Enum Attribute 

#[non_exhaustive]
pub enum Attribute {
    RecoveredByFec,
    Retransmission,
    DeliverToApplication,
    TargetBitrateChanged {
        bits_per_second: f64,
    },
    ForcePli {
        ssrcs: Option<Vec<u32>>,
    },
    Custom(Arc<dyn Any + Send + Sync>),
}

A fact about a packet, attached by one interceptor and readable by the rest.

Why it rides with the packet

Because it has to survive the journey. An interceptor that queues a packet and emits it later puts it back on the belt behind itself, where every interceptor ahead sees it again — so what was learned about that packet has to travel with it or be worked out twice. A side channel cannot manage that: it has no way to say which packet it refers to once the packet has been held, reordered or duplicated.

With Ein/Eout left as (), this is the only way information crosses interceptors.

Cost

AttributedPacket holds a Vec, which does not allocate while empty — and most packets carry nothing. Lookup is a linear scan of a handful of words, cheaper than hashing.

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.

RecoveredByFec

Rebuilt by FEC rather than received: these bytes never arrived on the wire.

A NACK generator that sees this must not ask for the packet again.

Retransmission

A retransmission answering a NACK, not a first transmission.

Still new bytes on the wire, which is why a send history has to count it — counting it as an original tells a bandwidth estimator the path is carrying less than it is.

DeliverToApplication

Inbound RTCP an interceptor has decided the application should see.

NoopInterceptor ends the inbound RTCP path unless the packet carries this, which makes forwarding a per-packet judgement by whichever interceptor is qualified to make it, rather than a chain-wide setting.

TargetBitrateChanged

The congestion controller’s estimate, in bits per second.

Rides outbound so the pacer reads it on the way past. A bitrate is connection state rather than a property of the packet carrying it — it travels this way because with no event channel there is nowhere else for it to go.

Fields

bits_per_second: f64

The new target, in bits per second.

ForcePli

Ask the keyframe generator to send a Picture Loss Indication now.

Fields

ssrcs: Option<Vec<u32>>

Which streams to request a keyframe for, or None for all of them.

Custom(Arc<dyn Any + Send + Sync>)

Anything an application defines, so this enum is never a bottleneck on it.

Arc rather than Box so an attributed packet stays cheap to clone — the NACK responder clones into its send buffer and the FEC encoder into its block, and neither should deep-copy an application’s payload. Reached by type: AttributedPacket::custom.

Trait Implementations

impl Clone for Attribute

fn clone(&self) -> Attribute

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Attribute

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

Formats the value using the given formatter.