Adding components

Adding additional components to our module

A single component is like a single function. A collection of components is like a library. It’s a collection of related functions.

Before we think about writing code, we have to define the contract first. The contract is a schema that describes the inputs, outputs, and configuration for a component.

Use wafl component new [component name] to create a new schema quickly. Let’s call this component concatenate.

$ wafl component new concatenate
2022-06-20T22:09:04  INFO Creating new schema for concatenate at schemas/concatenate.apex

Edit the Inputs and Outputs in your schema to look like the following.

type Inputs {
  left: string
  right: string
}

type Outputs {
  output: string
}
Note

Without knowing anything about the implementation, can you guess what this component will do? If you guessed that it is going combine two strings together as output, you’re correct!

Of course this scenario is contrived, but it’s a signature part of contract driven development and extends beyond “Hello World” style tutorials. The contract is often more important than the name.

Generate the new code

The wasmflow code generator will generate all the necessary files based off the .apex files found in ./schemas/.

Run it automatically with:

$ make codegen

Add our concatenation logic

Add this rust code to the new src/components/concatenate.rs file.

pub use crate::components::generated::concatenate::*;

#[async_trait::async_trait]
impl wasmflow_sdk::v1::ephemeral::BatchedComponent for Component {
    async fn job(
        inputs: Self::Inputs,
        outputs: Self::Outputs,
        config: Option<Self::Config>,
    ) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
        outputs
            .output
            .done(format!("{} {}", inputs.left, inputs.right))?;
        Ok(())
    }
}

Build and run our new component

This command looks similar to our last command, but take note that we’re sending data on multiple ports now.

$ make
$ wasmflow invoke ./build/my_project.signed.wasm concatenate -- --left=Hello --right=World
{"output":{"value":"Hello World"}}

Success! Now that we’ve got a module, let’s see how we can turn it into a microservice.