Net 3181 consul gh issue 15709 allow log file naming like nomad - fix bug

.changelog/18631.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+agent: Fixed an issue that could cause previous log lines to be overwritten
+```

logging/logfile.go

@@ -60,19 +60,24 @@
 }
 
 func (l *LogFile) openNew() error {
-	createTime := now()
 	newfileName := l.fileName
 	newfilePath := filepath.Join(l.logPath, newfileName)
 
-	// Try creating a file. We truncate the file because we are the only authority to write the logs
-	filePointer, err := os.OpenFile(newfilePath, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0640)
+	// Try creating or opening the active log file. Since the active log file
+	// always has the same name, append log entries to prevent overwriting
+	// previous log data.
+	filePointer, err := os.OpenFile(newfilePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0640)
 	if err != nil {
 		return err
 	}
 
 	l.FileInfo = filePointer
+	stat, err := filePointer.Stat()
+	if err != nil {
+		return err
+	}
 	// New file, new bytes tracker, new creation time :)
-	l.LastCreated = createTime
+	l.LastCreated = l.createTime(stat)
 	l.BytesWritten = 0
 	return nil
 }

logging/logfile_bsd.go

@@ -0,0 +1,16 @@
+//go:build darwin || freebsd || netbsd || openbsd
+// +build darwin freebsd netbsd openbsd
+
+package logging
+
+import (
+	"os"
+	"syscall"
+	"time"
+)
+
+func (l *LogFile) createTime(stat os.FileInfo) time.Time {
+	stat_t := stat.Sys().(*syscall.Stat_t)
+	createTime := stat_t.Ctimespec
+	return time.Unix(int64(createTime.Sec), int64(createTime.Nsec))
+}

logging/logfile_linux.go

@@ -0,0 +1,17 @@
+//go:build dragonfly || linux || solaris
+// +build dragonfly linux solaris
+
+package logging
+
+import (
+	"os"
+	"syscall"
+	"time"
+)
+
+func (l *LogFile) createTime(stat os.FileInfo) time.Time {
+	stat_t := stat.Sys().(*syscall.Stat_t)
+	createTime := stat_t.Ctim
+	// Sec and Nsec are int32 in 32-bit architectures.
+	return time.Unix(int64(createTime.Sec), int64(createTime.Nsec)) //nolint:unconvert
+}

logging/logfile_windows.go

@@ -0,0 +1,14 @@
+package logging
+
+import (
+	"os"
+	"time"
+)
+
+func (l *LogFile) createTime(stat os.FileInfo) time.Time {
+	// Use `ModTime` as an approximation if the exact create time is not
+	// available.
+	// On Windows, the file create time is not updated after the active log
+	// rotates, so use `ModTime` as an approximation as well.
+	return stat.ModTime()
+}