Make Mount.openForRead always return a SeekableByteChannel

I want to make some further changes to Mount here, but this helps
simplify BinaryReadableHandle a little.

projects/core-api/src/main/java/dan200/computercraft/api/filesystem/Mount.java

@@ -8,7 +8,7 @@ package dan200.computercraft.api.filesystem;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 
 import java.io.IOException;
-import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.SeekableByteChannel;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.util.List;
 
@@ -60,15 +60,13 @@ public interface Mount {
     long getSize(String path) throws IOException;
 
     /**
-     * Opens a file with a given path, and returns an {@link ReadableByteChannel} representing its contents.
+     * Opens a file with a given path, and returns a {@link SeekableByteChannel} representing its contents.
      *
      * @param path A file path in normalised format, relative to the mount location. ie: "programs/myprogram".
-     * @return A channel representing the contents of the file. If the channel implements
+     * @return A channel representing the contents of the file.
-     * {@link java.nio.channels.SeekableByteChannel}, one will be able to seek to arbitrary positions when using binary
-     * mode.
      * @throws IOException If the file does not exist, or could not be opened.
      */
-    ReadableByteChannel openForRead(String path) throws IOException;
+    SeekableByteChannel openForRead(String path) throws IOException;
 
     /**
      * Get attributes about the given file.

projects/core/src/main/java/dan200/computercraft/core/apis/handles/BinaryReadableHandle.java

@@ -8,13 +8,11 @@ package dan200.computercraft.core.apis.handles;
 import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.api.lua.LuaFunction;
 import dan200.computercraft.core.filesystem.TrackingCloseable;
-import dan200.computercraft.core.util.Nullability;
 
 import javax.annotation.Nullable;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.nio.ByteBuffer;
-import java.nio.channels.ReadableByteChannel;
 import java.nio.channels.SeekableByteChannel;
 import java.util.ArrayList;
 import java.util.List;
@@ -29,22 +27,19 @@ import java.util.Optional;
 public class BinaryReadableHandle extends HandleGeneric {
     private static final int BUFFER_SIZE = 8192;
 
-    private final ReadableByteChannel reader;
+    private final SeekableByteChannel channel;
-    final @Nullable SeekableByteChannel seekable;
     private final ByteBuffer single = ByteBuffer.allocate(1);
 
-    BinaryReadableHandle(ReadableByteChannel reader, @Nullable SeekableByteChannel seekable, TrackingCloseable closeable) {
+    BinaryReadableHandle(SeekableByteChannel channel, TrackingCloseable closeable) {
         super(closeable);
-        this.reader = reader;
+        this.channel = channel;
-        this.seekable = seekable;
     }
 
-    public static BinaryReadableHandle of(ReadableByteChannel channel, TrackingCloseable closeable) {
+    public static BinaryReadableHandle of(SeekableByteChannel channel, TrackingCloseable closeable) {
-        var seekable = asSeekable(channel);
+        return new BinaryReadableHandle(channel, closeable);
-        return seekable == null ? new BinaryReadableHandle(channel, null, closeable) : new Seekable(seekable, closeable);
     }
 
-    public static BinaryReadableHandle of(ReadableByteChannel channel) {
+    public static BinaryReadableHandle of(SeekableByteChannel channel) {
         return of(channel, new TrackingCloseable.Impl(channel));
     }
 
@@ -69,21 +64,19 @@ public class BinaryReadableHandle extends HandleGeneric {
             if (countArg.isPresent()) {
                 int count = countArg.get();
                 if (count < 0) throw new LuaException("Cannot read a negative number of bytes");
-                if (count == 0 && seekable != null) {
+                if (count == 0) return channel.position() >= channel.size() ? null : new Object[]{ "" };
-                    return seekable.position() >= seekable.size() ? null : new Object[]{ "" };
-                }
 
                 if (count <= BUFFER_SIZE) {
                     var buffer = ByteBuffer.allocate(count);
 
-                    var read = reader.read(buffer);
+                    var read = channel.read(buffer);
                     if (read < 0) return null;
                     buffer.flip();
                     return new Object[]{ buffer };
                 } else {
                     // Read the initial set of characters, failing if none are read.
                     var buffer = ByteBuffer.allocate(BUFFER_SIZE);
-                    var read = reader.read(buffer);
+                    var read = channel.read(buffer);
                     if (read < 0) return null;
 
                     // If we failed to read "enough" here, let's just abort
@@ -99,7 +92,7 @@ public class BinaryReadableHandle extends HandleGeneric {
                     parts.add(buffer);
                     while (read >= BUFFER_SIZE && totalRead < count) {
                         buffer = ByteBuffer.allocate(Math.min(BUFFER_SIZE, count - totalRead));
-                        read = reader.read(buffer);
+                        read = channel.read(buffer);
                         if (read < 0) break;
 
                         totalRead += read;
@@ -117,7 +110,7 @@ public class BinaryReadableHandle extends HandleGeneric {
                 }
             } else {
                 single.clear();
-                var b = reader.read(single);
+                var b = channel.read(single);
                 return b == -1 ? null : new Object[]{ single.get(0) & 0xFF };
             }
         } catch (IOException e) {
@@ -139,14 +132,14 @@ public class BinaryReadableHandle extends HandleGeneric {
         checkOpen();
         try {
             var expected = 32;
-            if (seekable != null) expected = Math.max(expected, (int) (seekable.size() - seekable.position()));
+            expected = Math.max(expected, (int) (channel.size() - channel.position()));
             var stream = new ByteArrayOutputStream(expected);
 
             var buf = ByteBuffer.allocate(8192);
             var readAnything = false;
             while (true) {
                 buf.clear();
-                var r = reader.read(buf);
+                var r = channel.read(buf);
                 if (r == -1) break;
 
                 readAnything = true;
@@ -179,7 +172,7 @@ public class BinaryReadableHandle extends HandleGeneric {
             boolean readAnything = false, readRc = false;
             while (true) {
                 single.clear();
-                var read = reader.read(single);
+                var read = channel.read(single);
                 if (read <= 0) {
                     // Nothing else to read, and we saw no \n. Return the array. If we saw a \r, then add it
                     // back.
@@ -211,11 +204,6 @@ public class BinaryReadableHandle extends HandleGeneric {
         }
     }
 
-    public static class Seekable extends BinaryReadableHandle {
-        Seekable(SeekableByteChannel seekable, TrackingCloseable closeable) {
-            super(seekable, seekable, closeable);
-        }
-
     /**
      * Seek to a new position within the file, changing where bytes are written to. The new position is an offset
      * given by {@code offset}, relative to a start position determined by {@code whence}:
@@ -239,7 +227,6 @@ public class BinaryReadableHandle extends HandleGeneric {
     @LuaFunction
     public final Object[] seek(Optional<String> whence, Optional<Long> offset) throws LuaException {
         checkOpen();
-            return handleSeek(Nullability.assertNonNull(seekable), whence, offset);
+        return handleSeek(channel, whence, offset);
-        }
     }
 }

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

@@ -14,7 +14,7 @@ import dan200.computercraft.core.apis.handles.ArrayByteChannel;
 
 import javax.annotation.Nullable;
 import java.io.IOException;
-import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.SeekableByteChannel;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.util.List;
 import java.util.Map;
@@ -110,7 +110,7 @@ public abstract class ArchiveMount<T extends ArchiveMount.FileEntry<T>> implemen
     protected abstract long getSize(T file) throws IOException;
 
     @Override
-    public ReadableByteChannel openForRead(String path) throws IOException {
+    public SeekableByteChannel openForRead(String path) throws IOException {
         var file = get(path);
         if (file == null || file.isDirectory()) throw new FileOperationException(path, NO_SUCH_FILE);
 

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

@@ -182,7 +182,7 @@ public class FileMount implements WritableMount {
     }
 
     @Override
-    public ReadableByteChannel openForRead(String path) throws IOException {
+    public SeekableByteChannel openForRead(String path) throws IOException {
         if (created()) {
             var file = getRealPath(path);
             if (file.exists() && !file.isDirectory()) return FileChannel.open(file.toPath(), READ_OPTIONS);

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

@@ -18,7 +18,7 @@ import java.lang.ref.Reference;
 import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
 import java.nio.channels.Channel;
-import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.SeekableByteChannel;
 import java.nio.channels.WritableByteChannel;
 import java.nio.file.AccessDeniedException;
 import java.nio.file.attribute.BasicFileAttributes;
@@ -346,7 +346,7 @@ public class FileSystem {
         }
     }
 
-    public synchronized <T extends Closeable> FileSystemWrapper<T> openForRead(String path, Function<ReadableByteChannel, T> open) throws FileSystemException {
+    public synchronized <T extends Closeable> FileSystemWrapper<T> openForRead(String path, Function<SeekableByteChannel, T> open) throws FileSystemException {
         cleanup();
 
         path = sanitizePath(path);

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

@@ -11,7 +11,7 @@ import dan200.computercraft.api.filesystem.WritableMount;
 
 import javax.annotation.Nullable;
 import java.io.IOException;
-import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.SeekableByteChannel;
 import java.nio.channels.WritableByteChannel;
 import java.nio.file.AccessDeniedException;
 import java.nio.file.attribute.BasicFileAttributes;
@@ -120,7 +120,7 @@ class MountWrapper {
         }
     }
 
-    public ReadableByteChannel openForRead(String path) throws FileSystemException {
+    public SeekableByteChannel openForRead(String path) throws FileSystemException {
         path = toLocal(path);
         try {
             if (mount.exists(path) && !mount.isDirectory(path)) {

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

@@ -8,7 +8,7 @@ package dan200.computercraft.core.filesystem;
 import dan200.computercraft.api.filesystem.Mount;
 
 import java.io.IOException;
-import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.SeekableByteChannel;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.util.List;
 
@@ -42,7 +42,7 @@ public class SubMount implements Mount {
     }
 
     @Override
-    public ReadableByteChannel openForRead(String path) throws IOException {
+    public SeekableByteChannel openForRead(String path) throws IOException {
         return parent.openForRead(getFullPath(path));
     }
 

projects/core/src/testFixtures/java/dan200/computercraft/test/core/filesystem/MemoryMount.java

@@ -13,7 +13,7 @@ import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;
 import java.nio.channels.Channels;
-import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.SeekableByteChannel;
 import java.nio.channels.WritableByteChannel;
 import java.nio.charset.StandardCharsets;
 import java.util.*;
@@ -111,7 +111,7 @@ public class MemoryMount implements WritableMount {
     }
 
     @Override
-    public ReadableByteChannel openForRead(String path) throws FileOperationException {
+    public SeekableByteChannel openForRead(String path) throws FileOperationException {
         var file = files.get(path);
         if (file == null) throw new FileOperationException(path, "File not found");
         return new ArrayByteChannel(file);