Access the raw body of a request in koa.js

Question

I have created an API using io.js and koa.js.

As a body parser middleware I am using koa-body, which in turn uses co-body.

On one of my API endpoints I am receiving POST requests, and I need access to the raw body of the request, because I need to encode it to verify if the request is valid.

Is there any way to access the raw body of the request? I tried to use the raw-body middleware, but if I use it before I call koa-body, the co-body used in koa-body breaks. If I use it after koa-body it does not work.

   app.use(function*(next){
    let rawRequestBody = yield rawBody(this.req);
    this.rawRequestBody = rawRequestBody;

    yield next;
  });

---

EDIT:

I think that I found a workaround, but I don't know if this is the best solution. I think that @greim answer may be a better solution to this problem.

I added the following code before I use koa-body:

app.use(function *(next) {

    let url = this.req.url;

    if(this.req.method == 'POST') {
      let that = this;
      this.req.rawBody = '';

      this.req.on('data', function(chunk) {
        that.req.rawBody += chunk;
      });
    }

    yield next;
  });

Answer 1

It only makes sense to capture the stream once.

You can capture the request body as a string or buffer (I assume this is what you mean by "raw" body) using the raw-body utility, and then keep a reference to it as shown in your own code, such that:

let rawRequestBody = yield rawBody(this.req);
this.rawRequestBody = rawRequestBody;
console.log(typeof this.rawRequestBody); // "string"

Once you do that, don't also use koa-body or co-body, since those are also stream-capturing utilities which assume you haven't yet captured the stream. To make the request body accessible as JSON (for example) simply do this:

this.jsonRequestBody = JSON.parse(this.rawRequestBody);
console.log(typeof this.jsonRequestBody); // "object"

Answer 2

Why we can't use multiple body parser(co-body, koa-body) is because by defination it must prepare ctx.request.body for next middleware to use, this means when a body parser middleware "await next()" to transfer control to next middleware the ctx.req is consumed(or end).

Any body parser middleware for coordination with other request body consumer(one that listen "data" or "end" event on ctx.req), must makesure it "synchronize" listen events(like "data" or "end") on ctx.req. This is not true for co-body and koa-body(use co-body) which do it in "Promise.resolve().then", if "data" or "end" events triggered before one listen these event, data missing(lose "data" event) or error(listen on ended stream) will happen.

@greim is right, but most of the time, we use a high level middleware(such as joi-router) which has force to use a body parser middleware and we have no control, this is still a problem.