axum/json.rs
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use crate::extract::Request;
use crate::extract::{rejection::*, FromRequest};
use async_trait::async_trait;
use axum_core::response::{IntoResponse, Response};
use bytes::{BufMut, Bytes, BytesMut};
use http::{
header::{self, HeaderMap, HeaderValue},
StatusCode,
};
use serde::{de::DeserializeOwned, Serialize};
/// JSON Extractor / Response.
///
/// When used as an extractor, it can deserialize request bodies into some type that
/// implements [`serde::de::DeserializeOwned`]. The request will be rejected (and a [`JsonRejection`] will
/// be returned) if:
///
/// - The request doesn't have a `Content-Type: application/json` (or similar) header.
/// - The body doesn't contain syntactically valid JSON.
/// - The body contains syntactically valid JSON, but it couldn't be deserialized into the target type.
/// - Buffering the request body fails.
///
/// ⚠️ Since parsing JSON requires consuming the request body, the `Json` extractor must be
/// *last* if there are multiple extractors in a handler.
/// See ["the order of extractors"][order-of-extractors]
///
/// [order-of-extractors]: crate::extract#the-order-of-extractors
///
/// See [`JsonRejection`] for more details.
///
/// # 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));
/// # let _: Router = app;
/// ```
///
/// 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));
/// # let _: Router = app;
/// ```
#[derive(Debug, Clone, Copy, Default)]
#[cfg_attr(docsrs, doc(cfg(feature = "json")))]
#[must_use]
pub struct Json<T>(pub T);
#[async_trait]
impl<T, S> FromRequest<S> for Json<T>
where
T: DeserializeOwned,
S: Send + Sync,
{
type Rejection = JsonRejection;
async fn from_request(req: Request, state: &S) -> Result<Self, Self::Rejection> {
if json_content_type(req.headers()) {
let bytes = Bytes::from_request(req, state).await?;
Self::from_bytes(&bytes)
} else {
Err(MissingJsonContentType.into())
}
}
}
fn json_content_type(headers: &HeaderMap) -> bool {
let content_type = if let Some(content_type) = headers.get(header::CONTENT_TYPE) {
content_type
} else {
return false;
};
let content_type = if let Ok(content_type) = content_type.to_str() {
content_type
} else {
return false;
};
let mime = if let Ok(mime) = content_type.parse::<mime::Mime>() {
mime
} else {
return false;
};
let is_json_content_type = mime.type_() == "application"
&& (mime.subtype() == "json" || mime.suffix().map_or(false, |name| name == "json"));
is_json_content_type
}
axum_core::__impl_deref!(Json);
impl<T> From<T> for Json<T> {
fn from(inner: T) -> Self {
Self(inner)
}
}
impl<T> Json<T>
where
T: DeserializeOwned,
{
/// Construct a `Json<T>` from a byte slice. Most users should prefer to use the `FromRequest` impl
/// but special cases may require first extracting a `Request` into `Bytes` then optionally
/// constructing a `Json<T>`.
pub fn from_bytes(bytes: &[u8]) -> Result<Self, JsonRejection> {
let deserializer = &mut serde_json::Deserializer::from_slice(bytes);
let value = match serde_path_to_error::deserialize(deserializer) {
Ok(value) => value,
Err(err) => {
let rejection = match err.inner().classify() {
serde_json::error::Category::Data => JsonDataError::from_err(err).into(),
serde_json::error::Category::Syntax | serde_json::error::Category::Eof => {
JsonSyntaxError::from_err(err).into()
}
serde_json::error::Category::Io => {
if cfg!(debug_assertions) {
// we don't use `serde_json::from_reader` and instead always buffer
// bodies first, so we shouldn't encounter any IO errors
unreachable!()
} else {
JsonSyntaxError::from_err(err).into()
}
}
};
return Err(rejection);
}
};
Ok(Json(value))
}
}
impl<T> IntoResponse for Json<T>
where
T: Serialize,
{
fn into_response(self) -> Response {
// Use a small initial capacity of 128 bytes like serde_json::to_vec
// https://docs.rs/serde_json/1.0.82/src/serde_json/ser.rs.html#2189
let mut buf = BytesMut::with_capacity(128).writer();
match serde_json::to_writer(&mut buf, &self.0) {
Ok(()) => (
[(
header::CONTENT_TYPE,
HeaderValue::from_static(mime::APPLICATION_JSON.as_ref()),
)],
buf.into_inner().freeze(),
)
.into_response(),
Err(err) => (
StatusCode::INTERNAL_SERVER_ERROR,
[(
header::CONTENT_TYPE,
HeaderValue::from_static(mime::TEXT_PLAIN_UTF_8.as_ref()),
)],
err.to_string(),
)
.into_response(),
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::{routing::post, test_helpers::*, Router};
use serde::Deserialize;
use serde_json::{json, Value};
#[crate::test]
async fn deserialize_body() {
#[derive(Debug, Deserialize)]
struct Input {
foo: String,
}
let app = Router::new().route("/", post(|input: Json<Input>| async { input.0.foo }));
let client = TestClient::new(app);
let res = client.post("/").json(&json!({ "foo": "bar" })).await;
let body = res.text().await;
assert_eq!(body, "bar");
}
#[crate::test]
async fn consume_body_to_json_requires_json_content_type() {
#[derive(Debug, Deserialize)]
struct Input {
foo: String,
}
let app = Router::new().route("/", post(|input: Json<Input>| async { input.0.foo }));
let client = TestClient::new(app);
let res = client.post("/").body(r#"{ "foo": "bar" }"#).await;
let status = res.status();
assert_eq!(status, StatusCode::UNSUPPORTED_MEDIA_TYPE);
}
#[crate::test]
async fn json_content_types() {
async fn valid_json_content_type(content_type: &str) -> bool {
println!("testing {content_type:?}");
let app = Router::new().route("/", post(|Json(_): Json<Value>| async {}));
let res = TestClient::new(app)
.post("/")
.header("content-type", content_type)
.body("{}")
.await;
res.status() == StatusCode::OK
}
assert!(valid_json_content_type("application/json").await);
assert!(valid_json_content_type("application/json; charset=utf-8").await);
assert!(valid_json_content_type("application/json;charset=utf-8").await);
assert!(valid_json_content_type("application/cloudevents+json").await);
assert!(!valid_json_content_type("text/json").await);
}
#[crate::test]
async fn invalid_json_syntax() {
let app = Router::new().route("/", post(|_: Json<serde_json::Value>| async {}));
let client = TestClient::new(app);
let res = client
.post("/")
.body("{")
.header("content-type", "application/json")
.await;
assert_eq!(res.status(), StatusCode::BAD_REQUEST);
}
#[derive(Deserialize)]
struct Foo {
#[allow(dead_code)]
a: i32,
#[allow(dead_code)]
b: Vec<Bar>,
}
#[derive(Deserialize)]
struct Bar {
#[allow(dead_code)]
x: i32,
#[allow(dead_code)]
y: i32,
}
#[crate::test]
async fn invalid_json_data() {
let app = Router::new().route("/", post(|_: Json<Foo>| async {}));
let client = TestClient::new(app);
let res = client
.post("/")
.body("{\"a\": 1, \"b\": [{\"x\": 2}]}")
.header("content-type", "application/json")
.await;
assert_eq!(res.status(), StatusCode::UNPROCESSABLE_ENTITY);
let body_text = res.text().await;
assert_eq!(
body_text,
"Failed to deserialize the JSON body into the target type: b[0]: missing field `y` at line 1 column 23"
);
}
}