Create new Format interface for creating CIDs.

cid.go

@@ -145,6 +145,7 @@ func NewCidV1(codecType uint64, mhash mh.Multihash) *Cid {
 }
 
 // NewPrefixV0 returns a CIDv0 prefix with the specified multihash type.
+// DEPRECATED: Use FormatV0
 func NewPrefixV0(mhType uint64) Prefix {
 	return Prefix{
 		MhType:   mhType,
@@ -156,6 +157,7 @@ func NewPrefixV0(mhType uint64) Prefix {
 
 // NewPrefixV1 returns a CIDv1 prefix with the specified codec and multihash
 // type.
+// DEPRECATED: Use FormatV1
 func NewPrefixV1(codecType uint64, mhType uint64) Prefix {
 	return Prefix{
 		MhType:   mhType,
@@ -451,6 +453,7 @@ type Prefix struct {
 
 // Sum uses the information in a prefix to perform a multihash.Sum()
 // and return a newly constructed Cid with the resulting multihash.
+// DEPRECATED: Use PrefixToFormat(p).Sum(data)
 func (p Prefix) Sum(data []byte) (*Cid, error) {
 	hash, err := mh.Sum(data, p.MhType, p.MhLength)
 	if err != nil {

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
+}

format_test.go

@@ -0,0 +1,58 @@
+package cid
+
+import (
+	"testing"
+
+	mh "github.com/multiformats/go-multihash"
+)
+
+func TestFormatV1(t *testing.T) {
+	data := []byte("this is some test content")
+
+	// Construct c1
+	format := FormatV1{Codec: DagCBOR, HashFun: mh.SHA2_256}
+	c1, err := format.Sum(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Construct c2
+	hash, err := mh.Sum(data, mh.SHA2_256, -1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	c2 := NewCidV1(DagCBOR, hash)
+
+	if !c1.Equals(c2) {
+		t.Fatal("cids mismatch")
+	}
+	if c1.Prefix() != c2.Prefix() {
+		t.Fatal("prefixes mismatch")
+	}
+}
+
+func TestFormatV0(t *testing.T) {
+	data := []byte("this is some test content")
+
+	// Construct c1
+	format := FormatV0{}
+	c1, err := format.Sum(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Construct c2
+	hash, err := mh.Sum(data, mh.SHA2_256, -1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	c2 := NewCidV0(hash)
+
+	if !c1.Equals(c2) {
+		t.Fatal("cids mismatch")
+	}
+	if c1.Prefix() != c2.Prefix() {
+		t.Fatal("prefixes mismatch")
+	}
+}
+