Enum Boundaries 

#[repr(u32)]
pub enum Boundaries {
    Fuse = 0,
    Preserve = 1,
    Seal = 2,
    Split = 3,
}

What a stage does to the message boundaries passing through it.

Read once, after tocat_init, out of the low two bits of tocat_boundaries. The host folds these along the chain to answer one question per requiring stage: do that stage’s units survive as far as they have to. Nothing here is consulted on the per-chunk path.

Fuse is the default and the safe answer, because it claims nothing: a stage that has not thought about boundaries cannot be relied on to keep them.

Variants

Fuse = 0

Preserve = 1

Seal = 2

Split = 3

Implementations

impl Boundaries

pub const fn from_u32(value: u32) -> Option<Boundaries>

pub const fn as_u32(self) -> u32

pub const fn preserves_messages(self) -> bool

Whether one message arriving still means one message leaving.

True for Preserve and Seal: sealing writes framing into the payload, which changes the bytes of a datagram without changing how many there are. This is what the host warns about on a path whose destination is a datagram endpoint.

pub const fn passes_downstream(self) -> bool

Whether a requirement scanning downwards passes this stage without being settled either way.

Only Preserve does. Seal settles it in favour, the other two against, which is why the scan stops at all three and asks satisfies_downstream which it was.

pub const fn passes_upstream(self) -> bool

Whether a requirement scanning upwards passes this stage without being settled either way.

Seal does, because it emits one unit for every unit it was given; sealing only settles a scan going the other way.

pub const fn satisfies_downstream(self) -> bool

Whether a downstream requirement that reached this stage is met by it, so that nothing below can invalidate it.

pub const fn satisfies_upstream(self) -> bool

Whether an upstream requirement that reached this stage is met by it.

Trait Implementations

impl Clone for Boundaries

fn clone(&self) -> Boundaries

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Boundaries

impl Debug for Boundaries

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

Formats the value using the given formatter.

impl Default for Boundaries

fn default() -> Boundaries

Returns the “default value” for a type.

impl Eq for Boundaries

impl PartialEq for Boundaries

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Boundaries