prometheus: respect the http-method data source setting (#42753)

* prometheus: respect the http-method data source setting

* removed forgotten if-true section

* refactored json-check

pkg/tsdb/prometheus/force_http_get_middleware.go

@@ -0,0 +1,29 @@
+package prometheus
+
+import (
+	"net/http"
+
+	sdkhttpclient "github.com/grafana/grafana-plugin-sdk-go/backend/httpclient"
+	"github.com/grafana/grafana/pkg/infra/log"
+)
+
+func forceHttpGetMiddleware(logger log.Logger) sdkhttpclient.Middleware {
+	return sdkhttpclient.NamedMiddlewareFunc("force-http-get", func(opts sdkhttpclient.Options, next http.RoundTripper) http.RoundTripper {
+		// the prometheus library we use does not allow us to set the http method.
+		// it's behavior is to first try POST, and if it fails in certain ways
+		// (for example, by returning a method-not-allowed error), it will try GET.
+		// so here, we check if the http-method is POST, and if it is, we
+		// return an artificial method-not-allowed response.
+		// this will cause the prometheus library to retry with GET.
+		return sdkhttpclient.RoundTripperFunc(func(req *http.Request) (*http.Response, error) {
+			if req.Method == http.MethodPost {
+				resp := &http.Response{
+					StatusCode: http.StatusMethodNotAllowed,
+				}
+				return resp, nil
+			}
+
+			return next.RoundTrip(req)
+		})
+	})
+}

pkg/tsdb/prometheus/force_http_get_middleware_test.go

@@ -0,0 +1,84 @@
+package prometheus
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend/httpclient"
+	"github.com/grafana/grafana/pkg/infra/log"
+	"github.com/stretchr/testify/require"
+)
+
+func TestForceGet(t *testing.T) {
+	t.Run("With nil jsonOpts, should not force get-method", func(t *testing.T) {
+		var jsonOpts map[string]interface{}
+		require.False(t, forceHttpGet(jsonOpts))
+	})
+
+	t.Run("With empty jsonOpts, should not force get-method", func(t *testing.T) {
+		jsonOpts := make(map[string]interface{})
+		require.False(t, forceHttpGet(jsonOpts))
+	})
+
+	t.Run("With httpMethod=nil, should not not force get-method", func(t *testing.T) {
+		jsonOpts := map[string]interface{}{
+			"httpMethod": nil,
+		}
+		require.False(t, forceHttpGet(jsonOpts))
+	})
+
+	t.Run("With httpMethod=post, should not force get-method", func(t *testing.T) {
+		jsonOpts := map[string]interface{}{
+			"httpMethod": "POST",
+		}
+		require.False(t, forceHttpGet(jsonOpts))
+	})
+
+	t.Run("With httpMethod=get, should force get-method", func(t *testing.T) {
+		jsonOpts := map[string]interface{}{
+			"httpMethod": "get",
+		}
+		require.True(t, forceHttpGet(jsonOpts))
+	})
+
+	t.Run("With httpMethod=GET, should force get-method", func(t *testing.T) {
+		jsonOpts := map[string]interface{}{
+			"httpMethod": "GET",
+		}
+		require.True(t, forceHttpGet(jsonOpts))
+	})
+}
+
+func TestEnsureHttpMethodMiddleware(t *testing.T) {
+	t.Run("Name should be correct", func(t *testing.T) {
+		finalRoundTripper := httpclient.RoundTripperFunc(func(req *http.Request) (*http.Response, error) {
+			return &http.Response{StatusCode: http.StatusOK}, nil
+		})
+		mw := forceHttpGetMiddleware(log.New("test"))
+		rt := mw.CreateMiddleware(httpclient.Options{}, finalRoundTripper)
+		require.NotNil(t, rt)
+		middlewareName, ok := mw.(httpclient.MiddlewareName)
+		require.True(t, ok)
+		require.Equal(t, "force-http-get", middlewareName.MiddlewareName())
+	})
+
+	t.Run("Should force GET method", func(t *testing.T) {
+		finalRoundTripper := httpclient.RoundTripperFunc(func(req *http.Request) (*http.Response, error) {
+			return &http.Response{StatusCode: http.StatusOK}, nil
+		})
+
+		mw := forceHttpGetMiddleware(log.New("test"))
+		rt := mw.CreateMiddleware(httpclient.Options{}, finalRoundTripper)
+		require.NotNil(t, rt)
+
+		req, err := http.NewRequest(http.MethodPost, "http://example.com", nil)
+		require.NoError(t, err)
+		res, err := rt.RoundTrip(req)
+		require.NoError(t, err)
+		require.NotNil(t, res)
+		require.Equal(t, res.StatusCode, http.StatusMethodNotAllowed)
+		if res.Body != nil {
+			require.NoError(t, res.Body.Close())
+		}
+	})
+}

pkg/tsdb/prometheus/prometheus.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"regexp"
+	"strings"
 
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
 	"github.com/grafana/grafana-plugin-sdk-go/backend/datasource"
@@ -55,6 +56,24 @@ func ProvideService(cfg *setting.Cfg, httpClientProvider httpclient.Provider, pl
 	return s, nil
 }
 
+func forceHttpGet(settingsJson map[string]interface{}) bool {
+	methodInterface, exists := settingsJson["httpMethod"]
+	if !exists {
+		return false
+	}
+
+	method, ok := methodInterface.(string)
+	if !ok {
+		return false
+	}
+
+	if strings.ToLower(method) != "get" {
+		return false
+	}
+
+	return true
+}
+
 func newInstanceSettings(httpClientProvider httpclient.Provider) datasource.InstanceFactoryFunc {
 	return func(settings backend.DataSourceInstanceSettings) (instancemgmt.Instance, error) {
 		jsonData := map[string]interface{}{}
@@ -86,7 +105,7 @@ func newInstanceSettings(httpClientProvider httpclient.Provider) datasource.Inst
 			}
 		}
 
-		client, err := createClient(settings.URL, httpCliOpts, httpClientProvider)
+		client, err := createClient(settings.URL, httpCliOpts, httpClientProvider, forceHttpGet(jsonData))
 		if err != nil {
 			return nil, err
 		}
@@ -124,9 +143,13 @@ func (s *Service) QueryData(ctx context.Context, req *backend.QueryDataRequest)
 	return result, err
 }
 
-func createClient(url string, httpOpts sdkhttpclient.Options, clientProvider httpclient.Provider) (apiv1.API, error) {
+func createClient(url string, httpOpts sdkhttpclient.Options, clientProvider httpclient.Provider, forceHttpGet bool) (apiv1.API, error) {
-	customMiddlewares := customQueryParametersMiddleware(plog)
+	customParamsMiddleware := customQueryParametersMiddleware(plog)
-	httpOpts.Middlewares = []sdkhttpclient.Middleware{customMiddlewares}
+	middlewares := []sdkhttpclient.Middleware{customParamsMiddleware}
+	if forceHttpGet {
+		middlewares = append(middlewares, forceHttpGetMiddleware(plog))
+	}
+	httpOpts.Middlewares = middlewares
 
 	roundTripper, err := clientProvider.GetTransport(httpOpts)
 	if err != nil {