Better document msg fuzz target behavior and be slightly more strict

diff --git a/fuzz/src/msg_targets/utils.rs b/fuzz/src/msg_targets/utils.rs
index a5257ba0f80c1fea24f399018103da37f572c763..2a7731ccd136d2185414b4b73f7510a7bebe8397 100644 (file)
--- a/fuzz/src/msg_targets/utils.rs
+++ b/fuzz/src/msg_targets/utils.rs
@@ -13,6 +13,15 @@ impl Writer for VecWriter {
        }
 }
 
+// We attempt to test the strictest behavior we can for a given message, however, some messages
+// have different expected behavior. You can see which messages have which behavior in
+// gen_target.sh, but, in general, the *_announcement messages have to round-trip exactly (as
+// otherwise we'd invalidate the signatures), most messages just need to round-trip up to the
+// amount of data we know how to interpret, and some messages we may throw out invalid stuff (eg
+// if an error message isn't valid UTF-8 we cant String-ize it), so they wont roundtrip correctly.
+
+// Tests a message that must survive roundtrip exactly, though may not empty the read buffer
+// entirely
 #[macro_export]
 macro_rules! test_msg {
        ($MsgType: path, $data: ident) => {
@@ -31,6 +40,8 @@ macro_rules! test_msg {
        }
 }
 
+// Tests a message that may lose data on roundtrip, but shoulnd't lose data compared to our
+// re-serialization.
 #[macro_export]
 macro_rules! test_msg_simple {
        ($MsgType: path, $data: ident) => {
@@ -40,11 +51,18 @@ macro_rules! test_msg_simple {
                        if let Ok(msg) = <$MsgType as Readable<::std::io::Cursor<&[u8]>>>::read(&mut r) {
                                let mut w = VecWriter(Vec::new());
                                msg.write(&mut w).unwrap();
+
+                               let msg = <$MsgType as Readable<::std::io::Cursor<&[u8]>>>::read(&mut ::std::io::Cursor::new(&w.0)).unwrap();
+                               let mut w_two = VecWriter(Vec::new());
+                               msg.write(&mut w_two).unwrap();
+                               assert_eq!(&w.0[..], &w_two.0[..]);
                        }
                }
        }
 }
 
+// Tests a message that must survive roundtrip exactly, and must exactly empty the read buffer and
+// split it back out on re-serialization.
 #[macro_export]
 macro_rules! test_msg_exact {
        ($MsgType: path, $data: ident) => {
@@ -54,13 +72,14 @@ macro_rules! test_msg_exact {
                        if let Ok(msg) = <$MsgType as Readable<::std::io::Cursor<&[u8]>>>::read(&mut r) {
                                let mut w = VecWriter(Vec::new());
                                msg.write(&mut w).unwrap();
-
                                assert_eq!(&r.into_inner()[..], &w.0[..]);
                        }
                }
        }
 }
 
+// Tests a message that must survive roundtrip exactly, modulo one "hole" which may be set to 0s on
+// re-serialization.
 #[macro_export]
 macro_rules! test_msg_hole {
        ($MsgType: path, $data: ident, $hole: expr, $hole_len: expr) => {