log: Only chmod if permission bits differ; make log dir (#6761)

* log: Only chmod if permission bits differ

Follow-up to #6314 and https://caddy.community/t/caddy-2-9-0-breaking-change/27576/11

* Fix test

* Refactor FileWriter

* Ooooh octal... right...

modules/logging/filewriter.go

@@ -20,6 +20,7 @@ import (
 	"io"
 	"math"
 	"os"
+	"path/filepath"
 	"strconv"
 
 	"github.com/dustin/go-humanize"
@@ -146,12 +147,47 @@ 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
+	modeIfCreating := os.FileMode(fw.Mode)
+	if modeIfCreating == 0 {
+		modeIfCreating = 0o600
 	}
 
-	// roll log files by default
-	if fw.Roll == nil || *fw.Roll {
+	// roll log files as a sensible default to avoid disk space exhaustion
+	roll := fw.Roll == nil || *fw.Roll
+
+	// create the file if it does not exist; create with the configured mode, or default
+	// to restrictive if not set. (lumberjack will reuse the file mode across log rotation)
+	if err := os.MkdirAll(filepath.Dir(fw.Filename), 0o700); err != nil {
+		return nil, err
+	}
+	file, err := os.OpenFile(fw.Filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, modeIfCreating)
+	if err != nil {
+		return nil, err
+	}
+	info, err := file.Stat()
+	if roll {
+		file.Close() // lumberjack will reopen it on its own
+	}
+
+	// Ensure already existing files have the right mode, since OpenFile will not set the mode in such case.
+	if configuredMode := os.FileMode(fw.Mode); configuredMode != 0 {
+		if err != nil {
+			return nil, fmt.Errorf("unable to stat log file to see if we need to set permissions: %v", err)
+		}
+		// only chmod if the configured mode is different
+		if info.Mode()&os.ModePerm != configuredMode&os.ModePerm {
+			if err = os.Chmod(fw.Filename, configuredMode); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	// if not rolling, then the plain file handle is all we need
+	if !roll {
+		return file, nil
+	}
+
+	// otherwise, return a rolling log
 	if fw.RollSizeMB == 0 {
 		fw.RollSizeMB = 100
 	}
@@ -165,20 +201,6 @@ func (fw FileWriter) OpenWriter() (io.WriteCloser, error) {
 	if fw.RollKeepDays == 0 {
 		fw.RollKeepDays = 90
 	}
-
-		// create the file if it does not exist with the right mode.
-		// lumberjack will reuse the file mode across log rotation.
-		f_tmp, err := os.OpenFile(fw.Filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, os.FileMode(fw.Mode))
-		if err != nil {
-			return nil, err
-		}
-		f_tmp.Close()
-		// ensure already existing files have the right mode,
-		// since OpenFile will not set the mode in such case.
-		if err = os.Chmod(fw.Filename, os.FileMode(fw.Mode)); err != nil {
-			return nil, err
-		}
-
 	return &lumberjack.Logger{
 		Filename:   fw.Filename,
 		MaxSize:    fw.RollSizeMB,
@@ -187,10 +209,6 @@ func (fw FileWriter) OpenWriter() (io.WriteCloser, error) {
 		LocalTime:  fw.RollLocalTime,
 		Compress:   *fw.RollCompress,
 	}, nil
-	}
-
-	// otherwise just open a regular file
-	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:

modules/logging/filewriter_test.go

@@ -20,6 +20,7 @@ import (
 	"encoding/json"
 	"os"
 	"path"
+	"path/filepath"
 	"syscall"
 	"testing"
 
@@ -77,7 +78,7 @@ func TestFileCreationMode(t *testing.T) {
 				t.Fatalf("failed to create tempdir: %v", err)
 			}
 			defer os.RemoveAll(dir)
-			fpath := path.Join(dir, "test.log")
+			fpath := filepath.Join(dir, "test.log")
 			tt.fw.Filename = fpath
 
 			logger, err := tt.fw.OpenWriter()
@@ -92,7 +93,7 @@ func TestFileCreationMode(t *testing.T) {
 			}
 
 			if st.Mode() != tt.wantMode {
-				t.Errorf("file mode is %v, want %v", st.Mode(), tt.wantMode)
+				t.Errorf("%s: file mode is %v, want %v", tt.name, st.Mode(), tt.wantMode)
 			}
 		})
 	}