gate all serde_json use on a new "json" feature

Cargo.toml

@@ -24,10 +24,11 @@ features = ["docs"]
 rustdoc-args = ["--cfg", "feature=\"docs\""]
 
 [features]
-default = ["h1-server"]
+default = ["h1-server", "json"]
 h1-server = ["async-h1"]
 docs = ["unstable"]
 unstable = []
+json = ["serde_json"]
 # DO NOT USE. Only exists to expose internals so they can be benchmarked.
 __internal__bench = []
 
@@ -42,7 +43,7 @@ mime = "0.3.14"
 mime_guess = "2.0.3"
 route-recognizer = "0.1.13"
 serde = "1.0.102"
-serde_json = "1.0.41"
+serde_json = { version = "1.0.41", optional = true }
 serde_qs = "0.5.0"
 
 [dev-dependencies]

src/lib.rs

@@ -212,6 +212,7 @@ pub use redirect::Redirect;
 pub use request::Request;
 pub use response::Response;
 pub use route::Route;
+#[cfg(feature = "json")]
 pub use serde_json;
 pub use server::Server;
 

src/request.rs

@@ -259,6 +259,7 @@ impl<State> Request<State> {
  ///
  /// If the body cannot be interpreted as valid json for the target type `T`,
  /// an `Err` is returned.
+ #[cfg(feature = "json")]
  pub async fn body_json<T: serde::de::DeserializeOwned>(&mut self) -> std::io::Result<T> {
  let body_bytes = self.body_bytes().await?;
  Ok(serde_json::from_slice(&body_bytes).map_err(|_| std::io::ErrorKind::InvalidData)?)

src/response.rs

@@ -175,11 +175,13 @@ impl Response {
  .set_mime(mime::APPLICATION_WWW_FORM_URLENCODED))
  }
 
+
  /// Encode a struct as a form and set as the response body.
  ///
  /// # Mime
  ///
  /// The encoding is set to `application/json`.
+ #[cfg(feature = "json")]
  pub fn body_json(mut self, json: &impl Serialize) -> serde_json::Result<Self> {
  self.res.set_body(serde_json::to_vec(json)?);
  Ok(self.set_mime(mime::APPLICATION_JSON))
@@ -282,6 +284,7 @@ impl Into<http::Response> for Response {
  }
 }
 
+#[cfg(feature = "json")]
 impl From<serde_json::Value> for Response {
  fn from(json_value: serde_json::Value) -> Self {
  Response::new(StatusCode::Ok)