created_at2023-03-02 16:45:30.371779
updated_at2024-04-24 18:04:40.035631
description🌊 The stream processing toolkit for Rust
Chris Tsang (tyt2y3)




🌊 A real-time stream processing toolkit for Rust

crate docs build status

SeaStreamer is a toolkit to help you build real-time stream processors in Rust.


  1. Async

SeaStreamer provides an async API, and it supports both tokio and async-std. In tandem with other async Rust libraries, you can build highly concurrent stream processors.

  1. Generic

We provide integration for Redis & Kafka / Redpanda behind a generic trait interface, so your program can be backend-agnostic.

  1. Testable

SeaStreamer also provides a set of tools to work with streams via unix pipes, so it is testable without setting up a cluster, and extremely handy when working locally.

  1. Micro-service Oriented

Let's build real-time (multi-threaded, no GC), self-contained (aka easy to deploy), low-resource-usage, long-running stream processors in Rust!

Quick Start

Add the following to your Cargo.toml

sea-streamer = { version = "0", features = ["kafka", "redis", "stdio", "socket", "runtime-tokio"] }

Here is a basic stream consumer:

async fn main() -> Result<()> {

    let Args { stream } = Args::parse();

    let streamer = SeaStreamer::connect(stream.streamer(), Default::default()).await?;

    let mut options = SeaConsumerOptions::new(ConsumerMode::RealTime);

    let consumer: SeaConsumer = streamer
        .create_consumer(stream.stream_keys(), options)

    loop {
        let mess: SeaMessage =;
        println!("[{}] {}", mess.timestamp(), mess.message().as_str()?);

Here is a basic stream producer:

async fn main() -> Result<()> {

    let Args { stream } = Args::parse();

    let streamer = SeaStreamer::connect(stream.streamer(), Default::default()).await?;

    let producer: SeaProducer = streamer
        .create_producer(stream.stream_key()?, Default::default())

    for tick in 0..100 {
        let message = format!(r#""tick {tick}""#);

    producer.end().await?; // flush


Here is a basic stream processor. See also other advanced stream processors.

async fn main() -> Result<()> {

    let Args { input, output } = Args::parse();

    let streamer = SeaStreamer::connect(input.streamer(), Default::default()).await?;
    let options = SeaConsumerOptions::new(ConsumerMode::RealTime);
    let consumer: SeaConsumer = streamer
        .create_consumer(input.stream_keys(), options)

    let streamer = SeaStreamer::connect(output.streamer(), Default::default()).await?;
    let producer: SeaProducer = streamer
        .create_producer(output.stream_key()?, Default::default())

    loop {
        let message: SeaMessage =;
        let message = process(message).await?;
        producer.send(message)?; // send is non-blocking

Now, let's put them into action.

With Redis / Kafka:

STREAMER_URI="redis://localhost:6379" # or

# Produce some input
cargo run --bin producer -- --stream $STREAMER_URI/hello1 &
# Start the processor, producing some output
cargo run --bin processor -- --input $STREAMER_URI/hello1 --output $STREAMER_URI/hello2 &
# Replay the output
cargo run --bin consumer -- --stream $STREAMER_URI/hello2
# Remember to stop the processes
kill %1 %2

With Stdio:

# Pipe the producer to the processor
cargo run --bin producer -- --stream stdio:///hello1 | \
cargo run --bin processor -- --input stdio:///hello1 --output stdio:///hello2


The architecture of sea-streamer is constructed by a number of sub-crates:

All crates share the same major version. So 0.1 of sea-streamer depends on 0.1 of sea-streamer-socket.

sea-streamer-types: Traits & Types

This crate defines all the traits and types for the SeaStreamer API, but does not provide any implementation.

sea-streamer-socket: Backend-agnostic Socket API

Akin to how SeaORM allows you to build applications for different databases, SeaStreamer allows you to build stream processors for different streaming servers.

While the sea-streamer-types crate provides a nice trait-based abstraction, this crates provides a concrete-type API, so that your program can stream from/to any SeaStreamer backend selected by the user on runtime.

This allows you to do neat things, like generating data locally and then stream them to Redis / Kafka. Or in the other way, sink data from server to work on them locally. All without recompiling the stream processor.

If you only ever work with one backend, feel free to depend on sea-streamer-redis / sea-streamer-kafka directly.

A small number of cli programs are provided for demonstration. Let's set them up first:

# The `clock` program generate messages in the form of `{ "tick": N }`
alias clock='cargo run --package sea-streamer-stdio  --features=executables --bin clock'
# The `relay` program redirect messages from `input` to `output`
alias relay='cargo run --package sea-streamer-socket --features=executables,backend-kafka,backend-redis --bin relay'

Here is how to stream from Stdio ➡️ Redis / Kafka. We generate messages using clock and then pipe it to relay, which then streams to Redis / Kafka:

# Stdio -> Redis
clock -- --stream clock --interval 1s | \
relay -- --input stdio:///clock --output redis://localhost:6379/clock
# Stdio -> Kafka
clock -- --stream clock --interval 1s | \
relay -- --input stdio:///clock --output kafka://localhost:9092/clock

Here is how to stream between Redis ↔️ Kafka:

# Redis -> Kafka
relay -- --input redis://localhost:6379/clock --output kafka://localhost:9092/clock
# Kafka -> Redis
relay -- --input kafka://localhost:9092/clock --output redis://localhost:6379/clock

Here is how to replay the stream from Kafka / Redis:

relay -- --input redis://localhost:6379/clock --output stdio:///clock --offset start
relay -- --input kafka://localhost:9092/clock --output stdio:///clock --offset start

sea-streamer-kafka: Kafka / Redpanda Backend

This is the Kafka / Redpanda backend implementation for SeaStreamer. This crate provides a comprehensive type system that makes working with Kafka easier and safer.

First of all, all API (many are sync) are properly wrapped as async. Methods are also marked &mut to eliminate possible race conditions.

KafkaConsumerOptions has typed parameters.

KafkaConsumer allows you to seek to point in time, rewind to particular offset, and commit message read.

KafkaProducer allows you to await a send Receipt or discard it if you are uninterested. You can also flush the Producer.

KafkaStreamer allows you to flush all producers on disconnect.

See tests for an illustration of the stream semantics.

This crate depends on rdkafka, which in turn depends on librdkafka-sys, which itself is a wrapper of librdkafka.

Configuration Reference:

sea-streamer-redis: Redis Backend

This is the Redis backend implementation for SeaStreamer. This crate provides a high-level async API on top of Redis that makes working with Redis Streams fool-proof:

  • Implements the familiar SeaStreamer abstract interface
  • A comprehensive type system that guides/restricts you with the API
  • High-level API, so you don't call XADD, XREAD or XACK anymore
  • Mutex-free implementation: concurrency achieved by message passing
  • Pipelined XADD and paged XREAD, with a throughput in the realm of 100k messages per second

While we'd like to provide a Kafka-like client experience, there are some fundamental differences between Redis and Kafka:

  1. In Redis sequence numbers are not contiguous
    1. In Kafka sequence numbers are contiguous
  2. In Redis messages are dispatched to consumers among group members in a first-ask-first-served manner, which leads to the next point
    1. In Kafka consumer <-> shard is 1 to 1 in a consumer group
  3. In Redis ACK has to be done per message
    1. In Kafka only 1 Ack (read-up-to) is needed for a series of reads

What's already implemented:

  • RealTime mode with AutoStreamReset
  • Resumable mode with auto-ack and/or auto-commit
  • LoadBalanced mode with failover behaviour
  • Seek/rewind to point in time
  • Basic stream sharding: split a stream into multiple sub-streams

It's best to look through the tests for an illustration of the different streaming behaviour.

How SeaStreamer offers better concurrency?

Consider the following simple stream processor:

loop {
    let input = XREAD.await;
    let output = process(input).await;

When it's reading or writing, it's not processing. So it's wasting time idle and reading messages with a higher delay, which in turn limits the throughput. In addition, the ideal batch size for reads may not be the ideal batch size for writes.

With SeaStreamer, the read and write loops are separated from your process loop, so they can all happen in parallel (async in Rust is multi-threaded, so it is truely parallel)!

If you are reading from a consumer group, you also have to consider when to ACK and how many ACKs to batch in one request. SeaStreamer can commit in the background on a regular interval, or you can commit asynchronously without blocking your process loop.

In the future, we'd like to support Redis Cluster, because sharding without clustering is not very useful. Right now it's pretty much a work-in-progress. It's quite a difficult task, because clients have to take responsibility when working with a cluster. In Redis, shards and nodes is a M-N mapping - shards can be moved among nodes at any time. It makes testing much more difficult. Let us know if you'd like to help!

There is also a small utility to dump Redis Streams messages into a SeaStreamer file.

This crate is built on top of redis.

sea-streamer-stdio: Standard I/O Backend

This is the stdio backend implementation for SeaStreamer. It is designed to be connected together with unix pipes, enabling great flexibility when developing stream processors or processing data locally.

You can connect processors together with pipes: processor_a | processor_b.

You can also connect them asynchronously:

touch stream # set up an empty file
tail -f stream | processor_b # program b can be spawned anytime
processor_a >> stream # append to the file

You can also use cat to replay a file, but it runs from start to end as fast as possible then stops, which may or may not be the desired behavior.

You can write any valid UTF-8 string to stdin and each line will be considered a message. In addition, you can write some message meta in a simple format:

[timestamp | stream_key | sequence | shard_id] payload

Note: the square brackets are literal [ ].

The following are all valid:

a plain, raw message
[2022-01-01T00:00:00] { "payload": "anything" }
[2022-01-01T00:00:00.123 | my_topic] "a string payload"
[2022-01-01T00:00:00 | my-topic-2 | 123] ["array", "of", "values"]
[2022-01-01T00:00:00 | my-topic-2 | 123 | 4] { "payload": "anything" }
[my_topic] a string payload
[my_topic | 123] { "payload": "anything" }
[my_topic | 123 | 4] { "payload": "anything" }

The following are all invalid:

[Jan 1, 2022] { "payload": "anything" }
[2022-01-01T00:00:00] 12345

If no stream key is given, it will be assigned the name broadcast and sent to all consumers.

You can create consumers that subscribe to only a subset of the topics.

Consumers in the same ConsumerGroup will be load balanced (in a round-robin fashion), meaning you can spawn multiple async tasks to process messages in parallel.

sea-streamer-file: File Backend

This is very similar to sea-streamer-stdio, but the difference is SeaStreamerStdio works in real-time, while sea-streamer-file works in real-time and replay. That means, SeaStreamerFile has the ability to traverse a .ss (sea-stream) file and seek/rewind to a particular timestamp/offset.

In addition, Stdio can only work with UTF-8 text data, while File is able to work with binary data. In Stdio, there is only one Streamer per process. In File, there can be multiple independent Streamers in the same process. Afterall, a Streamer is just a file.

The basic idea of SeaStreamerFile is like a tail -f with one message per line, with a custom message frame carrying binary payloads. The interesting part is, in SeaStreamer, we do not use delimiters to separate messages. This removes the overhead of encoding/decoding message payloads. But it added some complexity to the file format.

The SeaStreamerFile format is designed for efficient fast-forward and seeking. This is enabled by placing an array of Beacons at fixed interval in the file. A Beacon contains a summary of the streams, so it acts like an inplace index. It also allows readers to align with the message boundaries. To learn more about the file format, read src/

On top of that, are the high-level SeaStreamer multi-producer, multi-consumer stream semantics, resembling the behaviour of other SeaStreamer backends. In particular, the load-balancing behaviour is same as Stdio, i.e. round-robin.


We provide a small utility to decode .ss files:

cargo install sea-streamer-file --features=executables --bin ss-decode
 # local version
alias ss-decode='cargo run --package sea-streamer-file --features=executables --bin ss-decode'
ss-decode -- --file <file> --format <format>

Pro tip: pipe it to less for pagination

ss-decode --file | less

Example log format:

 # header
[2023-06-05T13:55:53.001 | hello | 1 | 0] message-1
 # beacon

Example ndjson format:

/* header */
/* beacon */

There is also a Typescript implementation under sea-streamer-file-reader.


  1. Resumable: currently unimplemented. A potential implementation might be to commit into a local SQLite database.
  2. Sharding: currently it only streams to Shard ZERO.
  3. Verify: a utility program to verify and repair SeaStreamer binary file.

sea-streamer-runtime: Async runtime abstraction

This crate provides a small set of functions aligning the type signatures between async-std and tokio, so that you can build applications generic to both runtimes.


Licensed under either of

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We invite you to participate, contribute and together help build Rust's future.

Commit count: 344

cargo fmt