Duplicate header key leads to 500 error for a route with Go plugin trying to fetch request headers

[orangejohny]

Is there an existing issue for this?

• I have searched the existing issues

Kong version ($ kong version)

2.8.1

Current Behavior

I have a plugin written in Go that calls kong.Request.GetHeaders(-1) during Access phase.

When making a request to route with enabled plugin Kong returns 500 HTTP error:

$ curl -v --location --request GET 'http://localhost:8000/SuiteHeadersKey/get' \
--header 'X-Test-H: 123' \
--header 'X-Test-H: 567'
Note: Unnecessary use of -X or --request, GET is already inferred.
*   Trying 127.0.0.1:8000...
* Connected to localhost (127.0.0.1) port 8000 (#0)
> GET /SuiteHeadersKey/get HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.79.1
> Accept: */*
> X-Test-H: 123
> X-Test-H: 567
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 500 Internal Server Error
< Date: Thu, 28 Apr 2022 13:46:30 GMT
< Content-Type: application/json; charset=utf-8
< Connection: keep-alive
< Content-Length: 42
< X-Kong-Response-Latency: 0
< Server: kong/2.8.1
< 
* Connection #0 to host localhost left intact
{"message":"An unexpected error occurred"}

Kong logs show following error:

2022/04/28 13:50:38 [error] 1117#0: *375 [kong] init.lua:297 [kong-go-cache] ...cal/share/lua/5.1/kong/runloop/plugin_servers/pb_rpc.lua:259: bad argument #2 to 'encode' (string expected for field 'key', got number), client: 172.18.0.1, server: kong, request: "GET /SuiteHeadersKey/get HTTP/1.1", host: "localhost:8000"

kong.Request.GetHeaders(-1) call receives EOF error from Kong.

Expected Behavior

kong.Request.GetHeaders(-1) returns client's request headers correctly.

Kong returns response from the upstream correctly:

$ curl -v --location --request GET 'http://localhost:8000/SuiteHeadersKey/get' \
--header 'X-Test-H: 123' \
--header 'X-Test-H: 567'
Note: Unnecessary use of -X or --request, GET is already inferred.
*   Trying 127.0.0.1:8000...
* Connected to localhost (127.0.0.1) port 8000 (#0)
> GET /SuiteHeadersKey/get HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.79.1
> Accept: */*
> X-Test-H: 123
> X-Test-H: 567
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Content-Type: application/json
< Content-Length: 426
< Connection: keep-alive
< Date: Thu, 28 Apr 2022 14:10:16 GMT
< Server: gunicorn/19.9.0
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Credentials: true
< X-Kong-Upstream-Latency: 273
< X-Kong-Proxy-Latency: 2
< Via: kong/2.8.1
< 
{
  "args": {}, 
  "headers": {
    "Accept": "*/*", 
    "Host": "httpbin.org", 
    "User-Agent": "curl/7.79.1", 
    "X-Amzn-Trace-Id": "Root=1-626aa048-7ac54e37762209633233c3e2", 
    "X-Forwarded-Host": "localhost", 
    "X-Forwarded-Path": "/SuiteHeadersKey/get", 
    "X-Forwarded-Prefix": "/SuiteHeadersKey", 
    "X-Test-H": "123,567"
  }, 
  "origin": "172.18.0.1, 95.31.162.132", 
  "url": "http://localhost/get"
}
* Connection #0 to host localhost left intact

Steps To Reproduce

There is a plugin example for which the issue reproduces:

package main

import (
	"github.com/Kong/go-pdk/server"

	"github.com/Kong/go-pdk"
)

const Version = "1.0"
const Priority = 1

func main() {
	server.StartServer(New, Version, Priority)
}

type Config struct{}

func New() interface{} {
	return &Config{}
}

func (conf Config) Access(kong *pdk.PDK) {
	_, err := kong.Request.GetHeaders(-1)
	if err != nil {
		kong.Log.Err(err.Error())
	}
}

You need to deploy a Kong instance with this plugin included to reproduce the issue. After that follow the steps bellow.

1. Create a service:

curl --location --request POST 'http://localhost:8001/services' \
--header 'Content-Type: application/json' \
--data-raw '{
    "name": "svc",
    "url": "http://httpbin.org"
}'

2. Create a route:

curl --location --request POST 'http://localhost:8001/services/svc/routes' \
--header 'Content-Type: application/json' \
--data-raw '{
    "name": "route",
    "paths": ["/httpbin"],
    "protocols": ["http"]
}'

3. Create a plugin:

curl --location --request POST 'http://localhost:8001/routes/route/plugins' \
--header 'Content-Type: application/json' \
--data-raw '{
    "enabled": true,
    "config": {},
    "name": "test-plugin"
}'

4. Make a request:

curl --location --request GET 'http://localhost:8000/httpbin/get' \
--header 'X-Test-H: 123' \
--header 'X-Test-H: 567'

Anything else?

It seems that Kong plugin server receives request from the Go plugin correctly but fails to encode a result from https://github.com/Kong/kong/blob/master/kong/pdk/request.lua#L610 method.