Checkpoint.

cid.go

@@ -138,15 +138,15 @@ type Cid struct {
 // compatibility with the plain-multihash format used used in IPFS.
 // NewCidV1 should be used preferentially.
 func NewCidV0(mhash mh.Multihash) (*Cid, error) {
-	if mhash[0] != mh.SHA2_256 && mhash[1] != byte(mh.DefaultLengths[mh.SHA2_256]) {
-		return nil, ErrCid0OnlySHA256
-	}
-
 	c := &Cid{
 		version: 0,
 		codec:   DagProtobuf,
 		hash:    mhash,
 	}
+	err := ValidateCid(c)
+	if err != nil {
+		return nil, err
+	}
 	return c, nil
 }
 

validate.go

@@ -46,6 +46,13 @@ func IsGoodHash(code uint64) bool {
 
 func ValidateCid(c *Cid) error {
 	pref := c.Prefix()
+	if pref.Version == 0 {
+		if pref.MhType != mh.SHA2_256 || pref.MhLength != mh.DefaultLengths[mh.SHA2_256] {
+			return ErrCid0OnlySHA256
+		}
+		return nil
+	}
+
 	if !IsGoodHash(pref.MhType) {
 		return fmt.Errorf("potentially insecure hash functions not allowed")
 	}

validate_test.go

@@ -30,7 +30,20 @@ func TestValidateCids(t *testing.T) {
 
 	assertFalse(IsGoodHash(mh.BLAKE2B_MIN + 5))
 
-	mhcid := func(code uint64, length int) *Cid {
+	mhcid0 := func(code uint64, length int) *Cid {
+		c := &Cid{
+			version: 0,
+			codec:   DagProtobuf,
+		}
+		mhash, err := mh.Sum([]byte{}, code, length)
+		if err != nil {
+			t.Fatal(err)
+		}
+		c.hash = mhash
+		return c
+	}
+
+	mhcid1 := func(code uint64, length int) *Cid {
 		c := &Cid{
 			version: 1,
 			codec:   DagCBOR,
@@ -47,9 +60,13 @@ func TestValidateCids(t *testing.T) {
 		cid *Cid
 		err string
 	}{
-		{mhcid(mh.SHA2_256, 32), ""},
-		{mhcid(mh.SHA2_256, 16), "hashes must be at least 20 bytes long"},
-		{mhcid(mh.MURMUR3, 4), "potentially insecure hash functions not allowed"},
+		{mhcid0(mh.SHA2_256, 32), ""},
+		{mhcid0(mh.SHA3_256, 32), "cidv0 accepts only SHA256 hashes of standard length"},
+		{mhcid0(mh.SHA2_256, 16), "cidv0 accepts only SHA256 hashes of standard length"},
+		{mhcid0(mh.MURMUR3, 4), "cidv0 accepts only SHA256 hashes of standard length"},
+		{mhcid1(mh.SHA2_256, 32), ""},
+		{mhcid1(mh.SHA2_256, 16), "hashes must be at least 20 bytes long"},
+		{mhcid1(mh.MURMUR3, 4), "potentially insecure hash functions not allowed"},
 	}
 
 	for i, cas := range cases {