Hello! I'm working on getting Etsy's custom StackdriverJsonLayout Log4J plugin to work with our Bazel-based build system and wanted to run a few ideas by you.
The first problem I ran into was stdout messages breaking the PluginProcessor annotation processor when run by Bazel. My PR here[1] fixed that for us. The problem we have now is with "fat jars" and the plugin cache file (META-INF/org/apache/logging/log4j/core/config/plugins/Log4j2Plugins.dat)[2]. When Bazel builds a "deploy" jar, it combines an application's classes and the classes of its transitive dependencies into a single "fat" JAR. During this process it needs to intelligently combine any duplicate JAR entries it finds. Right now, Bazel does not know about the plugin cache file[3], so it keeps the first one it encounters and discards any others. So, our custom plugin's plugin cache file is discarded in the process.[4] Even if Bazel knew about the plugin cache file, I don't think the binary format is easily concatenated, due to the length header. [5] I have a few suggestions for fixing this that I'd like to run by you all before submitting a patch: Make the .dat files concatenateable, either textually (i.e. inserting a \n between combined files) or as binary data (i.e. no inserted bytes). This makes the job of the build tool much easier. There seem to be two options: a) Move from a binary format to textual (say, tab delimited PluginEntry fields) and combine the dat files as plain text. If this option is chosen, we could either teach Bazel's DefaultJarEntry filter to combine the plugin cache file textually or move it into META-INF/services, where all files are combined as textual data.[6] b) Remove the length header and allow the .dat files to be combined as binary data. If we choose this option, we would need to teach Bazel's DefaultJarEntryFilter to combine the plugin cache file as binary, as it does for proto files.[7] What do you think? Thanks for the consideration! Gregg [1]: https://github.com/apache/logging-log4j2/pull/301 [2]: https://github.com/apache/logging-log4j2/blob/cd87dd40405166a4d5f6707a27cbaf7ddcf833b6/log4j-plugins/src/main/java/org/apache/logging/log4j/plugins/processor/PluginProcessor.java#L67 [3]: https://github.com/bazelbuild/bazel/blob/master/src/java_tools/singlejar/java/com/google/devtools/build/singlejar/DefaultJarEntryFilter.java [4]: https://github.com/bazelbuild/bazel/blob/0d39361075b05919618720f961870d3863a726ac/src/java_tools/singlejar/java/com/google/devtools/build/singlejar/ZipEntryFilter.java#L87:L91 [5]: - https://github.com/apache/logging-log4j2/blob/92d19c8da6591a706a2df9875c7e41f6fb20bd66/log4j-core/src/main/java/org/apache/logging/log4j/core/config/plugins/processor/PluginCache.java#L73 - https://github.com/apache/logging-log4j2/blob/92d19c8da6591a706a2df9875c7e41f6fb20bd66/log4j-core/src/main/java/org/apache/logging/log4j/core/config/plugins/processor/PluginCache.java#L101 [6]: https://github.com/bazelbuild/bazel/blob/447e0f1aedb1d83feba2298b1e251b4e34ed9a70/src/java_tools/singlejar/java/com/google/devtools/build/singlejar/DefaultJarEntryFilter.java#L99:L101 [7]: https://github.com/bazelbuild/bazel/blob/447e0f1aedb1d83feba2298b1e251b4e34ed9a70/src/java_tools/singlejar/java/com/google/devtools/build/singlejar/DefaultJarEntryFilter.java#L115:L117
