Create new Builder interface for creating CIDs.

builder.go

@@ -0,0 +1,92 @@
+package cid
+
+import (
+	mh "github.com/multiformats/go-multihash"
+)
+
+type Builder interface {
+	Sum(data []byte) (*Cid, error)
+	GetCodec() uint64
+	WithCodec(uint64) Builder
+}
+
+type V0Builder struct{}
+
+type V1Builder struct {
+	Codec   uint64
+	HashFun uint64
+	HashLen int // HashLen <= 0 means the default length
+}
+
+func PrefixToBuilder(p Prefix) Builder {
+	if p.Version == 0 {
+		return V0Builder{}
+	}
+	mhLen := p.MhLength
+	if p.MhType == mh.ID {
+		mhLen = 0
+	}
+	if mhLen < 0 {
+		mhLen = 0
+	}
+	return V1Builder{
+		Codec:   p.Codec,
+		HashFun: p.MhType,
+		HashLen: mhLen,
+	}
+}
+
+func (p Prefix) GetCodec() uint64 {
+	return p.Codec
+}
+
+func (p Prefix) WithCodec(c uint64) Builder {
+	if c == p.Codec {
+		return p
+	}
+	p.Codec = c
+	if c != DagProtobuf {
+		p.Version = 1
+	}
+	return p
+}
+
+func (p V0Builder) 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 V0Builder) GetCodec() uint64 {
+	return DagProtobuf
+}
+
+func (p V0Builder) WithCodec(c uint64) Builder {
+	if c == DagProtobuf {
+		return p
+	}
+	return V1Builder{Codec: c, HashFun: mh.SHA2_256}
+}
+
+func (p V1Builder) 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
+}
+
+func (p V1Builder) GetCodec() uint64 {
+	return p.Codec
+}
+
+func (p V1Builder) WithCodec(c uint64) Builder {
+	p.Codec = c
+	return p
+}

builder_test.go

@@ -0,0 +1,57 @@
+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 := V1Builder{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 := V0Builder{}
+	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")
+	}
+}

cid.go

@@ -144,27 +144,6 @@ func NewCidV1(codecType uint64, mhash mh.Multihash) *Cid {
 	}
 }
 
-// NewPrefixV0 returns a CIDv0 prefix with the specified multihash type.
-func NewPrefixV0(mhType uint64) Prefix {
-	return Prefix{
-		MhType:   mhType,
-		MhLength: mh.DefaultLengths[mhType],
-		Version:  0,
-		Codec:    DagProtobuf,
-	}
-}
-
-// NewPrefixV1 returns a CIDv1 prefix with the specified codec and multihash
-// type.
-func NewPrefixV1(codecType uint64, mhType uint64) Prefix {
-	return Prefix{
-		MhType:   mhType,
-		MhLength: mh.DefaultLengths[mhType],
-		Version:  1,
-		Codec:    codecType,
-	}
-}
-
 // Cid represents a self-describing content adressed
 // identifier. It is formed by a Version, a Codec (which indicates
 // a multicodec-packed content type) and a Multihash.
@@ -442,6 +421,8 @@ func (c *Cid) Prefix() Prefix {
 // that is, the Version, the Codec, the Multihash type
 // and the Multihash length. It does not contains
 // any actual content information.
+// NOTE: The use -1 in MhLength to mean default length is deprecated,
+//   use the V0Builder or V1Builder structures instead
 type Prefix struct {
 	Version  uint64
 	Codec    uint64

deprecated.go

@@ -0,0 +1,28 @@
+package cid
+
+import (
+	mh "github.com/multiformats/go-multihash"
+)
+
+// NewPrefixV0 returns a CIDv0 prefix with the specified multihash type.
+// DEPRECATED: Use FormatV0
+func NewPrefixV0(mhType uint64) Prefix {
+	return Prefix{
+		MhType:   mhType,
+		MhLength: mh.DefaultLengths[mhType],
+		Version:  0,
+		Codec:    DagProtobuf,
+	}
+}
+
+// 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,
+		MhLength: mh.DefaultLengths[mhType],
+		Version:  1,
+		Codec:    codecType,
+	}
+}