From dfc48d3ec4812d9b0203edd8f0b517f2273604e0 Mon Sep 17 00:00:00 2001
From: Kevin Atkinson <k@kevina.org>
Date: Mon, 10 Sep 2018 05:10:23 -0400
Subject: [PATCH] Make sure we have a SHA2_256, length 32 hash when creating a
 CidV0.

---
 cid.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/cid.go b/cid.go
index ececb26..cfcbcde 100644
--- a/cid.go
+++ b/cid.go
@@ -133,6 +133,15 @@ var CodecToStr = map[uint64]string{
 // compatibility with the plain-multihash format used used in IPFS.
 // NewCidV1 should be used preferentially.
 func NewCidV0(mhash mh.Multihash) Cid {
+	// Need to make sure hash is valid for CidV0 otherwise we will
+	// incorrectly detect it as CidV1 in the Version() method
+	dec, err := mh.Decode(mhash)
+	if err != nil {
+		panic(err)
+	}
+	if dec.Code != mh.SHA2_256 || dec.Length != 32 {
+		panic("invalid hash for cidv0")
+	}
 	return Cid{string(mhash)}
 }