Actually make headless work on arm aarch64

Following the two comments at
https://code.briarproject.org/briar/briar/-/issues/1854#note_44340

.jar files now get built with

    $ ./gradlew --configure-on-demand briar-headless:x86LinuxJar
    $ ./gradlew --configure-on-demand briar-headless:aarch64LinuxJar

Related to #1854

bramble-java/src/main/java/org/briarproject/bramble/plugin/tor/UnixTorPluginFactory.java

@@ -96,15 +96,21 @@ public class UnixTorPluginFactory implements DuplexPluginFactory {
 		String architecture = null;
 		if (isLinux()) {
 			String arch = System.getProperty("os.arch");
+			LOG.info("System's os.arch is " + arch);
 			if (arch.equals("amd64")) {
 				architecture = "linux-x86_64";
 			}
+			else if (arch.equals("aarch64")) {
+				architecture = "linux-aarch64";
+			}
 		}
 		if (architecture == null) {
 			LOG.info("Tor is not supported on this architecture");
 			return null;
 		}
 
+		LOG.info("The selected architecture for Tor is " + architecture);
+
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		TorRendezvousCrypto torRendezvousCrypto = new TorRendezvousCryptoImpl();

briar-headless/README.md

@@ -11,9 +11,10 @@ The REST API peer comes as a `jar` file
 and needs a Java Runtime Environment (JRE) that supports at least Java 8.
 It currently works only on GNU/Linux operating systems.
 
-To build the `jar` file, you can do this:
+To build the `jar` file, you need to specify the combination of architecture and platform:
 
-    $ ./gradlew --configure-on-demand briar-headless:jar
+    $ ./gradlew --configure-on-demand briar-headless:x86LinuxJar
+    $ ./gradlew --configure-on-demand briar-headless:aarch64LinuxJar
 
 You can start the peer (and its API server) like this:
 

briar-headless/build.gradle

@@ -44,18 +44,32 @@ dependencies {
 	kaptTest "com.google.dagger:dagger-compiler:$daggerVersion"
 }
 
-jar {
-	manifest {
+void jarFactory(Jar jarTask, jarArchitecture) {
+	jarTask.doFirst {
+		println 'Building ' + jarArchitecture + ' version has started'
+	}
+	jarTask.manifest {
 		attributes(
 				'Main-Class': 'org.briarproject.briar.headless.MainKt'
 		)
 	}
-	from {
+	jarTask.setArchiveClassifier(jarArchitecture)
+	jarTask.from {
 		configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) }
 	}
-	doLast() {
+			{
+				String[] architectures = ["linux-aarch64", "linux-x86_64"]
+				for (String arch : architectures) {
+					if (arch != jarArchitecture) {
+						exclude "obfs4proxy_" + arch + ".zip"
+						exclude "tor_" + arch + ".zip"
+					}
+				}
+			}
+	jarTask.with jar
+	jarTask.doLast {
 		// Rename the original jar
-		File jar = project.jar.archivePath
+		File jar = jarTask.archivePath
 		String srcPath = jar.toString().replaceFirst('\\.jar$', '.unsorted.jar')
 		File srcFile = new File(srcPath)
 		jar.renameTo(srcFile)
@@ -80,9 +94,18 @@ jar {
 		}
 		destStream.close()
 		srcJarFile.close()
+		println 'Building ' + jarArchitecture + ' version has finished'
 	}
 }
 
+task aarch64LinuxJar(type: Jar) {
+	jarFactory(it, 'linux-aarch64')
+}
+
+task x86LinuxJar(type: Jar) {
+	jarFactory(it, 'linux-x86_64')
+}
+
 // At the moment for non-Android projects we need to explicitly mark the code generated by kapt
 // as 'generated source code' for correct highlighting and resolve in IDE.
 idea {