doc(examples): add examples with custom error handling

Cargo.toml

@@ -86,3 +86,8 @@ path = "examples/chaining.rs"
 
 name = "form_data"
 path = "examples/form_data/form_data.rs"
+
+[[example]]
+
+name = "error_handling"
+path = "examples/error_handling.rs"

examples/error_handling.rs

@@ -0,0 +1,77 @@
+#[macro_use] extern crate nickel;
+
+use nickel::{Nickel, Request, Response, MiddlewareResult, HttpRouter};
+use nickel::status::StatusCode;
+use std::{error,io, fmt};
+
+#[derive(Debug)]
+pub enum AppError {
+  Io(io::Error),
+  Custom(String)
+}
+
+impl fmt::Display for AppError {
+  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+    match *self {
+      AppError::Custom(ref msg) => write!(f, "Custom error: {}", msg),
+      AppError::Io(ref err)     => write!(f, "IO error: {}", err)
+    }
+  }
+}
+
+impl error::Error for AppError {
+  fn description(&self) -> &str {
+    match *self {
+      AppError::Custom(ref msg) => msg,
+      AppError::Io(ref err)     => err.description()
+    }
+  }
+
+  fn cause(&self) -> Option<&error::Error> {
+    match *self {
+      AppError::Custom(_)   => None,
+      AppError::Io(ref err) => Some(err)
+    }
+  }
+}
+
+impl<'a> From<&'a AppError> for StatusCode {
+  fn from(err: &AppError) -> StatusCode {
+    match *err {
+      AppError::Custom(_) => StatusCode::BadRequest,
+      AppError::Io(_)     => StatusCode::InternalServerError
+    }
+  }
+}
+
+type AppResult<T> = Result<T,AppError>;
+
+fn will_fail() -> AppResult<String> {
+  Err(AppError::Custom("uups".to_string()))
+}
+
+fn will_work() -> AppResult<String> {
+  Ok("foo".to_string())
+}
+
+fn foo_handler<'a, D>(_: &mut Request<D>, mut res: Response<'a,D>) -> MiddlewareResult<'a, D> {
+
+  let x: AppResult<String> = (||Ok({
+    try!(will_fail());
+    try!(will_work())
+  }))();
+
+  match x {
+    Ok(s)    => res.send(s),
+    Err(ref err) => {
+      res.set(StatusCode::from(err));
+      res.send(err.to_string())
+    }
+  }
+}
+
+fn main() {
+  let mut server = Nickel::new();
+  server.get("foo/", foo_handler);
+  server.listen("127.0.0.1:6767");
+}