Struct SubscribeIdAllocator 

pub struct SubscribeIdAllocator {
    next_id: u64,
    max_id: u64,
}

Allocates the Subscribe IDs this endpoint sends.

Section 8.6 defines the field: “Subscribe ID is a variable length integer that MUST be unique and monotonically increasing within a session and MUST be less than the session’s Maximum Subscribe ID.” SUBSCRIBE and FETCH draw from the same sequence, so one allocator serves both.

This draft states no parity rule - the client’s and the server’s ids are not separated by their least significant bit, as they are from draft-11 on - so the sequence simply starts at 0 and steps by one.

The ceiling is exclusive. Section 8.4 gives the Maximum Subscribe ID a starting value of 0 and reads that as “the peer MUST NOT create subscriptions”, which holds only if a ceiling of 0 forbids the id 0 as well.

The ceiling here is the one the peer granted this endpoint. The ceiling a peer’s ids are measured against is the one this endpoint advertised, which is a different number and lives on the endpoint rather than here.

Fields

next_id: u64

max_id: u64

Implementations

impl SubscribeIdAllocator

pub fn new() -> Self

Create an allocator starting at subscribe ID 0, blocked until a peer raises the maximum.

pub fn allocate(&mut self) -> Result<VarInt, SubscribeIdError>

Allocate the next Subscribe ID.

Errors

SubscribeIdError::Blocked if the next id would reach the ceiling.

pub fn update_max(&mut self, new_max: u64) -> Result<(), SubscribeIdError>

Raise the maximum Subscribe ID this endpoint may use.

Section 8.4: “The Maximum Subscribe ID MUST only increase within a session, and receipt of a MAX_SUBSCRIBE_ID message with an equal or smaller Subscribe ID value is a ‘Protocol Violation’.”

Errors

SubscribeIdError::Decreased if the value does not strictly increase.

pub fn is_blocked(&self) -> bool

Whether the next allocation would reach the ceiling.

pub fn max_id(&self) -> u64

The maximum Subscribe ID the peer has granted this endpoint.

Trait Implementations

impl Default for SubscribeIdAllocator

fn default() -> Self

Returns the “default value” for a type.