How to intercept node.js express request

Question

In express, I have defined some routes

app.post("/api/v1/client", Client.create);
app.get("/api/v1/client", Client.get);
...

I have defined how to handle requests inside a Client controller. Is there a way that I can do some pre-processing to the requests, before handling them in my controller? I specifically want to check if the API caller is authorized to access the route, using the notion of access levels. Any advice would be appreciated.

Gumbo

Think of connect/express as a masseur with many hands, each hand being a middleware that massages your request into the correct response. So what Ryan Olds says is 100% correct. ;) – Aimeeaimil

Answer 1

You can do what you need in a couple of ways.

This will place a middleware that will be used before hitting the router. Make sure the router is added with app.use() after. Middleware order is important.

app.use(function(req, res, next) {
  // Put some preprocessing here.
  next();
});
app.use(app.router);

You can also use a route middleware.

var someFunction = function(req, res, next) {
  // Put the preprocessing here.
  next();
};
app.post("/api/v1/client", someFunction, Client.create);

This will do a preprocessing step for that route.

Note: Make sure your app.use() invokes are before your route definitions. Defining a route automatically adds app.router to the middleware chain, which may put it ahead of the user defined middleware.

Minify

@ryan-olds, How Do I check 'Content-Type'? I have to set expiry on JSON only, not in all responce. – Owner

This is simple interception concept. Are you familiar with more generic, formed way to do this?Thank you – Durtschi

I'm wondering if there is anyway to do this and inspect the body as well. #35165308 – Trenchant

There is, but a body parser needs to be earlier in the stack/middleware. – Minify

for your first solution "app.use(app.router);" is no longer requested (and will cause a deprecated exception). Just remove it, and it's perfect – Giles

app.router is depricated – Cyaneous