added support to enable opt-in for forwarding exit spans without an entry span (#684)

added support for opt-in exit spans without an entry span.

Author: Angith

README.md

@@ -145,6 +145,14 @@ col.StartSpan("log.go", []ot.StartSpanOption{
 
 This log can then be visualized in the dashboard under Analytics/Logs. You can add a filter by service name. In our example, the service name is "My Go App".
 
+### Opt-in Exit Spans
+
+ Go tracer support the opt-in feature for the exit spans. When enabled, the collector can start capturing exit spans, even without an entry span. This capability is particularly useful for scenarios like cronjobs and other background tasks, enabling the users to tailor the tracing according to their specific requirements. By setting the `INSTANA_ALLOW_ROOT_EXIT_SPAN` variable, users can choose whether the tracer should start a trace with an exit span or not. The environment variable can have 2 values. (1: Tracer should record exit spans for the outgoing calls, when it has no active entry span. 0 or any other values: Tracer should not start a trace with an exit span).
+
+ ```bash
+export INSTANA_ALLOW_ROOT_EXIT_SPAN=1
+ ```
+
 ### Complete Example
 
 [Basic Usage](./example/basic_usage/main.go)

instrumentation_http.go

@@ -182,23 +182,27 @@ func RoundTripper(sensor TracerLogger, original http.RoundTripper) http.RoundTri
 	}
 	return tracingRoundTripper(func(req *http.Request) (*http.Response, error) {
 		ctx := req.Context()
-		parentSpan, ok := SpanFromContext(ctx)
-		if !ok {
-			// don't trace the exit call if there was no entry span provided
-			return original.RoundTrip(req)
-		}
 
 		sanitizedURL := cloneURL(req.URL)
 		sanitizedURL.RawQuery = ""
 		sanitizedURL.User = nil
 
-		span := sensor.Tracer().StartSpan("http",
+		opts := []ot.StartSpanOption{
 			ext.SpanKindRPCClient,
-			ot.ChildOf(parentSpan.Context()),
 			ot.Tags{
 				"http.url":    sanitizedURL.String(),
 				"http.method": req.Method,
-			})
+			},
+		}
+
+		tracer := sensor.Tracer()
+		parentSpan, ok := SpanFromContext(ctx)
+		if ok {
+			tracer = parentSpan.Tracer()
+			opts = append(opts, ot.ChildOf(parentSpan.Context()))
+		}
+
+		span := tracer.StartSpan("http", opts...)
 		defer span.Finish()
 
 		// clone the request since the RoundTrip should not modify the original one

instrumentation_http_test.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"strings"
 	"testing"
 
@@ -580,8 +581,10 @@ func TestRoundTripper_WithoutParentSpan(t *testing.T) {
 	defer instana.ShutdownSensor()
 
 	rt := instana.RoundTripper(s, testRoundTripper(func(req *http.Request) (*http.Response, error) {
-		assert.Empty(t, req.Header.Get(instana.FieldT))
-		assert.Empty(t, req.Header.Get(instana.FieldS))
+		// These fields will be present, as an exit span would be created
+		// However the exit spans will not be recorded, as they are discarded before sending to the agent.
+		assert.NotEmpty(t, req.Header.Get(instana.FieldT))
+		assert.NotEmpty(t, req.Header.Get(instana.FieldS))
 
 		return &http.Response{
 			Status:     http.StatusText(http.StatusNotImplemented),
@@ -596,6 +599,40 @@ func TestRoundTripper_WithoutParentSpan(t *testing.T) {
 	assert.Empty(t, recorder.GetQueuedSpans())
 }
 
+func TestRoundTripper_AllowRootExitSpan(t *testing.T) {
+
+	os.Setenv("INSTANA_ALLOW_ROOT_EXIT_SPAN", "1")
+	defer func() {
+		os.Unsetenv("INSTANA_ALLOW_ROOT_EXIT_SPAN")
+	}()
+
+	recorder := instana.NewTestRecorder()
+	s := instana.NewSensorWithTracer(instana.NewTracerWithEverything(&instana.Options{AgentClient: alwaysReadyClient{}}, recorder))
+	defer instana.ShutdownSensor()
+
+	rt := instana.RoundTripper(s, testRoundTripper(func(req *http.Request) (*http.Response, error) {
+		// These fields will be present as an exit span would be created
+		assert.NotEmpty(t, req.Header.Get(instana.FieldT))
+		assert.NotEmpty(t, req.Header.Get(instana.FieldS))
+
+		return &http.Response{
+			Status:     http.StatusText(http.StatusNotImplemented),
+			StatusCode: http.StatusNotImplemented,
+		}, nil
+	}))
+
+	resp, err := rt.RoundTrip(httptest.NewRequest("GET", "http://example.com/hello", nil))
+	require.NoError(t, err)
+	assert.Equal(t, http.StatusNotImplemented, resp.StatusCode)
+
+	// the spans are present in the recorder as INSTANA_ALLOW_ROOT_EXIT_SPAN is configured
+	spans := recorder.GetQueuedSpans()
+	require.Len(t, spans, 1)
+	span := spans[0]
+	assert.Equal(t, 0, span.Ec)
+	assert.EqualValues(t, instana.ExitSpanKind, span.Kind)
+}
+
 func TestRoundTripper_Error(t *testing.T) {
 	serverErr := errors.New("something went wrong")
 

instrumentation_sql_go1.10_test.go

@@ -18,6 +18,7 @@ import (
 )
 
 func TestWrapSQLConnector_Exec(t *testing.T) {
+
 	recorder := instana.NewTestRecorder()
 	s := instana.NewSensorWithTracer(instana.NewTracerWithEverything(&instana.Options{
 		Service:     "go-sensor-test",
@@ -27,7 +28,13 @@ func TestWrapSQLConnector_Exec(t *testing.T) {
 
 	db := sql.OpenDB(instana.WrapSQLConnector(s, "connection string", sqlConnector{}))
 
-	res, err := db.Exec("TEST QUERY")
+	pSpan := s.Tracer().StartSpan("parent-span")
+	ctx := context.Background()
+	if pSpan != nil {
+		ctx = instana.ContextWithSpan(ctx, pSpan)
+	}
+
+	res, err := db.ExecContext(ctx, "TEST QUERY")
 	require.NoError(t, err)
 
 	lastID, err := res.LastInsertId()
@@ -60,18 +67,25 @@ func TestWrapSQLConnector_Exec(t *testing.T) {
 }
 
 func TestWrapSQLConnector_Exec_Error(t *testing.T) {
+
 	recorder := instana.NewTestRecorder()
 	s := instana.NewSensorWithTracer(instana.NewTracerWithEverything(&instana.Options{
 		Service:     "go-sensor-test",
 		AgentClient: alwaysReadyClient{},
 	}, recorder))
 	defer instana.ShutdownSensor()
 
+	pSpan := s.Tracer().StartSpan("parent-span")
+	ctx := context.Background()
+	if pSpan != nil {
+		ctx = instana.ContextWithSpan(ctx, pSpan)
+	}
+
 	db := sql.OpenDB(instana.WrapSQLConnector(s, "connection string", sqlConnector{
 		Error: errors.New("something went wrong"),
 	}))
 
-	_, err := db.Exec("TEST QUERY")
+	_, err := db.ExecContext(ctx, "TEST QUERY")
 	assert.Error(t, err)
 
 	spans := recorder.GetQueuedSpans()
@@ -101,16 +115,23 @@ func TestWrapSQLConnector_Exec_Error(t *testing.T) {
 }
 
 func TestWrapSQLConnector_Query(t *testing.T) {
+
 	recorder := instana.NewTestRecorder()
 	s := instana.NewSensorWithTracer(instana.NewTracerWithEverything(&instana.Options{
 		Service:     "go-sensor-test",
 		AgentClient: alwaysReadyClient{},
 	}, recorder))
 	defer instana.ShutdownSensor()
 
+	pSpan := s.Tracer().StartSpan("parent-span")
+	ctx := context.Background()
+	if pSpan != nil {
+		ctx = instana.ContextWithSpan(ctx, pSpan)
+	}
+
 	db := sql.OpenDB(instana.WrapSQLConnector(s, "connection string", sqlConnector{}))
 
-	res, err := db.Query("TEST QUERY")
+	res, err := db.QueryContext(ctx, "TEST QUERY")
 	require.NoError(t, err)
 
 	cols, err := res.Columns()
@@ -143,6 +164,7 @@ func TestWrapSQLConnector_Query(t *testing.T) {
 }
 
 func TestWrapSQLConnector_Query_Error(t *testing.T) {
+
 	recorder := instana.NewTestRecorder()
 	s := instana.NewSensorWithTracer(instana.NewTracerWithEverything(&instana.Options{
 		Service:     "go-sensor-test",
@@ -155,7 +177,13 @@ func TestWrapSQLConnector_Query_Error(t *testing.T) {
 		Error: dbErr,
 	}))
 
-	_, err := db.Query("TEST QUERY")
+	pSpan := s.Tracer().StartSpan("parent-span")
+	ctx := context.Background()
+	if pSpan != nil {
+		ctx = instana.ContextWithSpan(ctx, pSpan)
+	}
+
+	_, err := db.QueryContext(ctx, "TEST QUERY")
 	assert.Error(t, err)
 
 	spans := recorder.GetQueuedSpans()