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Update libSession to 1.9.4 and cap the QUIC UDP payload at 1372 - #810
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mpretty-cyro merged 1 commit intoOct 8, 2026
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1.9.4 adds quic_max_udp_payload. Setting it replaces quic_disable_mtu_discovery, which pinned datagrams to the 1200-byte minimum and advertised that as the client's maximum. Path-MTU discovery can now grow up to 1372 bytes, but no further.
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Changes
libsession-util-spmfrom 1.9.2 to 1.9.4 (exactVersionin the project;Package.resolved→1743d909e49a).config.quic_disable_mtu_discovery = truewithconfig.quic_max_udp_payload = 1372inLibSession+Networking.swift.quic_max_udp_payloadis new in libsession 1.9.3/1.9.4 (a9bafa6c, "Add opt::quic_max_udp_payload"). When non-zero it takes precedence overquic_disable_mtu_discovery, which with libquic 1.11 amounts to a hard 1200-byte cap. With that cap, the client also advertises 1200 as its maximum UDP payload, so service nodes send it smaller packets, which probably slows downloads. The new setting still prevents oversized datagrams, which some mobile networks silently drop, but lets path-MTU discovery go up to 1372 bytes.1.9.4 is used rather than 1.9.3 because the 1.9.3 xcframework doesn't link: it shipped without its bundled dependencies. That was fixed in session-foundation/libsession#181.
The 1.9.4 package relies on the system
iconv: its modulemap autolinks it for the SPM path, and #809 covers the build-from-source path.Verification
Xcode 27.0 (27A266a), iPhone 17 simulator, iOS 27.0, on
dev048c84636c:link "iconv"in its modulemap. The Session 2.0 regression build also built it independently.SessionTests,SessionMessagingKitTests,SessionNetworkingKitTests,SessionUtilitiesKitTests,SessionUIKitTests) against the published 1.9.4 package at1af286ce8d: 2252/2252 passed, 0 failed.ThreadDisappearingMessagesSettingsViewModelSpecis flaky on 1.9.2 too (4 of 5 runs fail), so one red run of it isn't caused by this change.