How to set timeout for HTTP requests in Perl LWP::UserAgent?

The LWP::UserAgent module is the standard way in Perl to perform HTTP requests, and it allows setting a timeout attribute to limit how long it waits for connections and responses. However, attempting to test actual network requests to external URLs (like http://httpbin.org) can fail or hang indefinitely in restricted or sandboxed environments without network access. This causes the script to time out or exit unexpectedly.

To demonstrate setting the timeout correctly yet still have a runnable example that works in a sandbox without network access, you can simulate an HTTP request using LWP::UserAgent with a localhost or dummy request that does not require external connectivity. For demonstration, making a request to http://localhost:1/ (a port that likely refuses connection immediately) will trigger a timeout or connection failure quickly, allowing the timeout feature to be exercised without hanging.

Setting Timeout in LWP::UserAgent

• Create the LWP::UserAgent object with a timeout in seconds.
• Use $ua->timeout($seconds) to modify it later if needed.
• The timeout includes all phases: DNS lookup, connect, and reading response.
• Check $response->is_success to verify if the request was successful.

Runnable Example (Sandbox Safe)

This example sets a 1-second timeout and attempts to connect to localhost on a port that will refuse, triggering a timeout or connection fail immediately. It prints the error message to STDOUT, showing how timeouts or failures are handled gracefully.

use strict;
use warnings;
use LWP::UserAgent;

# Create a user agent with 1-second timeout
my $ua = LWP::UserAgent->new(timeout => 1);

# A URL that will refuse connection quickly on most machines (non-open port)
my $url = "http://localhost:1/";

print "Attempting HTTP GET to $url with 1-second timeout...\n";

my $response = $ua->get($url);

if ($response->is_success) {
    print "Success! Response content:\n";
    print $response->decoded_content;
} else {
    print "Fail: " . $response->status_line . "\n";
}

Explanation

• The LWP::UserAgent object is configured with timeout => 1 to limit waiting to 1 second.
• The URL points to localhost at port 1, which usually does not accept connections, causing immediate failure or timeout.
• This avoids the need for actual external network access, so the code runs quickly and safely in sandboxes.
• The HTTP response is checked using is_success to distinguish success and failure.
• If the timeout occurs, or connection is refused, status_line reports the error, e.g. 500 Can't connect to localhost:1.

Perl Concepts: Sigils, Context, and TMTOWTDI

In Perl, scalar variables like $ua and $response hold references or objects and are prefixed with $. Calling methods like get returns a scalar HTTP::Response object. The timeout attribute is a scalar number. Perl’s "There's more than one way to do it" (TMTOWTDI) philosophy means you could also set timeout separately by $ua->timeout(1).

Common Pitfalls

• Testing with external URLs in a sandbox or no-network environment causes hanging or failures unrelated to your code.
• Timeouts apply to the entire request - a short timeout may cause failed requests on slow networks.
• Always check $response->is_success instead of assuming requests succeeded.
• Perl versions earlier than 5.10 may have different LWP timeout behavior.

Summary

Use LWP::UserAgent’s timeout attribute to control how long your HTTP requests wait. To test timeout behavior in network-restricted environments, target a localhost port that will not accept connections, triggering failure quickly and allowing your script to demonstrate timeout handling without hanging or errors.