Add fs.getCapacity and fs.attributes (#365)

- fs.getCapacity just returns the capacity of the current drive, if
   available. This will be nil on rom mounts.
 - fs.attributes returns an lfs like table of various file attributes.
   Currently, this contains:
    - access, modification, created: When this file was last accessed,
      modified and created. Time is measured in milliseconds since the
      epoch, same as os.epoch("utc") and what is accepted by os.date.
    - size: Same as fs.getSize
    - isDir: same as fs.isDir

Closes #262

src/main/java/dan200/computercraft/api/filesystem/FileAttributes.java

@@ -0,0 +1,81 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2020. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+package dan200.computercraft.api.filesystem;
+
+import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.FileTime;
+import java.time.Instant;
+
+/**
+ * A simple version of {@link BasicFileAttributes}, which provides what information a {@link IMount} already exposes.
+ */
+final class FileAttributes implements BasicFileAttributes
+{
+    private static final FileTime EPOCH = FileTime.from( Instant.EPOCH );
+
+    private final boolean isDirectory;
+    private final long size;
+
+    FileAttributes( boolean isDirectory, long size )
+    {
+        this.isDirectory = isDirectory;
+        this.size = size;
+    }
+
+    @Override
+    public FileTime lastModifiedTime()
+    {
+        return EPOCH;
+    }
+
+    @Override
+    public FileTime lastAccessTime()
+    {
+        return EPOCH;
+    }
+
+    @Override
+    public FileTime creationTime()
+    {
+        return EPOCH;
+    }
+
+    @Override
+    public boolean isRegularFile()
+    {
+        return !isDirectory;
+    }
+
+    @Override
+    public boolean isDirectory()
+    {
+        return isDirectory;
+    }
+
+    @Override
+    public boolean isSymbolicLink()
+    {
+        return false;
+    }
+
+    @Override
+    public boolean isOther()
+    {
+        return false;
+    }
+
+    @Override
+    public long size()
+    {
+        return size;
+    }
+
+    @Override
+    public Object fileKey()
+    {
+        return null;
+    }
+}

src/main/java/dan200/computercraft/api/filesystem/IMount.java

@@ -14,6 +14,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.nio.channels.Channels;
 import java.nio.channels.ReadableByteChannel;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.List;
 
 /**
@@ -93,4 +94,18 @@ public interface IMount
     {
         return Channels.newChannel( openForRead( path ) );
     }
+
+    /**
+     * Get attributes about the given file.
+     *
+     * @param path The path to query.
+     * @return File attributes for the given file.
+     * @throws IOException If the file does not exist, or attributes could not be fetched.
+     */
+    @Nonnull
+    default BasicFileAttributes getAttributes( @Nonnull String path ) throws IOException
+    {
+        if( !exists( path ) ) throw new FileOperationException( path, "No such file" );
+        return new FileAttributes( isDirectory( path ), getSize( path ) );
+    }
 }

src/main/java/dan200/computercraft/api/filesystem/IWritableMount.java

@@ -14,6 +14,7 @@ import java.io.IOException;
 import java.io.OutputStream;
 import java.nio.channels.Channels;
 import java.nio.channels.WritableByteChannel;
+import java.util.OptionalLong;
 
 /**
  * Represents a part of a virtual filesystem that can be mounted onto a computer using {@link IComputerAccess#mount(String, IMount)}
@@ -105,4 +106,16 @@ public interface IWritableMount extends IMount
      * @throws IOException If the remaining space could not be computed.
      */
     long getRemainingSpace() throws IOException;
+
+    /**
+     * Get the capacity of this mount. This should be equal to the size of all files/directories on this mount, minus
+     * the {@link #getRemainingSpace()}.
+     *
+     * @return The capacity of this mount, in bytes.
+     */
+    @Nonnull
+    default OptionalLong getCapacity()
+    {
+        return OptionalLong.empty();
+    }
 }

src/main/java/dan200/computercraft/core/apis/FSAPI.java

@@ -22,6 +22,10 @@ import java.io.BufferedReader;
 import java.io.BufferedWriter;
 import java.nio.channels.ReadableByteChannel;
 import java.nio.channels.WritableByteChannel;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.OptionalLong;
 import java.util.function.Function;
 
 import static dan200.computercraft.api.lua.ArgumentHelper.getString;
@@ -76,6 +80,8 @@ public class FSAPI implements ILuaAPI
             "getFreeSpace",
             "find",
             "getDir",
+            "getCapacity",
+            "attributes",
         };
     }
 
@@ -315,9 +321,8 @@ public class FSAPI implements ILuaAPI
                     throw new LuaException( e.getMessage() );
                 }
             }
-            case 14:
+            case 14: // find
             {
-                // find
                 String path = getString( args, 0 );
                 try
                 {
@@ -329,12 +334,42 @@ public class FSAPI implements ILuaAPI
                     throw new LuaException( e.getMessage() );
                 }
             }
-            case 15:
+            case 15: // getDir
             {
-                // getDir
                 String path = getString( args, 0 );
                 return new Object[] { FileSystem.getDirectory( path ) };
             }
+            case 16: // getCapacity
+            {
+                String path = getString( args, 0 );
+                try
+                {
+                    OptionalLong capacity = m_fileSystem.getCapacity( path );
+                    return new Object[] { capacity.isPresent() ? capacity.getAsLong() : null };
+                }
+                catch( FileSystemException e )
+                {
+                    throw new LuaException( e.getMessage() );
+                }
+            }
+            case 17: // attributes
+            {
+                String path = getString( args, 0 );
+                try
+                {
+                    BasicFileAttributes attributes = m_fileSystem.getAttributes( path );
+                    Map<String, Object> result = new HashMap<>();
+                    result.put( "modification", attributes.lastModifiedTime().toMillis() );
+                    result.put( "created", attributes.creationTime().toMillis() );
+                    result.put( "size", attributes.isDirectory() ? 0 : attributes.size() );
+                    result.put( "isDir", attributes.isDirectory() );
+                    return new Object[] { result };
+                }
+                catch( FileSystemException e )
+                {
+                    throw new LuaException( e.getMessage() );
+                }
+            }
             default:
                 assert false;
                 return null;

src/main/java/dan200/computercraft/core/filesystem/ComboMount.java

@@ -12,6 +12,7 @@ import javax.annotation.Nonnull;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.channels.ReadableByteChannel;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
@@ -143,4 +144,19 @@ public class ComboMount implements IMount
         }
         throw new FileOperationException( path, "No such file" );
     }
+
+    @Nonnull
+    @Override
+    public BasicFileAttributes getAttributes( @Nonnull String path ) throws IOException
+    {
+        for( int i = m_parts.length - 1; i >= 0; --i )
+        {
+            IMount part = m_parts[i];
+            if( part.exists( path ) && !part.isDirectory( path ) )
+            {
+                return part.getAttributes( path );
+            }
+        }
+        throw new FileOperationException( path, "No such file" );
+    }
 }

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

@@ -16,8 +16,10 @@ import java.nio.channels.*;
 import java.nio.file.Files;
 import java.nio.file.OpenOption;
 import java.nio.file.StandardOpenOption;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.Collections;
 import java.util.List;
+import java.util.OptionalLong;
 import java.util.Set;
 
 public class FileMount implements IWritableMount
@@ -224,6 +226,19 @@ public class FileMount implements IWritableMount
         throw new FileOperationException( path, "No such file" );
     }
 
+    @Nonnull
+    @Override
+    public BasicFileAttributes getAttributes( @Nonnull String path ) throws IOException
+    {
+        if( created() )
+        {
+            File file = getRealPath( path );
+            if( file.exists() ) return Files.readAttributes( file.toPath(), BasicFileAttributes.class );
+        }
+
+        throw new FileOperationException( path, "No such file" );
+    }
+
     // IWritableMount implementation
 
     @Override
@@ -360,6 +375,13 @@ public class FileMount implements IWritableMount
         return Math.max( m_capacity - m_usedSpace, 0 );
     }
 
+    @Nonnull
+    @Override
+    public OptionalLong getCapacity()
+    {
+        return OptionalLong.of( m_capacity - MINIMUM_FILE_SIZE );
+    }
+
     private File getRealPath( String path )
     {
         return new File( m_rootPath, path );

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

@@ -7,7 +7,6 @@ package dan200.computercraft.core.filesystem;
 
 import com.google.common.io.ByteStreams;
 import dan200.computercraft.ComputerCraft;
-import dan200.computercraft.api.filesystem.FileOperationException;
 import dan200.computercraft.api.filesystem.IFileSystem;
 import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.api.filesystem.IWritableMount;
@@ -23,6 +22,7 @@ import java.nio.channels.Channel;
 import java.nio.channels.ReadableByteChannel;
 import java.nio.channels.WritableByteChannel;
 import java.nio.file.AccessDeniedException;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.*;
 import java.util.function.Function;
 import java.util.regex.Pattern;
@@ -37,303 +37,8 @@ public class FileSystem
      */
     private static final int MAX_COPY_DEPTH = 128;
 
-    private static class MountWrapper
-    {
-        private String m_label;
-        private String m_location;
-
-        private IMount m_mount;
-        private IWritableMount m_writableMount;
-
-        MountWrapper( String label, String location, IMount mount )
-        {
-            m_label = label;
-            m_location = location;
-            m_mount = mount;
-            m_writableMount = null;
-        }
-
-        MountWrapper( String label, String location, IWritableMount mount )
-        {
-            this( label, location, (IMount) mount );
-            m_writableMount = mount;
-        }
-
-        public String getLabel()
-        {
-            return m_label;
-        }
-
-        public String getLocation()
-        {
-            return m_location;
-        }
-
-        public long getFreeSpace()
-        {
-            if( m_writableMount == null )
-            {
-                return 0;
-            }
-
-            try
-            {
-                return m_writableMount.getRemainingSpace();
-            }
-            catch( IOException e )
-            {
-                return 0;
-            }
-        }
-
-        public boolean isReadOnly( String path )
-        {
-            return m_writableMount == null;
-        }
-
-        // IMount forwarders:
-
-        public boolean exists( String path ) throws FileSystemException
-        {
-            path = toLocal( path );
-            try
-            {
-                return m_mount.exists( path );
-            }
-            catch( IOException e )
-            {
-                throw new FileSystemException( e.getMessage() );
-            }
-        }
-
-        public boolean isDirectory( String path ) throws FileSystemException
-        {
-            path = toLocal( path );
-            try
-            {
-                return m_mount.exists( path ) && m_mount.isDirectory( path );
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        public void list( String path, List<String> contents ) throws FileSystemException
-        {
-            path = toLocal( path );
-            try
-            {
-                if( m_mount.exists( path ) && m_mount.isDirectory( path ) )
-                {
-                    m_mount.list( path, contents );
-                }
-                else
-                {
-                    throw localExceptionOf( path, "Not a directory" );
-                }
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        public long getSize( String path ) throws FileSystemException
-        {
-            path = toLocal( path );
-            try
-            {
-                if( m_mount.exists( path ) )
-                {
-                    if( m_mount.isDirectory( path ) )
-                    {
-                        return 0;
-                    }
-                    else
-                    {
-                        return m_mount.getSize( path );
-                    }
-                }
-                else
-                {
-                    throw localExceptionOf( path, "No such file" );
-                }
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        public ReadableByteChannel openForRead( String path ) throws FileSystemException
-        {
-            path = toLocal( path );
-            try
-            {
-                if( m_mount.exists( path ) && !m_mount.isDirectory( path ) )
-                {
-                    return m_mount.openChannelForRead( path );
-                }
-                else
-                {
-                    throw localExceptionOf( path, "No such file" );
-                }
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        // IWritableMount forwarders:
-
-        public void makeDirectory( String path ) throws FileSystemException
-        {
-            if( m_writableMount == null ) throw exceptionOf( path, "Access denied" );
-
-            path = toLocal( path );
-            try
-            {
-                if( m_mount.exists( path ) )
-                {
-                    if( !m_mount.isDirectory( path ) ) throw localExceptionOf( path, "File exists" );
-                }
-                else
-                {
-                    m_writableMount.makeDirectory( path );
-                }
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        public void delete( String path ) throws FileSystemException
-        {
-            if( m_writableMount == null ) throw exceptionOf( path, "Access denied" );
-
-            try
-            {
-                path = toLocal( path );
-                if( m_mount.exists( path ) )
-                {
-                    m_writableMount.delete( path );
-                }
-            }
-            catch( AccessDeniedException e )
-            {
-                throw new FileSystemException( "Access denied" );
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        public WritableByteChannel openForWrite( String path ) throws FileSystemException
-        {
-            if( m_writableMount == null ) throw exceptionOf( path, "Access denied" );
-
-            path = toLocal( path );
-            try
-            {
-                if( m_mount.exists( path ) && m_mount.isDirectory( path ) )
-                {
-                    throw localExceptionOf( path, "Cannot write to directory" );
-                }
-                else
-                {
-                    if( !path.isEmpty() )
-                    {
-                        String dir = getDirectory( path );
-                        if( !dir.isEmpty() && !m_mount.exists( path ) )
-                        {
-                            m_writableMount.makeDirectory( dir );
-                        }
-                    }
-                    return m_writableMount.openChannelForWrite( path );
-                }
-            }
-            catch( AccessDeniedException e )
-            {
-                throw new FileSystemException( "Access denied" );
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        public WritableByteChannel openForAppend( String path ) throws FileSystemException
-        {
-            if( m_writableMount == null ) throw exceptionOf( path, "Access denied" );
-
-            path = toLocal( path );
-            try
-            {
-                if( !m_mount.exists( path ) )
-                {
-                    if( !path.isEmpty() )
-                    {
-                        String dir = getDirectory( path );
-                        if( !dir.isEmpty() && !m_mount.exists( path ) )
-                        {
-                            m_writableMount.makeDirectory( dir );
-                        }
-                    }
-                    return m_writableMount.openChannelForWrite( path );
-                }
-                else if( m_mount.isDirectory( path ) )
-                {
-                    throw localExceptionOf( path, "Cannot write to directory" );
-                }
-                else
-                {
-                    return m_writableMount.openChannelForAppend( path );
-                }
-            }
-            catch( AccessDeniedException e )
-            {
-                throw new FileSystemException( "Access denied" );
-            }
-            catch( IOException e )
-            {
-                throw localExceptionOf( e );
-            }
-        }
-
-        private String toLocal( String path )
-        {
-            return FileSystem.toLocal( path, m_location );
-        }
-
-        private FileSystemException localExceptionOf( IOException e )
-        {
-            if( !m_location.isEmpty() && e instanceof FileOperationException )
-            {
-                FileOperationException ex = (FileOperationException) e;
-                if( ex.getFilename() != null ) return localExceptionOf( ex.getFilename(), ex.getMessage() );
-            }
-
-            return new FileSystemException( e.getMessage() );
-        }
-
-        private FileSystemException localExceptionOf( String path, String message )
-        {
-            if( !m_location.isEmpty() ) path = path.isEmpty() ? m_location : m_location + "/" + path;
-            return exceptionOf( path, message );
-        }
-
-        private static FileSystemException exceptionOf( String path, String message )
-        {
-            return new FileSystemException( "/" + path + ": " + message );
-        }
-    }
-
     private final FileSystemWrapperMount m_wrapper = new FileSystemWrapperMount( this );
-    private final Map<String, MountWrapper> m_mounts = new HashMap<>();
+    private final Map<String, MountWrapper> mounts = new HashMap<>();
 
     private final HashMap<WeakReference<FileSystemWrapper<?>>, ChannelWrapper<?>> m_openFiles = new HashMap<>();
     private final ReferenceQueue<FileSystemWrapper<?>> m_openFileQueue = new ReferenceQueue<>();
@@ -363,10 +68,7 @@ public class FileSystem
     {
         if( mount == null ) throw new NullPointerException();
         location = sanitizePath( location );
-        if( location.contains( ".." ) )
+        if( location.contains( ".." ) ) throw new FileSystemException( "Cannot mount below the root" );
-        {
-            throw new FileSystemException( "Cannot mount below the root" );
-        }
         mount( new MountWrapper( label, location, mount ) );
     }
 
@@ -387,14 +89,13 @@ public class FileSystem
     private synchronized void mount( MountWrapper wrapper )
     {
         String location = wrapper.getLocation();
-        m_mounts.remove( location );
+        mounts.remove( location );
-        m_mounts.put( location, wrapper );
+        mounts.put( location, wrapper );
     }
 
     public synchronized void unmount( String path )
     {
-        path = sanitizePath( path );
+        mounts.remove( sanitizePath( path ) );
-        m_mounts.remove( path );
     }
 
     public synchronized String combine( String path, String childPath )
@@ -438,27 +139,20 @@ public class FileSystem
     public static String getName( String path )
     {
         path = sanitizePath( path, true );
-        if( path.isEmpty() )
+        if( path.isEmpty() ) return "root";
-        {
-            return "root";
-        }
 
         int lastSlash = path.lastIndexOf( '/' );
-        if( lastSlash >= 0 )
+        return lastSlash >= 0 ? path.substring( lastSlash + 1 ) : path;
-        {
-            return path.substring( lastSlash + 1 );
-        }
-        else
-        {
-            return path;
-        }
     }
 
     public synchronized long getSize( String path ) throws FileSystemException
     {
-        path = sanitizePath( path );
+        return getMount( sanitizePath( path ) ).getSize( sanitizePath( path ) );
-        MountWrapper mount = getMount( path );
+    }
-        return mount.getSize( path );
+
+    public synchronized BasicFileAttributes getAttributes( String path ) throws FileSystemException
+    {
+        return getMount( sanitizePath( path ) ).getAttributes( sanitizePath( path ) );
     }
 
     public synchronized String[] list( String path ) throws FileSystemException
@@ -471,7 +165,7 @@ public class FileSystem
         mount.list( path, list );
 
         // Add any mounts that are mounted at this location
-        for( MountWrapper otherMount : m_mounts.values() )
+        for( MountWrapper otherMount : mounts.values() )
         {
             if( getDirectory( otherMount.getLocation() ).equals( path ) )
             {
@@ -733,17 +427,25 @@ public class FileSystem
         return null;
     }
 
-    public long getFreeSpace( String path ) throws FileSystemException
+    public synchronized long getFreeSpace( String path ) throws FileSystemException
     {
         path = sanitizePath( path );
         MountWrapper mount = getMount( path );
         return mount.getFreeSpace();
     }
 
-    private MountWrapper getMount( String path ) throws FileSystemException
+    @Nonnull
+    public synchronized OptionalLong getCapacity( String path ) throws FileSystemException
+    {
+        path = sanitizePath( path );
+        MountWrapper mount = getMount( path );
+        return mount.getCapacity();
+    }
+
+    private synchronized MountWrapper getMount( String path ) throws FileSystemException
     {
         // Return the deepest mount that contains a given path
-        Iterator<MountWrapper> it = m_mounts.values().iterator();
+        Iterator<MountWrapper> it = mounts.values().iterator();
         MountWrapper match = null;
         int matchLength = 999;
         while( it.hasNext() )

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

@@ -23,6 +23,8 @@ import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
 import java.nio.channels.Channels;
 import java.nio.channels.ReadableByteChannel;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.FileTime;
 import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.List;
@@ -221,6 +223,20 @@ public class JarMount implements IMount
         throw new FileOperationException( path, "No such file" );
     }
 
+    @Nonnull
+    @Override
+    public BasicFileAttributes getAttributes( @Nonnull String path ) throws IOException
+    {
+        FileEntry file = get( path );
+        if( file != null )
+        {
+            ZipEntry entry = zip.getEntry( file.path );
+            if( entry != null ) return new ZipEntryAttributes( entry );
+        }
+
+        throw new FileOperationException( path, "No such file" );
+    }
+
     private static class FileEntry
     {
         String path;
@@ -261,4 +277,68 @@ public class JarMount implements IMount
         Reference<? extends JarMount> next;
         while( (next = MOUNT_QUEUE.poll()) != null ) IoUtil.closeQuietly( ((MountReference) next).file );
     }
+
+    private static class ZipEntryAttributes implements BasicFileAttributes
+    {
+        private final ZipEntry entry;
+
+        ZipEntryAttributes( ZipEntry entry )
+        {
+            this.entry = entry;
+        }
+
+        @Override
+        public FileTime lastModifiedTime()
+        {
+            return entry.getLastModifiedTime();
+        }
+
+        @Override
+        public FileTime lastAccessTime()
+        {
+            return entry.getLastAccessTime();
+        }
+
+        @Override
+        public FileTime creationTime()
+        {
+            return entry.getCreationTime();
+        }
+
+        @Override
+        public boolean isRegularFile()
+        {
+            return !entry.isDirectory();
+        }
+
+        @Override
+        public boolean isDirectory()
+        {
+            return entry.isDirectory();
+        }
+
+        @Override
+        public boolean isSymbolicLink()
+        {
+            return false;
+        }
+
+        @Override
+        public boolean isOther()
+        {
+            return false;
+        }
+
+        @Override
+        public long size()
+        {
+            return entry.getSize();
+        }
+
+        @Override
+        public Object fileKey()
+        {
+            return null;
+        }
+    }
 }

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

@@ -0,0 +1,312 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2020. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.core.filesystem;
+
+import dan200.computercraft.api.filesystem.FileOperationException;
+import dan200.computercraft.api.filesystem.IMount;
+import dan200.computercraft.api.filesystem.IWritableMount;
+
+import javax.annotation.Nonnull;
+import java.io.IOException;
+import java.nio.channels.ReadableByteChannel;
+import java.nio.channels.WritableByteChannel;
+import java.nio.file.AccessDeniedException;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.List;
+import java.util.OptionalLong;
+
+class MountWrapper
+{
+    private String label;
+    private String location;
+
+    private IMount mount;
+    private IWritableMount writableMount;
+
+    MountWrapper( String label, String location, IMount mount )
+    {
+        this.label = label;
+        this.location = location;
+        this.mount = mount;
+        writableMount = null;
+    }
+
+    MountWrapper( String label, String location, IWritableMount mount )
+    {
+        this( label, location, (IMount) mount );
+        writableMount = mount;
+    }
+
+    public String getLabel()
+    {
+        return label;
+    }
+
+    public String getLocation()
+    {
+        return location;
+    }
+
+    public long getFreeSpace()
+    {
+        if( writableMount == null ) return 0;
+
+        try
+        {
+            return writableMount.getRemainingSpace();
+        }
+        catch( IOException e )
+        {
+            return 0;
+        }
+    }
+
+    public OptionalLong getCapacity()
+    {
+        return writableMount == null ? OptionalLong.empty() : writableMount.getCapacity();
+    }
+
+    public boolean isReadOnly( String path )
+    {
+        return writableMount == null;
+    }
+
+    public boolean exists( String path ) throws FileSystemException
+    {
+        path = toLocal( path );
+        try
+        {
+            return mount.exists( path );
+        }
+        catch( IOException e )
+        {
+            throw new FileSystemException( e.getMessage() );
+        }
+    }
+
+    public boolean isDirectory( String path ) throws FileSystemException
+    {
+        path = toLocal( path );
+        try
+        {
+            return mount.exists( path ) && mount.isDirectory( path );
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    public void list( String path, List<String> contents ) throws FileSystemException
+    {
+        path = toLocal( path );
+        try
+        {
+            if( !mount.exists( path ) || !mount.isDirectory( path ) )
+            {
+                throw localExceptionOf( path, "Not a directory" );
+            }
+
+            mount.list( path, contents );
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    public long getSize( String path ) throws FileSystemException
+    {
+        path = toLocal( path );
+        try
+        {
+            if( !mount.exists( path ) ) throw localExceptionOf( path, "No such file" );
+            return mount.isDirectory( path ) ? 0 : mount.getSize( path );
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    @Nonnull
+    public BasicFileAttributes getAttributes( String path ) throws FileSystemException
+    {
+        path = toLocal( path );
+        try
+        {
+            if( !mount.exists( path ) ) throw localExceptionOf( path, "No such file" );
+            return mount.getAttributes( path );
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    public ReadableByteChannel openForRead( String path ) throws FileSystemException
+    {
+        path = toLocal( path );
+        try
+        {
+            if( mount.exists( path ) && !mount.isDirectory( path ) )
+            {
+                return mount.openChannelForRead( path );
+            }
+            else
+            {
+                throw localExceptionOf( path, "No such file" );
+            }
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    public void makeDirectory( String path ) throws FileSystemException
+    {
+        if( writableMount == null ) throw exceptionOf( path, "Access denied" );
+
+        path = toLocal( path );
+        try
+        {
+            if( mount.exists( path ) )
+            {
+                if( !mount.isDirectory( path ) ) throw localExceptionOf( path, "File exists" );
+            }
+            else
+            {
+                writableMount.makeDirectory( path );
+            }
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    public void delete( String path ) throws FileSystemException
+    {
+        if( writableMount == null ) throw exceptionOf( path, "Access denied" );
+
+        try
+        {
+            path = toLocal( path );
+            if( mount.exists( path ) )
+            {
+                writableMount.delete( path );
+            }
+        }
+        catch( AccessDeniedException e )
+        {
+            throw new FileSystemException( "Access denied" );
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    public WritableByteChannel openForWrite( String path ) throws FileSystemException
+    {
+        if( writableMount == null ) throw exceptionOf( path, "Access denied" );
+
+        path = toLocal( path );
+        try
+        {
+            if( mount.exists( path ) && mount.isDirectory( path ) )
+            {
+                throw localExceptionOf( path, "Cannot write to directory" );
+            }
+            else
+            {
+                if( !path.isEmpty() )
+                {
+                    String dir = FileSystem.getDirectory( path );
+                    if( !dir.isEmpty() && !mount.exists( path ) )
+                    {
+                        writableMount.makeDirectory( dir );
+                    }
+                }
+                return writableMount.openChannelForWrite( path );
+            }
+        }
+        catch( AccessDeniedException e )
+        {
+            throw new FileSystemException( "Access denied" );
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    public WritableByteChannel openForAppend( String path ) throws FileSystemException
+    {
+        if( writableMount == null ) throw exceptionOf( path, "Access denied" );
+
+        path = toLocal( path );
+        try
+        {
+            if( !mount.exists( path ) )
+            {
+                if( !path.isEmpty() )
+                {
+                    String dir = FileSystem.getDirectory( path );
+                    if( !dir.isEmpty() && !mount.exists( path ) )
+                    {
+                        writableMount.makeDirectory( dir );
+                    }
+                }
+                return writableMount.openChannelForWrite( path );
+            }
+            else if( mount.isDirectory( path ) )
+            {
+                throw localExceptionOf( path, "Cannot write to directory" );
+            }
+            else
+            {
+                return writableMount.openChannelForAppend( path );
+            }
+        }
+        catch( AccessDeniedException e )
+        {
+            throw new FileSystemException( "Access denied" );
+        }
+        catch( IOException e )
+        {
+            throw localExceptionOf( e );
+        }
+    }
+
+    private String toLocal( String path )
+    {
+        return FileSystem.toLocal( path, location );
+    }
+
+    private FileSystemException localExceptionOf( IOException e )
+    {
+        if( !location.isEmpty() && e instanceof FileOperationException )
+        {
+            FileOperationException ex = (FileOperationException) e;
+            if( ex.getFilename() != null ) return localExceptionOf( ex.getFilename(), ex.getMessage() );
+        }
+
+        return new FileSystemException( e.getMessage() );
+    }
+
+    private FileSystemException localExceptionOf( String path, String message )
+    {
+        if( !location.isEmpty() ) path = path.isEmpty() ? location : location + "/" + path;
+        return exceptionOf( path, message );
+    }
+
+    private static FileSystemException exceptionOf( String path, String message )
+    {
+        return new FileSystemException( "/" + path + ": " + message );
+    }
+}

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

@@ -11,43 +11,42 @@ import javax.annotation.Nonnull;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.channels.ReadableByteChannel;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.List;
 
 public class SubMount implements IMount
 {
-    private IMount m_parent;
+    private IMount parent;
-    private String m_subPath;
+    private String subPath;
 
     public SubMount( IMount parent, String subPath )
     {
-        m_parent = parent;
+        this.parent = parent;
-        m_subPath = subPath;
+        this.subPath = subPath;
     }
 
-    // IMount implementation
-
     @Override
     public boolean exists( @Nonnull String path ) throws IOException
     {
-        return m_parent.exists( getFullPath( path ) );
+        return parent.exists( getFullPath( path ) );
     }
 
     @Override
     public boolean isDirectory( @Nonnull String path ) throws IOException
     {
-        return m_parent.isDirectory( getFullPath( path ) );
+        return parent.isDirectory( getFullPath( path ) );
     }
 
     @Override
     public void list( @Nonnull String path, @Nonnull List<String> contents ) throws IOException
     {
-        m_parent.list( getFullPath( path ), contents );
+        parent.list( getFullPath( path ), contents );
     }
 
     @Override
     public long getSize( @Nonnull String path ) throws IOException
     {
-        return m_parent.getSize( getFullPath( path ) );
+        return parent.getSize( getFullPath( path ) );
     }
 
     @Nonnull
@@ -55,25 +54,25 @@ public class SubMount implements IMount
     @Deprecated
     public InputStream openForRead( @Nonnull String path ) throws IOException
     {
-        return m_parent.openForRead( getFullPath( path ) );
+        return parent.openForRead( getFullPath( path ) );
     }
 
     @Nonnull
     @Override
     public ReadableByteChannel openChannelForRead( @Nonnull String path ) throws IOException
     {
-        return m_parent.openChannelForRead( getFullPath( path ) );
+        return parent.openChannelForRead( getFullPath( path ) );
+    }
+
+    @Nonnull
+    @Override
+    public BasicFileAttributes getAttributes( @Nonnull String path ) throws IOException
+    {
+        return parent.getAttributes( getFullPath( path ) );
     }
 
     private String getFullPath( String path )
     {
-        if( path.isEmpty() )
+        return path.isEmpty() ? subPath : subPath + "/" + path;
-        {
-            return m_subPath;
-        }
-        else
-        {
-            return m_subPath + "/" + path;
-        }
     }
 }

src/test/java/dan200/computercraft/core/ComputerTestDelegate.java

@@ -79,7 +79,7 @@ public class ComputerTestDelegate
         ComputerCraft.log = LogManager.getLogger( ComputerCraft.MOD_ID );
 
         Terminal term = new Terminal( 78, 20 );
-        IWritableMount mount = new FileMount( new File( "test-files/mount" ), Long.MAX_VALUE );
+        IWritableMount mount = new FileMount( new File( "test-files/mount" ), 10_000_000 );
 
         // Remove any existing files
         List<String> children = new ArrayList<>();

src/test/resources/test-rom/spec/apis/fs_spec.lua

@@ -149,4 +149,44 @@ describe("The fs library", function()
             expect.error(fs.move, "rom", "test-files"):eq("Access denied")
         end)
     end)
+
+    describe("fs.getCapacity", function()
+        it("returns nil on read-only mounts", function()
+            expect(fs.getCapacity("rom")):eq(nil)
+        end)
+
+        it("returns the capacity on the root mount", function()
+            expect(fs.getCapacity("")):eq(10000000)
+        end)
+    end)
+
+    describe("fs.attributes", function()
+        it("errors on non-existent files", function()
+            expect.error(fs.attributes, "xuxu_nao_existe"):eq("/xuxu_nao_existe: No such file")
+        end)
+
+        it("returns information about read-only mounts", function()
+            expect(fs.attributes("rom")):matches { isDir = true, size = 0 }
+        end)
+
+        it("returns information about files", function()
+            local now = os.epoch("utc")
+
+            fs.delete("/tmp/basic-file")
+            local h = fs.open("/tmp/basic-file", "w")
+            h.write("A reasonably sized string")
+            h.close()
+
+            local attributes = fs.attributes("tmp/basic-file")
+            expect(attributes):matches { isDir = false, size = 25 }
+
+            if attributes.created - now >= 1000 then
+                fail(("Expected created time (%d) to be within 1000ms of now (%d"):format(attributes.created, now))
+            end
+
+            if attributes.modification - now >= 1000 then
+                fail(("Expected modification time (%d) to be within 1000ms of now (%d"):format(attributes.modification, now))
+            end
+        end)
+    end)
 end)