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Postings from April 2011
Greetings,
I've been looking at what feels to me like a bug with the handling of
proxy configuration. When a HTTP::Request is made through an
LWP::UserAgent with a proxy configured the HTTP::Request is changed by
LWP::UserAgent::__need_proxy:
sub _need_proxy {
...
$req->{proxy} = $HTTP::URI_CLASS->new($proxy);
}
"proxy" is not a documented attribute of the HTTP::Request class, but
when it is set _need_proxy ignores the current LWP::UserAgent proxy
settings:
sub _need_proxy {
my($req, $ua) = @_;
return if exists $req->{proxy};
...
}
This becomes a problem when trying to use a single HTTP::Request
instance across multiple proxies - for example:
my $request = HTTP::Request->new(GET => 'http://www.example.com/');
my $ua = LWP::UserAgent->new();
$ua->proxy('http', 'http://proxy_one.example.org:12345/');
# This first request goes through proxy_one
$ua->request($request);
# Now change the proxy on the LWP::UserAgent
$ua->proxy('http', 'http://proxy_two.example.org:12345/');
# This second request goes through proxy_one still because
# $request->{proxy} == "http://proxy_one.example.org:12345/"
$ua->request($request);
This can be worked around in the calling software by deleting
$request->{proxy} between requests but it's a hack (and one which could
fail at any time given that this is a non-documented attribute).
I've thought of a few possible patches:
PATCH 1:
Remove the "return if exists $req->{proxy};" line from _need_proxy. I
think this is the cleanest approach.
Thinking of reasons not to do this: that it incurs some extra processing
cost per request (but only in the case that a single request is used
over and over again); it might break existing code that relies on the
undocumented "proxy" attribute (where people are building requests with
proxies rather than configuring via LWP::UserAgent). If this is a
concern see 2.
PATCH 1 GIT:
diff --git a/lib/LWP/UserAgent.pm b/lib/LWP/UserAgent.pm
index 1ee9ffb..945cd8a 100644
--- a/lib/LWP/UserAgent.pm
+++ b/lib/LWP/UserAgent.pm
@@ -934,7 +934,6 @@ sub mirror
sub _need_proxy {
my($req, $ua) = @_;
- return if exists $req->{proxy};
my $proxy = $ua->{proxy}{$req->uri->scheme} || return;
if ($ua->{no_proxy}) {
if (my $host = eval { $req->uri->host }) {
PATCH 2:
A more expensive option would be to check if the LWP::UserAgent has a
proxy configured and if it is different from the proxy attribute on the
HTTP::Request.
If it is different I would argue that LWP::UserAgent value should
override the requestm, so if the values were different the
LWP::UserAgent could change the value of the proxy atttribute.
I've not included a git patch for this option but could supply one if it
was of interest.
PATCH 3:
At the moment $request->{proxy} has to be set because the request is
passed out of the LWP::UserAgent to a protocol handler. As I recall at
this stage the LWP::UserAgent is not visible to the protocol handler, so
$request is used to pass on the proxy configuration.
A much bigger change to the code would have the protocol handler given
access to the LWP::UserAgent so that the proxy did not have to be
attached to the HTTP::Request. The same decision still needs to be made
as in PATCH 2 (ie what happens if someone has set the proxy attribute).
As with patch 2, I've not included a git patch for this option but could
supply one if it was of interest.
Cheerio,
Brad
--
Bradley Dean
Email: bjdean@bjdean.id.au Skype: skype@bjdean.id.au
Mobile(Aus): +61-413014395 WWW: http://bjdean.id.au/
S/MIME: http://bjdean.id.au/certs/email-public-rsa.txt
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