Implement single file operations for all file systems

fs/fs.go

@@ -18,9 +18,15 @@ var (
 
 // Filesystem info
 type FsInfo struct {
-	Name    string                           // name of this fs
-	NewFs   func(string, string) (Fs, error) // create a new file system
-	Config  func(string)                     // function to call to help with config
+	// Name of this fs
+	Name string
+	// Create a new file system.  If root refers to an existing
+	// object, then it should return a Fs which only returns that
+	// object.
+	NewFs func(name string, root string) (Fs, error)
+	// Function to call to help with config
+	Config func(string)
+	// Options for the Fs configuration
 	Options []Option
 }
 

fs/limited.go

@@ -0,0 +1,88 @@
+package fs
+
+import (
+	"fmt"
+	"io"
+	"time"
+)
+
+// This defines a Limited Fs which can only return the Objects passed in from the Fs passed in
+type Limited struct {
+	objects []Object
+	fs      Fs
+}
+
+// NewLimited maks a limited Fs limited to the objects passed in
+func NewLimited(fs Fs, objects ...Object) Fs {
+	f := &Limited{
+		objects: objects,
+		fs:      fs,
+	}
+	return f
+}
+
+// String returns a description of the FS
+func (f *Limited) String() string {
+	return fmt.Sprintf("%s limited to %d objects", f.fs.String(), len(f.objects))
+}
+
+// List the Fs into a channel
+func (f *Limited) List() ObjectsChan {
+	out := make(ObjectsChan, Config.Checkers)
+	go func() {
+		for _, obj := range f.objects {
+			out <- obj
+		}
+		close(out)
+	}()
+	return out
+}
+
+// List the Fs directories/buckets/containers into a channel
+func (f *Limited) ListDir() DirChan {
+	out := make(DirChan, Config.Checkers)
+	close(out)
+	return out
+}
+
+// Find the Object at remote.  Returns nil if can't be found
+func (f *Limited) NewFsObject(remote string) Object {
+	for _, obj := range f.objects {
+		if obj.Remote() == remote {
+			return obj
+		}
+	}
+	return nil
+}
+
+// Put in to the remote path with the modTime given of the given size
+//
+// May create the object even if it returns an error - if so
+// will return the object and the error, otherwise will return
+// nil and the error
+func (f *Limited) Put(in io.Reader, remote string, modTime time.Time, size int64) (Object, error) {
+	obj := f.NewFsObject(remote)
+	if obj == nil {
+		return nil, fmt.Errorf("Can't create %q in limited fs", remote)
+	}
+	return obj, obj.Update(in, modTime, size)
+}
+
+// Make the directory (container, bucket)
+func (f *Limited) Mkdir() error {
+	// All directories are already made - just ignore
+	return nil
+}
+
+// Remove the directory (container, bucket) if empty
+func (f *Limited) Rmdir() error {
+	return fmt.Errorf("Can't rmdir in limited fs")
+}
+
+// Precision of the ModTimes in this Fs
+func (f *Limited) Precision() time.Duration {
+	return f.fs.Precision()
+}
+
+// Check the interfaces are satisfied
+var _ Fs = &Limited{}