logging: add '-l' arg to set logging level

cmd/cmd.go

@@ -21,6 +21,7 @@ var (
 	sentHeaders  bool
 	privMode     bool
 	printVersion bool
+	logLevel     string
 )
 
 func init() {
@@ -37,6 +38,7 @@ func init() {
 	pflag.BoolVarP(&privMode, "privacy", "P", false, "Drop X-Forwarded and Cloudflare headers from request headers echoed in the response body")
 	pflag.BoolVarP(&sentHeaders, "sent", "s", false, "Dump the HTTP headers added in the response in the response body")
 	pflag.BoolVarP(&printVersion, "version", "v", false, "Print version and exit")
+	pflag.StringVarP(&logLevel, "log-level", "l", "", "Logging level: TRACE, DEBUG, INFO, WARN, ERROR (overrides the LOG_LEVEL env variable)")
 }
 
 type server struct {
@@ -67,6 +69,7 @@ func (s *server) Get(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusOK)
 
 	if s.sentHeaders {
+		logging.Tracef("Dumping sent headers to response body")
 		xHeaders := hdrs.ToMap(w.Header(), nil, false)
 		xHeadersPtr = &xHeaders
 	}
@@ -100,11 +103,32 @@ func Execute() error {
 		fmt.Println(getVersion())
 		return nil
 	}
+
+	// Init logging level
+	if logLevel != "" {
+		os.Setenv("LOG_LEVEL", logLevel)
+	}
+	if err := logging.Init(logLevel); err != nil {
+		logging.Fatalf("Failed to initialize logging: %v", err)
+	}
+
+	logging.Infof("Starting HeaderTrace version %s", getVersion())
+
 	// Parse custom headers
 	customHeaders, err := hdrs.SliceToMap(headers)
 	if err != nil {
-		logging.Fatalf("%v", err)
+		logging.Fatalf("Custom headers: %v", err)
 	}
+	if len(customHeaders) > 0 {
+		logging.Debugf("Custom headers to add in responses: %v", customHeaders)
+	}
+
+	if len(dropHeaders) > 0 {
+		logging.Debugf("Headers to drop from echoed request headers: %v", dropHeaders)
+	}
+
+	logging.Debugf("Privacy mode: %v", privMode)
+	logging.Debugf("Dump sent headers: %v", sentHeaders)
 
 	// Create server instance
 	srv := &server{headers: customHeaders,

main.go

@@ -6,7 +6,6 @@ import (
 )
 
 func main() {
-	logging.Init()
 	if err := cmd.Execute(); err != nil {
 		logging.Fatalf("%v", err)
 	}

pkg/headers/headers.go

@@ -37,16 +37,17 @@ func ToMap(headers http.Header, dropHeaders []string, privMode bool) map[string]
 	for key, values := range headers {
 		lowerKey := strings.ToLower(key)
 		if slices.Contains(normalizedDropHeaders, lowerKey) {
-			logging.Debugf("Dropping header '%s':'%s'", key, strings.Join(values, ","))
+			logging.Debugf("Redact header '%s':'%s'", key, strings.Join(values, ","))
 			continue
 		}
 		if privMode {
 			if isCloudflareHeader(lowerKey) || isXForwardedHeader(lowerKey) {
-				logging.Debugf("Dropping header '%s':'%s' (privacy mode)", key, strings.Join(values, ","))
+				logging.Debugf("Redact header '%s':'%s' (privacy mode)", key, strings.Join(values, ","))
 				continue
 			}
 		}
 		headerMap[key] = strings.Join(values, ",")
+		logging.Tracef("Dump header '%s':'%s'", key, headerMap[key])
 	}
 	return headerMap
 }

pkg/logging/logging.go

@@ -1,6 +1,7 @@
 package logging
 
 import (
+	"fmt"
 	"log"
 	"os"
 	"strings"
@@ -9,7 +10,8 @@ import (
 type level int
 
 const (
-	DEBUG level = iota
+	TRACE level = iota
+	DEBUG
 	INFO
 	WARN
 	ERROR
@@ -18,21 +20,39 @@ const (
 var lvl = INFO
 
 // Init configures the logger. It reads LOG_LEVEL from the environment
-// (one of: DEBUG, INFO, WARN, ERROR) and sets a simple prefix.
-func Init() {
-	if v := os.Getenv("LOG_LEVEL"); v != "" {
-		switch strings.ToUpper(v) {
-		case "DEBUG":
-			lvl = DEBUG
-		case "INFO":
-			lvl = INFO
-		case "WARN":
-			lvl = WARN
-		case "ERROR":
-			lvl = ERROR
-		}
+// (one of: TRACE, DEBUG, INFO, WARN, ERROR) and sets a simple prefix.
+func Init(levelStr string) error {
+	if levelStr == "" {
+		levelStr = os.Getenv("LOG_LEVEL")
 	}
+	if levelStr == "" {
+		levelStr = "INFO"
+	}
+
+	switch strings.ToUpper(levelStr) {
+	case "TRACE":
+		lvl = TRACE
+	case "DEBUG":
+		lvl = DEBUG
+	case "INFO":
+		lvl = INFO
+	case "WARN":
+		lvl = WARN
+	case "ERROR":
+		lvl = ERROR
+	default:
+		return fmt.Errorf("invalid log level: %s", levelStr)
+	}
+
 	log.SetFlags(log.LstdFlags)
+	Tracef("loglevel set to %s", strings.ToUpper(levelStr))
+	return nil
+}
+
+func Tracef(format string, v ...interface{}) {
+	if lvl <= TRACE {
+		log.Printf("TRACE: "+format, v...)
+	}
 }
 
 func Debugf(format string, v ...interface{}) {