Module logfmt 

Formatting helpers for log fields.

Operator-facing fields print the value, never Rust’s Option spelling: a line reads alpn=h3, not alpn=Some("h3"). When the value is absent the field still appears, carrying ABSENT — dropping it instead would make the shape of the line depend on its contents, which is exactly what a grep or a log shipper cannot cope with.

The rule is about audience, not about level: info/warn lines are read by whoever is running the server, so they print values. The debug forensic dump in crate::conn deliberately keeps Debug shapes — there the Rust spelling of a header map, or of an absent :protocol, is the evidence D3 is waiting for.

The third rule is about provenance: or_dash prints with Display, which escapes nothing, so it is only for values the server produced or validated itself — the ALPN it negotiated from its own list, the SNI rustls accepted as a DNS name, a SocketAddr it resolved. Bytes the peer chose (the user-id of a rejected credential) are recorded as a plain str field instead, which tracing prints quoted and Debug-escaped: username="user1", and a newline or a terminal escape sequence inside it stays on the one line, spelled out. systemd splits a service’s stdout on \n, so an unescaped newline would otherwise hand an unauthenticated client a journal entry of its own.

The fourth rule is about size: several of those peer-chosen values are a whole field section’s worth of bytes, so bounded caps what any one of them can write into the journal. Length and provenance are separate concerns, and both apply to the same fields – bounded does not escape anything, and recording its result with % would undo the third rule.

Some peer bytes have no field of their own to be recorded in: they arrive already inside somebody else’s Display, and the log sees only the sentence they ended up in – a QUIC close reason phrase inside the error the closing line reports, say. The sigil cannot save those, because by the time the sigil is chosen the peer’s bytes are already part of a value that formats itself. escaped_bytes is the answer for them: applied where the peer’s bytes enter the value rather than where the value is logged, it applies both rules at once and hands back something the rest of the program may print with Display from then on. peer_error is that answer applied to the value this server meets it in – a QUIC connection error – so that the two places one of those reaches a log line apply the rule by calling the same name.

Structs

Sampler

How often a warning a peer can repeat at will is allowed to be loud.

Constants

ABSENT

What an absent value prints as.

Functions

addresses

Renders a resolved address list at a length a log line can afford.

bounded

Caps a peer-chosen token at what a log line can afford to carry.

bounded_bytes

bounded for bytes that are not known to be UTF-8.

escaped_bytes

bounded_bytes with the escaping applied too, for peer bytes that will be printed with Display.

or_dash

Formats an optional log field: the value itself, or ABSENT.

peer_error

The same error, with any reason phrase the peer wrote passed through escaped_bytes.