This Week in Fluvio #12

Welcome to This Week in Fluvio, our weekly newsletter for development updates to Fluvio open source. Fluvio is a distributed, programmable streaming platform written in Rust.

This is an addition to last week’s release of ArrayMap. We have some new examples.

• ArrayMap w/ JSON array inputs
• ArrayMap w/ JSON object inputs
• ArrayMap example code from our previous blog post

Prior to this release, trying to use invalid SmartStream code (but valid Rust code) with a consumer would result in the stream closing without a specific reason being reported to the user.

A user can compile their own SmartStream code, but if they forget to decorate their function with the #[smartstream] attribute, it will still compile because it is valid Rust. However, not all valid Rust code is valid SmartStream code.

Example invalid SmartStream code:

use fluvio_smartstream::{Record, Result};

// Note the missing #[smartstream] attribute that should be here!
pub fn filter(record: &Record) -> Result<bool> {
    let string = std::str::from_utf8(record.value.as_ref())?;
    Ok(string.contains('a'))
}

Previous experience using the invalid SmartStream filter:

$ fluvio consume fruits --tail --filter=crates/fluvio-smartstream/examples/target/wasm32-unknown-unknown/debug/fluvio_wasm_filter.wasm
Consuming records starting 10 from the end of topic 'fruits'
Consumer stream has closed

Now, if a user tries to use incorrectly compiled SmartStream code they will receive an error message.

$ fluvio consume fruits --tail --filter=crates/fluvio-smartstream/examples/target/wasm32-unknown-unknown/debug/fluvio_wasm_filter.wasm
Consuming records starting 10 from the end of topic 'fruits'
Error:
   0: Fluvio client error
   1: SmartStream error
   2: WASM module is not a valid 'filter' SmartStream. Are you missing a #[smartstream(filter)] attribute?

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For the full list of changes this week, be sure to check out our CHANGELOG.

Until next week!