1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165

use crate::{extract::rejection::*, response::IntoResponseParts};
use async_trait::async_trait;
use axum_core::{
    extract::FromRequestParts,
    response::{IntoResponse, Response, ResponseParts},
};
use http::{request::Parts, Request};
use std::{
    convert::Infallible,
    task::{Context, Poll},
};
use tower_service::Service;

/// Extractor and response for extensions.
///
/// # As extractor
///
/// This is commonly used to share state across handlers.
///
/// ```rust,no_run
/// use axum::{
///     Router,
///     Extension,
///     routing::get,
/// };
/// use std::sync::Arc;
///
/// // Some shared state used throughout our application
/// struct State {
///     // ...
/// }
///
/// async fn handler(state: Extension<Arc<State>>) {
///     // ...
/// }
///
/// let state = Arc::new(State { /* ... */ });
///
/// let app = Router::new().route("/", get(handler))
///     // Add middleware that inserts the state into all incoming request's
///     // extensions.
///     .layer(Extension(state));
/// # let _: Router = app;
/// ```
///
/// If the extension is missing it will reject the request with a `500 Internal
/// Server Error` response.
///
/// # As response
///
/// Response extensions can be used to share state with middleware.
///
/// ```rust
/// use axum::{
///     Extension,
///     response::IntoResponse,
/// };
///
/// async fn handler() -> (Extension<Foo>, &'static str) {
///     (
///         Extension(Foo("foo")),
///         "Hello, World!"
///     )
/// }
///
/// #[derive(Clone)]
/// struct Foo(&'static str);
/// ```
#[derive(Debug, Clone, Copy, Default)]
#[must_use]
pub struct Extension<T>(pub T);

#[async_trait]
impl<T, S> FromRequestParts<S> for Extension<T>
where
    T: Clone + Send + Sync + 'static,
    S: Send + Sync,
{
    type Rejection = ExtensionRejection;

    async fn from_request_parts(req: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
        let value = req
            .extensions
            .get::<T>()
            .ok_or_else(|| {
                MissingExtension::from_err(format!(
                    "Extension of type `{}` was not found. Perhaps you forgot to add it? See `axum::Extension`.",
                    std::any::type_name::<T>()
                ))
            }).cloned()?;

        Ok(Extension(value))
    }
}

axum_core::__impl_deref!(Extension);

impl<T> IntoResponseParts for Extension<T>
where
    T: Clone + Send + Sync + 'static,
{
    type Error = Infallible;

    fn into_response_parts(self, mut res: ResponseParts) -> Result<ResponseParts, Self::Error> {
        res.extensions_mut().insert(self.0);
        Ok(res)
    }
}

impl<T> IntoResponse for Extension<T>
where
    T: Clone + Send + Sync + 'static,
{
    fn into_response(self) -> Response {
        let mut res = ().into_response();
        res.extensions_mut().insert(self.0);
        res
    }
}

impl<S, T> tower_layer::Layer<S> for Extension<T>
where
    T: Clone + Send + Sync + 'static,
{
    type Service = AddExtension<S, T>;

    fn layer(&self, inner: S) -> Self::Service {
        AddExtension {
            inner,
            value: self.0.clone(),
        }
    }
}

/// Middleware for adding some shareable value to [request extensions].
///
/// See [Sharing state with handlers](index.html#sharing-state-with-handlers)
/// for more details.
///
/// [request extensions]: https://docs.rs/http/latest/http/struct.Extensions.html
#[derive(Clone, Copy, Debug)]
pub struct AddExtension<S, T> {
    pub(crate) inner: S,
    pub(crate) value: T,
}

impl<ResBody, S, T> Service<Request<ResBody>> for AddExtension<S, T>
where
    S: Service<Request<ResBody>>,
    T: Clone + Send + Sync + 'static,
{
    type Response = S::Response;
    type Error = S::Error;
    type Future = S::Future;

    #[inline]
    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, mut req: Request<ResBody>) -> Self::Future {
        req.extensions_mut().insert(self.value.clone());
        self.inner.call(req)
    }
}