Fix serialization expected lengths and check them in test/fuzzing

[TheBlueMatt]

No description provided.

[codecov]

Codecov Report

Merging #854 (ee0ffe5) into main (8a8c75a) will decrease coverage by 0.24%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #854      +/-   ##
==========================================
- Coverage   90.59%   90.35%   -0.25%     
==========================================
  Files          51       57       +6     
  Lines       27109    29353    +2244     
==========================================
+ Hits        24560    26522    +1962     
- Misses       2549     2831     +282     

Impacted Files	Coverage Δ
lightning/src/util/config.rs	47.61% <ø> (ø)
lightning/src/ln/chan_utils.rs	97.34% <100.00%> (+<0.01%)	⬆️
lightning/src/ln/msgs.rs	88.76% <100.00%> (ø)
lightning/src/util/ser_macros.rs	96.73% <100.00%> (+0.15%)	⬆️
lightning/src/util/events.rs	18.26% <0.00%> (-5.63%)	⬇️
lightning-persister/src/lib.rs	94.06% <0.00%> (-1.55%)	⬇️
lightning/src/routing/router.rs	96.21% <0.00%> (-0.76%)	⬇️
lightning/src/util/test_utils.rs	83.23% <0.00%> (-0.42%)	⬇️
lightning/src/ln/functional_test_utils.rs	95.08% <0.00%> (-0.14%)	⬇️
lightning/src/ln/features.rs	98.81% <0.00%> (-0.11%)	⬇️
... and 19 more

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[valentinewallace]

Nice improvement! 🥇 Minor feedback only here.

[valentinewallace]

Cool that macros can allow this type of thing!

[TheBlueMatt]

Used the constant instead and added a comment to clarify it:

$ git diff-tree -U1 a3163f1dc ee0ffe5df
diff --git a/lightning/src/ln/chan_utils.rs b/lightning/src/ln/chan_utils.rs
index 71cab6af0..da7ba15a1 100644
--- a/lightning/src/ln/chan_utils.rs
+++ b/lightning/src/ln/chan_utils.rs
@@ -41,2 +41,3 @@ use chain;
 
+// Maximum size of a serialized HTLCOutputInCommitment
 const HTLC_OUTPUT_IN_COMMITMENT_SIZE: usize = 1 + 8 + 4 + 32 + 5;
@@ -431,3 +432,3 @@ pub struct HTLCOutputInCommitment {
 impl_writeable_len_match!(HTLCOutputInCommitment, {
-		{ HTLCOutputInCommitment { transaction_output_index: None, .. }, 1 + 8 + 4 + 32 + 1},
+		{ HTLCOutputInCommitment { transaction_output_index: None, .. }, HTLC_OUTPUT_IN_COMMITMENT_SIZE - 4 },
 		{ _, HTLC_OUTPUT_IN_COMMITMENT_SIZE }