From f42dea2b1e89f1f11bc1c1e59913eb24ca989fdf Mon Sep 17 00:00:00 2001
From: George Tankersley <george.tankersley@gmail.com>
Date: Fri, 16 Nov 2018 21:57:21 +0000
Subject: [PATCH] parser: present block hashes in big endian order

---
 parser/block_header.go      | 7 +++++++
 parser/block_header_test.go | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/parser/block_header.go b/parser/block_header.go
index 739116a..c00f120 100644
--- a/parser/block_header.go
+++ b/parser/block_header.go
@@ -150,6 +150,7 @@ func parseNBits(b []byte) *big.Int {
 	return new(big.Int).SetBytes(targetBytes)
 }
 
+// GetHash returns the bytes of a block hash in big-endian order.
 func (hdr *blockHeader) GetHash() []byte {
 	if hdr.cachedHash != nil {
 		return hdr.cachedHash
@@ -165,6 +166,12 @@ func (hdr *blockHeader) GetHash() []byte {
 	digest := sha256.Sum256(serializedHeader)
 	digest = sha256.Sum256(digest[:])
 
+	// Reverse byte order
+	for i := 0; i < len(digest)/2; i++ {
+		j := len(digest) - 1 - i
+		digest[i], digest[j] = digest[j], digest[i]
+	}
+
 	hdr.cachedHash = digest[:]
 	return hdr.cachedHash
 }
diff --git a/parser/block_header_test.go b/parser/block_header_test.go
index 400a296..5a493d5 100644
--- a/parser/block_header_test.go
+++ b/parser/block_header_test.go
@@ -126,9 +126,9 @@ func TestBlockHeader(t *testing.T) {
 		hash := blockHeader.GetHash()
 
 		// This is not necessarily true for anything but our current test cases.
-		for _, b := range hash[28:] {
+		for _, b := range hash[:4] {
 			if b != 0 {
-				t.Errorf("Hash lacked trailing zeros")
+				t.Errorf("Hash lacked leading zeros: %x", hash)
 			}
 		}
 	}