Moving our endpoints to a library

The idea behind this section is to move our endpoints to a library so that we can reuse them in case we want to provide a different binary that doesn't rely on Shuttle.

Imagine, for example, that you want to deploy your API to your cloud of choice. Most probably you'll want to use a container to do so. In that case, having our endpoints in a library will allow us to create a binary that works purely on Actix Web.

Adding a local dependency

Remember that we already created a lib crate in one of the previous sections? Well, we are going to use that crate to move our endpoints there.

But first of all, we need to add a dependency to our api-shuttle Cargo.toml file. We can do so by adding the following line:

[dependencies]
...
api-lib = { path = "../lib" }

api-lib is the name we gave to that library (you can check that in the Cargo.toml file in the api > lib folder).

Compile and check that you don't receive any compiler error:

# just compile
cargo build
# or compile in watch mode
cargo watch -x build
# or run the binary
cargo shuttle run
# or run the binary in watch mode
cargo watch -x "shuttle run"

As you can see, adding a local dependency is trivial. You just need to specify the path to the library.

Moving the endpoints

Open the api > lib > src folder and create a new file called health.rs. This file will contain just one endpoint that will be used to check the health of the API, but for the sake of the example, we are going to temporary move our previous endpoints here.

Copy the following code in api > shuttle > src > main.rs to our recently created file health.rs:

#![allow(unused)]
fn main() {
#[get("/")]
async fn hello_world() -> &'static str {
    "Hello World!"
}

#[get("/version")]
async fn version(db: actix_web::web::Data<sqlx::PgPool>) -> String {
    tracing::info!("Getting version");
    let result: Result<String, sqlx::Error> = sqlx::query_scalar("SELECT version()")
        .fetch_one(db.get_ref())
        .await;

    match result {
        Ok(version) => version,
        Err(e) => format!("Error: {:?}", e),
    }
}
}

Let's use it now. Open the api > lib > src > lib.rs file, remove all the content, and add the following line at the top of the file:

#![allow(unused)]
fn main() {
pub mod health;
}

A couple of things to take into account here:

• lib.rs files are the default entrypoint for library crates.
• The line we introduced in the lib.rs file is doing two things.
  • First of all, it is declaring a new module called health (hence the compiler will care about our health.rs file's content).
  • Secondly, it is making that module public. This means that we can access everything that we export from that module.

Now, if you compile, you should be getting errors from the compiler complaining about dependencies. Let's add them to the Cargo.toml file:

[dependencies]
# actix
actix-web = "4.3.1"
# database
sqlx = { version = "0.7", default-features = false, features = [
    "tls-native-tls",
    "macros",
    "postgres",
    "uuid",
    "chrono",
    "json",
] }
# tracing
tracing = "0.1"

We will be adding more dependencies in the future, but for now, this is enough.

Finally, to make the compiler happy, let's import this in the top of the health.rs file:

#![allow(unused)]
fn main() {
use actix_web::get;
}

Everything should compile by now.

Using the endpoints

Now that we have our endpoints in a library, we can use them in our main.rs file. Let's do that.

Open the api > shuttle > src > main.rs file and remove the endpoints code that we copied before. Get rid of the unused use statements as well.

Do you know what to do next?

#![allow(unused)]
fn main() {
use api_lib::health::{hello_world, version};
}

Is it working? It should!

Commit your changes:

git add .
git commit -m "move endpoints to a library"