Make FileSystem.toLocal private

Use a custom to-local function in the various ArchiveMounts, which don't
faff around with sanitising paths.

projects/common/src/main/java/dan200/computercraft/shared/computer/core/ResourceMount.java

@@ -7,7 +7,6 @@ package dan200.computercraft.shared.computer.core;
 import com.google.common.annotations.VisibleForTesting;
 import dan200.computercraft.api.filesystem.FileOperationException;
 import dan200.computercraft.core.filesystem.ArchiveMount;
-import dan200.computercraft.core.filesystem.FileSystem;
 import net.minecraft.ResourceLocationException;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.server.MinecraftServer;
@@ -65,9 +64,10 @@ public final class ResourceMount extends ArchiveMount<ResourceMount.FileEntry> {
             existingNamespace = file.getNamespace();
 
             if (!file.getNamespace().equals(namespace)) continue;
-            if (!FileSystem.contains(subPath, file.getPath())) continue; // Some packs seem to include the parent?
 
-            var localPath = FileSystem.toLocal(file.getPath(), subPath);
+            var localPath = getLocalPath(file.getPath(), subPath);
+            if (localPath == null) continue;
+
             try {
                 getOrCreateChild(newRoot, localPath, this::createEntry);
             } catch (ResourceLocationException e) {

projects/core/src/main/java/dan200/computercraft/core/filesystem/ArchiveMount.java

@@ -8,6 +8,7 @@ import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
 import dan200.computercraft.core.apis.handles.ArrayByteChannel;
 
+import javax.annotation.Nullable;
 import java.io.IOException;
 import java.nio.channels.SeekableByteChannel;
 import java.util.concurrent.TimeUnit;
@@ -82,6 +83,24 @@ public abstract class ArchiveMount<T extends ArchiveMount.FileEntry<T>> extends
      */
     protected abstract byte[] getFileContents(String path, T file) throws IOException;
 
+    /**
+     * Convert an absolute path to one relative to {@code root}. If this path is not a child of {@code root}, return
+     * {@code null}.
+     *
+     * @param path The full path.
+     * @param root The root directory to be relative to.
+     * @return The relativised path, or {@code null}.
+     */
+    protected static @Nullable String getLocalPath(String path, String root) {
+        // Some packs seem to include files not under the root, so drop them immediately.
+        if (!path.startsWith(root)) return null;
+
+        if (path.length() == root.length()) return "";
+
+        if (path.charAt(root.length()) != '/') return null;
+        return path.substring(root.length() + 1);
+    }
+
     protected static class FileEntry<T extends FileEntry<T>> extends AbstractInMemoryMount.FileEntry<T> {
         long size = -1;
     }

projects/core/src/main/java/dan200/computercraft/core/filesystem/FileSystem.java

@@ -404,7 +404,7 @@ public class FileSystem {
         return String.join("/", outputParts);
     }
 
-    public static boolean contains(String pathA, String pathB) {
+    private static boolean contains(String pathA, String pathB) {
         pathA = sanitizePath(pathA).toLowerCase(Locale.ROOT);
         pathB = sanitizePath(pathB).toLowerCase(Locale.ROOT);
 
@@ -421,7 +421,7 @@ public class FileSystem {
         }
     }
 
-    public static String toLocal(String path, String location) {
+    static String toLocal(String path, String location) {
         path = sanitizePath(path);
         location = sanitizePath(location);
 

projects/core/src/main/java/dan200/computercraft/core/filesystem/JarMount.java

@@ -49,10 +49,9 @@ public final class JarMount extends ArchiveMount<JarMount.FileEntry> implements
         while (zipEntries.hasMoreElements()) {
             var entry = zipEntries.nextElement();
 
-            var entryPath = entry.getName();
+            var localPath = getLocalPath(entry.getName(), subPath);
-            if (!entryPath.startsWith(subPath)) continue;
+            if (localPath == null) continue;
 
-            var localPath = FileSystem.toLocal(entryPath, subPath);
             getOrCreateChild(root, localPath, x -> new FileEntry()).setup(entry);
         }
     }