NAME
XML::LibXML::Proxy - Force LibXML to use a proxy for HTTP/HTTPS external entities
SYNOPSIS
use XML::LibXML;
use XML::LibXML::Proxy;
XML::LibXML::Proxy->set('http://127.0.0.1:8080');
# Use XML::LibXML normally...DESCRIPTION
Force XML::LibXML to use a proxy using LWP::UserAgent as its external entity loader, instead of connecting directly to remote servers. Adds HTTPS support as a bonus.
LibXML's native HTTP client has no proxy support, and the mere parsing or validating of an XML document risks making network requests to obtain referenced DTDs. This causes slow performance and unnecessary strain on network resources and the remote server.
When dealing just with slow-changing standards, such as XHTML 1.1 Strict, downloading the necessary DTDs locally and setting up a "catalog" for LibXML to map known remote DTDs to local files is cumbersome but tolerable. Some standards however, evolve more rapidly and have large numbers of versions in the wild, making maintaining a complete catalog near-impossible.
Forcing LibXML to request DTDs through a caching forward proxy is an elegant solution to this problem (and is recommended by the W3 Consortium). Short of LibXML doing it, now the proxy can do proper caching based on HTTP response headers.
CLASS METHODS
KNOWN BUGS
There was absolutely no way to override Libxml's built-in "nanohttp" client for HTTP URIs using any mechanism described in XML::LibXML::InputCallback, so I had to resort to using XML::LibXML::externalEntityLoader() which overrides 100% of external entity loading.
This means that file:/// and other schemes ARE NO LONGER SUPPORTED when using this proxy.
EXAMPLES
For a quick caching forward proxy, I'm using Nginx with the following configuration:
server {
listen 127.0.0.1:8080;
location / {
proxy_buffering on;
resolver 8.8.8.8 8.8.4.4;
expires max;
proxy_cache forward-zone;
proxy_cache_valid 200 302 301 1w;
proxy_cache_valid any 1m;
proxy_cache_key "$scheme:$proxy_host:$request_uri";
proxy_pass $scheme://$host$request_uri;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_ignore_headers "Set-Cookie";
}
}AUTHOR
Stéphane Lavergne https://github.com/vphantom
ACKNOWLEDGEMENTS
Graph X Design Inc. https://www.gxd.ca/ sponsored this project.
COPYRIGHT & LICENSE
Copyright (c) 2017-2018 Stéphane Lavergne https://github.com/vphantom
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.