parser: replace genesis "blockheight" with zero

parser/block.go

@@ -52,6 +52,9 @@ func (b *block) HasSaplingTransactions() bool {
 	return false
 }
 
+// see https://github.com/zcash-hackworks/lightwalletd/issues/17#issuecomment-467110828
+const genesisTargetDifficulty = 520617983
+
 // GetHeight() extracts the block height from the coinbase transaction. See
 // BIP34. Returns block height on success, or -1 on error.
 func (b *block) GetHeight() int {
@@ -74,6 +77,11 @@ func (b *block) GetHeight() int {
 		blockHeight <<= 8
 		blockHeight = blockHeight | uint32(heightBytes[i])
 	}
+
+	if blockHeight == genesisTargetDifficulty {
+		blockHeight = 0
+	}
+
 	b.height = int(blockHeight)
 	return int(blockHeight)
 }

parser/block_test.go

@@ -42,6 +42,46 @@ func TestBlockParser(t *testing.T) {
 			t.Error("Read wrong version in a test block.")
 			break
 		}
+
+		if block.GetTxCount() < 1 {
+			t.Error("No transactions in block")
+			break
+		}
+	}
+}
+
+func TestGenesisBlockParser(t *testing.T) {
+	blockFile, err := os.Open("../testdata/mainnet_genesis")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer blockFile.Close()
+
+	scan := bufio.NewScanner(blockFile)
+	for i := 0; scan.Scan(); i++ {
+		blockDataHex := scan.Text()
+		blockData, err := hex.DecodeString(blockDataHex)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+
+		block := NewBlock()
+		blockData, err = block.ParseFromSlice(blockData)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+
+		// Some basic sanity checks
+		if block.hdr.Version != 4 {
+			t.Error("Read wrong version in genesis block.")
+			break
+		}
+
+		if block.GetHeight() != 0 {
+			t.Errorf("Got wrong height for genesis block: %d", block.GetHeight())
+		}
 	}
 }