Add support for generating a log message to stdout (#19)

* add support for generating a log message to stdout

* update README

README.md

@@ -44,6 +44,13 @@ func main() {
 
 	fmt.Println(event)
 
+	// send a CEF event as log message to stdout
+	event.Log()
+
+	// or if you want to do error handling when
+	// sending the log
+	_, err := event.Log()
+
 }
 
 ```
@@ -54,6 +61,13 @@ $ ./cef
 CEF:0|Cool Vendor|Cool Product|1.0|FLAKY_EVENT|Something flaky happened.|3|sourceAddress=127.0.0.1 requestClientApplication=Go-http-client/1.1
 ```
 
+### Example log output
+
+```bash
+$ ./ceflog
+2020/03/11 21:49:45 CEF:0|Cool Vendor|Cool Product|1.0|FLAKY_EVENT|Something flaky happened.|3|sourceAddress=127.0.0.1 requestClientApplication=Go-http-client/1.1
+```
+
 ## Not yet implemented
 
 * Field limits according to format standard for [known](https://community.microfocus.com/t5/ArcSight-Connectors/ArcSight-Common-Event-Format-CEF-Implementation-Standard/ta-p/1645557?attachment-id=68077) CEF fields

cefevent/cefevent.go

@@ -3,13 +3,16 @@ package cefevent
 import (
 	"errors"
 	"fmt"
+	"log"
+	"os"
 	"reflect"
 	"strings"
 )
 
 type CefEventer interface {
 	Generate() (string, error)
 	Validate() bool
+	Log() (bool, error)
 }
 
 type CefEvent struct {
@@ -74,6 +77,26 @@ func (event *CefEvent) Validate() bool {
 
 }
 
+// Log should be used as a stub in most cases, it either
+// succeeds generating the CEF event and send it to stdout
+// or doesnt and logs that to stderr. This function
+// plays well inside containers.
+func (event *CefEvent) Log() (bool, error) {
+
+	logMessage, err := event.Generate()
+
+	if err != nil {
+		log.SetOutput(os.Stderr)
+		errMsg := "Unable to generate and thereby log the CEF message."
+		log.Println(errMsg)
+		return false, errors.New(errMsg)
+	}
+
+	log.SetOutput(os.Stdout)
+	log.Println(logMessage)
+	return true, nil
+}
+
 func (event CefEvent) Generate() (string, error) {
 
 	if !CefEventer.Validate(&event) {

cefevent_test.go

@@ -143,3 +143,23 @@ func TestCefEventerValidate(t *testing.T) {
 		t.Errorf("Validation should fail here.")
 	}
 }
+
+func TestCefEventerLoggingSuccess(t *testing.T) {
+
+	_, err := event.Log()
+
+	if err != nil {
+		t.Errorf("%v", err)
+	}
+}
+
+func TestCefEventerLoggingFail(t *testing.T) {
+
+	brokenEvent := event
+	brokenEvent.Version = ""
+	_, err := brokenEvent.Log()
+
+	if err == nil {
+		t.Errorf("%v", err)
+	}
+}