如何防止通用路由在Express.js中的特定路由中设置标头？

Question

Here are my route definitions in Express.js:

// Building specific routes defined by a route file
routes.use(this.initialize.bind(this));
routes.use(this.isAuthenticated.bind(this));
routes.use(this.isAuthorized.bind(this));
if (Route.METHOD == 'POST') {
    routes.use(route.post.bind(route));
} else {
    routes.use(route.get.bind(route));
}
routes.use(this.finalize.bind(this));

router.use('/webstore/' + Route.RESOURCE + (parameters.length != 0 ? '/' : '') + parameters.join('/'), routes);

//router.use('/webstore/session', routes);

// Building generic routes
console.log('Creating GET route: ' + 
            '/:connectionName(webstore|localdatastore)/:objectName');
router.get('/:connectionName(webstore|localdatastore)/:objectName', 
    this.initialize.bind(this), this.isAuthenticated.bind(this), this.isAuthorized.bind(this), this.get.bind(this), this.finalize.bind(this));
console.log('Creating POST route: ' + 
    '/:connectionName(webstore|localdatastore)/:objectName');
router.post('/:connectionName(webstore|localdatastore)/:objectName', 
    this.initialize.bind(this), this.isAuthenticated.bind(this), this.isAuthorized.bind(this), this.get.bind(this), this.finalize.bind(this));

If I try to access generic routes, such as /webstore/user defined in the two lines above, my code works fine, however, if I try to use a specific route defined above from a route file, such as /webstore/session , I receive this error:

Error: Can't set headers after they are sent.
    at ServerResponse.setHeader (_http_outgoing.js:371:11)
    at ServerResponse.header (./node_modules/express/lib/response.js:767:10)
    at ServerResponse.contentType (./node_modules/express/lib/response.js:595:15)
    at Server.finalize (./dist/server.js:1156:17)
    at Layer.handle [as handle_request] (./node_modules/express/lib/router/layer.js:95:5)
    ...

I would like my API to remain flat, and not have to add an alias to remove this error. How do I prevent Express from setting headers because the generic and defined routes collide?

Answer 1

Because you are trying to send second response which is not possible. Check below lines and it' content.

routes.use(this.finalize.bind(this));

router.use('/webstore/' + Route.RESOURCE + (parameters.length != 0 ? '/' : '') + parameters.join('/'), routes);

Basically when you have this in some route:

res.send("...");

and you do this in some other middleware route

res.send("....");

you get that error.

Add the following code to the finalize method and any 404/500 error handlers to prevent sending headers a second time. However, the code is still processing all the logic in both branches if there is session manipulation, database calls, etc.

if (res.headersSent) {
    return next();
}