microsoft/msquic

Simplify ALPN re-negotiation path

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#6,239 opened on Aug 18, 2026

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Area: Coregood first issue

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Description

We could probably simplify the ALPN negotiation by only storing the list until the ALPN is fully negotiated.

• In  QuicBindingAcceptConnection , own-copy  ClientAlpnList  but leave  NegotiatedAlpn == NULL . - ClientAlpnList can use SmallAlpnBuffer if the full list fit in it • In  QuicCryptoReNegotiateAlpn , remove the  PrevNegotiatedAlpn  fast path and single-ALPN fallback. • Select from the copied client list, then allocate/copy and assign NegotiatedAlpn . • Preserve Info->NegotiatedAlpn ; the listener callback still exposes that independently. • Keep teardown null-safe.

Originally posted by @guhetier in https://github.com/microsoft/msquic/pull/6171#discussion_r3799265048

Contributor guide

Research direction
Explore the MSQuic repository, locate the QUIC binding accept flow and the ALPN re negotiation logic, review the referenced PR discussion for context, and outline a minimal refactoring plan that follows the suggested steps.
Tech stack
c
Domain
networkingbackend
Issue type
Refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
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Active
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Clear
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CGit
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60