Getting "The response is not writable." error

This is my first time using Oak, and I’m running into an error that is making me scratch my head quite a bit. I can provide more code if need but it seems isolated to this chunk. I’m getting this error:

error: Uncaught Error: The response is not writable.
      throw new Error("The response is not writable.");
            ^
    at Response.set body (https://deno.land/x/oak/response.ts:120:13)
    at file:///C:/Users/TARS/projects/deno-elixir/src/app.ts:31:24

but I don’t even have to adjust my response to get it to go away. I can just comment out the line above setting the response and it works. Returns “random string” in the body like expected.:

.get('/games', async (context) => {
		// const gamesResponse = await API.get("/games");
		context.response.body = "random string";
	})

But if I uncomment that line back into the code, don’t change the response body and keep it as that random string, it crashes with that error. This errors out:

.get('/games', async (context) => {
		const gamesResponse = await API.get("/games");
		context.response.body = "random string";
	})

I have no idea what could be causing that line to be affecting the next line, but the API.get request is fulfilled, I get a 200 and the data I’m expecting to store in the variable gamesResponse, but something about context.response.body doesn’t like that line.

Apologies if the problem is obvious, I’m still a junior dev and this is my first dive into Deno and using this package.

[Nick-Pashkov]

I had the same problem on routes that used a JWT auth middleware, my solution was to append await before my next() call, so instead of having:

if(token && csrfHeader) {
    if((await validateJwt(token, key)).isValid && validateCSRF(csrfCookie, csrfHeader)) {
       next()
    }

...

}

I changed it to:

if(token && csrfHeader) {
    if((await validateJwt(token, key)).isValid && validateCSRF(csrfCookie, csrfHeader)) {
       await next()
    }

...

}

It works fine, and no errors 😉

[wongjiahau]

Apparently, for me the problem is that I didn’t return a Promise in the middleware, my code was something like this:

app.use((ctx, next) => {
  doSomething((result) => {
    ctx.response.body.result
    next()
  })
})

However, since I’m not return a promise, this line was immediately invoked even before doSomething finished, which will in turn turn the response unwritable.

So, by returning a promise as follows, I don’t face this problem anymore.

app.use((ctx, next) => {
  return new Promise(resolve => {
    doSomething((result) => {
      ctx.response.body.result
      resolve()
    })
  })
  .then(next)
})