Double encoding of slashes when using replace.json with response-transformer

[chrisbaldauf]

Overview

I'm seeing an issue where values for config.replace.json in the response-transformer plugin are showing up with doubly encoded slashes. This is an issue for me because I'm using kong with path based routing to serve swagger documents that need to have their basePath transformed to match the paths from which the APIs are being served.

Kong version: 0.7.0
Platform: Docker container

Use Case

What is being served by the underlying / backing service:

{
  "swagger": 2.0,
  "basePath": "/",
  ...
}

What I'd like kong to return by configuring the response-transformer:

{
  "swagger": 2.0,
  "basePath": "\/some\/other\/path",
  ...
}

What I'm actually seeing:

{
  "swagger": 2.0,
  "basePath": "\\\/some\\\/other\\\/path",
  ...
}

Steps to Reproduce

$ curl localhost:8001/apis -X POST -d "request_path=/test" \
  -d "upstream_url=http://mockbin.com" \
  -d "strip_request_path=true" 
{"upstream_url":"http:\/\/mockbin.com","request_path":"\/test","id":"22bc1328-1a91-4f45-b3d2-d8df73a2e87d","name":"test","created_at":1461937139000,"strip_request_path":true}

$ curl localhost:8000/test/headers -i
{
  "headers": [
    {
      "name": "host",
      "value": "mockbin.com"
    },
    ...
  ],
  "headersSize": 469
}

$ curl localhost:8001/apis/test/plugins -X POST -d "name=response-transformer" \
  -d "config.replace.json=headers:/foo/bar" 
{"api_id":"22bc1328-1a91-4f45-b3d2-d8df73a2e87d","id":"37c75e16-4a2e-427a-92d6-4b840b169148","created_at":1461937139000,"enabled":true,"name":"response-transformer","config":{"replace":{"json":["headers:\/foo\/bar"],"headers":{}},"add":{"headers":{},"json":{}},"remove":{"headers":{},"json":{}},"append":{"headers":{},"json":{}}}}

$ curl localhost:8000/test/headers 
{"headersSize":469,"headers":"\\\/foo\\\/bar"}

How I patched this

Patched from https://github.com/Mashape/kong/blob/0.7.0/kong/plugins/response-transformer/body_transformer.lua#L59

  -- replace  key:value to body
  for _, name, value in iter(conf.replace.json) do
    local v = cjson.encode(value)
    if stringy.startswith(v, "\"") and stringy.endswith(v, "\"") then
      v = v:sub(2, v:len() - 1):gsub("\\\"", "\"") -- To prevent having double encoded quotes
    end
    -- BEGIN PATCH
    -- Correct double encoding of forward slashes
    v = v:gsub("\\/", "/")
    -- END PATCH
    if json_body[name] then
      json_body[name] = v
    end
  end

I'd be curious to know if anyone else has run into this and if so how they solved it. If you can repro the issue and think the approach taken in the patch is viable, I can work on a PR for all of the config.json.* methods to make sure that forward slashes are handled appropriately.

[subnetmarco]

The fix will be available in the next version.

[chrisbaldauf]

Thanks!