Eclipse m2e Nexus Index

I recently got in a fight with Eclipse Juno and the m2e plugin. Read entire post or skip to end read summary of what I learned.

The pom.xml editor's dependency tab would show "0 results" no matter what I typed in when I tried to add a dependency.

I had ran into this before so thinking I was smart I immediately went to Window -> Preferences -> Maven to check the "Automatically download indexes on startup" checkbox only to find that it was already checked. Normally I would just check this, restart eclipse and everything would be fine.

A quick Google pointed me to a view that I had never used before just because I hadn't needed too. I went to Window -> Show View... -> Maven -> Maven Repositories. This view shows your repositories as they are configured in your settings.xml and allows you to Update or Rebuild Indexes for them.

I tried the Update and Rebuild commands only to find that my error log kept repeating the same message "Unable to update index for nexus: http://.....". This was showing up in the Error Log view and also in my .metadata/.log file with no other details.

More Google-ing pointed me to a ton of proxy issues; however, they were older posts. I spent forever turning on/off proxy settings in Window -> Preferences... -> General -> Network Connections trying every variation possible that I found even though I think the issues the posts were referring too had long since been solved.

I found out that it's possible for your index to get corrupt somehow in Eclipse. To fix this you are supposed to delete .metadata/.plugins/org.eclipse.m2e.core/nexus directory while Eclipse is not running and then when Eclipse starts, m2e will rebuild it. This didn't help me either. I kept getting the same "Unable to update index" messages.

While digging around in the Eclipse sub-directories I saw a org.eclipse.m2e.logback.config directory. Looking in there I saw that not only does it log to the Eclipse .metadata/.log but also to another file (0.log in the same directory in my case). Looking in there I finally figured out the actual cause of the error "401 unauthorized". Finally, I was on to something.

I tried entering the URL that m2e was attempting to access into my browser and everything worked fine. Again, I started thinking proxy issues like maybe my browser was doing something different than m2e. To figure out exactly what it was doing I used Wireshark to sniff the packets and saw that m2e was sending a HTTP GET request with BASIC authentication set. The response was a 401 unathorized from a Tomcat server stating I needed HTTP authentication.

I turned to my settings.xml to find that my <servers> were defined with encrypted passwords which I did not have the master password set up for (see Maven documentation for more information). I don't need those passwords since I don't deploy anyways so I removed them... no luck. Sniffing the packets still showed that BASIC auth was being sent. So I also removed the usernames from the <servers> and voila! My indexes started updating.

I don't remember this happening in the past so something must have changed with m2e. I'm too lazy to look through the codebase and compare (and I don't know what the old version was I used to use) so I can only speculate that m2e used to not try sending authentication if only usernames were specified without passwords in the <servers> section of settings.xml.

So my problem was finally fixed and along the way I learned a few things about m2e.

1. There is a handy Maven Repositories view
2. It stores indexes in org.eclipse.m2e.core/nexus
3. It logs more details in org.eclipse.m2e.logback.config
4. It will use HTTP BASIC authentication for repositories that have an username AND/OR a password defined in the <servers> section of settings.xml