Examples: add error handling example

Related to #549

Cargo.toml

@@ -51,6 +51,7 @@ surf = { git = "https://github.com/Fishrock123/surf", branch = "deps-http-types-
 serde = { version = "1.0.102", features = ["derive"] }
 criterion = "0.3.1"
 tempfile = "3.1.0"
+url = "2.1.1"
 
 [[test]]
 name = "nested"

examples/error_handling.rs

@@ -0,0 +1,26 @@
+use tide::{Request, Response, Result, StatusCode};
+use tide::utils::After;
+
+#[async_std::main]
+async fn main() -> Result<()> {
+    tide::log::start();
+    let mut app = tide::new();
+
+    app.middleware(After(|mut res: Response| async move {
+        if let Some(err) = res.downcast_error::<url::ParseError>() {
+            let msg = err.to_string().to_owned();
+            res.set_status(StatusCode::ImATeapot);
+            res.set_body(format!("Teapot Status: {}", msg));
+        }
+        Ok(res)
+    }));
+
+    app.at("/").get(|_req: Request<_>| async move {
+        let path = url::Url::parse("")?;
+        Ok(format!("Path is {}", path))
+    });
+
+    app.listen("127.0.0.1:8080").await?;
+
+    Ok(())
+}