Can't resolve `Responder<'_, '_>` is not implemented for `rocket_contrib::json::Json`

Question

I'm trying to return Json data with a rocket handler. I've seen many other posts with the same issue, where the solution for basically everyone where that they hadn't implemented serde::Deserialize/serde::Serialize. Does anyone have a solution?

rocket_contrib docs

use rocket_contrib::json::Json;
use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize)]
pub struct MyStruct;

pub fn get_timestamps(pool: &State<Pool>) -> Json<MyStruct> {
    ^^^^^^^^^^^^^^ the trait `Responder<'_, '_>` is not implemented for `rocket_contrib::json::Json<MyStruct>`

Cargo.toml

[dependencies]
rand = "0.8.4"
bytes = "1"
mysql = "*"
dotenv = "0.15.0"
serde = { version = "1", features = ["derive"] }
serde_derive = "1.0.127"
diesel = "1.4.7"
chrono = "0.4.19"
serde_json = "1.0"
rocket = "0.5.0-rc.1"

[dependencies.rocket_contrib]
version = "0.4"
default-features = false
features = ["json"]

Answer 1

Since now we are at rocket v5 (the rocket_contrib crate was valid only for rocket v4), and checking that Cargo.toml have these dependencies:

...

[dependencies]
rocket = { version = "0.5.0-rc.2", features = ["json"] }
serde = "1.0.152"

...

To use the Json struct apply the following trait to MyStruct struct:

use rocket::serde::{json::Json, Serialize};

#[derive(Serialize)]
pub struct MyStruct;

pub fn get_timestamps(pool: &State<Pool>) -> Json<MyStruct> {...}

Having pumped your MyStruct struct with the rocket methods, you should be able to work with rocket::serde::json::Json

Answer 2

I recommend to instead of

use rocket_contrib::json::Json;;

use this

use rocket::serde::json::Json;