Struct FileBatchContext 

pub struct FileBatchContext { /* private fields */ }

The file transport’s subscription-scoped batch context: the subscription’s own seeker, shared by every delivery of the batch.

The runtime builds one per dispatched batch from the batch’s first delivery, and a batch body reads it by key - SeekHandle. Per-delivery data (a Position) has no place here: a batch spans many deliveries, so the position a body reacts to rides the elements themselves, and keeping this a separate type from FileContext is what rejects a batch body asking for per-delivery fields at compile time.

Examples

The batch settles first, so a seek from its body applies to the batches after it:

use ruststream_sea_file::file::prelude::*;
use serde::Deserialize;

#[derive(Debug, Deserialize)]
struct Job {
    id: u64,
    resume_at: Option<u64>,
}

#[subscriber(FileStream::new("jobs"), start_at(FilePosition::beginning()))]
async fn drain(jobs: &[Job], ctx: &mut Context<'_, FileBatchContext>) -> HandlerOutcome {
    tracing::info!(jobs = jobs.len(), "drained");
    let Some(resume_at) = jobs.iter().find_map(|job| job.resume_at) else {
        return HandlerOutcome::ack();
    };
    if let Err(error) = ctx
        .context(SeekHandle)
        .seek(FilePosition::sequence(resume_at))
        .await
    {
        tracing::warn!(resume_at, %error, "seek refused");
    }
    HandlerOutcome::ack()
}

#[ruststream::app]
fn app() -> impl App {
    RustStream::new(AppInfo::new("worker", "0.1.0"))
        .with_broker(FileBroker::new("/tmp/jobs.ss"), |b| {
            b.include(drain.batch(nonzero!(3)));
        })
}

A batch body that asks for a per-delivery position does not compile: Position is a key of FileContext alone.

use ruststream_sea_file::file::prelude::*;
use serde::Deserialize;

#[derive(Debug, Deserialize)]
struct Job {
    id: u64,
}

#[subscriber(FileStream::new("jobs"))]
async fn drain(jobs: &[Job], ctx: &mut Context<'_, FileBatchContext>) -> HandlerOutcome {
    let first: FilePosition = ctx.context(Position);
    tracing::info!(jobs = jobs.len(), ?first, "drained");
    HandlerOutcome::ack()
}

Trait Implementations

impl BuildBatchContext<FileMessage> for FileBatchContext

fn build(first: &FileMessage) -> Self

Builds the context value by reading subscription-scoped fields out of the batch’s first delivery, or out of the batch itself where it lends its values as one slice.

impl Debug for FileBatchContext

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

Formats the value using the given formatter.

impl Field<FileBatchContext> for SeekHandle

type Value<'a> = &'a FileSeeker

The value read through this key, borrowed from the source for 'a.

fn get(self, src: &FileBatchContext) -> &FileSeeker

Reads this key’s field out of src.