Struct CutReader 

pub struct CutReader { /* private fields */ }

Reads the cuts a barrier coordinator published to __barrier_state.

The reader drives the runtime’s own RecordFetcher with a manual read of every partition of the topic, so it joins no consumer group and needs no new broker RPC. The first read starts at offset 0 of each partition. A later read continues where the previous one stopped, so it costs one fetch per partition of the records the coordinator published since.

The reader keeps complete cuts only. A partial cut names partitions that never received the epoch’s marker, so a task that waited for one would wait forever. That is why the coordinator publishes partial cuts at all: a reader skips the epoch instead of stalling on markers that never arrive.

Examples

use std::sync::Arc;

use krabka_client_streams::{barrier::CutReader, runtime::RecordFetcher};

let mut reader = CutReader::new(fetcher);
if let Some(cut) = reader.latest_complete_cut("transactions").await? {
    println!("epoch {} at {:?}", cut.epoch, cut.offsets);
}

Implementations

impl CutReader

pub fn new(fetcher: Arc<dyn RecordFetcher>) -> Self

Creates a reader over the __barrier_state topic.

pub fn with_topic( fetcher: Arc<dyn RecordFetcher>, topic: impl Into<String>, ) -> Self

Creates a reader over another topic than __barrier_state.

pub async fn latest_complete_cut( &mut self, group: &str, ) -> Result<Option<BarrierCut>, StreamsClientError>

The complete cut of a barrier group with the highest epoch.

The result is None when the topic holds no complete cut of that group.

Errors

Returns the fetcher’s error, or StreamsClientError::BarrierFormat when a record does not match the frozen layout.

pub async fn complete_cuts_after( &mut self, group: &str, epoch: i64, ) -> Result<Vec<BarrierCut>, StreamsClientError>

The complete cuts of a barrier group above epoch, oldest first.

Pass -1 to get every complete cut. Partial cuts are left out.

Errors

Returns the fetcher’s error, or StreamsClientError::BarrierFormat when a record does not match the frozen layout.

pub async fn complete_cut_at( &mut self, group: &str, epoch: i64, ) -> Result<Option<BarrierCut>, StreamsClientError>

The complete cut of one epoch, or None when the topic holds no such cut.

Errors

Returns the fetcher’s error, or StreamsClientError::BarrierFormat when a record does not match the frozen layout.