Jetty Conflicts (Datomic Cloud)

Jetty Conflicts

Figwheel currently uses the same Jetty webserver version that the Ring Jetty Adapter uses. Unfortunately Jetty is packaged in a way that is prone to version conflicts.

Moving to Jetty means that Figwheel is using the same server that many Clojure applications are already using. While this can be helpful in terms of consistent behavior, supporting HTTPS and miniming dependencies, this also leads to inevitable version conflicts because of the way Jetty is packeged. The most common conflict that folks experience is when they include the Datomic Cloud client.

The ultimate solution to this problem may be turning away from Jetty entirely and writing a simpler server based on Netty, or perhaps using Undertow.

Fixing the Datomic Cloud Conflict

Currently if I add com.datomic/client-cloud {:mvn/version "0.8.63"} to a deps.edn file along with com.bhauman/figwheel-main, trying to start a build with figwheel.main with fail with

java.lang.NoClassDefFoundError: org/eclipse/jetty/http/HttpParser$ProxyHandler

This is due to a dependency missmatch.

You can fix this by excluding the conflicting dependencies from the com.datomic/client-cloud dependenciy in your deps.edn file:

com.datomic/client-cloud {:mvn/version "0.8.63"
                          :exclusions [org.eclipse.jetty/jetty-http

The next time you start Figwheel the error should be gone.

Conflicts in general

You can detect these conflicts by looking at the dependency tree of your application.

Leinigen has excellent support for pointing out these conflicts.

If you are using Leiningen then you can run the lein deps :tree command.

Take some time and carefully read the output. It will print out dependency conflicts and make suggestions as to how you can fix them.

It also prints out the dependency tree that it is using, so take some time to examine that as well.

with Clojure CLI tools

Clojure CLI tools doesn’t have the helpful output that Leinigen currently supplies. It can print out the dependency tree:

$ clj -S:tree