parser: present block hashes in big endian order

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
 }

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)
 			}
 		}
 	}