[invoice] Fix non-recoverable sig handling and bogus SI prefix err

This adds two additional tests from the BOLT 11 invalid invoice
tests, fixing the two errors that broke them. It fixes a panic on
the "nonrecoverable signature" test and makes the error variant
more sensible on the bogus SI prefix test.

Author: TheBlueMatt

lightning-invoice/src/de.rs

@@ -77,7 +77,7 @@ mod hrp_sm {
 					} else if ['m', 'u', 'n', 'p'].contains(&read_symbol) {
 						Ok(States::ParseAmountSiPrefix)
 					} else {
-						Err(super::ParseError::MalformedHRP)
+						Err(super::ParseError::UnknownSiPrefix)
 					}
 				},
 				States::ParseAmountSiPrefix => Err(super::ParseError::MalformedHRP),

lightning-invoice/src/lib.rs

@@ -1059,7 +1059,9 @@ impl Invoice {
 		match self.signed_invoice.recover_payee_pub_key() {
 			Err(secp256k1::Error::InvalidRecoveryId) =>
 				return Err(SemanticError::InvalidRecoveryId),
-			Err(_) => panic!("no other error may occur"),
+			Err(secp256k1::Error::InvalidSignature) =>
+				return Err(SemanticError::InvalidSignature),
+			Err(e) => panic!("no other error may occur, got {:?}", e),
 			Ok(_) => {},
 		}
 

lightning-invoice/tests/ser_de.rs

@@ -163,7 +163,13 @@ fn test_bolt_invaoid_invoices() {
 	assert_eq!(Invoice::from_str(
 		"LNBC2500u1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdpquwpc4curk03c9wlrswe78q4eyqc7d8d0xqzpuyk0sg5g70me25alkluzd2x62aysf2pyy8edtjeevuv4p2d5p76r4zkmneet7uvyakky2zr4cusd45tftc9c5fh0nnqpnl2jfll544esqchsrny"
 		), Err(ParseOrSemanticError::ParseError(ParseError::Bech32Error(bech32::Error::MixedCase))));
+	assert_eq!(Invoice::from_str(
+		"lnbc2500u1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5xysxxatsyp3k7enxv4jsxqzpuaxtrnwngzn3kdzw5hydlzf03qdgm2hdq27cqv3agm2awhz5se903vruatfhq77w3ls4evs3ch9zw97j25emudupq63nyw24cg27h2rspk28uwq"
+		), Err(ParseOrSemanticError::SemanticError(SemanticError::InvalidSignature)));
 	assert_eq!(Invoice::from_str(
 		"lnbc1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdpl2pkx2ctnv5sxxmmwwd5kgetjypeh2ursdae8g6na6hlh"
 		), Err(ParseOrSemanticError::ParseError(ParseError::TooShortDataPart)));
+	assert_eq!(Invoice::from_str(
+		"lnbc2500x1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5xysxxatsyp3k7enxv4jsxqzpujr6jxr9gq9pv6g46y7d20jfkegkg4gljz2ea2a3m9lmvvr95tq2s0kvu70u3axgelz3kyvtp2ywwt0y8hkx2869zq5dll9nelr83zzqqpgl2zg"
+		), Err(ParseOrSemanticError::ParseError(ParseError::UnknownSiPrefix)));
 }