Enum Failure 

#[non_exhaustive]
pub enum Failure {
    Connection,
    Exhausted,
    Unknown,
}

What a failed accept(2) means for the listener that saw it.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Connection

One pending connection died on its way to us: the peer reset it before we dequeued it, a firewall rule dropped it, its handshake timed out.

Ordinary traffic, and never a fault of the listener. The queue entry is consumed, so the very next accept makes progress and delaying it would only punish the connections queued behind the dead one, at whatever rate a remote peer chooses to supply them.

How reachable that is depends on the platform. Linux surfaces a new socket’s already-pending network errors through accept (which BSD does not, and which is why the list is as long as it is), but drops a connection reset before accept from the queue silently rather than reporting ECONNABORTED. So the simplest flood is louder on BSD than on Linux; the handling is the same either way.

Exhausted

A resource accept needs is exhausted process-wide or host-wide: the process fd table (EMFILE), the system-wide one (ENFILE), or kernel memory for the new socket (ENOBUFS/ENOMEM).

The connection stays queued, so the listener is instantly readable and instantly failing until something outside this loop returns the resource.

Unknown

An errno we don’t recognize. Worth backing off on, never worth claiming a cause for: an unrecognized failure on ordinary traffic could be driven by a remote peer, so escalating on it hands out a remote lever.

Implementations

impl Failure

pub const ALL: &'static [Failure]

Every class, for a caller enumerating Health::failures into a metrics endpoint.

A slice rather than an array: the length of an array is part of the type, so [Failure; 3] would make adding a class a breaking change for every caller that named the type, defeating the #[non_exhaustive] above.

pub fn classify(err: &Error) -> Self

Classify a failed accept(2).

Unrecognized is Unknown, never Connection: the default has to be the one that paces, because guessing “per connection” on a listener-wide failure is the mistake that spins.

pub const fn as_str(self) -> &'static str

The stable lowercase name used in logs and metric labels.

Trait Implementations

impl Clone for Failure

fn clone(&self) -> Failure

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Failure

impl Debug for Failure

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for Failure

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Failure

impl Hash for Failure

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Failure

fn eq(&self, other: &Failure) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Failure