From 87a0018e3ebf7d47086032d817a9e671c359214e Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Fri, 27 Dec 2019 17:29:51 -0500
Subject: [PATCH] Better document msg fuzz target behavior and be slightly more
 strict

---
 fuzz/src/msg_targets/utils.rs | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/fuzz/src/msg_targets/utils.rs b/fuzz/src/msg_targets/utils.rs
index a5257ba0f..2a7731ccd 100644
--- 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) => {
-- 
2.39.5