fix: handle fragmented ClientHello in auto-sense server#87
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Fixes #88 |
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Firefox 148+ sends X25519MLKEM768 as its primary key_share, making the ClientHello too large for a single DTLS record. The supported_versions extension ends up in a later fragment, causing the auto-sense server to miss it and fall back to DTLS 1.2. Replace the lightweight packet-sniffing version detection (ServerPending) with a design that uses Server13 directly in auto mode. The DTLS 1.3 engine handles fragment reassembly natively. After reassembling the complete ClientHello: - If supported_versions contains DTLS 1.3: proceed as 1.3 (zero overhead) - If not: return Error::Dtls12Fallback, create Server12, replay packets Changes: - Add Error::Dtls12Fallback variant - Add auto_mode + auto_packets to Server13 - Remove ServerPending from Inner enum and detect.rs - new_auto() creates Server13::new_auto(), falls back to Server12 on Dtls12Fallback or ParseError - Server13 buffers raw packets during AwaitClientHello, frees on commit - 47 new tests: server_fallback (15) + cross_matrix (32) covering all version combinations at normal/fragmented/heavy MTU
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algesten
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Mar 9, 2026
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Firefox 148+ sends X25519MLKEM768 as its primary key_share, making the ClientHello too large for a single DTLS record. The supported_versions extension ends up in a later fragment, causing the auto-sense server to miss it and fall back to DTLS 1.2.
Replace the lightweight packet-sniffing version detection (ServerPending) with a design that uses Server13 directly in auto mode. The DTLS 1.3 engine handles fragment reassembly natively. After reassembling the complete ClientHello:
Changes: