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//! This module contains Iron's middleware and handler system, the fundamental //! building blocks for handling HTTP requests and generating responses. //! //! # Handlers //! //! A `Handler` will produce a `Response` given a `Request`. Most handlers are //! functions or closures that accept a `&mut Request` as an argument and return //! an `IronResult` containing a `Response`. An `IronResult` is returned instead of //! directly returning a `Response` in order to indicate a possibility of //! failure (e.g. database timeout). //! //! Here's an example of a `Handler`: //! //! ```rust //! use iron::prelude::*; //! use iron::Handler; //! use iron::status; //! //! fn hello_handler(req: &mut Request) -> IronResult<Response> { //! Ok(Response::with((status::Ok, "Hello world!"))) //! }; //! ``` //! //! # Middleware //! //! In situations involving more complex logic, it may be desirable to transform //! `Request`s passed to a `Handler` or altering `Response`s sent to the //! clients. For example, an authorization step could only allow requests sent //! by authorized users to be passed to a `Handler` and respond to all other //! requests with a 403 status code. To faciliate such use cases, Iron's //! middleware system allows `Handler`s to be extended by defining middleware, //! which will perform transformations. //! //! There are three types of middleware: //! //! * A `BeforeMiddleware` alters a `Request`. It can be useful for handling //! control flow (e.g. routing and authorization). //! * An `AroundMiddleware` wraps a `Handler`, changing both the `Response` //! passed to the `Handler` and the returned `Response`. //! * An `AfterMiddleware` performs `Response` post-processing. It can be used //! for editing headers or logging `Response`s, but it should _not_ be used for //! changing the body of a `Response`. //! //! See the documentation for each middleware for more details. //! //! ## Defining the middleware pipeline //! //! A `Chain` is a `Handler` that wraps another `Handler`. It is used to attach //! middleware to the wrapped `Handler` using a `link` method corresponding to //! each type of middleware. A sample middleware pipeline is shown below: //! //! ```rust //! use iron::prelude::*; //! use iron::middleware::*; //! //! # use iron::status; //! # fn hello_handler(req: &mut Request) -> IronResult<Response> { //! # Ok(Response::with((status::Ok, "Hello world!"))) //! # }; //! //! struct RequestLoggingMiddleware; //! impl BeforeMiddleware for RequestLoggingMiddleware { //! fn before(&self, req: &mut Request) -> IronResult<()> { //! println!("{:?}", req); //! Ok(()) //! } //! } //! //! let mut chain = Chain::new(hello_handler); //! chain.link_before(RequestLoggingMiddleware {}); //! // Since a Chain is a Handler, chain can be passed to Iron::new without any problems. //! // Iron::new(chain).http("localhost:3000").unwrap(); //! ``` //! //! # The Request Handling Flow //! //! A diagram modeling the entire middleware system process is shown below: //! //! ```plain //! [b] = BeforeMiddleware //! [a] = AfterMiddleware //! [[h]] = AroundMiddleware //! [h] = Handler //! ``` //! //! With no errors, the flow looks like: //! //! ```plain //! [b] -> [b] -> [b] -> [[[[h]]]] -> [a] -> [a] -> [a] -> [a] //! ``` //! //! A request first travels through all `BeforeMiddleware`, then a `Response` is //! generated by the `Handler`, which can be an arbitrary nesting of //! `AroundMiddleware`, then all `AfterMiddleware` are called with both the //! `Request` and `Response`. After all `AfterMiddleware` have been fired, the //! response is written back to the client. //! //! Iron's error handling system is pragmatic and focuses on tracking two pieces //! of information for error receivers (other middleware): //! //! * The cause of the error //! * The result (what to do about) the error. //! //! The cause of the error is represented simply by the error itself, and the //! result of the error, representing the action to take in response to the //! error, is a complete Response, which will be sent at the end of the error //! flow. //! //! When an error is thrown in Iron by any middleware or handler returning an //! `Err` variant with an `IronError`, the flow of the `Request` switches to the //! error flow, which proceeds to just call the `catch` method of middleware and //! sidesteps the `Handler` entirely, since there is already a `Response` in the //! error. //! //! A `Request` can exit the error flow by returning an Ok from any of the catch //! methods. This resumes the flow at the middleware immediately following the //! middleware which handled the error. It is impossible to "go back" to an //! earlier middleware that was skipped. //! //! Generally speaking, returning a 5XX error code means that the error flow //! should be entered by raising an explicit error. Dealing with 4XX errors is //! trickier, since the server may not want to recognize an error that is //! entirely the clients fault; handling of 4XX error codes is up to to each //! application and middleware author. //! //! Middleware authors should be cognizant that their middleware may be skipped //! during the error flow. Anything that *must* be done to each `Request` or //! `Response` should be run during both the normal and error flow by //! implementing the `catch` method to also do the necessary action. use std::sync::Arc; use {Request, Response, IronResult, IronError}; /// `Handler`s are responsible for handling requests by creating Responses from Requests. pub trait Handler: Send + Sync + 'static { /// Produce a `Response` from a Request, with the possibility of error. fn handle(&self, &mut Request) -> IronResult<Response>; } /// `BeforeMiddleware` are fired before a `Handler` is called inside of a Chain. /// /// `BeforeMiddleware` are responsible for doing request pre-processing that requires /// the ability to change control-flow, such as authorization middleware, or for editing /// the request by modifying the headers. /// /// `BeforeMiddleware` only have access to the Request, if you need to modify or read /// a Response, you will need `AfterMiddleware`. Middleware which wishes to send an /// early response that is not an error cannot be `BeforeMiddleware`, but should /// instead be `AroundMiddleware`. pub trait BeforeMiddleware: Send + Sync + 'static { /// Do whatever work this middleware should do with a `Request` object. fn before(&self, _: &mut Request) -> IronResult<()> { Ok(()) } /// Respond to an error thrown by a previous `BeforeMiddleware`. /// /// Returning a `Ok` will cause the request to resume the normal flow at the /// next `BeforeMiddleware`, or if this was the last `BeforeMiddleware`, /// at the `Handler`. fn catch(&self, _: &mut Request, err: IronError) -> IronResult<()> { Err(err) } } /// `AfterMiddleware` are fired after a `Handler` is called inside of a Chain. /// /// `AfterMiddleware` receive both a `Request` and a `Response` and are responsible for doing /// any response post-processing. /// /// `AfterMiddleware` should *not* overwrite the contents of a Response. In /// the common case, a complete response is generated by the Chain's `Handler` and /// `AfterMiddleware` simply do post-processing of that Response, such as /// adding headers or logging. pub trait AfterMiddleware: Send + Sync + 'static { /// Do whatever post-processing this middleware should do. fn after(&self, _: &mut Request, res: Response) -> IronResult<Response> { Ok(res) } /// Respond to an error thrown by previous `AfterMiddleware`, the `Handler`, /// or a `BeforeMiddleware`. /// /// Returning `Ok` will cause the request to resume the normal flow at the /// next `AfterMiddleware`. fn catch(&self, _: &mut Request, err: IronError) -> IronResult<Response> { Err(err) } } /// `AroundMiddleware` are used to wrap and replace the `Handler` in a `Chain`. /// /// `AroundMiddleware` produce `Handler`s through their `around` method, which is /// called once on insertion into a `Chain` or can be called manually outside of a /// `Chain`. pub trait AroundMiddleware { /// Produce a `Handler` from this `AroundMiddleware` given another `Handler`. /// /// Usually this means wrapping the handler and editing the `Request` on the /// way in and the `Response` on the way out. /// /// This is called only once, when an `AroundMiddleware` is added to a `Chain` /// using `Chain::around`, it is passed the `Chain`'s current `Handler`. fn around(self, handler: Box<Handler>) -> Box<Handler>; } /// The middleware chain used in Iron. /// /// This is a canonical implementation of Iron's middleware system, /// but Iron's infrastructure is flexible enough to allow alternate /// systems. pub struct Chain { befores: Vec<Box<BeforeMiddleware>>, afters: Vec<Box<AfterMiddleware>>, // Internal invariant: this is always Some handler: Option<Box<Handler>> } impl Chain { /// Construct a new ChainBuilder from a `Handler`. pub fn new<H: Handler>(handler: H) -> Chain { Chain { befores: vec![], afters: vec![], handler: Some(Box::new(handler) as Box<Handler>) } } /// Link both a before and after middleware to the chain at once. /// /// Middleware that have a Before and After piece should have a constructor /// which returns both as a tuple, so it can be passed directly to link. pub fn link<B, A>(&mut self, link: (B, A)) -> &mut Chain where A: AfterMiddleware, B: BeforeMiddleware { let (before, after) = link; self.befores.push(Box::new(before) as Box<BeforeMiddleware>); self.afters.push(Box::new(after) as Box<AfterMiddleware>); self } /// Link a `BeforeMiddleware` to the `Chain`, after all previously linked /// `BeforeMiddleware`. pub fn link_before<B>(&mut self, before: B) -> &mut Chain where B: BeforeMiddleware { self.befores.push(Box::new(before) as Box<BeforeMiddleware>); self } /// Link a `AfterMiddleware` to the `Chain`, after all previously linked /// `AfterMiddleware`. pub fn link_after<A>(&mut self, after: A) -> &mut Chain where A: AfterMiddleware { self.afters.push(Box::new(after) as Box<AfterMiddleware>); self } /// Apply an `AroundMiddleware` to the `Handler` in this `Chain`. /// /// Note: This function is being renamed `link_around()`, and will /// eventually be removed. pub fn around<A>(&mut self, around: A) -> &mut Chain where A: AroundMiddleware { self.link_around(around) } /// Apply an `AroundMiddleware` to the `Handler` in this `Chain`. pub fn link_around<A>(&mut self, around: A) -> &mut Chain where A: AroundMiddleware { let mut handler = self.handler.take().unwrap(); handler = around.around(handler); self.handler = Some(handler); self } } impl Handler for Chain { fn handle(&self, req: &mut Request) -> IronResult<Response> { // Kick off at befores, which will continue into handler // then afters. self.continue_from_before(req, 0) } } impl Chain { ///////////////// Implementation Helpers ///////////////// // Enter the error flow from a before middleware, starting // at the passed index. // // If the index is out of bounds for the before middleware Vec, // this instead behaves the same as fail_from_handler. fn fail_from_before(&self, req: &mut Request, index: usize, mut err: IronError) -> IronResult<Response> { // If this was the last before, yield to next phase. if index >= self.befores.len() { return self.fail_from_handler(req, err) } for (i, before) in self.befores[index..].iter().enumerate() { err = match before.catch(req, err) { Err(err) => err, Ok(()) => return self.continue_from_before(req, index + i + 1) }; } // Next phase self.fail_from_handler(req, err) } // Enter the error flow from an errored handle, starting with the // first AfterMiddleware. fn fail_from_handler(&self, req: &mut Request, err: IronError) -> IronResult<Response> { // Yield to next phase, nothing to do here. self.fail_from_after(req, 0, err) } // Enter the error flow from an errored after middleware, starting // with the passed index. // // If the index is out of bounds for the after middleware Vec, // this instead just returns the passed error. fn fail_from_after(&self, req: &mut Request, index: usize, mut err: IronError) -> IronResult<Response> { // If this was the last after, we're done. if index == self.afters.len() { return Err(err) } for (i, after) in self.afters[index..].iter().enumerate() { err = match after.catch(req, err) { Err(err) => err, Ok(res) => return self.continue_from_after(req, index + i + 1, res) } } // Done Err(err) } // Enter the normal flow in the before middleware, starting with the passed // index. fn continue_from_before(&self, req: &mut Request, index: usize) -> IronResult<Response> { // If this was the last beforemiddleware, start at the handler. if index >= self.befores.len() { return self.continue_from_handler(req) } for (i, before) in self.befores[index..].iter().enumerate() { match before.before(req) { Ok(()) => {}, Err(err) => return self.fail_from_before(req, index + i + 1, err) } } // Yield to next phase. self.continue_from_handler(req) } // Enter the normal flow at the handler. fn continue_from_handler(&self, req: &mut Request) -> IronResult<Response> { // unwrap is safe because it's always Some match self.handler.as_ref().unwrap().handle(req) { Ok(res) => self.continue_from_after(req, 0, res), Err(err) => self.fail_from_handler(req, err) } } // Enter the normal flow in the after middleware, starting with the passed // index. fn continue_from_after(&self, req: &mut Request, index: usize, mut res: Response) -> IronResult<Response> { // If this was the last after middleware, we're done. if index >= self.afters.len() { return Ok(res); } for (i, after) in self.afters[index..].iter().enumerate() { res = match after.after(req, res) { Ok(r) => r, Err(err) => return self.fail_from_after(req, index + i + 1, err) } } // We made it with no error! Ok(res) } } impl<F> Handler for F where F: Send + Sync + 'static + Fn(&mut Request) -> IronResult<Response> { fn handle(&self, req: &mut Request) -> IronResult<Response> { (*self)(req) } } impl Handler for Box<Handler> { fn handle(&self, req: &mut Request) -> IronResult<Response> { (**self).handle(req) } } impl<F> BeforeMiddleware for F where F: Send + Sync + 'static + Fn(&mut Request) -> IronResult<()> { fn before(&self, req: &mut Request) -> IronResult<()> { (*self)(req) } } impl BeforeMiddleware for Box<BeforeMiddleware> { fn before(&self, req: &mut Request) -> IronResult<()> { (**self).before(req) } fn catch(&self, req: &mut Request, err: IronError) -> IronResult<()> { (**self).catch(req, err) } } impl<T> BeforeMiddleware for Arc<T> where T: BeforeMiddleware { fn before(&self, req: &mut Request) -> IronResult<()> { (**self).before(req) } fn catch(&self, req: &mut Request, err: IronError) -> IronResult<()> { (**self).catch(req, err) } } impl<F> AfterMiddleware for F where F: Send + Sync + 'static + Fn(&mut Request, Response) -> IronResult<Response> { fn after(&self, req: &mut Request, res: Response) -> IronResult<Response> { (*self)(req, res) } } impl AfterMiddleware for Box<AfterMiddleware> { fn after(&self, req: &mut Request, res: Response) -> IronResult<Response> { (**self).after(req, res) } fn catch(&self, req: &mut Request, err: IronError) -> IronResult<Response> { (**self).catch(req, err) } } impl<T> AfterMiddleware for Arc<T> where T: AfterMiddleware { fn after(&self, req: &mut Request, res: Response) -> IronResult<Response> { (**self).after(req, res) } fn catch(&self, req: &mut Request, err: IronError) -> IronResult<Response> { (**self).catch(req, err) } } impl<F> AroundMiddleware for F where F: FnOnce(Box<Handler>) -> Box<Handler> { fn around(self, handler: Box<Handler>) -> Box<Handler> { self(handler) } } #[cfg(test)] mod test;