Add with_headers() method to RemoteHttpPlugin (#15651)

# Objective

- fulfill the needs presented in this issue, which requires the ability
to set custom HTTP headers for responses in the Bevy Remote Protocol
server. #15551

## Solution

- Created a `Headers` struct to store custom HTTP headers as key-value
pairs.
- Added a `headers` field to the `RemoteHttpPlugin` struct.
- Implemented a `with_headers` method in `RemoteHttpPlugin` to allow
users to set custom headers.
- Passed the headers into the processing chain.

## Testing

- I added cors_headers in example/remote/server.rs and tested it with a
static html
[file](https://github.com/spacemen0/bevy/blob/test_file/test.html)

---

crates/bevy_remote/src/http.rs

@@ -17,14 +17,15 @@ use bevy_ecs::system::{Res, Resource};
 use bevy_tasks::IoTaskPool;
 use core::net::{IpAddr, Ipv4Addr};
 use http_body_util::{BodyExt as _, Full};
+pub use hyper::header::{HeaderName, HeaderValue};
 use hyper::{
     body::{Bytes, Incoming},
-    header::HeaderValue,
     server::conn::http1,
     service, Request, Response,
 };
 use serde_json::Value;
 use smol_hyper::rt::{FuturesIo, SmolTimer};
+use std::collections::HashMap;
 use std::net::TcpListener;
 use std::net::TcpStream;
 
@@ -36,6 +37,37 @@ pub const DEFAULT_PORT: u16 = 15702;
 /// The default host address that Bevy will use for its server.
 pub const DEFAULT_ADDR: IpAddr = IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1));
 
+/// A struct that holds a collection of HTTP headers.
+///
+/// This struct is used to store a set of HTTP headers as key-value pairs, where the keys are
+/// of type [`HeaderName`] and the values are of type [`HeaderValue`].
+///
+#[derive(Debug, Resource, Clone)]
+pub struct Headers {
+    headers: HashMap<HeaderName, HeaderValue>,
+}
+
+impl Headers {
+    /// Create a new instance of `Headers`.
+    pub fn new() -> Self {
+        Self {
+            headers: HashMap::new(),
+        }
+    }
+
+    /// Add a key value pair to the `Headers` instance.
+    pub fn add(mut self, key: HeaderName, value: HeaderValue) -> Self {
+        self.headers.insert(key, value);
+        self
+    }
+}
+
+impl Default for Headers {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Add this plugin to your [`App`] to allow remote connections over HTTP to inspect and modify entities.
 /// It requires the [`RemotePlugin`](super::RemotePlugin).
 ///
@@ -44,11 +76,32 @@ pub const DEFAULT_ADDR: IpAddr = IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1));
 /// The defaults are:
 /// - [`DEFAULT_ADDR`] : 127.0.0.1.
 /// - [`DEFAULT_PORT`] : 15702.
+///
+/// /// # Example
+///
+/// ```ignore
+///
+/// // Create CORS headers
+/// let cors_headers = Headers::new()
+///     .add(HeaderName::from_static("Access-Control-Allow-Origin"), HeaderValue::from_static("*"))
+///     .add(HeaderName::from_static("Access-Control-Allow-Headers"), HeaderValue::from_static("Content-Type, Authorization"));
+///
+/// // Create the Bevy app and add the RemoteHttpPlugin with CORS headers
+/// fn main() {
+///     App::new()
+///     .add_plugins(DefaultPlugins)
+///     .add_plugins(RemoteHttpPlugin::default()
+///         .with_headers(cors_headers))
+///     .run();
+/// }
+/// ```
 pub struct RemoteHttpPlugin {
     /// The address that Bevy will bind to.
     address: IpAddr,
     /// The port that Bevy will listen on.
     port: u16,
+    /// The headers that Bevy will include in its HTTP responses
+    headers: Headers,
 }
 
 impl Default for RemoteHttpPlugin {
@@ -56,6 +109,7 @@ impl Default for RemoteHttpPlugin {
         Self {
             address: DEFAULT_ADDR,
             port: DEFAULT_PORT,
+            headers: Headers::new(),
         }
     }
 }
@@ -64,6 +118,7 @@ impl Plugin for RemoteHttpPlugin {
     fn build(&self, app: &mut App) {
         app.insert_resource(HostAddress(self.address))
             .insert_resource(HostPort(self.port))
+            .insert_resource(HostHeaders(self.headers.clone()))
             .add_systems(Startup, start_http_server);
     }
 }
@@ -75,13 +130,34 @@ impl RemoteHttpPlugin {
         self.address = address.into();
         self
     }
-
     /// Set the remote port that the server will listen on.
     #[must_use]
     pub fn with_port(mut self, port: u16) -> Self {
         self.port = port;
         self
     }
+    /// Set the extra headers that the response will include.
+    #[must_use]
+    pub fn with_headers(mut self, headers: Headers) -> Self {
+        self.headers = headers;
+        self
+    }
+    /// Add a single header to the response headers.
+    #[must_use]
+    pub fn with_header(
+        mut self,
+        name: impl TryInto<HeaderName>,
+        value: impl TryInto<HeaderValue>,
+    ) -> Self {
+        let Ok(header_name) = name.try_into() else {
+            panic!("Invalid header name")
+        };
+        let Ok(header_value) = value.try_into() else {
+            panic!("Invalid header value")
+        };
+        self.headers = self.headers.add(header_name, header_value);
+        self
+    }
 }
 
 /// A resource containing the IP address that Bevy will host on.
@@ -98,17 +174,24 @@ pub struct HostAddress(pub IpAddr);
 #[derive(Debug, Resource)]
 pub struct HostPort(pub u16);
 
+/// A resource containing the headers that Bevy will include in its HTTP responses.
+///
+#[derive(Debug, Resource)]
+struct HostHeaders(pub Headers);
+
 /// A system that starts up the Bevy Remote Protocol HTTP server.
 fn start_http_server(
     request_sender: Res<BrpSender>,
     address: Res<HostAddress>,
     remote_port: Res<HostPort>,
+    headers: Res<HostHeaders>,
 ) {
     IoTaskPool::get()
         .spawn(server_main(
             address.0,
             remote_port.0,
             request_sender.clone(),
+            headers.0.clone(),
         ))
         .detach();
 }
@@ -118,10 +201,12 @@ async fn server_main(
     address: IpAddr,
     port: u16,
     request_sender: Sender<BrpMessage>,
+    headers: Headers,
 ) -> AnyhowResult<()> {
     listen(
         Async::<TcpListener>::bind((address, port))?,
         &request_sender,
+        &headers,
     )
     .await
 }
@@ -129,14 +214,16 @@ async fn server_main(
 async fn listen(
     listener: Async<TcpListener>,
     request_sender: &Sender<BrpMessage>,
+    headers: &Headers,
 ) -> AnyhowResult<()> {
     loop {
         let (client, _) = listener.accept().await?;
 
         let request_sender = request_sender.clone();
+        let headers = headers.clone();
         IoTaskPool::get()
             .spawn(async move {
-                let _ = handle_client(client, request_sender).await;
+                let _ = handle_client(client, request_sender, headers).await;
             })
             .detach();
     }
@@ -145,12 +232,15 @@ async fn listen(
 async fn handle_client(
     client: Async<TcpStream>,
     request_sender: Sender<BrpMessage>,
+    headers: Headers,
 ) -> AnyhowResult<()> {
     http1::Builder::new()
         .timer(SmolTimer::new())
         .serve_connection(
             FuturesIo::new(client),
-            service::service_fn(|request| process_request_batch(request, &request_sender)),
+            service::service_fn(|request| {
+                process_request_batch(request, &request_sender, &headers)
+            }),
         )
         .await?;
 
@@ -162,6 +252,7 @@ async fn handle_client(
 async fn process_request_batch(
     request: Request<Incoming>,
     request_sender: &Sender<BrpMessage>,
+    headers: &Headers,
 ) -> AnyhowResult<Response<Full<Bytes>>> {
     let batch_bytes = request.into_body().collect().await?.to_bytes();
     let batch: Result<BrpBatch, _> = serde_json::from_slice(&batch_bytes);
@@ -198,6 +289,9 @@ async fn process_request_batch(
         hyper::header::CONTENT_TYPE,
         HeaderValue::from_static("application/json"),
     );
+    for (key, value) in &headers.headers {
+        response.headers_mut().insert(key, value.clone());
+    }
     Ok(response)
 }