logging: Support placeholders in level and filename (#2872)

* Add support for placeholders in Config

Fixes #2870

* Replace placeholders only in logging config.

Placeholders in log level and filename incase of file output are replaced.

* Add Provision to filewriter module for replacing placeholders

2 files changed, 29 insertions, 2 deletions

diff --git a/logging.go b/logging.go
index e809617..97c0513 100644
--- a/logging.go
+++ b/logging.go
@@ -280,8 +280,15 @@ type CustomLog struct {
 }
 
 func (cl *CustomLog) provision(ctx Context, logging *Logging) error {
+	// Replace placeholder for log level
+	repl := NewReplacer()
+	level, err := repl.ReplaceOrErr(cl.Level, true, true)
+	if err != nil {
+		return fmt.Errorf("invalid log level: %v", err)
+	}
+
 	// set up the log level
-	switch cl.Level {
+	switch level {
 	case "debug":
 		cl.levelEnabler = zapcore.DebugLevel
 	case "", "info":
@@ -351,7 +358,7 @@ func (cl *CustomLog) provision(ctx Context, logging *Logging) error {
 	if cl.writerOpener == nil {
 		cl.writerOpener = StderrWriter{}
 	}
-	var err error
+
 	cl.writer, _, err = logging.openWriter(cl.writerOpener)
 	if err != nil {
 		return fmt.Errorf("opening log writer using %#v: %v", cl.writerOpener, err)
diff --git a/modules/logging/filewriter.go b/modules/logging/filewriter.go
index 29e805e..6957b6a 100644
--- a/modules/logging/filewriter.go
+++ b/modules/logging/filewriter.go
@@ -15,6 +15,7 @@
 package logging
 
 import (
+	"fmt"
 	"io"
 	"os"
 	"path/filepath"
@@ -46,6 +47,19 @@ func (FileWriter) CaddyModule() caddy.ModuleInfo {
 	}
 }
 
+// Provision sets up the module
+func (fw *FileWriter) Provision(ctx caddy.Context) error {
+	// Replace placeholder in filename
+	repl := caddy.NewReplacer()
+	filename, err := repl.ReplaceOrErr(fw.Filename, true, true)
+	if err != nil {
+		return fmt.Errorf("invalid filename for log file: %v", err)
+	}
+
+	fw.Filename = filename
+	return nil
+}
+
 func (fw FileWriter) String() string {
 	fpath, err := filepath.Abs(fw.Filename)
 	if err == nil {
@@ -76,6 +90,7 @@ func (fw FileWriter) OpenWriter() (io.WriteCloser, error) {
 		if fw.RollKeepDays == 0 {
 			fw.RollKeepDays = 90
 		}
+
 		return &lumberjack.Logger{
 			Filename:   fw.Filename,
 			MaxSize:    fw.RollSizeMB,
@@ -89,3 +104,8 @@ 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, 0666)
 }
+
+// Interface guards
+var (
+	_ caddy.Provisioner = (*FileWriter)(nil)
+)