Add log file handling and viewing capabilities

This commit introduces the ability to handle log files through the API and
provides a new log viewing page. The API now supports GET and DELETE methods
for log file operations, allowing retrieval and deletion of log contents.
A new log.html page has been added for viewing logs in the browser, with
automatic refresh every 5 seconds and styling based on log levels.

The app.go file has been updated to include a GetLogFilepath function that
retrieves or generates the log file path. The NewLogger function now accepts
a file parameter to enable file logging. The main.js file has been updated
to include a link to the new log.html page.

This enhancement improves the observability and management of the application
by providing real-time access to logs and the ability to clear them directly
from the web interface.

internal/app/app.go

@@ -5,6 +5,7 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -21,6 +22,7 @@ var Version = "1.8.4"
 var UserAgent = "go2rtc/" + Version
 
 var ConfigPath string
+var LogFilePath string
 var Info = map[string]any{
 	"version": Version,
 }
@@ -77,16 +79,66 @@ func Init() {
 
 	LoadConfig(&cfg)
 
-	log.Logger = NewLogger(cfg.Mod["format"], cfg.Mod["level"])
+	log.Logger = NewLogger(cfg.Mod["format"], cfg.Mod["level"], GetLogFilepath())
 
 	modules = cfg.Mod
 
 	log.Info().Msgf("go2rtc version %s %s/%s", Version, runtime.GOOS, runtime.GOARCH)
+	log.Debug().Msgf("[log] file: %s", GetLogFilepath())
 
 	migrateStore()
 }
 
-func NewLogger(format string, level string) zerolog.Logger {
+// GetLogFilepath retrieves the file path for the log file from the application's configuration.
+// The configuration is expected to be in YAML format and contain a "log" section with a "file" key.
+// It uses the LoadConfig function to populate the cfg structure with the configuration data.
+//
+// Returns:
+//
+//	string: The file path of the log file as specified in the configuration.
+//
+// Note:
+//
+//	The function assumes that the LoadConfig function is defined elsewhere and is responsible
+//	for loading and parsing the configuration into the provided struct.
+//	The cfg struct is an anonymous struct with a Mod field, which is a map with string keys and values.
+//	The "log" key within the Mod map is expected to contain a sub-map with the "file" key that holds the log file path.
+//
+// Example of expected YAML configuration:
+//
+//	log:
+//	  file: "/path/to/logfile.log"
+//
+// If the "file" key is not found within the "log" section of the configuration, the function will return an empty string.
+func GetLogFilepath() string {
+	var cfg struct {
+		Mod map[string]string `yaml:"log"`
+	}
+
+	if LogFilePath != "" {
+		return LogFilePath
+	}
+
+	LoadConfig(&cfg)
+
+	if cfg.Mod["file"] == "" {
+		// Generate temporary log file
+		tmpFile, err := ioutil.TempFile("", "go2rtc*.log")
+		if err != nil {
+			return ""
+		}
+		defer tmpFile.Close()
+
+		LogFilePath = tmpFile.Name()
+
+	} else {
+		LogFilePath = cfg.Mod["file"]
+	}
+
+	return LogFilePath
+}
+
+func NewLogger(format string, level string, file string) zerolog.Logger {
 	var writer io.Writer = os.Stdout
 
 	if format != "json" {
@@ -96,6 +148,19 @@ func NewLogger(format string, level string) zerolog.Logger {
 		}
 	}
 
+	if file != "" {
+		fileHandler, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
+		fileLogger := zerolog.ConsoleWriter{
+			Out: fileHandler, TimeFormat: "15:04:05.000",
+			NoColor: true,
+		}
+
+		if err == nil {
+			writer = zerolog.MultiLevelWriter(writer, fileLogger)
+		}
+
+	}
+
 	zerolog.TimeFieldFormat = time.RFC3339Nano
 
 	lvl, err := zerolog.ParseLevel(level)