add some more helper functions to ease integration into go-ipfs

cid.go

@@ -145,3 +145,22 @@ func (c *Cid) Equals(o *Cid) bool {
 		c.version == o.version &&
 		bytes.Equal(c.hash, o.hash)
 }
+
+func (c *Cid) UnmarshalJSON(b []byte) error {
+	if len(b) < 2 {
+		return fmt.Errorf("invalid cid json blob")
+	}
+	out, err := Decode(string(b[1 : len(b)-1]))
+	if err != nil {
+		return err
+	}
+
+	c.version = out.version
+	c.hash = out.hash
+	c.codec = out.codec
+	return nil
+}
+
+func (c *Cid) MarshalJSON() ([]byte, error) {
+	return []byte(fmt.Sprintf("\"%s\"", c.String())), nil
+}

set.go

@@ -33,3 +33,12 @@ func (s *Set) Keys() []*Cid {
 	}
 	return out
 }
+
+func (s *Set) Visit(c *Cid) bool {
+	if !s.Has(c) {
+		s.Add(c)
+		return true
+	}
+
+	return false
+}