Create new Format interface for creating CIDs.

format.go

@@ -0,0 +1,55 @@
+package cid
+
+import (
+	mh "github.com/multiformats/go-multihash"
+)
+
+type Format interface {
+	Sum(data []byte) (*Cid, error)
+}
+
+type FormatV0 struct{}
+
+type FormatV1 struct {
+	Codec   uint64
+	HashFun uint64
+	HashLen int // HashLen <= 0 means the default length
+}
+
+func PrefixToFormat(p Prefix) Format {
+	if p.Version == 0 {
+		return FormatV0{}
+	}
+	mhLen := p.MhLength
+	if p.MhType == mh.ID {
+		mhLen = 0
+	}
+	if mhLen < 0 {
+		mhLen = 0
+	}
+	return FormatV1{
+		Codec:   p.Codec,
+		HashFun: p.MhType,
+		HashLen: mhLen,
+	}
+}
+
+func (p FormatV0) Sum(data []byte) (*Cid, error) {
+	hash, err := mh.Sum(data, mh.SHA2_256, -1)
+	if err != nil {
+		return nil, err
+	}
+	return NewCidV0(hash), nil
+}
+
+func (p FormatV1) Sum(data []byte) (*Cid, error) {
+	mhLen := p.HashLen
+	if mhLen <= 0 {
+		mhLen = -1
+	}
+	hash, err := mh.Sum(data, p.HashFun, mhLen)
+	if err != nil {
+		return nil, err
+	}
+	return NewCidV1(p.Codec, hash), nil
+}