How can I make a callback that requires info of its child function

Question

I am working in a project that uses Node.js for a Haraka (an smtp server) plugin.

This is Node.JS and I have a little problem whith callbacks. I haven't been able to convert this particular code to use a callback.

So, this is the code that I have:

exports.hook_data = function (next, connection) {
    connection.transaction.add_body_filter('', function (content_type, encoding, body_buffer) {
        var header = connection.transaction.header.get("header");
        if (header == null || header == undefined || header == '') return body_buffer;

        var url = 'https://server.com/api?header=' + header ;
        var request = require('request');
        request.get({ uri: url },
          function (err, resp, body) {
              var resultFromServer = JSON.parse(body);
              return ChangeBuffer(content_type, encoding, body_buffer, resultFromServer);
          }
        );
    });
    return next();
}

This code does not work because It doesn't wait the callback of the Request to continue. I need to finish the request before next();

And these are the requirements:

1. At the end of exports.hook_data is mandatory to return next(). But it only have to return it after the request.
2. I need to return a Buffer in add_body_filter but I need to create the buffer with information getted from a server.
3. To make the Get Request I need to use a parameter (header) that I only have inside add_body_filter.

So the issue is that I can not make the request before add_body_filter and put the result inside a callback because the parameter that I need to make the request are only inside add_body_filter.

Any advice please?

Answer 1

Unless you are willing to use synchronous, blocking functions, it is impossible to satisfy the requirements you have numbered.

I would examine reasons underlying each requirement and see if you accomplish your goals in a different way.

On face value, looking at just the code you have there, I would look for a way to alter the contract of exports.hook_data so that you're able to call next() from inside the request.get callback.