting the header is often redundant but can help with HTTP/1.0 servers.
• Using LWP::UserAgent’s verbose debug output (with LWP::Debug) or network tools help trace actual connection reuse.
• Ensure your environment allows network access if you intend to perform real HTTP requests.

In summary, setting the Connection: keep-alive header is straightforward with LWP::UserAgent. In sandboxed or restricted environments, simulating requests without network calls is a useful testing approach.