proxy mode: operate on http responses rather than requests

[aidansteele]

I moved the proxy mode logic into the response-handling function of goproxy, so that we have access to the response status code as per the TODO.

I also extracted the AWS hostname regexp to a global variable for a (probably irrelevant) speedup

[aidansteele]

I moved the request body draining into this handleAWSRequest function to more closely match e.g. what httputil.DumpRequest does.

[iann0036]

Looks like this isn't working based on my initial tests. Can you confirm whether it worked for you?

[aidansteele]

Nice catch. I missed that because my testing didn't involve POST bodies. I've since fixed that and added a basic E2E test to avoid regression. If you add some credentials to this repo, you could have a GitHub action to exercise these tests like:

on: [push, pull_request]
name: CI
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2

      - uses: actions/setup-go@v1
        with:
          go-version: 1.16

      - name: test
        run: go test -v ./...
        env:
          AWS_REGION: ap-southeast-2
          AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
          AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}

[aidansteele]

This is pretty ugly, but I figured I didn't want to make bigger changes in a single PR