Fix stable sort order of query response when encoded to JSON (#425)

This will make sure that the order of query responses (refIDs) are always 
stable (increasing order, e.g. A, B, C even if query requests has the order C, A, B.

Fixes #366

Magefile.go

@@ -1,4 +1,5 @@
-//+build mage
+//go:build mage
+// +build mage
 
 package main
 
@@ -30,6 +31,11 @@ func Test() error {
 	return sh.RunV("go", "test", "./...")
 }
 
+// TestRace runs the test suite with the data race detector enabled.
+func TestRace() error {
+	return sh.RunV("go", "test", "-race", "./...")
+}
+
 func Lint() error {
 	if err := sh.RunV("golangci-lint", "run", "./..."); err != nil {
 		return err

backend/json.go

@@ -2,6 +2,7 @@ package backend
 
 import (
 	"fmt"
+	"sort"
 	"unsafe"
 
 	"github.com/grafana/grafana-plugin-sdk-go/data"
@@ -84,12 +85,20 @@ func writeQueryDataResponseJSON(qdr *QueryDataResponse, stream *jsoniter.Stream)
 	stream.WriteObjectStart()
 	started := false
 
+	refIDs := []string{}
+	for refID := range qdr.Responses {
+		refIDs = append(refIDs, refID)
+	}
+	sort.Strings(refIDs)
+
 	// Make sure all keys in the result are written
-	for id, res := range qdr.Responses {
+	for _, refID := range refIDs {
+		res := qdr.Responses[refID]
+
 		if started {
 			stream.WriteMore()
 		}
-		stream.WriteObjectField(id)
+		stream.WriteObjectField(refID)
 		obj := res // avoid implicit memory
 		writeDataResponseJSON(&obj, stream)
 		started = true

backend/json_test.go

@@ -2,6 +2,7 @@ package backend_test
 
 import (
 	"encoding/json"
+	"fmt"
 	"sync"
 	"testing"
 	"time"
@@ -83,14 +84,14 @@ func TestDataResponseMarshalJSONConcurrent(t *testing.T) {
 	var wg sync.WaitGroup
 	for i := 0; i < 2; i++ {
 		wg.Add(1)
-		go func() {
+		go func(dr backend.DataResponse) {
 			defer wg.Done()
 			for j := 0; j < 100; j++ {
 				jsonData, err := json.Marshal(dr)
 				require.NoError(t, err)
 				require.JSONEq(t, string(initialJSON), string(jsonData))
 			}
-		}()
+		}(dr)
 	}
 	wg.Wait()
 }
@@ -103,14 +104,27 @@ func TestQueryDataResponseMarshalJSONConcurrent(t *testing.T) {
 	var wg sync.WaitGroup
 	for i := 0; i < 2; i++ {
 		wg.Add(1)
-		go func() {
+		go func(qdr *backend.QueryDataResponse) {
 			defer wg.Done()
 			for j := 0; j < 100; j++ {
 				jsonData, err := json.Marshal(qdr)
 				require.NoError(t, err)
 				require.JSONEq(t, string(initialJSON), string(jsonData))
 			}
-		}()
+		}(qdr)
 	}
 	wg.Wait()
 }
+
+func TestQueryDataResponseOrdering(t *testing.T) {
+	qdr := backend.NewQueryDataResponse()
+	qdr.Responses["C"] = testDataResponse()
+	qdr.Responses["A"] = testDataResponse()
+	qdr.Responses["B"] = testDataResponse()
+	b, err := json.Marshal(qdr)
+	require.NoError(t, err)
+
+	expectedDataResponse := `{"frames":[{"schema":{"name":"simple","fields":[{"name":"time","type":"time","typeInfo":{"frame":"time.Time"}},{"name":"valid","type":"boolean","typeInfo":{"frame":"bool"}}]},"data":{"values":[[1577934240000,1577934300000],[true,false]]}},{"schema":{"name":"other","fields":[{"name":"value","type":"number","typeInfo":{"frame":"float64"}}]},"data":{"values":[[1]]}}]}`
+	expected := fmt.Sprintf(`{"results":{"A":%s,"B":%s,"C":%s}}`, expectedDataResponse, expectedDataResponse, expectedDataResponse)
+	require.Equal(t, expected, string(b))
+}