Merge rust-bitcoin/rust-bitcoin#939: fix: reject message (de)serialization

548725c5fb test: reject message (de)serialization (0xb10c)
fc572aba86 fix: use var_str in 'reject' msgs (0xb10c)

Pull request description:

  [BIP-61 defines `response-to-msg`][bip61] (`Reject::message` in rust-bitcoin; the message that triggered the reject) to be a `var_str`. However, by using the `CommandString` it was (de)serialized as 12 byte string. A test is added that de- and serializes two reject messages received from an older Bitcoin Core peer.

  Reject message sending has been removed from Bitcoin Core, I'm still receiving them from older peers from time to time.

  [bip61]: https://github.com/bitcoin/bips/blob/master/bip-0061.mediawiki#common-payload

  gh-ref: https://github.com/rust-bitcoin/rust-bitcoin/pull/323

ACKs for top commit:
  apoelstra:
    ACK 548725c5fb

Tree-SHA512: e5cbf215a471f113b4dd7f7fada162686fc6e8c7b1e2e9e641667208a36d3db610e57e8b549756ffe597656fee5444fe95466f1b88f45366595766f7c4640eea

src/network/message.rs

@@ -472,7 +472,7 @@ mod test {
             NetworkMessage::GetCFCheckpt(GetCFCheckpt{filter_type: 17, stop_hash: hash([25u8; 32]).into()}),
             NetworkMessage::CFCheckpt(CFCheckpt{filter_type: 27, stop_hash: hash([77u8; 32]).into(), filter_headers: vec![hash([3u8; 32]).into(), hash([99u8; 32]).into()]}),
             NetworkMessage::Alert(vec![45,66,3,2,6,8,9,12,3,130]),
-            NetworkMessage::Reject(Reject{message: CommandString::try_from("Test reject").unwrap(), ccode: RejectReason::Duplicate, reason: "Cause".into(), hash: hash([255u8; 32])}),
+            NetworkMessage::Reject(Reject{message: "Test reject".into(), ccode: RejectReason::Duplicate, reason: "Cause".into(), hash: hash([255u8; 32])}),
             NetworkMessage::FeeFilter(1000),
             NetworkMessage::WtxidRelay,
             NetworkMessage::AddrV2(vec![AddrV2Message{ addr: AddrV2::Ipv4(Ipv4Addr::new(127, 0, 0, 1)), port: 0, services: ServiceFlags::NONE, time: 0 }]),

src/network/message_network.rs

@@ -26,7 +26,6 @@ use network::address::Address;
 use network::constants::{self, ServiceFlags};
 use consensus::{Encodable, Decodable, ReadExt};
 use consensus::encode;
-use network::message::CommandString;
 use hashes::sha256d;
 
 /// Some simple messages
@@ -133,7 +132,7 @@ impl Decodable for RejectReason {
 #[derive(PartialEq, Eq, Clone, Debug)]
 pub struct Reject {
     /// message type rejected
-    pub message: CommandString,
+    pub message: Cow<'static, str>,
     /// reason of rejection as code
     pub ccode: RejectReason,
     /// reason of rejectection
@@ -147,8 +146,11 @@ impl_consensus_encoding!(Reject, message, ccode, reason, hash);
 #[cfg(test)]
 mod tests {
     use super::VersionMessage;
+    use super::Reject;
+    use super::RejectReason;
 
     use hashes::hex::FromHex;
+    use hashes::sha256d::Hash;
     use network::constants::ServiceFlags;
 
     use consensus::encode::{deserialize, serialize};
@@ -172,4 +174,37 @@ mod tests {
 
         assert_eq!(serialize(&real_decode), from_sat);
     }
+
+    #[test]
+    fn reject_message_test() {
+        let reject_tx_conflict = Vec::from_hex("027478121474786e2d6d656d706f6f6c2d636f6e666c69637405df54d3860b3c41806a3546ab48279300affacf4b88591b229141dcf2f47004").unwrap();
+        let reject_tx_nonfinal = Vec::from_hex("02747840096e6f6e2d66696e616c259bbe6c83db8bbdfca7ca303b19413dc245d9f2371b344ede5f8b1339a5460b").unwrap();
+
+        let decode_result_conflict: Result<Reject, _> = deserialize(&reject_tx_conflict);
+        let decode_result_nonfinal: Result<Reject, _> = deserialize(&reject_tx_nonfinal);
+
+        assert!(decode_result_conflict.is_ok());
+        assert!(decode_result_nonfinal.is_ok());
+
+        let conflict = decode_result_conflict.unwrap();
+        assert_eq!("tx", conflict.message);
+        assert_eq!(RejectReason::Duplicate, conflict.ccode);
+        assert_eq!("txn-mempool-conflict", conflict.reason);
+        assert_eq!(
+            Hash::from_hex("0470f4f2dc4191221b59884bcffaaf00932748ab46356a80413c0b86d354df05").unwrap(),
+            conflict.hash
+        );
+
+        let nonfinal = decode_result_nonfinal.unwrap();
+        assert_eq!("tx", nonfinal.message);
+        assert_eq!(RejectReason::NonStandard, nonfinal.ccode);
+        assert_eq!("non-final", nonfinal.reason);
+        assert_eq!(
+            Hash::from_hex("0b46a539138b5fde4e341b37f2d945c23d41193b30caa7fcbd8bdb836cbe9b25").unwrap(),
+            nonfinal.hash
+        );
+
+        assert_eq!(serialize(&conflict), reject_tx_conflict);
+        assert_eq!(serialize(&nonfinal), reject_tx_nonfinal);
+    }
 }