This may be actually a wagon-http problem but I'm opening it here since maven redistributes wagon-http.
Steps to reproduce:
Using maven 3.2.1 or later (i.e. wagon-http 2.6 or later):
- unzip attached userAgent.zip
- copy simplelogger.properties to $M2_HOME/conf/logging/ (as per instructions
- export MAVEN_OPTS="$MAVEN_OPTS -Djava.util.logging.config.file=$M2_HOME/conf/logging/simplelogger.properties"
- using pom.xml from attached userAgent.zip:
you can see in the build log that HTTP header "User-Agent" is sent twice:
when using maven 3.1.1 or earlier, "User-Agent" is sent only once.
You could argue that HTTP headers are map keys and sending them twice with the same value should not hurt. However, this causes an issue when deploying to Sonatype Nexus.
Background: Nexus uses the value of User-Agent to disambiguate deployments from multiple clients into separate staging repos. Nexus concatenates the two values instead, effectively using "<value>, <value>" as staging repo key. Not sure if this is a Nexus bug as well.