fix: encode events that have no data

sse-encoder.go

@@ -1,122 +1,136 @@
-// Copyright 2014 Manu Martinez-Almeida.  All rights reserved.
-// Use of this source code is governed by a MIT style
-// license that can be found in the LICENSE file.
-
-package sse
-
-import (
-	"encoding/json"
-	"fmt"
-	"io"
-	"net/http"
-	"reflect"
-	"strconv"
-	"strings"
-)
-
-// Server-Sent Events
-// W3C Working Draft 29 October 2009
-// http://www.w3.org/TR/2009/WD-eventsource-20091029/
-
-const ContentType = "text/event-stream;charset=utf-8"
-
-var (
-	contentType = []string{ContentType}
-	noCache     = []string{"no-cache"}
-)
-
-var fieldReplacer = strings.NewReplacer(
-	"\n", "\\n",
-	"\r", "\\r",
-)
-
-var dataReplacer = strings.NewReplacer(
-	"\n", "\ndata:",
-	"\r", "\\r",
-)
-
-type Event struct {
-	Event string
-	Id    string //nolint:staticcheck // ST1003: public API field Id kept for backward compatibility
-	Retry uint
-	Data  any
-}
-
-func Encode(writer io.Writer, event Event) error {
-	w := checkWriter(writer)
-	writeID(w, event.Id)
-	writeEvent(w, event.Event)
-	writeRetry(w, event.Retry)
-	return writeData(w, event.Data)
-}
-
-func writeID(w stringWriter, id string) {
-	if len(id) > 0 {
-		_, _ = w.WriteString("id:")
-		_, _ = fieldReplacer.WriteString(w, id)
-		_, _ = w.WriteString("\n")
-	}
-}
-
-func writeEvent(w stringWriter, event string) {
-	if len(event) > 0 {
-		_, _ = w.WriteString("event:")
-		_, _ = fieldReplacer.WriteString(w, event)
-		_, _ = w.WriteString("\n")
-	}
-}
-
-func writeRetry(w stringWriter, retry uint) {
-	if retry > 0 {
-		_, _ = w.WriteString("retry:")
-		_, _ = w.WriteString(strconv.FormatUint(uint64(retry), 10))
-		_, _ = w.WriteString("\n")
-	}
-}
-
-func writeData(w stringWriter, data any) error {
-	_, _ = w.WriteString("data:")
-
-	bData, ok := data.([]byte)
-	if ok {
-		_, _ = dataReplacer.WriteString(w, string(bData))
-		_, _ = w.WriteString("\n\n")
-		return nil
-	}
-
-	switch kindOfData(data) { //nolint:exhaustive // remaining kinds need no special encoding
-	case reflect.Struct, reflect.Slice, reflect.Map:
-		err := json.NewEncoder(w).Encode(data)
-		if err != nil {
-			return err
-		}
-		_, _ = w.WriteString("\n")
-	default:
-		_, _ = dataReplacer.WriteString(w, fmt.Sprint(data))
-		_, _ = w.WriteString("\n\n")
-	}
-	return nil
-}
-
-func (r Event) Render(w http.ResponseWriter) error {
-	r.WriteContentType(w)
-	return Encode(w, r)
-}
-
-func (r Event) WriteContentType(w http.ResponseWriter) {
-	header := w.Header()
-	header["Content-Type"] = contentType
-
-	if _, exist := header["Cache-Control"]; !exist {
-		header["Cache-Control"] = noCache
-	}
-}
-
-func kindOfData(data any) reflect.Kind {
-	value := reflect.ValueOf(data)
-	valueType := value.Kind()
-	if valueType == reflect.Pointer {
-		valueType = value.Elem().Kind()
-	}
-	return valueType
-}
+// Copyright 2014 Manu Martinez-Almeida.  All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package sse
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"reflect"
+	"strconv"
+	"strings"
+)
+
+// Server-Sent Events
+// W3C Working Draft 29 October 2009
+// http://www.w3.org/TR/2009/WD-eventsource-20091029/
+
+const ContentType = "text/event-stream;charset=utf-8"
+
+var (
+	contentType = []string{ContentType}
+	noCache     = []string{"no-cache"}
+)
+
+var fieldReplacer = strings.NewReplacer(
+	"\n", "\\n",
+	"\r", "\\r",
+)
+
+var dataReplacer = strings.NewReplacer(
+	"\n", "\ndata:",
+	"\r", "\\r",
+)
+
+type Event struct {
+	Event string
+	Id    string //nolint:staticcheck // ST1003: public API field Id kept for backward compatibility
+	Retry uint
+	Data  any
+}
+
+func Encode(writer io.Writer, event Event) error {
+	w := checkWriter(writer)
+	writeID(w, event.Id)
+	writeEvent(w, event.Event)
+	writeRetry(w, event.Retry)
+	return writeData(w, event.Data)
+}
+
+func writeID(w stringWriter, id string) {
+	if len(id) > 0 {
+		_, _ = w.WriteString("id:")
+		_, _ = fieldReplacer.WriteString(w, id)
+		_, _ = w.WriteString("\n")
+	}
+}
+
+func writeEvent(w stringWriter, event string) {
+	if len(event) > 0 {
+		_, _ = w.WriteString("event:")
+		_, _ = fieldReplacer.WriteString(w, event)
+		_, _ = w.WriteString("\n")
+	}
+}
+
+func writeRetry(w stringWriter, retry uint) {
+	if retry > 0 {
+		_, _ = w.WriteString("retry:")
+		_, _ = w.WriteString(strconv.FormatUint(uint64(retry), 10))
+		_, _ = w.WriteString("\n")
+	}
+}
+
+func writeData(w stringWriter, data any) error {
+	_, _ = w.WriteString("data:")
+
+	// A heartbeat often sets only Event. nil must not reach reflect.Value.Kind.
+	if data == nil {
+		_, _ = w.WriteString("\n\n")
+		return nil
+	}
+
+	bData, ok := data.([]byte)
+	if ok {
+		_, _ = dataReplacer.WriteString(w, string(bData))
+		_, _ = w.WriteString("\n\n")
+		return nil
+	}
+
+	switch kindOfData(data) { //nolint:exhaustive // remaining kinds need no special encoding
+	case reflect.Invalid:
+		_, _ = w.WriteString("\n\n")
+	case reflect.Struct, reflect.Slice, reflect.Map:
+		err := json.NewEncoder(w).Encode(data)
+		if err != nil {
+			return err
+		}
+		_, _ = w.WriteString("\n")
+	default:
+		_, _ = dataReplacer.WriteString(w, fmt.Sprint(data))
+		_, _ = w.WriteString("\n\n")
+	}
+	return nil
+}
+
+func (r Event) Render(w http.ResponseWriter) error {
+	r.WriteContentType(w)
+	return Encode(w, r)
+}
+
+func (r Event) WriteContentType(w http.ResponseWriter) {
+	header := w.Header()
+	header["Content-Type"] = contentType
+
+	if _, exist := header["Cache-Control"]; !exist {
+		header["Cache-Control"] = noCache
+	}
+}
+
+func kindOfData(data any) reflect.Kind {
+	value := reflect.ValueOf(data)
+	if !value.IsValid() {
+		return reflect.Invalid
+	}
+	valueType := value.Kind()
+	if valueType == reflect.Pointer {
+		if value.IsNil() {
+			return reflect.Invalid
+		}
+		valueType = value.Elem().Kind()
+	}
+	return valueType
+}