Add test for client's POST fallback

Signed-off-by: Thomas Jackson <jacksontj.89@gmail.com>

api/client.go

@@ -60,7 +60,7 @@ type Client interface {
 	Do(context.Context, *http.Request) (*http.Response, []byte, error)
 }
 
-// DoGetFallback will attempt to do the request as-is, and on a 405 it will fallback to a GET request
+// DoGetFallback will attempt to do the request as-is, and on a 405 it will fallback to a GET request.
 func DoGetFallback(c Client, ctx context.Context, u *url.URL, args url.Values) (*http.Response, []byte, error) {
 	req, err := http.NewRequest(http.MethodPost, u.String(), strings.NewReader(args.Encode()))
 	if err != nil {

api/client_test.go

@@ -16,9 +16,14 @@
 package api
 
 import (
+	"context"
+	"encoding/json"
 	"net/http"
+	"net/http/httptest"
 	"net/url"
 	"testing"
+
+	"github.com/prometheus/tsdb/testutil"
 )
 
 func TestConfig(t *testing.T) {
@@ -113,3 +118,70 @@ func TestClientURL(t *testing.T) {
 		}
 	}
 }
+
+func TestDoGetFallback(t *testing.T) {
+	v := url.Values{"a": []string{"1", "2"}}
+
+	type testResponse struct {
+		Values string
+		Method string
+	}
+
+	// Start a local HTTP server
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		req.ParseForm()
+		r := &testResponse{
+			Values: req.Form.Encode(),
+			Method: req.Method,
+		}
+
+		body, _ := json.Marshal(r)
+
+		if req.Method == http.MethodPost {
+			if req.URL.Path == "/blockPost" {
+				http.Error(w, string(body), http.StatusMethodNotAllowed)
+				return
+			}
+		}
+
+		w.Write(body)
+	}))
+	// Close the server when test finishes
+	defer server.Close()
+
+	u, err := url.Parse(server.URL)
+	testutil.Ok(t, err)
+	client := &httpClient{client: *(server.Client())}
+
+	// Do a post, and ensure that the post succeeds
+	_, b, err := DoGetFallback(client, context.TODO(), u, v)
+	if err != nil {
+		t.Fatalf("Error doing local request: %v", err)
+	}
+	resp := &testResponse{}
+	if err := json.Unmarshal(b, resp); err != nil {
+		t.Fatal(err)
+	}
+	if resp.Method != http.MethodPost {
+		t.Fatalf("Mismatch method")
+	}
+	if resp.Values != v.Encode() {
+		t.Fatalf("Mismatch in values")
+	}
+
+	// Do a fallbcak to a get
+	u.Path = "/blockPost"
+	_, b, err = DoGetFallback(client, context.TODO(), u, v)
+	if err != nil {
+		t.Fatalf("Error doing local request: %v", err)
+	}
+	if err := json.Unmarshal(b, resp); err != nil {
+		t.Fatal(err)
+	}
+	if resp.Method != http.MethodGet {
+		t.Fatalf("Mismatch method")
+	}
+	if resp.Values != v.Encode() {
+		t.Fatalf("Mismatch in values")
+	}
+}