Inter Process

SeaStreamer encourages you to write small stream processors and connect them together, instead of making one giant processor with lots of options.

The unix pipe is a great invention, which makes anyone a text processing wizard by assembling programs in the shell!

What if we can also work with event streams in the same way?

With SeaStreamer, you can connect processors together with pipes:

processor_a | processor_b

You can also connect them asynchronously with files:

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

Or with the File backend:

file=/tmp/sea-streamer-$(date +%s)
touch $file
processor_a --output file://$file
processor_b --input  file://$file

Trying out

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

Stdio message format

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.