L2 bridge: safer callhook interface

[pcarranzav]

• Make the L2 gateway functions non-reentrant for additional safety
• Change the callhooks to only call an onTokenTransfer function, to limit the potential impact of a compromised whitelisted L1 sender

[codecov]

Codecov Report

Base: 91.51% // Head: 91.53% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (394458d) compared to base (105b4f0).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 394458d differs from pull request most recent head 8aa3bd6. Consider uploading reports for the commit 8aa3bd6 to get more accurate results

Additional details and impacted files

@@                Coverage Diff                @@
##           pcv/l2-bridge     #719      +/-   ##
=================================================
+ Coverage          91.51%   91.53%   +0.01%     
=================================================
  Files                 41       42       +1     
  Lines               1980     1984       +4     
  Branches             346      346              
=================================================
+ Hits                1812     1816       +4     
  Misses               168      168              

Flag	Coverage Δ
unittests	91.53% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
contracts/l2/gateway/L2GraphTokenGateway.sol	100.00% <100.00%> (ø)
contracts/tests/CallhookReceiverMock.sol	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[tmigone]

Nice!

It might be overkill but how about adding another mock contract that doesn't implement the callhook interface and then adding a test to verify the callhook execution fails?

[pcarranzav]

Good idea on the additional test @tmigone - we can use any contract so I just used RewardsManager rather than adding a new mock