Struct Cursor 

pub struct Cursor {
    pub epoch: String,
    pub sequence: u64,
}

A place in one store’s arrival order, and which store’s order it is.

"<epoch>.<sequence>" on the wire, opaque to a caller. The epoch is minted when the store is created, so a cursor a daemon is holding across a restart names an order that no longer exists and is read as “from the beginning” rather than as a sequence this store has not reached yet.

Without it a restart strands every client: the counter begins again at zero, a daemon holding 3 asks for everything after 3, and the answer is empty for as long as it takes the new store to mint four records — which for a quiet account is never. The failure is silent on both sides, which is what makes it worth a self-describing cursor rather than a durable counter.

Fields

epoch: String

Which store’s arrival order this names.

sequence: u64

How far into that order the caller has read.

Implementations

impl Cursor

pub fn read(raw: Option<&str>, epoch: &str) -> u64

Reads a cursor a caller sent back, against the epoch in force now.

Anything that is not this store’s order — a different epoch, a malformed string, an absent cursor — is the beginning of this one. A caller is never told its cursor was discarded, because there is nothing it could usefully do differently: the answer it gets carries the current epoch, and sending that back works.

pub fn wire(epoch: &str, sequence: u64) -> String

The wire form.

Trait Implementations

impl Clone for Cursor

fn clone(&self) -> Cursor

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Cursor

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

Formats the value using the given formatter.

impl PartialEq for Cursor

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for Cursor

impl StructuralPartialEq for Cursor