express中间件机制补充说明
中间件2种用法
- 筒子
- 变胖的筒子
筒子
app.use('/1', function(req, res, next){
})
app.use('/2', function(req, res, next){
})
app.use('/3', function(req, res, next){
})
变胖的筒子
function m1(req, res, next){
}
function m2(req, res, next){
}
app.use('/', m1, m2, function(req, res, next){
})
路由匹配规则
- 先根据【筒子】栈,匹配到请求
- 然后看该请求,是不是【变胖的筒子】,如果是,还需要继续解析该路由上的横向的栈
express的next说明
4.0.0 / 2014年04月09日
==================
* remove:
- node 0.8 support
- connect and connect's patches except for charset handling
- express(1) - moved to [express-generator](https://github.com/expressjs/generator)
- `express.createServer()` - it has been deprecated for a long time. Use `express()`
- `app.configure` - use logic in your own app code
- `app.router` - is removed
- `req.auth` - use `basic-auth` instead
- `req.accepted*` - use `req.accepts*()` instead
- `res.location` - relative URL resolution is removed
- `res.charset` - include the charset in the content type when using `res.set()`
- all bundled middleware except `static`
* change:
- `app.route` -> `app.mountpath` when mounting an express app in another express app
- `json spaces` no longer enabled by default in development
- `req.accepts*` -> `req.accepts*s` - i.e. `req.acceptsEncoding` -> `req.acceptsEncodings`
- `req.params` is now an object instead of an array
- `res.locals` is no longer a function. It is a plain js object. Treat it as such.
- `res.headerSent` -> `res.headersSent` to match node.js ServerResponse object
* refactor:
- `req.accepts*` with [accepts](https://github.com/expressjs/accepts)
- `req.is` with [type-is](https://github.com/expressjs/type-is)
- [path-to-regexp](https://github.com/component/path-to-regexp)
* add:
- `app.router()` - returns the app Router instance
- `app.route()` - Proxy to the app's `Router#route()` method to create a new route
- Router & Route - public API
大家知道变更即可,过多细节也没啥用
express里的use
主要2个
- app.use
- 还有router.use
给出application里的use实现
app.use = function use(fn) {
var offset = 0;
var path = '/';
// default path to '/'
// disambiguate app.use([fn])
if (typeof fn !== 'function') {
var arg = fn;
while (Array.isArray(arg) && arg.length !== 0) {
arg = arg[0];
}
// first arg is the path
if (typeof arg !== 'function') {
offset = 1;
path = fn;
}
}
var fns = flatten(slice.call(arguments, offset));
if (fns.length === 0) {
throw new TypeError('app.use() requires middleware functions');
}
// setup router
this.lazyrouter();
var router = this._router;
fns.forEach(function (fn) {
// non-express app
if (!fn || !fn.handle || !fn.set) {
return router.use(path, fn);
}
debug('.use app under %s', path);
fn.mountpath = path;
fn.parent = this;
// restore .app property on req and res
router.use(path, function mounted_app(req, res, next) {
var orig = req.app;
fn.handle(req, res, function (err) {
req.__proto__ = orig.request;
res.__proto__ = orig.response;
next(err);
});
});
// mounted an app
fn.emit('mount', this);
}, this);
return this;
};
简单点说就是把中间件变成了路由来处理。
所有的fns中间件都被router.use真正处理了
router.use(path, function mounted_app(req, res, next) {
var orig = req.app;
fn.handle(req, res, function (err) {
req.__proto__ = orig.request;
res.__proto__ = orig.response;
next(err);
});
});
给出router里use实现
/**
* Use the given middleware function, with optional path, defaulting to "/".
*
* Use (like `.all`) will run for any http METHOD, but it will not add
* handlers for those methods so OPTIONS requests will not consider `.use`
* functions even if they could respond.
*
* The other difference is that _route_ path is stripped and not visible
* to the handler function. The main effect of this feature is that mounted
* handlers can operate without any code changes regardless of the "prefix"
* pathname.
*
* @public
*/
proto.use = function use(fn) {
var offset = 0;
var path = '/';
// default path to '/'
// disambiguate router.use([fn])
if (typeof fn !== 'function') {
var arg = fn;
while (Array.isArray(arg) && arg.length !== 0) {
arg = arg[0];
}
// first arg is the path
if (typeof arg !== 'function') {
offset = 1;
path = fn;
}
}
var callbacks = flatten(slice.call(arguments, offset));
if (callbacks.length === 0) {
throw new TypeError('Router.use() requires middleware functions');
}
for (var i = 0; i < callbacks.length; i++) {
var fn = callbacks[i];
if (typeof fn !== 'function') {
throw new TypeError('Router.use() requires middleware function but got a ' + gettype(fn));
}
// add the middleware
debug('use %s %s', path, fn.name || '<anonymous>');
var layer = new Layer(path, {
sensitive: this.caseSensitive,
strict: false,
end: false
}, fn);
layer.route = undefined;
this.stack.push(layer);
}
return this;
};
- 把参数搞成callbacks
var callbacks = flatten(slice.call(arguments, offset));
- 遍历callback,转成中间件
var layer = new Layer(path, {
sensitive: this.caseSensitive,
strict: false,
end: false
}, fn);
layer.route = undefined;
- 入栈
this.stack.push(layer);
总结一下:核心还是在Layer里
Layer
layer代码非常少,也就100多,方法不过5个
构造函数
function Layer(path, options, fn) {
if (!(this instanceof Layer)) {
return new Layer(path, options, fn);
}
debug('new %s', path);
var opts = options || {};
this.handle = fn;
this.name = fn.name || '<anonymous>';
this.params = undefined;
this.path = undefined;
this.regexp = pathRegexp(path, this.keys = [], opts);
if (path === '/' && opts.end === false) {
this.regexp.fast_slash = true;
}
}
主要看看this上有那些变量,这是一个请求会产生处理的。比如name我们在遍历中间件的时候可能会出现anonymous,原因就在这里。
通过pathRegexp进行匹配url,然后把fn处理了,很明显这是单个的或者说是final的处理。
var pathRegexp = require('path-to-regexp');
- handle_error
- handle_request
Layer.prototype.handle_request = function handle(req, res, next) {
var fn = this.handle;
if (fn.length > 3) {
// not a standard request handler
return next();
}
try {
fn(req, res, next);
} catch (err) {
next(err);
}
};
不知道大家是否好奇
给出express 4.x里的express/lib/router/index.js里的实现
proto.handle = function handle(req, res, out) {
var self = this;
debug('dispatching %s %s', req.method, req.url);
var search = 1 + req.url.indexOf('?');
var pathlength = search ? search - 1 : req.url.length;
var fqdn = req.url[0] !== '/' && 1 + req.url.substr(0, pathlength).indexOf('://');
var protohost = fqdn ? req.url.substr(0, req.url.indexOf('/', 2 + fqdn)) : '';
var idx = 0;
var removed = '';
var slashAdded = false;
var paramcalled = {};
// store options for OPTIONS request
// only used if OPTIONS request
var options = [];
// middleware and routes
var stack = self.stack;
// manage inter-router variables
var parentParams = req.params;
var parentUrl = req.baseUrl || '';
var done = restore(out, req, 'baseUrl', 'next', 'params');
// setup next layer
req.next = next;
// for options requests, respond with a default if nothing else responds
if (req.method === 'OPTIONS') {
done = wrap(done, function(old, err) {
if (err || options.length === 0) return old(err);
sendOptionsResponse(res, options, old);
});
}
// setup basic req values
req.baseUrl = parentUrl;
req.originalUrl = req.originalUrl || req.url;
next();
function next(err) {
var layerError = err === 'route'
? null
: err;
// remove added slash
if (slashAdded) {
req.url = req.url.substr(1);
slashAdded = false;
}
// restore altered req.url
if (removed.length !== 0) {
req.baseUrl = parentUrl;
req.url = protohost + removed + req.url.substr(protohost.length);
removed = '';
}
// no more matching layers
if (idx >= stack.length) {
setImmediate(done, layerError);
return;
}
// get pathname of request
var path = getPathname(req);
if (path == null) {
return done(layerError);
}
// find next matching layer
var layer;
var match;
var route;
while (match !== true && idx < stack.length) {
layer = stack[idx++];
match = matchLayer(layer, path);
route = layer.route;
if (typeof match !== 'boolean') {
// hold on to layerError
layerError = layerError || match;
}
if (match !== true) {
continue;
}
if (!route) {
// process non-route handlers normally
continue;
}
if (layerError) {
// routes do not match with a pending error
match = false;
continue;
}
var method = req.method;
var has_method = route._handles_method(method);
// build up automatic options response
if (!has_method && method === 'OPTIONS') {
appendMethods(options, route._options());
}
// don't even bother matching route
if (!has_method && method !== 'HEAD') {
match = false;
continue;
}
}
// no match
if (match !== true) {
return done(layerError);
}
// store route for dispatch on change
if (route) {
req.route = route;
}
// Capture one-time layer values
req.params = self.mergeParams
? mergeParams(layer.params, parentParams)
: layer.params;
var layerPath = layer.path;
// this should be done for the layer
self.process_params(layer, paramcalled, req, res, function (err) {
if (err) {
return next(layerError || err);
}
if (route) {
return layer.handle_request(req, res, next);
}
trim_prefix(layer, layerError, layerPath, path);
});
}
function trim_prefix(layer, layerError, layerPath, path) {
var c = path[layerPath.length];
if (c && '/' !== c && '.' !== c) return next(layerError);
// Trim off the part of the url that matches the route
// middleware (.use stuff) needs to have the path stripped
if (layerPath.length !== 0) {
debug('trim prefix (%s) from url %s', layerPath, req.url);
removed = layerPath;
req.url = protohost + req.url.substr(protohost.length + removed.length);
// Ensure leading slash
if (!fqdn && req.url[0] !== '/') {
req.url = '/' + req.url;
slashAdded = true;
}
// Setup base URL (no trailing slash)
req.baseUrl = parentUrl + (removed[removed.length - 1] === '/'
? removed.substring(0, removed.length - 1)
: removed);
}
debug('%s %s : %s', layer.name, layerPath, req.originalUrl);
if (layerError) {
layer.handle_error(layerError, req, res, next);
} else {
layer.handle_request(req, res, next);
}
}
};
核心在next();方法
while (match !== true && idx < stack.length) {
layer = stack[idx++];
match = matchLayer(layer, path);
route = layer.route;
if (typeof match !== 'boolean') {
// hold on to layerError
layerError = layerError || match;
}
if (match !== true) {
continue;
}
if (!route) {
// process non-route handlers normally
continue;
}
if (layerError) {
// routes do not match with a pending error
match = false;
continue;
}
var method = req.method;
var has_method = route._handles_method(method);
// build up automatic options response
if (!has_method && method === 'OPTIONS') {
appendMethods(options, route._options());
}
// don't even bother matching route
if (!has_method && method !== 'HEAD') {
match = false;
continue;
}
}
看到这个
layer = stack[idx++];
你会想到什么?遍历栈要做什么呢?
一个路由,其实就是stack,可以1个也可以多个中间件,想想上面说的"先根据【筒子】栈,匹配到请求"
然后,根据遍历结果,match和route来处理。只有匹配了路由,才会走到具体的处理
// no match
if (match !== true) {
return done(layerError);
}
// store route for dispatch on change
if (route) {
req.route = route;
}
// Capture one-time layer values
req.params = self.mergeParams
? mergeParams(layer.params, parentParams)
: layer.params;
var layerPath = layer.path;
// this should be done for the layer
self.process_params(layer, paramcalled, req, res, function (err) {
if (err) {
return next(layerError || err);
}
if (route) {
return layer.handle_request(req, res, next);
}
trim_prefix(layer, layerError, layerPath, path);
});
整体来说,设计的职责清晰,还算是比较精巧的。代码的可读性能做到这样,还是真的很难得的,推荐学习。
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