Backend Plugins: Convert test data source to use SDK contracts (#29916)

Converts the core testdata data source to use the SDK contracts and by that 
implementing a backend plugin in core Grafana in similar manner as an external one.

Co-authored-by: Will Browne <will.browne@grafana.com>
Co-authored-by: Marcus Efraimsson <marefr@users.noreply.github.com>
Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

pkg/tsdb/testdatasource/resource_handler.go

@@ -0,0 +1,157 @@
+package testdatasource
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"sort"
+	"strconv"
+	"time"
+
+	"github.com/grafana/grafana/pkg/infra/log"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend/resource/httpadapter"
+)
+
+func (p *testDataPlugin) registerRoutes(mux *http.ServeMux) {
+	mux.HandleFunc("/", p.testGetHandler)
+	mux.HandleFunc("/scenarios", p.getScenariosHandler)
+	mux.HandleFunc("/stream", p.testStreamHandler)
+	mux.Handle("/test", createJSONHandler(p.logger))
+	mux.Handle("/test/json", createJSONHandler(p.logger))
+	mux.HandleFunc("/boom", p.testPanicHandler)
+}
+
+func (p *testDataPlugin) testGetHandler(rw http.ResponseWriter, req *http.Request) {
+	p.logger.Debug("Received resource call", "url", req.URL.String(), "method", req.Method)
+
+	if req.Method != http.MethodGet {
+		return
+	}
+
+	if _, err := rw.Write([]byte("Hello world from test datasource!")); err != nil {
+		p.logger.Error("Failed to write response", "error", err)
+		return
+	}
+	rw.WriteHeader(http.StatusOK)
+}
+
+func (p *testDataPlugin) getScenariosHandler(rw http.ResponseWriter, req *http.Request) {
+	result := make([]interface{}, 0)
+
+	scenarioIds := make([]string, 0)
+	for id := range p.scenarios {
+		scenarioIds = append(scenarioIds, id)
+	}
+	sort.Strings(scenarioIds)
+
+	for _, scenarioID := range scenarioIds {
+		scenario := p.scenarios[scenarioID]
+		result = append(result, map[string]interface{}{
+			"id":          scenario.ID,
+			"name":        scenario.Name,
+			"description": scenario.Description,
+			"stringInput": scenario.StringInput,
+		})
+	}
+
+	bytes, err := json.Marshal(&result)
+	if err != nil {
+		p.logger.Error("Failed to marshal response body to JSON", "error", err)
+	}
+
+	rw.Header().Set("Content-Type", "application/json")
+	rw.WriteHeader(http.StatusOK)
+	if _, err := rw.Write(bytes); err != nil {
+		p.logger.Error("Failed to write response", "error", err)
+	}
+}
+
+func (p *testDataPlugin) testStreamHandler(rw http.ResponseWriter, req *http.Request) {
+	p.logger.Debug("Received resource call", "url", req.URL.String(), "method", req.Method)
+
+	if req.Method != http.MethodGet {
+		return
+	}
+
+	count := 10
+	countstr := req.URL.Query().Get("count")
+	if countstr != "" {
+		if i, err := strconv.Atoi(countstr); err == nil {
+			count = i
+		}
+	}
+
+	sleep := req.URL.Query().Get("sleep")
+	sleepDuration, err := time.ParseDuration(sleep)
+	if err != nil {
+		sleepDuration = time.Millisecond
+	}
+
+	rw.Header().Set("Content-Type", "text/plain")
+	rw.WriteHeader(http.StatusOK)
+
+	for i := 1; i <= count; i++ {
+		if _, err := io.WriteString(rw, fmt.Sprintf("Message #%d", i)); err != nil {
+			p.logger.Error("Failed to write response", "error", err)
+			return
+		}
+		rw.(http.Flusher).Flush()
+		time.Sleep(sleepDuration)
+	}
+}
+
+func createJSONHandler(logger log.Logger) http.Handler {
+	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		logger.Debug("Received resource call", "url", req.URL.String(), "method", req.Method)
+
+		var reqData map[string]interface{}
+		if req.Body != nil {
+			defer func() {
+				if err := req.Body.Close(); err != nil {
+					logger.Warn("Failed to close response body", "err", err)
+				}
+			}()
+			b, err := ioutil.ReadAll(req.Body)
+			if err != nil {
+				logger.Error("Failed to read request body to bytes", "error", err)
+			} else {
+				err := json.Unmarshal(b, &reqData)
+				if err != nil {
+					logger.Error("Failed to unmarshal request body to JSON", "error", err)
+				}
+
+				logger.Debug("Received resource call body", "body", reqData)
+			}
+		}
+
+		config := httpadapter.PluginConfigFromContext(req.Context())
+
+		data := map[string]interface{}{
+			"message": "Hello world from test datasource!",
+			"request": map[string]interface{}{
+				"method":  req.Method,
+				"url":     req.URL,
+				"headers": req.Header,
+				"body":    reqData,
+				"config":  config,
+			},
+		}
+		bytes, err := json.Marshal(&data)
+		if err != nil {
+			logger.Error("Failed to marshal response body to JSON", "error", err)
+		}
+
+		rw.Header().Set("Content-Type", "application/json")
+		rw.WriteHeader(http.StatusOK)
+		if _, err := rw.Write(bytes); err != nil {
+			logger.Error("Failed to write response", "error", err)
+		}
+	})
+}
+
+func (p *testDataPlugin) testPanicHandler(rw http.ResponseWriter, req *http.Request) {
+	panic("BOOM")
+}