fastify-onheader

This is deprecated and not be updated anymore. Since Fastify v0.30, you can do it natively with the onSend hook, that is better, and fully asynchronous. It's kept just for version prior v0.30

Execute a listener when a response is about to write headers for Fastify.

This uses github.com/jshttp/on-headers under the hood

Install

npm install --save fastify-onheader

Usage

Add it to you project with register and you are done!

You can now configure a new route, and call the new reply.onheader() to add a function that will be called just before the request is send to modify the headers.

// Register the plugin
fastify.register(require("fastify-onheader"));
fastify.after((err) => {
    if (err) {
      throw err;
    }
});


// Define a new route in hapijs notation
fastify.route({
  method: "GET",
  url: "/header-hapi",
  handler: (request, reply) => {
    reply.onheader(function() {
      this.setHeader("X-Powered-By", "Fastify - Hapi notations");
    });
  }
});

// Define a new route in express notation
fastify.get("/header-express", (request, reply) => {
  reply.onheader(function() {
    this.setHeader("X-Powered-By", "Fastify - Express notations");
  });
  reply.send({hello: "world"});
});

Please note that the callback function will be binded to a ServerResponse NodeJS object.

Have a look at nodejs.org/dist/latest/docs/api/http.html for more informations about what it could be permitted to do, but all function can be used safely.

If you are unsure about what to use, here is the list of functions that deals only with headers:

• getHeader(name): return the content of a header (name is case insensitive)
• hasHeader(name): return trueif the header exists (case insensitive)
• removeHeader(name): prevent the header from being send
• setHeader(name, value): set a new value, or overwrite a previous