added package with tools for Relay

relay/relay.go

@@ -0,0 +1,44 @@
+package relay
+
+import (
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"strings"
+
+	"encoding/json"
+
+	graphql "github.com/neelance/graphql-go"
+)
+
+func MarshalID(kind string, spec interface{}) graphql.ID {
+	d, err := json.Marshal(spec)
+	if err != nil {
+		panic(fmt.Errorf("relay.MarshalID: %s", err))
+	}
+	return graphql.ID(base64.URLEncoding.EncodeToString(append([]byte(kind+":"), d...)))
+}
+
+func UnmarshalKind(id graphql.ID) string {
+	s, err := base64.URLEncoding.DecodeString(string(id))
+	if err != nil {
+		return ""
+	}
+	i := strings.IndexByte(string(s), ':')
+	if i == -1 {
+		return ""
+	}
+	return string(s[:i])
+}
+
+func UnmarshalSpec(id graphql.ID, v interface{}) error {
+	s, err := base64.URLEncoding.DecodeString(string(id))
+	if err != nil {
+		return err
+	}
+	i := strings.IndexByte(string(s), ':')
+	if i == -1 {
+		return errors.New("invalid graphql.ID")
+	}
+	return json.Unmarshal([]byte(s[i+1:]), v)
+}