Extend ReturnOverrides

[matiasinsaurralde]

See #762.

As a sample plugin (test_app.py)

from tyk.decorators import *

@Hook
def MyCustomMiddleware(request, session, spec):
    print("my_middleware: MyCustomMiddleware")
    request.object.return_overrides.headers['content-type'] = 'application/json'
    request.object.return_overrides.response_code = 200
    request.object.return_overrides.response_error = "{\"key\": \"value\"}\n"
    return request, session

With manifest:

{
  "file_list": [
    "test_app.py"
  ],
  "custom_middleware": {
    "post": [
      {"name": "MyCustomMiddleware"}
    ],
    "driver": "python"
  }
}

Curl output:

% curl localhost:8080/test-api/headers -v
*   Trying ::1...
* Connected to localhost (::1) port 8080 (#0)
> GET /test-api/headers HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.43.0
> Accept: */*
> 
< HTTP/1.1 200
< Content-Type: application/json
< Date: Wed, 24 May 2017 08:32:50 GMT
< Content-Length: 17
< 
{"key": "value"}
* Connection #0 to host localhost left intact

[mvdan]

LGTM, but worried about no test. Maybe it's time we add coprocess tests? The more logic we add without tests, the worse off we'll be in the long run.

[mvdan]

What does 666 mean here?

[lonelycode]

666 is a magic return code that makes the gateway halt MW processing and respond

[mvdan]

Ah, I see we have 1666 also - we should use constants for these to make them more obvious, like return nil, mwStatusRespond. I'll ticket that up to do once this is merged.

[lonelycode]

That's a fantastic idea, let's do that! So much clearer

[matiasinsaurralde]

@mvdan Just updated the tests, let's wait for #764 to replace the integers with constants.
I'm also extending the rest of the CP tests, trying to enhance them, will be a separate PR.

[mvdan]

Looks fine to me, but I'm not very familiar with this code so I'd have another set of eyes on it before merging.

[mvdan]

You can use a nil body

[matiasinsaurralde]

A nil body panics 😮

[mvdan]

Something is buggy somewhere... forget I said anything for now :)

[mvdan]

rogue empty line?

[buger]

@matiasinsaurralde can we fix tests?

[mvdan]

@buger tests are fixed, FYI

[buger]

I'm right that this is similar to what we have now with Virtual Endpoints in our JS middleware?
Previously we already had option to add new headers, but with this functionality it is now possible to write any logic. Right?

Also, does it affect only Coprocess (Lua, Python) plugins, or gRPC ones too (because I see that you changed protobuffers files as well)?

[matiasinsaurralde]

I'm not very familiar with the virtual endpoint feature. Yes, basically it's possible to take control of the request flow and return a custom body.
There is an existing feature to add headers from the CP middleware, but it's for request headers (before they hit the upstream API). The funcionality covered by this PR is specific to the response object, and the headers that are specified here are received by the client.
It affects all the plugins and will work as long as you're using the latest definitions and/or bindings provided by us.