krafka 0.7.0

A pure Rust, async-native Apache Kafka client
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94

//! Async [`Stream`] adapter for the consumer.
//!
//! [`ConsumerStream`] wraps a reference to a [`Consumer`] and implements
//! [`futures_core::Stream`], yielding individual [`ConsumerRecord`]s.
//! This enables interop with the `tokio-stream` combinator ecosystem
//! (`.map()`, `.filter()`, `.take()`, `.buffer_unordered()`, etc.).
//!
//! # Example
//!
//! ```ignore
//! use tokio_stream::StreamExt;
//!
//! let mut stream = consumer.stream();
//! while let Some(result) = stream.next().await {
//!     let record = result?;
//!     println!("{}: {}", record.topic, record.offset);
//! }
//! ```
//!
//! [`Stream`]: futures_core::Stream

use std::pin::Pin;
use std::task::{Context, Poll};

use futures_core::Stream;
use tokio_util::sync::ReusableBoxFuture;

use super::Consumer;
use super::record::ConsumerRecord;
use crate::error::Result;

/// Async stream of [`ConsumerRecord`]s from a [`Consumer`].
///
/// Created by [`Consumer::stream()`]. Each call to [`Stream::poll_next()`]
/// drives the underlying [`Consumer::recv()`] method, which handles polling
/// the broker, buffering, auto-commit, rebalancing, and shutdown detection.
///
/// The stream terminates (returns `None`) when the consumer is closed.
/// Errors from the broker or network are propagated as `Some(Err(...))`.
pub struct ConsumerStream<'a> {
    consumer: &'a Consumer,
    /// Reusable boxed future for the in-progress `recv()` call.
    /// Avoids a fresh heap allocation per record by reusing the box
    /// when the future's size and alignment match (which they always
    /// do since `recv()` returns the same concrete type each time).
    fut: ReusableBoxFuture<'a, Result<Option<ConsumerRecord>>>,
    /// Set to `true` once `recv()` returns `Ok(None)` (consumer closed).
    /// After that, `poll_next` returns `None` without starting new calls.
    done: bool,
}

impl<'a> ConsumerStream<'a> {
    /// Create a new stream wrapping the given consumer.
    pub(super) fn new(consumer: &'a Consumer) -> Self {
        Self {
            fut: ReusableBoxFuture::new(consumer.recv()),
            consumer,
            done: false,
        }
    }
}

impl Stream for ConsumerStream<'_> {
    type Item = Result<ConsumerRecord>;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let this = self.get_mut();

        if this.done {
            return Poll::Ready(None);
        }

        match this.fut.poll(cx) {
            Poll::Pending => Poll::Pending,
            Poll::Ready(result) => match result {
                Ok(Some(record)) => {
                    // Reuse the allocation for the next recv() call.
                    this.fut.set(this.consumer.recv());
                    Poll::Ready(Some(Ok(record)))
                }
                Ok(None) => {
                    // Consumer closed — fuse the stream.
                    this.done = true;
                    Poll::Ready(None)
                }
                Err(e) => {
                    // Reuse the allocation for the next recv() call.
                    this.fut.set(this.consumer.recv());
                    Poll::Ready(Some(Err(e)))
                }
            },
        }
    }
}