axum/src/json.rs

use crate::BoxError;
use crate::{
    extract::{rejection::*, take_body, FromRequest, RequestParts},
    response::IntoResponse,
};
use async_trait::async_trait;
use bytes::Bytes;
use http::{
    header::{self, HeaderValue},
    StatusCode,
};
use http_body::Full;
use hyper::Response;
use serde::{de::DeserializeOwned, Serialize};
use std::{
    convert::Infallible,
    ops::{Deref, DerefMut},
};

/// JSON Extractor / Response.
///
/// When used as an extractor, it can deserialize request bodies into some type that
/// implements [`serde::Deserialize`]. If the request body cannot be parsed, or it does not contain
/// the `Content-Type: application/json` header, it will reject the request and return a
/// `400 Bad Request` response.
///
/// # Extractor example
///
/// ```rust,no_run
/// use axum::{
///     extract,
///     routing::post,
///     Router,
/// };
/// use serde::Deserialize;
///
/// #[derive(Deserialize)]
/// struct CreateUser {
///     email: String,
///     password: String,
/// }
///
/// async fn create_user(extract::Json(payload): extract::Json<CreateUser>) {
///     // payload is a `CreateUser`
/// }
///
/// let app = Router::new().route("/users", post(create_user));
/// # async {
/// # axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
/// # };
/// ```
///
/// When used as a response, it can serialize any type that implements [`serde::Serialize`] to `JSON`,
/// and will automatically set `Content-Type: application/json` header.
///
/// # Response example
///
/// ```
/// use axum::{
///     extract::Path,
///     routing::get,
///     Router,
///     Json,
/// };
/// use serde::Serialize;
/// use uuid::Uuid;
///
/// #[derive(Serialize)]
/// struct User {
///     id: Uuid,
///     username: String,
/// }
///
/// async fn get_user(Path(user_id) : Path<Uuid>) -> Json<User> {
///     let user = find_user(user_id).await;
///     Json(user)
/// }
///
/// async fn find_user(user_id: Uuid) -> User {
///     // ...
///     # unimplemented!()
/// }
///
/// let app = Router::new().route("/users/:id", get(get_user));
/// # async {
/// # axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
/// # };
/// ```
#[derive(Debug, Clone, Copy, Default)]
#[cfg_attr(docsrs, doc(cfg(feature = "json")))]
pub struct Json<T>(pub T);

#[async_trait]
impl<T, B> FromRequest<B> for Json<T>
where
    T: DeserializeOwned,
    B: http_body::Body + Send,
    B::Data: Send,
    B::Error: Into<BoxError>,
{
    type Rejection = JsonRejection;

    async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
        use bytes::Buf;

        if json_content_type(req)? {
            let body = take_body(req)?;

            let buf = hyper::body::aggregate(body)
                .await
                .map_err(InvalidJsonBody::from_err)?;

            let value = serde_json::from_reader(buf.reader()).map_err(InvalidJsonBody::from_err)?;

            Ok(Json(value))
        } else {
            Err(MissingJsonContentType.into())
        }
    }
}

fn json_content_type<B>(req: &RequestParts<B>) -> Result<bool, HeadersAlreadyExtracted> {
    let content_type = if let Some(content_type) = req
        .headers()
        .ok_or(HeadersAlreadyExtracted)?
        .get(header::CONTENT_TYPE)
    {
        content_type
    } else {
        return Ok(false);
    };

    let content_type = if let Ok(content_type) = content_type.to_str() {
        content_type
    } else {
        return Ok(false);
    };

    let mime = if let Ok(mime) = content_type.parse::<mime::Mime>() {
        mime
    } else {
        return Ok(false);
    };

    let is_json_content_type = mime.type_() == "application"
        && (mime.subtype() == "json" || mime.suffix().filter(|name| *name == "json").is_some());

    Ok(is_json_content_type)
}

impl<T> Deref for Json<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<T> DerefMut for Json<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl<T> From<T> for Json<T> {
    fn from(inner: T) -> Self {
        Self(inner)
    }
}

impl<T> IntoResponse for Json<T>
where
    T: Serialize,
{
    type Body = Full<Bytes>;
    type BodyError = Infallible;

    fn into_response(self) -> Response<Self::Body> {
        let bytes = match serde_json::to_vec(&self.0) {
            Ok(res) => res,
            Err(err) => {
                return Response::builder()
                    .status(StatusCode::INTERNAL_SERVER_ERROR)
                    .header(header::CONTENT_TYPE, "text/plain")
                    .body(Full::from(err.to_string()))
                    .unwrap();
            }
        };

        let mut res = Response::new(Full::from(bytes));
        res.headers_mut().insert(
            header::CONTENT_TYPE,
            HeaderValue::from_static("application/json"),
        );
        res
    }
}