added leveldb implementation.

leveldb.go

+package leveldb
+
+import (
+  ds "github.com/jbenet/datastore.go"
+  "github.com/syndtr/goleveldb/leveldb"
+  "github.com/syndtr/goleveldb/leveldb/opt"
+)
+
+// Datastore uses a standard Go map for internal storage.
+type Datastore struct {
+  DB *leveldb.DB
+}
+
+type Options opt.Options
+
+func NewDatastore(path string, opts *Options) (*Datastore, error) {
+  nopts := opt.Options(*opts)
+  db, err := leveldb.OpenFile(path, &nopts)
+  if err != nil {
+    return nil, err
+  }
+
+  return &Datastore{
+    DB: db,
+  }, nil
+}
+
+// Returns ErrInvalidType if value is not of type []byte.
+//
+// Note: using sync = false.
+// see http://godoc.org/github.com/syndtr/goleveldb/leveldb/opt#WriteOptions
+func (d *Datastore) Put(key ds.Key, value interface{}) (err error) {
+  val, failed := value.([]byte)
+  if failed {
+    return ds.ErrInvalidType
+  }
+  return d.DB.Put(key.Bytes(), val, nil)
+}
+
+func (d *Datastore) Get(key ds.Key) (value interface{}, err error) {
+  val, err := d.DB.Get(key.Bytes(), nil)
+  if err != nil {
+    if err == leveldb.ErrNotFound {
+      return nil, ds.ErrNotFound
+    }
+    return nil, err
+  }
+  return val, nil
+}
+
+func (d *Datastore) Has(key ds.Key) (exists bool, err error) {
+  return ds.GetBackedHas(d, key)
+}
+
+func (d *Datastore) Delete(key ds.Key) (err error) {
+  err = d.DB.Delete(key.Bytes(), nil)
+  if err == leveldb.ErrNotFound {
+    return ds.ErrNotFound
+  }
+  return err
+}
+
+// LevelDB needs to be closed.
+func (d *Datastore) Close() (err error) {
+  return d.DB.Close()
+}