From ce9c9c3c64d46b7c631e5a51d91050878bf32246 Mon Sep 17 00:00:00 2001
From: Kevin Atkinson <k@kevina.org>
Date: Thu, 28 Jun 2018 21:44:58 -0400
Subject: [PATCH] Create new Format interface for creating CIDs.

---
 format.go      | 55 +++++++++++++++++++++++++++++++++++++++++++++++
 format_test.go | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 format.go
 create mode 100644 format_test.go

diff --git a/format.go b/format.go
new file mode 100644
index 0000000..b78872f
--- /dev/null
+++ b/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 // 0 (or -1 for compatibility) 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 == -1 {
+		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
+}
diff --git a/format_test.go b/format_test.go
new file mode 100644
index 0000000..3f74989
--- /dev/null
+++ b/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")
+	}
+}
+