Reject zero-count Miniscript fragments

Author: NicolasDorier

NBitcoin.Tests/MiniscriptTests.cs

@@ -86,6 +86,19 @@ public void RejectsNonCanonicalNumbers(string miniscript, bool expected)
 			Assert.Equal(expected, Miniscript.TryParse(miniscript, settings, out _));
 		}
 
+		[Theory]
+		[InlineData("thresh(0)", KeyType.Classic)]
+		[InlineData("multi(0)", KeyType.Classic)]
+		[InlineData("sortedmulti(0)", KeyType.Classic)]
+		[InlineData("multi_a(0)", KeyType.Taproot)]
+		[InlineData("sortedmulti_a(0)", KeyType.Taproot)]
+		public void RejectsZeroThreshold(string miniscript, KeyType keyType)
+		{
+			var settings = new MiniscriptParsingSettings(Network.Main, keyType) { AllowedParameters = ParameterTypeFlags.All };
+			Assert.False(Miniscript.TryParse(miniscript, settings, out var error, out _));
+			Assert.IsType<MiniscriptError.CountExpected>(error);
+		}
+
 		[Theory]
 		[InlineData(ParameterTypeFlags.All, "pkh(A)", true)]
 		[InlineData(ParameterTypeFlags.All, "pkh(@0/**)", true)]

NBitcoin/WalletPolicies/Miniscript.cs

@@ -227,7 +227,7 @@ private static bool TryParseParameterCount(ParsingContext ctx, [MaybeNullWhen(tr
 				error = new MiniscriptError.CountExpected(ctx.Offset);
 				return false;
 			}
-			if (uint.TryParse(match.Value, NumberStyles.Integer, CultureInfo.InvariantCulture, out var v) && v < Int32.MaxValue)
+			if (uint.TryParse(match.Value, NumberStyles.Integer, CultureInfo.InvariantCulture, out var v) && v > 0 && v < Int32.MaxValue)
 			{
 				ctx.Advance(match.Length);
 				node = new Value.CountValue((int)v);