1 files changed, 122 insertions, 0 deletions
diff --git a/third_party/rust/warp/examples/rejections.rs b/third_party/rust/warp/examples/rejections.rs
new file mode 100644
index 0000000000..721e69ecaa
--- /dev/null
+++ b/third_party/rust/warp/examples/rejections.rs
@@ -0,0 +1,122 @@
+#![deny(warnings)]
+
+use std::convert::Infallible;
+use std::error::Error;
+use std::num::NonZeroU16;
+
+use serde_derive::{Deserialize, Serialize};
+use warp::http::StatusCode;
+use warp::{reject, Filter, Rejection, Reply};
+
+/// Rejections represent cases where a filter should not continue processing
+/// the request, but a different filter *could* process it.
+#[tokio::main]
+async fn main() {
+    let math = warp::path!("math" / u16);
+    let div_with_header = math
+        .and(warp::get())
+        .and(div_by())
+        .map(|num: u16, denom: NonZeroU16| {
+            warp::reply::json(&Math {
+                op: format!("{} / {}", num, denom),
+                output: num / denom.get(),
+            })
+        });
+
+    let div_with_body =
+        math.and(warp::post())
+            .and(warp::body::json())
+            .map(|num: u16, body: DenomRequest| {
+                warp::reply::json(&Math {
+                    op: format!("{} / {}", num, body.denom),
+                    output: num / body.denom.get(),
+                })
+            });
+
+    let routes = div_with_header.or(div_with_body).recover(handle_rejection);
+
+    warp::serve(routes).run(([127, 0, 0, 1], 3030)).await;
+}
+
+/// Extract a denominator from a "div-by" header, or reject with DivideByZero.
+fn div_by() -> impl Filter<Extract = (NonZeroU16,), Error = Rejection> + Copy {
+    warp::header::<u16>("div-by").and_then(|n: u16| async move {
+        if let Some(denom) = NonZeroU16::new(n) {
+            Ok(denom)
+        } else {
+            Err(reject::custom(DivideByZero))
+        }
+    })
+}
+
+#[derive(Deserialize)]
+struct DenomRequest {
+    pub denom: NonZeroU16,
+}
+
+#[derive(Debug)]
+struct DivideByZero;
+
+impl reject::Reject for DivideByZero {}
+
+// JSON replies
+
+/// A successful math operation.
+#[derive(Serialize)]
+struct Math {
+    op: String,
+    output: u16,
+}
+
+/// An API error serializable to JSON.
+#[derive(Serialize)]
+struct ErrorMessage {
+    code: u16,
+    message: String,
+}
+
+// This function receives a `Rejection` and tries to return a custom
+// value, otherwise simply passes the rejection along.
+async fn handle_rejection(err: Rejection) -> Result<impl Reply, Infallible> {
+    let code;
+    let message;
+
+    if err.is_not_found() {
+        code = StatusCode::NOT_FOUND;
+        message = "NOT_FOUND";
+    } else if let Some(DivideByZero) = err.find() {
+        code = StatusCode::BAD_REQUEST;
+        message = "DIVIDE_BY_ZERO";
+    } else if let Some(e) = err.find::<warp::filters::body::BodyDeserializeError>() {
+        // This error happens if the body could not be deserialized correctly
+        // We can use the cause to analyze the error and customize the error message
+        message = match e.source() {
+            Some(cause) => {
+                if cause.to_string().contains("denom") {
+                    "FIELD_ERROR: denom"
+                } else {
+                    "BAD_REQUEST"
+                }
+            }
+            None => "BAD_REQUEST",
+        };
+        code = StatusCode::BAD_REQUEST;
+    } else if let Some(_) = err.find::<warp::reject::MethodNotAllowed>() {
+        // We can handle a specific error, here METHOD_NOT_ALLOWED,
+        // and render it however we want
+        code = StatusCode::METHOD_NOT_ALLOWED;
+        message = "METHOD_NOT_ALLOWED";
+    } else {
+        // We should have expected this... Just log and say its a 500
+        eprintln!("unhandled rejection: {:?}", err);
+        code = StatusCode::INTERNAL_SERVER_ERROR;
+        message = "UNHANDLED_REJECTION";
+    }
+
+    let json = warp::reply::json(&ErrorMessage {
+        code: code.as_u16(),
+        message: message.into(),
+    });
+
+    Ok(warp::reply::with_status(json, code))
+}