[backend] health service response should be consumed by application/json not text/plain

[hsinhoyeh]

Environment

• How did you deploy Kubeflow Pipelines (KFP)? install via kubeflow manifest with version v1.4
• KFP version: v1.7.0
• KFP SDK version: v1.7.0 (golang version under backend/api/go_http_client)

Steps to reproduce

1. start pipeline backend api server by listening port 8888
2. sent http request with swagger generated code stub with the following code example

package main

import (
	"github.com/go-openapi/strfmt"
	"github.com/go-openapi/runtime"
	healthz_client "github.com/kubeflow/pipelines/backend/api/go_http_client/healthz_client"
	healthz_service "github.com/kubeflow/pipelines/backend/api/go_http_client/healthz_client/healthz_service"
)

func main() {
	healthServiceClient := healthz_client.New(
		client.New(
			"localhost:8888",
			healthz_client.DefaultBasePath,
			[]string{"http"}),
		strfmt.NewFormats(),
	)
	
	clientAuthInfoWriter := runtime.ClientAuthInfoWriterFunc(func(clientRequest runtime.ClientRequest, registry strfmt.Registry) error {
		return nil
	})
	
	resp, err := p.HealthServiceClient.HealthzService.GetHealthz(healthz_service.NewGetHealthzParams, clientAuthInfoWriter)
        if err != nil {
            // should not be here
        }
}

3. When I was sent healthz endpoint (/apis/v1beta1/healthz) with go_http_client(swagger generated code stubs), the generated code stub failed to decode the response with the error message &{false} (*healthz_model.APIGetHealthzResponse) is not supported by the TextConsumer, can be resolved by supporting TextUnmarshaler interface

the http log are displayed below:

GET /apis/v1beta1/healthz HTTP/1.1
Host: 127.0.0.1:8888
User-Agent: Go-http-client/1.1
Accept: application/json
Accept-Encoding: gzip


HTTP/1.1 200 OK
Content-Length: 96
Content-Type: text/plain; charset=utf-8
Date: Wed, 06 Apr 2022 06:41:40 GMT

{"commit_sha":"6ccf5bcd0b9db955c91caab85fa130714527f414", "tag_name":"1.7.0", "multi_user":true}

however, the message was wrapped into a json struct but the content type was specified with text/plain.
This triggered APIGetHealthzResponse failed to decode the response, as it failed to implement TextUnmarshaler interface.

The server code (on v1.7.0 as well as on master) also confirmed this

pipelines/backend/src/apiserver/main.go

Line 146 in 74c7773

topMux.HandleFunc("/apis/v1beta1/healthz", func(w http.ResponseWriter, r *http.Request) {

, without proper set the content-type, the default one will determined by http.DetectContentType which will be 'text/plain'

Expected result

the golang example mentioned earier with swagger generated stub should work well.

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if this was confirmed as bug, I would like to submit a patch for this. Thanks

[zijianjoy]

@hsinhoyeh Thank you and we are happy to review the patch PR from you. cc @chensun

[hsinhoyeh]

Hi, @zijianjoy I have sent my PR here #7532 thanks. also cc @chensun