如何在Rust Rocket中返回JSON响应并进行自动字段反序列化？

Question

我正在尝试在 Rust 中创建一个打印服务器，当尝试发送 JSON 作为响应时遇到问题。

我在 Rocket 文档中发现，发送 JSON 作为响应非常容易：只需要使用 Serde 库即可。

不幸的是，对我来说这并不简单......

以下是我的当前代码：

#[derive(Serialize,Deserialize)]
pub struct Printers {
    pub printers: Vec<Printer>,
}

#[derive(Serialize,Deserialize)]
pub struct Printer {
    pub device_type: String,
    pub uid: String,
    pub provider: String,
    pub name: String,
    pub connection: String,
    pub version: u8,
    pub manufacturer: String,
}

/**
 * Here is my main problem 
 *   -> I want to send back the Printers Object as a JSON
 */
#[get("/printers")]
fn printers(key: ApiKey<'_>) -> Json<Printers> {
    let resp = crate::get_printers::get();
    Json(resp)
}

以下是错误代码：

   --> src/order_route.rs:25:33
    |
25  | fn printers(key: ApiKey<'_>) -> Json<Printers> {
    |                                 ^^^^^^^^^^^^^^ the trait `Responder<'_, '_>` is not implemented for `rocket_contrib::json::Json<order_route::Printers>`
    |
note: required by `route::handler::<impl Outcome<rocket::Response<'o>, Status, rocket::Data<'o>>>::from`
   --> ********/.cargo/registry/src/github.com-1ecc6299db9ec823/rocket-0.5.0-rc.1/src/route/handler.rs:188:5
    |
188 |     pub fn from<R: Responder<'r, 'o>>(req: &'r Request<'_>, responder: R) -> Outcome<'r> {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

看起来我需要一个 特质(trait) 来完成这个，但是不知道如何创建它， 如果有人能帮我找到解决方案，我将非常感激。

[编辑]

这是 Cargo.toml 文件

[package]
name = "test"
version = "0.0.0"
edition = "2018"
[dependencies]
rocket = "0.5.0-rc.1"
reqwest = { version = "0.11", features = ["blocking", "json"] }
openssl = { version = "0.10", features = ["vendored"] }
json = "0.12.4"
serde = "1.0.127"
serde_json = "1.0.66"

[dependencies.rocket_contrib]
version = "0.4.10"
default-features = false
features = ["json"]

[workspace]
members = [
    ""
]

以下是完整的堆栈跟踪信息：

*****:~/*****/label-printer-server-rust/server$ cargo run
   Compiling hello v0.0.0 (/home/*****/*****/label-printer-server-rust/server)
error[E0277]: the trait bound `rocket_contrib::json::Json<order_route::Printers>: Responder<'_, '_>` is not satisfied
   --> src/order_route.rs:25:33
    |
25  | fn printers(key: ApiKey<'_>) -> Json<Printers> {
    |                                 ^^^^^^^^^^^^^^ the trait `Responder<'_, '_>` is not implemented for `rocket_contrib::json::Json<order_route::Printers>`
    |
note: required by `route::handler::<impl Outcome<rocket::Response<'o>, Status, rocket::Data<'o>>>::from`
   --> /home/*****/.cargo/registry/src/github.com-1ecc6299db9ec823/rocket-0.5.0-rc.1/src/route/handler.rs:188:5
    |
188 |     pub fn from<R: Responder<'r, 'o>>(req: &'r Request<'_>, responder: R) -> Outcome<'r> {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0308]: mismatched types
  --> src/order_route.rs:27:10
   |
27 |     Json(resp)
   |          ^^^^ expected struct `order_route::Printers`, found enum `Result`
   |
   = note: expected struct `order_route::Printers`
                found enum `Result<structures::Printers, Box<dyn StdError>>`

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.
error: could not compile `hello` due to 2 previous errors

- DirBear

Answer 1

如果您发现有难度，这里是解决方案：

• Enable JSON feature for rocket rust in your Cargo.toml file

  [package]
  #...
  
  [dependencies.rocket]
  version = "0.5.0-rc.1"
  features = ["json"]
  
  [dependencies.serde]
  version = "1.0.136"
  features = ["derive"]
  
  [dependencies]
  #...
  
  # rocket_contrib not required anymore
  

• In your src/main.rs file

  // rocket v0.5.0-rc.1
  use rocket::{
     self,
     serde::{json::Json, Deserialize, Serialize},
  };
  
  #[derive(Deserialize, Serialize)]
  struct User {
     name: String,
     age: u8,
  }
  
  #[rocket::post("/post", format = "json", data = "<user>")]
  fn post_data(user: Json<User>) -> Json<User> {
     let name: String = user.name.clone();
     let age: u8 = user.age.clone();
  
     Json(User { name, age })
  }
  
  #[rocket::main]
  async fn main() {
     if let Err(err) = rocket::build()
        .mount("/", rocket::routes![post_data])
        .launch()
        .await
     {
        println!("Rocket Rust couldn't take off successfully!");
        drop(err); // Drop initiates Rocket-formatted panic
     }
  }
  

• Test API using cURL

  curl -d '{"age": 12,"name":"John Doe"}' -H 'Content-Type: application/json' 
  http://localhost:8000/post
  
  # Response
  # {"name":"John Doe","age":12}
  

- Abhishek Sriram

Answer 2

您正在使用 rocket 0.5.0-rc.1 和 rocket_contrib 0.4.10。虽然 rocket_contrib 中的 Json 实现了Responder, 但它实现的是 Rocket v4 的 Responder 特性，而不是 Rocket v5 的。

在 Rocket v5 中，Json 不再是 rocket_contib 的一部分，而是包含在 rocket crate 中（请注意，您需要在 rocket crate 上启用 json 特性）：

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

#[derive(Serialize, Deserialize)]
pub struct Printers {
    pub printers: Vec<Printer>,
}

#[derive(Serialize, Deserialize)]
pub struct Printer {
    pub device_type: String,
    pub uid: String,
    pub provider: String,
    pub name: String,
    pub connection: String,
    pub version: u8,
    pub manufacturer: String,
}

#[get("/printers")]
fn printers() -> Json<Printers> {
    todo!();
}

请注意，您现在可以从Cargo.toml中删除rocket_contrib（因为您没有使用其中的任何功能）。

- Elias Holzmann

---

感谢您的反馈！ 经过检查，我无法找到箱子 rocket::serde::json::Json。 也许我需要更新我的 Cargo.toml 文件？ - DirBear

你是否启用了 rocket 的 json 功能？ - Elias Holzmann

我只找到了如何在rocket_contrib中实现这一点的方法。请问您有解释此点的文档链接吗？ - DirBear

它必须看起来像这样。Cargo书还提供了有关如何在依赖项中启用功能以及一般情况下的Cargo.toml布局的更多信息。 - Elias Holzmann

再次感谢您的反馈，我在搜索时找到了Rocket文档中的规格说明，我在这里留下了链接，供那些遇到同样问题的人使用。JSON导入的Rocket文档链接！你让我的一天变得美好 :D - DirBear

Answer 3

我想补充一下Elias的答案，这些都在评论中提到了：

在你的cargo.toml文件中，你需要启用JSON功能：

[dependencies]
## SEE HERE!! 
rocket = {version ="0.5.0-rc.1", features=["json"]}

# other properties omitted for brevity 

# You can remove this!! Rocket Contrib doesn't exist in Rocket V0.5 
#[dependencies.rocket_contrib]
#version = "0.4.10"
#default-features = false
#features = ["json"]

- Jose A