How to merge Manifest sections with Gradle and shadowJar - gradle

Question

What I need
We package our products with Gradle and shadowJar. Some of the libraries we use, utilize individual sections in Jar Manifests, specifically attributes like Implementation-Title and
Implementation-Version. These sometimes show in (the outputs of) our products, so I'd like them to survive the shawdowJar-Process.
Example
lib1.jar/META-INF/MANIFEST.MF
Manifest-Version: 1.0
...
Name: org/some/lib
...
Implementation-Title: someLib
Implementation-Version: 2.3
...
lib2.jar/META-INF/MANIFEST.MF
Manifest-Version: 1.0
...
Name: org/some/other/lib
...
Implementation-Title: someOtherLib
Implementation-Version: 5.7-RC
...
=>
product.jar/META-INF/MANIFEST.MF
Manifest-Version: 1.0
...
Name: org/some/lib
...
Implementation-Title: someLib
Implementation-Version: 2.3
...
Name: org/some/other/lib
...
Implementation-Title: someOtherLib
Implementation-Version: 5.7-RC
...
What I found out
It is rather easy to manipulate the resulting Manifest with shadowJar:
project.shadowJar {
manifest {
attributes(["Implementation-Title" : "someLib"], "org/some/lib")
attributes(["Implementation-Title" : "someOtherLib"], "org/some/other/lib")
}
}
generates exactly what I want, statically.
shadowJar can provide me with a list of dependencies. However, when I iterate over the FileCollection like this
project.shadowJar {
manifest {
for (dependency in includedDependencies) {
// read in jar file and set attributes
}
}
}
Gradle is not happy: "Cannot change dependencies of dependency configuration ':project:products:<ProductName>:compile' after it has been included in dependency resolution."
When I define a new task
def dependencies = [];
project.tasks.register('resolveDependencies') {
doFirst {
gradleProject.configurations.compile.resolvedConfiguration.resolvedArtifacts.each {
dependencies.add(it.file)
}
}
}
project.tasks['shadowJar'].dependsOn(project.tasks['resolveDependencies']);
project.shadowJar {
manifest {
// dependencies will be empty when this code is called
for (dependency in dependencies) {
// read in jar file and set attributes
}
}
}
The dependencies are not resolved in time.
What I'd like to know
How can I access the dependencies without upsetting Gradle? Alternatively, is there another way to merge the named individual sections with shadowJar?

Answer 1

According to https://github.com/johnrengelman/shadow/issues/369 the Transformer interface of shadowJar should be used to do this.
So here comes:
import com.github.jengelman.gradle.plugins.shadow.transformers.Transformer;
import com.github.jengelman.gradle.plugins.shadow.transformers.TransformerContext;
import java.io.ByteArrayOutputStream;
import java.util.jar.Attributes;
import java.util.jar.Manifest;
import java.util.Map.Entry;
import shadow.org.apache.tools.zip.ZipOutputStream;
import shadow.org.apache.tools.zip.ZipEntry;
import shadow.org.codehaus.plexus.util.IOUtil;
import org.gradle.api.file.FileTreeElement;
import static java.nio.charset.StandardCharsets.*
import static java.util.jar.JarFile.*;
/**ManifestVersionMergeTransformer appends all version information sections from manifest files to the resulting manifest file.
* #author Robert Lichtenberger
*/
public class ManifestMergeTransformer implements Transformer {
String includePackages; // regular expression that must match a given package
String excludePackages; // regular expression that must not match a given package
private Manifest manifest;
#Override
public boolean canTransformResource(FileTreeElement element) {
MANIFEST_NAME.equalsIgnoreCase(element.relativePath.pathString);
}
#Override
public void transform(TransformerContext context) {
if (manifest == null) {
manifest = new Manifest(context.is);
} else {
Manifest toMerge = new Manifest(context.is);
for (Entry<String, Attributes> entry : toMerge.getEntries().entrySet()) {
if (mustInclude(entry.getKey())) {
manifest.getEntries().put(entry.getKey(), entry.getValue());
}
}
}
IOUtil.close(context.is);
}
private boolean mustInclude(String packageName) {
return (includePackages == null || packageName.matches(includePackages)) && (excludePackages == null || !packageName.matches(excludePackages));
}
#Override
public boolean hasTransformedResource() {
return true;
}
#Override
public void modifyOutputStream(ZipOutputStream os, boolean preserveFileTimestamps) {
ZipEntry entry = new ZipEntry(MANIFEST_NAME);
entry.time = TransformerContext.getEntryTimestamp(preserveFileTimestamps, entry.time);
os.putNextEntry(entry);
if (manifest != null) {
ByteArrayOutputStream manifestContents = new ByteArrayOutputStream();
manifest.write(manifestContents);
os.write(manifestContents.toByteArray());
}
}
}