feat: add rfc-compliant syn with payload handling #79
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Overview
This MR introduces SYN_WITH_PAYLOAD_ENABLED configuration option to handle the edge case where a SYN packet contains payload data, ensuring RFC compliance and robustness testing tools passes .
Current Behavior:
lwIP ignores payload in SYN packets and responds with ACK = seqno + 1
Only accounts for the SYN flag, not any accompanying data
Even if is very rarely this behavior is not strictly RFC-compliant ,and can be speculate by security scanners.
RFC Requirement:
According to TCP RFC specifications, the ACK number should reflect the sequence number incremented by:
New behavior:
lwIP SYN packets responds with correct ACK = seqno + the size of any received payload
Benefits:
Explicitly allowed by the TCP specification
Checked by robustness testing tools to validate TCP stack correctness
Used by security scanners to test RFC compliance
Interoperability: Works correctly with all TCP implementations