Add JarSplitter.

Still needs writing up.

src/main/java/net/fabricmc/loom/configuration/mods/JarSplitter.java

@@ -0,0 +1,178 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2022 FabricMC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.configuration.mods;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+import java.util.jar.Attributes;
+import java.util.jar.Manifest;
+import java.util.stream.Stream;
+
+import net.fabricmc.loom.task.AbstractRemapJarTask;
+import net.fabricmc.loom.util.FileSystemUtil;
+
+public class JarSplitter {
+	final Path inputJar;
+
+	public JarSplitter(Path inputJar) {
+		this.inputJar = inputJar;
+	}
+
+	public boolean split(Path commonOutputJar, Path clientOutputJar) throws IOException {
+		try (FileSystemUtil.Delegate input = FileSystemUtil.getJarFileSystem(inputJar)) {
+			final Manifest manifest = input.fromInputStream(Manifest::new, AbstractRemapJarTask.MANIFEST_PATH);
+			final List<String> clientEntries = readClientEntries(manifest);
+
+			if (clientEntries.isEmpty()) {
+				// No client entries, just copy the input jar
+				Files.copy(inputJar, commonOutputJar);
+				return false;
+			}
+
+			try (FileSystemUtil.Delegate commonOutput = FileSystemUtil.getJarFileSystem(commonOutputJar, true);
+					FileSystemUtil.Delegate clientOutput = FileSystemUtil.getJarFileSystem(clientOutputJar, true);
+					Stream<Path> walk = Files.walk(input.get().getPath("/"))) {
+				final Iterator<Path> iterator = walk.iterator();
+
+				while (iterator.hasNext()) {
+					final Path entry = iterator.next();
+
+					if (!Files.isRegularFile(entry)) {
+						continue;
+					}
+
+					final Path relativePath = input.get().getPath("/").relativize(entry);
+
+					if (relativePath.startsWith("META-INF")) {
+						if (isSignatureData(relativePath)) {
+							// Strip any signature data
+							continue;
+						}
+					}
+
+					final String entryPath = relativePath.toString();
+
+					/*
+					Copy the manifest to both jars
+					- Remove signature data
+					- Remove split data as its already been split.
+					 */
+					if (entryPath.equals(AbstractRemapJarTask.MANIFEST_PATH)) {
+						final Manifest outManifest = new Manifest(manifest);
+						final Attributes attributes = outManifest.getMainAttributes();
+						stripSignatureData(outManifest);
+
+						attributes.remove(Attributes.Name.SIGNATURE_VERSION);
+						Objects.requireNonNull(attributes.remove(AbstractRemapJarTask.MANIFEST_SPLIT_ENV_NAME));
+						Objects.requireNonNull(attributes.remove(AbstractRemapJarTask.MANIFEST_CLIENT_ENTRIES_NAME));
+
+						// TODO add an attribute to denote if the jar is common or client now
+
+						final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+						outManifest.write(out);
+						final byte[] manifestBytes = out.toByteArray();
+
+						writeBytes(manifestBytes, commonOutput.getPath(AbstractRemapJarTask.MANIFEST_PATH));
+						writeBytes(manifestBytes, clientOutput.getPath(AbstractRemapJarTask.MANIFEST_PATH));
+
+						continue;
+					}
+
+					final FileSystemUtil.Delegate target = clientEntries.contains(entryPath) ? clientOutput : commonOutput;
+					final Path outputEntry = target.getPath(entryPath);
+					final Path outputParent = outputEntry.getParent();
+
+					if (outputParent != null) {
+						Files.createDirectories(outputParent);
+					}
+
+					Files.copy(entry, outputEntry, StandardCopyOption.COPY_ATTRIBUTES);
+				}
+			}
+		}
+
+		return true;
+	}
+
+	private List<String> readClientEntries(Manifest manifest) {
+		final Attributes attributes = manifest.getMainAttributes();
+		final String splitEnvValue = attributes.getValue(AbstractRemapJarTask.MANIFEST_SPLIT_ENV_KEY);
+		final String clientEntriesValue = attributes.getValue(AbstractRemapJarTask.MANIFEST_CLIENT_ENTRIES_KEY);
+
+		if (splitEnvValue == null || !splitEnvValue.equals("true")) {
+			throw new UnsupportedOperationException("Cannot split jar that has not been built with a split env");
+		}
+
+		if (clientEntriesValue == null) {
+			throw new IllegalStateException("Split jar does not contain any client only classes");
+		}
+
+		return Arrays.stream(clientEntriesValue.split(";")).toList();
+	}
+
+	private boolean isSignatureData(Path path) {
+		final String fileName = path.getFileName().toString();
+		return fileName.endsWith(".SF")
+				|| fileName.endsWith(".DSA")
+				|| fileName.endsWith(".RSA")
+				|| fileName.startsWith("SIG-");
+	}
+
+	// Based off tiny-remapper's MetaInfFixer
+	private static void stripSignatureData(Manifest manifest) {
+		for (Iterator<Attributes> it = manifest.getEntries().values().iterator(); it.hasNext(); ) {
+			Attributes attrs = it.next();
+
+			for (Iterator<Object> it2 = attrs.keySet().iterator(); it2.hasNext(); ) {
+				Attributes.Name attrName = (Attributes.Name) it2.next();
+				String name = attrName.toString();
+
+				if (name.endsWith("-Digest") || name.contains("-Digest-") || name.equals("Magic")) {
+					it2.remove();
+				}
+			}
+
+			if (attrs.isEmpty()) it.remove();
+		}
+	}
+
+	private static void writeBytes(byte[] bytes, Path path) throws IOException {
+		final Path parent = path.getParent();
+
+		if (parent != null) {
+			Files.createDirectories(parent);
+		}
+
+		Files.write(path, bytes);
+	}
+}

src/main/java/net/fabricmc/loom/task/AbstractRemapJarTask.java

@@ -33,6 +33,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
+import java.util.jar.Attributes;
 import java.util.jar.Manifest;
 
 import javax.inject.Inject;
@@ -62,6 +63,10 @@ import net.fabricmc.loom.util.ZipUtils;
 public abstract class AbstractRemapJarTask extends Jar {
 	public static final String MANIFEST_PATH = "META-INF/MANIFEST.MF";
 	public static final String MANIFEST_NAMESPACE_KEY = "Fabric-Mapping-Namespace";
+	public static final String MANIFEST_SPLIT_ENV_KEY = "Fabric-Loom-Split-Environment";
+	public static final String MANIFEST_CLIENT_ENTRIES_KEY = "Fabric-Loom-Client-Only-Entries";
+	public static final Attributes.Name MANIFEST_SPLIT_ENV_NAME = new Attributes.Name(MANIFEST_SPLIT_ENV_KEY);
+	public static final Attributes.Name MANIFEST_CLIENT_ENTRIES_NAME = new Attributes.Name(MANIFEST_CLIENT_ENTRIES_KEY);
 
 	@InputFile
 	public abstract RegularFileProperty getInputFile();
@@ -141,8 +146,8 @@ public abstract class AbstractRemapJarTask extends Jar {
 
 	protected void applyClientOnlyManifestAttributes(AbstractRemapParams params, List<String> entries) {
 		params.getManifestAttributes().set(Map.of(
-				"Fabric-Loom-Split-Environment", "true",
-				"Fabric-Loom-Client-Only-Entries", String.join(";", entries)
+				MANIFEST_SPLIT_ENV_KEY, "true",
+				MANIFEST_CLIENT_ENTRIES_KEY, String.join(";", entries)
 		));
 	}
 

src/main/java/net/fabricmc/loom/util/FileSystemUtil.java

@@ -26,6 +26,7 @@ package net.fabricmc.loom.util;
 
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.URI;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.FileSystem;
@@ -38,8 +39,12 @@ import net.fabricmc.tinyremapper.FileSystemReference;
 
 public final class FileSystemUtil {
 	public record Delegate(FileSystemReference reference) implements AutoCloseable, Supplier<FileSystem> {
+		public Path getPath(String path, String... more) {
+			return get().getPath(path, more);
+		}
+
 		public byte[] readAllBytes(String path) throws IOException {
-			Path fsPath = get().getPath(path);
+			Path fsPath = getPath(path);
 
 			if (Files.exists(fsPath)) {
 				return Files.readAllBytes(fsPath);
@@ -48,6 +53,12 @@ public final class FileSystemUtil {
 			}
 		}
 
+		public <T> T fromInputStream(IOFunction<InputStream, T> function, String path, String... more) throws IOException {
+			try (InputStream inputStream = Files.newInputStream(getPath(path, more))) {
+				return function.apply(inputStream);
+			}
+		}
+
 		public String readString(String path) throws IOException {
 			return new String(readAllBytes(path), StandardCharsets.UTF_8);
 		}

src/main/java/net/fabricmc/loom/util/IOFunction.java

@@ -0,0 +1,32 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2022 FabricMC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.util;
+
+import java.io.IOException;
+
+@FunctionalInterface
+public interface IOFunction<T, R> {
+	R apply(T t) throws IOException;
+}