How to handle gzip compressed responses with LWP in Perl?

Handling gzip compressed HTTP responses in Perl using LWP::UserAgent is straightforward when you have network access and core modules available. Normally, setting the Accept-Encoding header and calling $response->decoded_content will automatically decompress gzip data.

However, in sandboxed or offline environments where network access is unavailable, we can simulate this by decompressing a hardcoded gzip binary string using the core module IO::Uncompress::Gunzip (available since Perl 5.10). This avoids external dependencies, filesystem or network usage, and runs quickly.

Key Points

• The $ sigil denotes scalar variables (strings, numbers).
• Using IO::Uncompress::Gunzip, you can decompress gzip data from a scalar reference.
• decoded_content in LWP::UserAgent wraps this functionality transparently in real HTTP requests.
• The example below unpacks a valid gzip binary of hello world\n and decompresses it to demonstrate the concept.
• Common pitfalls include using malformed gzip data or ignoring the $GunzipError message on failure.

Runnable Perl Code Example (Simulated gzip decompression)

use strict;
use warnings;
use IO::Uncompress::Gunzip qw(gunzip $GunzipError);

# Valid gzip compressed form of "hello world\n"
my $compressed_data = pack(
    "H*",
    "1f8b080000000000000fcb48cdc9c95728cf2fca49510400b1e6034e0d000000"
);

my $uncompressed = '';
my $status = gunzip(\$compressed_data, \$uncompressed);

if ($status) {
    print "Decompressed gzip content: $uncompressed";
    print "Length of decompressed content: ", length($uncompressed), "\n";
} else {
    die "Failed to decompress gzip data: $GunzipError\n";
}

# Note:
# In a real LWP::UserAgent scenario with gzip response,
# $response->decoded_content handles this transparently.
# This example shows manual decompression without network or file use.

Additional Tips

• Always verify your gzip data source is valid; otherwise, you will get Inflation Error: data error.
• When working with LWP::UserAgent, use $ua->default_header('Accept-Encoding'=>'gzip, deflate') to request compressed responses.
• Use decoded_content instead of content to automatically decompress when possible.
• Remember Perl's flexible context and sigils—scalars store single values, arrays and hashes handle lists and key-value pairs.

Summary

This approach demonstrates how to manually decompress gzip data in Perl without external dependencies or network. While LWP normally automates this, offline or sandboxed environments require manual handling. Using IO::Uncompress::Gunzip is a core and reliable way to achieve gzip decompression on scalar data.