Description of problem:

When configuring /etc/yum.conf to use a web proxy that does not require user/password, entering proxy_username= with no username causes yum not to work. That works in RedHat EL5, but RedHat EL6.0 amd 6.1 have the same bug.

Version-Release number of selected component (if applicable):
Tested bad in RHEL6.1 x86_64 yum 3.2.29 17.el6
              Fedora 14 x86_64 yum 3.2.28 6.fc14
              RHEL6.0 x86_64 yum 3.2.27 14.el6_0.1

Tested good in CentOS 5.6 x86_64 yum 3.2.22 33.el5.centos
              RHEL5.5 and RHEL5.6 x86_64 don't have yum versions available

How reproducible: Always

Steps to Reproduce: (all commands as root or using sudo)

1. Setup the test machine behind a firewall that prevents the test machine from accessing the outside Internet except through a squid http and ftp proxy server configured to not require user/password authentication. The test will go much faster if the firewall is configured to reject packets immediately instead of just blocking and making you wait for a timeout.

2. If the test machine is running RHEL6, set up a third party repo such as EPEL in /etc/yum.repos.d so there is something to test yum with. If you are testing Fedora you can use the Fedora repo that is already configured. However the URL used for the yum repo must be outside the firewall.

3. Run the commands "yum clean all" and then "yum update" to verify that the test machine cannot access the yum repository.

4. Add the line to /etc/yum.conf  "proxy=http://PROXY.EXAMPLE.COM:PORT" where you use the correct host name and port for the squid web proxy server.

5. Verify that yum clean all ; yum update now works properly

6. Add the lines to /etc/yum.conf "proxy_username=foo" and "proxy_password="

7. Verify that yum clean all ; yum update still works. This shows that if squid doesn't require a username/password, it doesn't care if you send it a username anyway.

8. Now change the line in /etc/yum.conf from "proxy_username=foo" to "proxy_username="

9. Try the commands "yum clean all ; yum update" again
  
Actual results:

You get errors indicating that yum update cannot reach the mirror server or the repositories on the outside Internet

Expected results:

Yum update should work without error, going through the proxy server

Additional info:

Steps 6 and 7 show that squid doesn't care if it is sent a user/password if none is needed, so the problem is not that "proxy_username=" causes some bogus user name to be sent. I suspect that yum is putting together a URL such as http://user:passwd@proxy.example.com:3187 which ends up as an invalid URL such as http://:@proxy.example.com:3187 that confuses a parser in yum or in squid.

This behaviour is a regression because RedHat EL5 and CentOS 5 do not exhibit the problem. It is a problem because it is surprising behaviour that used to work.