Return JSON with an HTTP status other than 200 in Rocket - rest

Question

I want my Rocket API to have a route like this:
#[post("create/thing", format = "application/json", data="<thing>")]
When the client sends { "name": "mything" }, everything should be alright and I know how to do that, but when it sends { "name": "foo" } it should respond with something like this:
HTTP/1.1 422 Unprocessable Entity
Content-Type: application/json
{
"errors": [
{
"status": "422",
"title": "Invalid thing name",
"detail": "The name for a thing must be at least 4 characters long."
}
]
}
How do I respond with a result like a JSON object and a HTTP status code different than 200 in Rocket?
This is what I tried so far:
impl FromRequest for my Thing type. This lets me choose a status code as I can write my own from_request function, but I can't return anything else.
Registering an error catcher like in this example, but this way I only can react to one HTTP status code without context. I have too many failure modes to reserve one HTTP status code for each.

Answer 1

With #hellow's help, I figured it out. The solution is to implement the Responder trait for a new struct ApiResponse, which contains a status code as well the Json. This way I can do exactly what I wanted:
#[post("/create/thing", format = "application/json", data = "<thing>")]
fn put(thing: Json<Thing>) -> ApiResponse {
let thing: Thing = thing.into_inner();
match thing.name.len() {
0...3 => ApiResponse {
json: json!({"error": {"short": "Invalid Name", "long": "A thing must have a name that is at least 3 characters long"}}),
status: Status::UnprocessableEntity,
},
_ => ApiResponse {
json: json!({"status": "success"}),
status: Status::Ok,
},
}
}
Here is the full code:
#![feature(proc_macro_hygiene)]
#![feature(decl_macro)]
#[macro_use]
extern crate rocket;
#[macro_use]
extern crate rocket_contrib;
extern crate serde;
#[macro_use]
extern crate serde_derive;
extern crate serde_json;
use rocket::http::{ContentType, Status};
use rocket::request::Request;
use rocket::response;
use rocket::response::{Responder, Response};
use rocket_contrib::json::{Json, JsonValue};
#[derive(Serialize, Deserialize, Debug)]
pub struct Thing {
pub name: String,
}
#[derive(Debug)]
struct ApiResponse {
json: JsonValue,
status: Status,
}
impl<'r> Responder<'r> for ApiResponse {
fn respond_to(self, req: &Request) -> response::Result<'r> {
Response::build_from(self.json.respond_to(&req).unwrap())
.status(self.status)
.header(ContentType::JSON)
.ok()
}
}
#[post("/create/thing", format = "application/json", data = "<thing>")]
fn put(thing: Json<Thing>) -> ApiResponse {
let thing: Thing = thing.into_inner();
match thing.name.len() {
0...3 => ApiResponse {
json: json!({"error": {"short": "Invalid Name", "long": "A thing must have a name that is at least 3 characters long"}}),
status: Status::UnprocessableEntity,
},
_ => ApiResponse {
json: json!({"status": "success"}),
status: Status::Ok,
},
}
}
fn main() {
rocket::ignite().mount("/", routes![put]).launch();
}

Answer 2

You need to build a response. Take a look at the ResponseBuilder. Your response might look something like this.
use std::io::Cursor;
use rocket::response::Response;
use rocket::http::{Status, ContentType};
let response = Response::build()
.status(Status::UnprocessableEntity)
.header(ContentType::Json)
.sized_body(Cursor::new("Your json body"))
.finalize();