1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369
//! Iron's Middleware and Handler System //! //! Iron's Middleware system is best modeled with a diagram. //! //! ```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::any::Any; 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 + Any { /// 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 + Any { /// 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 + Any { /// 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)) 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>); } /// Link a `BeforeMiddleware` to the `Chain`, after all previously linked /// `BeforeMiddleware`. pub fn link_before<B>(&mut self, before: B) where B: BeforeMiddleware { self.befores.push(Box::new(before) as Box<BeforeMiddleware>); } /// Link a `AfterMiddleware` to the `Chain`, after all previously linked /// `AfterMiddleware`. pub fn link_after<A>(&mut self, after: A) where A: AfterMiddleware { self.afters.push(Box::new(after) as Box<AfterMiddleware>); } /// Apply an `AroundMiddleware` to the `Handler` in this `Chain`. pub fn around<A>(&mut self, around: A) where A: AroundMiddleware { let mut handler = self.handler.take().unwrap(); handler = around.around(handler); self.handler = Some(handler); } } 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 + Any + 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 + Any + 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 + Any + 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;