Make ScriptParser.TryParse more safe

Author: joemphilips

NBitcoin.Tests/Generators/ScriptGenerator.cs

@@ -9,6 +9,9 @@ namespace NBitcoin.Tests.Generators
 	public class ScriptGenerator
 	{
 
+		public static Arbitrary<Script> RandomScriptArb()
+			=> Arb.From(RandomScriptSig());
+
 		#region script sig
 		// -------- legacy -------
 		// 1. p2pkh scriptSig

NBitcoin.Tests/MiniscriptTests.cs

@@ -20,6 +20,7 @@ public MiniscriptTests()
 		{
 			Arb.Register<AbstractPolicyGenerator>();
 			Arb.Register<CryptoGenerator>();
+			Arb.Register<ScriptGenerator>();
 			Network = Network.Main;
 			Keys = new Key[] { new Key(), new Key(), new Key() };
 		}
@@ -440,5 +441,11 @@ public void ShouldPlayWellWithTransactionBuilder_2()
 			b2.SetRelativeLockTimeTo(coins, 10000);
 			Assert.True(b2.Verify(b2.BuildTransaction(true)));
 		}
+		[Property]
+		[Trait("PropertyTest", "Verification")]
+		public void ShouldNotThrowErrorWhenTryParsingScript(Script sc)
+		{
+			Miniscript.Miniscript.TryParseScript(sc, out var res);
+		}
 	}
 }

NBitcoin/Miniscript/Parser/Parser.cs

@@ -54,7 +54,16 @@ internal static ParserResult<ScriptToken, T> TryParse<T>(this Parser<ScriptToken
 			if (input == null)
 				throw new System.ArgumentNullException(nameof(input));
 
-			return parser(new ScriptInput(input));
+			try
+			{
+				return parser(new ScriptInput(input));
+			}
+			// Catching exception here is bit ugly, but converting `Script` to `ScriptToken` is itself unsafe
+			// so this is good for assuring pureness of this method.
+			catch (ParseException e)
+			{
+				return ParserResult<ScriptToken, T>.Failure(new ScriptInput(new ScriptToken[]{}), e.Message);
+			}
 		}
 
 		internal static T Parse<T>(this Parser<ScriptToken, T> parser, Script input)