( short link: https://s.apache.org/reproducible-builds )

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But Maven plugins in the whole ecosystem (not only provided by Apache Maven team) sometimes add some variable parts that adds to the problem: timestamp text or username in MANIFEST.MF, ...

In 2015, reproducible-build-maven-plugin has been created to try to fix issues after packaging, by rewriting the archive and reworking content known for variable parts.

The goal of this proposal started in 2017 is to prepare a set of configuration and practices to have reproducible/verifiable builds at packaging time, both by enhancing java natural build behaviour and by removing some variability introduced by some Maven plugins (core plugins at first, but also in the Maven eco-system).
In parallel to this proposal, "Reproducible Maven Builds" site has been created to work on prototypes.

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• Timestamps:
  • Timestamps in ZIP/JAR files: file last modification time/date in central directory and file entry headers + possible optional fields "X5455_ExtendedTimestamp" (PLEXUS-ARCHIVER-48plexus-archiver PR #121)
  • Timestamp in pom.properties generated by maven-archiver (MSHARED-494 )
  • Timestamp in plugin.xml and plugin-help.xml descriptors generated by maven-plugin-tools-generator (MPLUGIN-326 )
  • Timestamp in MANIFEST.MF (Bnd-LastModified) generated by Felix maven-bundle-plugin
  • Timestamps in generated javadoc HTML files (can be disabled with javadoc options "notimestamp" and "bottom")
  • Timestamps in bytecode generated from Groovy code (added by GroovyClassLoader.addTimeStamp())
• Username:
  • UID/GID in tar file entries
  • Username in MANIFEST.MF (Built-By) generated by maven-archiver (MSHARED-661 )
• Ordering:
  • Order of the file entries in a ZIP/JAR file (depends on file system order)
  • Order of the entries in the MANIFEST (MSHARED-511)
  • Order of goals in plugin.xml generated by maven-plugin-tools (MPLUGIN-261)
  • Order of the methods of the ObjectFactory.java file generated by JAXB/xjc (JAXB-598)
  • Order of components in META-INF/plexus/components.xml generated by plexus metadata (issue #8)
• Tools Versions:
  • exact JDK version used to build in MANIFEST.MF (Build-Jdk) generated by maven-archiver (MSHARED-797)
    Notice that keeping the major version of the JDK used still makes sense, since it has an influence on generated bytecode: with the same source code and defined -target version, javac from JDK 6, 7, 8, ... do not produce the same bytecode. If we want to isolate the generated binary from JDK used, the compiler used will have to not be javac provided by running JDK (see Using Non-Javac Compilers)
  • exact Maven version used to build in MANIFEST.MF (Created-By) generated by maven-archiver (MSHARED-799)
  • exact Maven version used to build in META-INF/.../pom.properties generated by maven-archiver (MSHARED-800)

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Life would become easier if there was a dedicated POM element like ${project.build.outputTimestamp} (with an ISO - 8601 formatted date+time) which could be used to specify the timestamp value once per entire project. Every plugin could use it as default value, like it has been done with source files encoding:

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What are the issues to solve?

maven-archiver adds "Built-By: <username>" Manifest entry: the entry was removedTimestamp in Timestamp in plugin.xml and descriptors generated by maven-plugin-tools-generatorFELIX-TBD (maven-bundle-pluginMRRESOURCES-114 remoteresources- 170projectTimespan, as often printed in NOTICEplexus-archiver #124 MJAR-263 ( maven-jar-plugin 3order and timestamp of jar entries

issue tracking	description
MSHARED-661 ( maven-archiver 3.4.0)	META-INF/MANIFEST.MF
MSHARED-796 ( maven-archiver-3.4.0)	META-INF/MANIFEST.MF	maven-archiver adds "Built-Jdk: <detailed java version>" Manifest entry: better replaced with "Built-Jdk: <java specification version>"
MSHARED-494 ( maven-archiver 3.1.0)	META-INF/maven/$groupId/$artifactId/pom.properties	pom.properties
MSHARED-800	META-INF/maven/$groupId/$artifactId/pom.properties	Maven version in pom.properties
MPLUGIN-261 ( maven-plugin-plugin 3.3)	META-INF/maven/plugin.xml	generated plugin.xml is non-deterministic
MPLUGINMPLUGIN-326 ( maven-plugin-plugin 3.5.1)	META-INF/maven/plugin.xml META-INF/maven/$groupId/$artifactId/plugin-help.xml	plugin-help.xml
plexus-containers issue #8 ( plexus-component-metadata 2.0.0)	META-INF/plexus/components.xml	sort components when generating META-INF/plexus/components.xml
plexus-containers issue #27 ( plexus-component-metadata 2.1.0)	META-INF/plexus/components.xml	sort components when merging discovered components with manually crafted component files
bnd-maven-plugin #3521 ( bnd-maven-plugin configuration)	META-INF/MANIFEST.MF	"Private-Package" manifest entry content (created by felix:bundle) has not the same order between builds
sisu-maven-plugin PR#5 ( sisu.inject 0.3.4FELIX-6269 ( maven-bundle-plugin:manifest & bundle 4.2.2)	META-INF/sisu/javax.inject.Named	META-INF/sisu/javax.inject.Named content (created by sisu-maven-plugin) has non reproducible order for content	MANIFEST.MF
FELIX-6203	( maven-	bundle-	plugin	:bundle 4.	2.	2)	META-INF/	projectTimespan property, containing current year, is calculated using current date through new Date()
zip entries timestamp and order
COMPRESS-485 ( commons-compress 1.19)	keep entries order when gathering ParallelScatterZipCreator
plexus-archiver issue #48, PR #49 ( plexus-archiver 4.2.1)	avoid timestamp issues in archives created by plexus-archiver (widely used in Maven plugins creating jar, zip, war, tar... archives)
plexus-archiver issue #114 ( plexus-archiver 4.2.0)	To enable reproducible builds `AbstractArchiver#addFileSet` should add the files in order
MSHARED-837 ( maven-archiver 3.5.0)	support SOURCE_DATE_EPOCH environment variable or equivalent: see https://reproducible-builds.org/docs/timestamps/ => see "Output Archive Entries Timestamp" section of the proposal
maven/$groupId/$artifactId/pom.properties
sisu-maven-plugin 5e2377c ( sisu.inject 0.3.4)	META-INF/sisu/javax.inject.Named
sisu-maven-plugin annotation processor 570e81 ( sisu.inject 0.9.0.M1)	META-INF/sisu/javax.inject.Named
MRRESOURCES-114 ( maven-remote-resources-plugin 1.7.0)	projectTimespan, as often printed in META-INF/NOTICE
JDK-8240734 (JDK 15)	module-info.class
zip entries timestamp and order
COMPRESS-485 ( commons-compress 1.19)	keep entries order when gathering ParallelScatterZipCreator
plexus-archiver - PR #118	remove variation based on user's umask on Unixes		( plexus-archiver 4.2.0)	remove variation based on uid/gid & userName/groupName in tar		MSOURCES-120 ( maven-source-plugin 3 : predefined timestamp - PR #121 ( plexus-archiver 4.2.0)	apply reproducible zip (entries order and timestamp) to maven-source-plugin
MASSEMBLY-921 ( maven-assembly-plugin 3.2.0)	apply reproducible archive (entries order and timestamp) to maven-assembly-plugin
: manage TZ - PR #127 ( plexus-archiver 4.2.1): manage DST	avoid timestamp issues in archives created by plexus-archiver (widely used in Maven plugins creating jar, zip, war, tar... archives)
plexus-archiver issue #114 ( plexus-archiver 4	.2.0)	apply reproducible zip (entries order and timestamp) to maven-jar-plugin
MSITE-851 (maven-site-plugin)	apply reproducible zip (entries order and timestamp) to site:jar
MJAVADOC-627 (maven-javadoc-plugin)	apply reproducible zip (entries order and timestamp) to javadoc:*jar
MSHADE-347 ( maven-shade-plugin 3.2.2)	apply reproducible zip (entries order and timestamp) to shade:shade
issues fixed in maven-archiver will have to be picked by 9 other plugins managed by Apache Maven team (acr, ear, ejb, jlink, rar, war) and perhaps other plugins managed outside Apache Maven team
FELIX-6203 (maven-bundle-plugin)	current timestamp  in pom.properties
To enable reproducible builds `AbstractArchiver#addFileSet` should add the files in order
MSHARED-837 ( maven-archiver 3.5.0)	support SOURCE_DATE_EPOCH environment variable or equivalent: see https://reproducible-builds.org/docs/timestamps/ => see "Output Archive Entries Timestamp" section of the proposal
plexus-archiver #271 ( plexus-archiver 2.7.0)	remove variation based on user's umask on Unixes (particularly group write)
plexus-archiver #124 ( plexus-archiver 4.2.0)	remove variation based on uid/gid & userName/groupName in tar
MSOURCES-120 ( maven-source-plugin 3.2.0)	apply reproducible zip (entries order and timestamp) to maven-source-plugin
MSOURCES-137 ( maven-source-plugin 3.3.1)	apply 022 umask (to ease RB check: independent from env)
MASSEMBLY-921 ( maven-assembly-plugin 3.2.0)	apply reproducible archive (entries order and timestamp) to maven-assembly-plugin
MASSEMBLY-989 ( maven-assembly-plugin 3.6.0)	apply 022 umask (to ease RB check: independent from env)
MJAR-263 ( maven-jar-plugin 3.2.0)	apply reproducible zip (entries order and timestamp) to maven-jar-plugin
MSITE-851 ( maven-site-plugin 3.9.0)	apply reproducible zip (entries order and timestamp) to site:jar
MJAVADOC-627 ( maven-javadoc-plugin 3.2.0)	apply reproducible zip (entries order and timestamp) to javadoc:*jar
MSHADE-347 ( maven-shade-plugin 3.2.2)	apply reproducible zip (entries order and timestamp) to shade:shade
MSHADE-352 ( maven-shade-plugin 3.2.3)	keep reproducible timestamp when shading with transformer
MSHADE-420	mtime from extra field data from shaded dependency makes result builder's timezone sensitive
ARCHETYPE-590 ( maven-archetype-plugin 3.2.0)	apply reproducible zip (entries order and timestamp) to archetype:jar
MWAR-432 ( maven-war-plugin 3.3.0)	apply reproducible zip (entries order and timestamp) to war:jar
MACR-53 ( maven-acr-plugin 3.2.0)
MEAR-280 ( maven-ear-plugin 3.1.0)
MEJB-128 ( maven-ejb-plugin 3.1.0)
MRAR-86 ( maven-rar-plugin 3.0.0)
MJLINK-75 ( maven-jlink-plugin 3.0.0)	apply reproducible zip to the zip file created by the plugin
issues fixed in maven-archiver will have been picked by 9 other plugins managed by Apache Maven team (acr, ear, ejb, jlink, rar), probably other plugins creating zip/jar/tar archives managed outside Apache Maven team will require to do the same
FELIX-6304 ( maven-bundle-plugin:bundle 5.1.1)	order and timestamp of jar entries for bundle goal
FELIX-6404 ( maven-bundle-plugin 5.1.3)	regression in 5.1.2
FELIX-6495 ( maven-bundle-plugin 5.1.4)	bundle:manifest adds Bnd-LastModified even if outputTimestamp is defined
FELIX-6496 ( maven-bundle-plugin 5.1.5) require bnd #5021(6.2)	non-reproducible Export-Package and Private-Package values
FELIX-6602 ( maven-bundle-plugin 5.1.9)	non-reproducible Include-Resource entry
FELIX-6681	non-reproducible Export-Service entry
spring-boot-maven-plugin:repackage #20176 ( 2.3.0-M4)	timestamp
org.jboss.jandex:jandex-maven-plugin #26 ( 1.1.1)	unsorted files (notice: not sure that sorting files at plugin level is sufficient: it seems Jandex indexer itself produces non-reproducible output)
org.jboss.jandex:jandex-maven-plugin #35 1.2.3 replaced by io.smallrye:jandex-maven-plugin #286 ( 3.1.0)	jandex.idx output is not stable/reproducible
MJAR-275 (maven-jar-plugin 3.3.0)	outputTimestamp not applied to module-info.class
moditect-maven-plugin:add-module-info #185 ( 1.0.0.Final)	creates module-info.class with non-reproducible timestamp
moditect #222	timestamp is dependant on timezone
SM-5021 ServiceMix depends-maven-plugin:generate-depends-file (1.5.0)	timestamp in generated depends.txt
XBEAN-335 Geronimo maven-xbean-plugin	timestamp in generated /META-INF/spring-* (Properties format)
KARAF-7367 karaf-maven-plugin:kar #1492 ( 4.3.7)	does not take outputTimestamp into account
quarkus-extension-maven-plugin #38364	timestamp in generated properties META-INF/quarkus-extension.properties, META-INF/quarkus-javadoc.properties and sources *.jdp
tracking of plugins with issues and fixes is now also done in artifact:check-buildplan		FELIX-TBD (maven-bundle-plugin)

Debian approach

Debian has a strong reproducible builds structure working on the topic for a few years: see BuildinfoFiles for environment info recording.

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