Format log context only when a line is logged - #98
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The session loop built the `local { seq, ack }` string and the header
description for every packet, and poll_write another string for every
held write, whatever the log level. At the default level none of them is
ever printed, so every packet paid for an allocation and a format that
went unused. The context is now a value that formats itself when a log
line is emitted, and the header description is built only when trace is
enabled.
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The session loop builds
format!("local {{ seq: {seq}, ack: {ack} }}")andtcp_header_fmt(tcp_header)for every packet, andpoll_writebuilds another string for every held write, whatever the log level. At the default level none of them is printed, so every packet pays for allocations and formatting that go unused. In a profile of a 600 Mbit/s tunnel these showed up ascore::fmtplus the matchingmalloc/freeon every packet.l_infois now a smallLocalInfo(seq, ack)value that implementsDisplay, so it formats only inside a log line that is actually emitted. The six call sites are unchanged apart from the constructor.log::log_enabled!(log::Level::Trace).trace!.Log output is identical at every level.
cargo fmt --check,cargo clippy --all-targets(no warnings) andcargo testpass.🤖 Generated with Claude Code