Add decrypt, refactor

backend/generic.go

@@ -0,0 +1,84 @@
+package backend
+
+import (
+	"bytes"
+	"compress/zlib"
+	"crypto/sha256"
+	"io/ioutil"
+)
+
+// Each lists all entries of type t in the backend and calls function f() with
+// the id and data.
+func Each(be Server, t Type, f func(id ID, data []byte, err error)) error {
+	ids, err := be.List(t)
+	if err != nil {
+		return err
+	}
+
+	for _, id := range ids {
+		data, err := be.Get(t, id)
+		if err != nil {
+			f(id, nil, err)
+			continue
+		}
+
+		f(id, data, nil)
+	}
+
+	return nil
+}
+
+// Each lists all entries of type t in the backend and calls function f() with
+// the id.
+func EachID(be Server, t Type, f func(ID)) error {
+	ids, err := be.List(t)
+	if err != nil {
+		return err
+	}
+
+	for _, id := range ids {
+		f(id)
+	}
+
+	return nil
+}
+
+// Compress applies zlib compression to data.
+func Compress(data []byte) []byte {
+	// apply zlib compression
+	var b bytes.Buffer
+	w := zlib.NewWriter(&b)
+	_, err := w.Write(data)
+	if err != nil {
+		panic(err)
+	}
+	w.Close()
+
+	return b.Bytes()
+}
+
+// Uncompress reverses zlib compression on data.
+func Uncompress(data []byte) []byte {
+	b := bytes.NewBuffer(data)
+	r, err := zlib.NewReader(b)
+	if err != nil {
+		panic(err)
+	}
+
+	buf, err := ioutil.ReadAll(r)
+	if err != nil {
+		panic(err)
+	}
+
+	r.Close()
+
+	return buf
+}
+
+// Hash returns the ID for data.
+func Hash(data []byte) ID {
+	h := sha256.Sum256(data)
+	id := make(ID, 32)
+	copy(id, h[:])
+	return id
+}