logging: Customize log file permissions (#6314)

Adding a "mode" option to overwrite the default logfile permissions.
Default remains "0600" which is the one currently used by lumberjack.

modules/logging/filewriter.go

@@ -15,6 +15,7 @@
 package logging
 
 import (
+	"encoding/json"
 	"fmt"
 	"io"
 	"math"
@@ -33,6 +34,43 @@ func init() {
 	caddy.RegisterModule(FileWriter{})
 }
 
+// fileMode is a string made of 1 to 4 octal digits representing
+// a numeric mode as specified with the `chmod` unix command.
+// `"0777"` and `"777"` are thus equivalent values.
+type fileMode os.FileMode
+
+// UnmarshalJSON satisfies json.Unmarshaler.
+func (m *fileMode) UnmarshalJSON(b []byte) error {
+	if len(b) == 0 {
+		return io.EOF
+	}
+
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+
+	mode, err := parseFileMode(s)
+	if err != nil {
+		return err
+	}
+
+	*m = fileMode(mode)
+	return err
+}
+
+// parseFileMode parses a file mode string,
+// adding support for `chmod` unix command like
+// 1 to 4 digital octal values.
+func parseFileMode(s string) (os.FileMode, error) {
+	modeStr := fmt.Sprintf("%04s", s)
+	mode, err := strconv.ParseUint(modeStr, 8, 32)
+	if err != nil {
+		return 0, err
+	}
+	return os.FileMode(mode), nil
+}
+
 // FileWriter can write logs to files. By default, log files
 // are rotated ("rolled") when they get large, and old log
 // files get deleted, to ensure that the process does not
@@ -41,6 +79,10 @@ type FileWriter struct {
 	// Filename is the name of the file to write.
 	Filename string `json:"filename,omitempty"`
 
+	// The file permissions mode.
+	// 0600 by default.
+	Mode fileMode `json:"mode,omitempty"`
+
 	// Roll toggles log rolling or rotation, which is
 	// enabled by default.
 	Roll *bool `json:"roll,omitempty"`
@@ -100,6 +142,10 @@ func (fw FileWriter) WriterKey() string {
 
 // OpenWriter opens a new file writer.
 func (fw FileWriter) OpenWriter() (io.WriteCloser, error) {
+	if fw.Mode == 0 {
+		fw.Mode = 0o600
+	}
+
 	// roll log files by default
 	if fw.Roll == nil || *fw.Roll {
 		if fw.RollSizeMB == 0 {
@@ -116,6 +162,9 @@ func (fw FileWriter) OpenWriter() (io.WriteCloser, error) {
 			fw.RollKeepDays = 90
 		}
 
+		f_tmp, _ := os.OpenFile(fw.Filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, os.FileMode(fw.Mode))
+		f_tmp.Close()
+
 		return &lumberjack.Logger{
 			Filename:   fw.Filename,
 			MaxSize:    fw.RollSizeMB,
@@ -127,12 +176,13 @@ func (fw FileWriter) OpenWriter() (io.WriteCloser, error) {
 	}
 
 	// otherwise just open a regular file
-	return os.OpenFile(fw.Filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0o666)
+	return os.OpenFile(fw.Filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, os.FileMode(fw.Mode))
 }
 
 // UnmarshalCaddyfile sets up the module from Caddyfile tokens. Syntax:
 //
 //	file <filename> {
+//	    mode          <mode>
 //	    roll_disabled
 //	    roll_size     <size>
 //	    roll_uncompressed
@@ -150,7 +200,7 @@ func (fw FileWriter) OpenWriter() (io.WriteCloser, error) {
 // The roll_keep_for duration has day resolution.
 // Fractional values are rounded up to the next whole number of days.
 //
-// If any of the roll_size, roll_keep, or roll_keep_for subdirectives are
+// If any of the mode, roll_size, roll_keep, or roll_keep_for subdirectives are
 // omitted or set to a zero value, then Caddy's default value for that
 // subdirective is used.
 func (fw *FileWriter) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
@@ -165,6 +215,17 @@ func (fw *FileWriter) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 
 	for d.NextBlock(0) {
 		switch d.Val() {
+		case "mode":
+			var modeStr string
+			if !d.AllArgs(&modeStr) {
+				return d.ArgErr()
+			}
+			mode, err := parseFileMode(modeStr)
+			if err != nil {
+				return d.Errf("parsing mode: %v", err)
+			}
+			fw.Mode = fileMode(mode)
+
 		case "roll_disabled":
 			var f bool
 			fw.Roll = &f