zpay32: allow fuzzer to choose invoice net

We add a parameter to select which network will be used for the fuzz
tests, rather than hardcoding the network.

zpay32/fuzz_test.go

@@ -7,9 +7,44 @@ import (
 	"github.com/btcsuite/btcd/chaincfg"
 )
 
+// getPrefixAndChainParams selects network chain parameters based on the fuzzer-
+// selected input byte "net". 50% of the time mainnet is selected, while the
+// other 50% of the time one of the test networks is selected. For each network
+// the appropriate invoice HRP prefix is also returned, with a small chance that
+// no prefix is returned, allowing the fuzzer to generate invalid prefixes too.
+func getPrefixAndChainParams(net byte) (string, *chaincfg.Params) {
+	switch {
+	case net == 0x00:
+		return "", &chaincfg.RegressionNetParams
+	case net < 0x20:
+		return "lnbcrt", &chaincfg.RegressionNetParams
+
+	case net == 0x20:
+		return "", &chaincfg.TestNet3Params
+	case net < 0x40:
+		return "lntb", &chaincfg.TestNet3Params
+
+	case net == 0x40:
+		return "", &chaincfg.SimNetParams
+	case net < 0x60:
+		return "lnsb", &chaincfg.SimNetParams
+
+	case net == 0x60:
+		return "", &chaincfg.SigNetParams
+	case net < 0x80:
+		return "lntbs", &chaincfg.SigNetParams
+
+	case net == 0x80:
+		return "", &chaincfg.MainNetParams
+	default:
+		return "lnbc", &chaincfg.MainNetParams
+	}
+}
+
 func FuzzDecode(f *testing.F) {
-	f.Fuzz(func(t *testing.T, data string) {
-		_, _ = Decode(data, &chaincfg.TestNet3Params)
+	f.Fuzz(func(t *testing.T, net byte, data string) {
+		_, chainParams := getPrefixAndChainParams(net)
+		_, _ = Decode(data, chainParams)
 	})
 }
 
@@ -44,13 +79,14 @@ func appendChecksum(bech string) string {
 }
 
 func FuzzEncode(f *testing.F) {
-	f.Fuzz(func(t *testing.T, data string) {
+	f.Fuzz(func(t *testing.T, net byte, data string) {
 		// Make it easier for the fuzzer to generate valid invoice
 		// encodings by adding the required prefix and valid checksum.
-		data = "lnbc" + data
+		hrpPrefix, chainParams := getPrefixAndChainParams(net)
+		data = hrpPrefix + data
 		data = appendChecksum(data)
 
-		inv, err := Decode(data, &chaincfg.MainNetParams)
+		inv, err := Decode(data, chainParams)
 		if err != nil {
 			return
 		}