server+healthcheck: rename function, add absolute disk space function

With this commit we rename the existing AvailableDiskSpace function to
its correct name AvailableDiskSpaceRatio as it only returns a ratio. We
then go ahead and add a new function that returns the actual number of
free bytes available on a file system.

This also fixes some comments and always returns an error instead of
panicking.

healthcheck/diskcheck.go

@@ -4,8 +4,9 @@ package healthcheck
 
 import "syscall"
 
-// AvailableDiskSpace returns ratio of available disk space to total capacity.
-func AvailableDiskSpace(path string) (float64, error) {
+// AvailableDiskSpaceRatio returns ratio of available disk space to total
+// capacity.
+func AvailableDiskSpaceRatio(path string) (float64, error) {
 	s := syscall.Statfs_t{}
 	err := syscall.Statfs(path, &s)
 	if err != nil {
@@ -16,3 +17,17 @@ func AvailableDiskSpace(path string) (float64, error) {
 	// free blocks.
 	return float64(s.Bfree) / float64(s.Blocks), nil
 }
+
+// AvailableDiskSpace returns the available disk space in bytes of the given
+// file system.
+func AvailableDiskSpace(path string) (uint64, error) {
+	s := syscall.Statfs_t{}
+	err := syscall.Statfs(path, &s)
+	if err != nil {
+		return 0, err
+	}
+
+	// Some OSes have s.Bavail defined as int64, others as uint64, so we
+	// need the explicit type conversion here.
+	return uint64(s.Bavail) * uint64(s.Bsize), nil // nolint:unconvert
+}

healthcheck/diskcheck_netbsd.go

@@ -2,9 +2,9 @@ package healthcheck
 
 import "golang.org/x/sys/unix"
 
-// AvailableDiskSpace returns ratio of available disk space to total capacity
-// for solaris.
-func AvailableDiskSpace(path string) (float64, error) {
+// AvailableDiskSpaceRatio returns ratio of available disk space to total
+// capacity for netbsd.
+func AvailableDiskSpaceRatio(path string) (float64, error) {
 	s := unix.Statvfs_t{}
 	err := unix.Statvfs(path, &s)
 	if err != nil {
@@ -15,3 +15,15 @@ func AvailableDiskSpace(path string) (float64, error) {
 	// free blocks.
 	return float64(s.Bfree) / float64(s.Blocks), nil
 }
+
+// AvailableDiskSpace returns the available disk space in bytes of the given
+// file system for netbsd.
+func AvailableDiskSpace(path string) (uint64, error) {
+	s := unix.Statvfs_t{}
+	err := unix.Statvfs(path, &s)
+	if err != nil {
+		return 0, err
+	}
+
+	return s.Bavail * uint64(s.Bsize), nil
+}

healthcheck/diskcheck_openbsd.go

@@ -2,9 +2,9 @@ package healthcheck
 
 import "golang.org/x/sys/unix"
 
-// AvailableDiskSpace returns ratio of available disk space to total capacity
-// for solaris.
-func AvailableDiskSpace(path string) (float64, error) {
+// AvailableDiskSpaceRatio returns ratio of available disk space to total
+// capacity for openbsd.
+func AvailableDiskSpaceRatio(path string) (float64, error) {
 	s := unix.Statfs_t{}
 	err := unix.Statfs(path, &s)
 	if err != nil {
@@ -15,3 +15,15 @@ func AvailableDiskSpace(path string) (float64, error) {
 	// free blocks.
 	return float64(s.F_bfree) / float64(s.F_blocks), nil
 }
+
+// AvailableDiskSpace returns the available disk space in bytes of the given
+// file system for openbsd.
+func AvailableDiskSpace(path string) (uint64, error) {
+	s := unix.Statfs_t{}
+	err := unix.Statfs(path, &s)
+	if err != nil {
+		return 0, err
+	}
+
+	return uint64(s.F_bavail) * uint64(s.F_bsize), nil
+}

healthcheck/diskcheck_solaris.go

@@ -2,9 +2,9 @@ package healthcheck
 
 import "golang.org/x/sys/unix"
 
-// AvailableDiskSpace returns ratio of available disk space to total capacity
-// for solaris.
-func AvailableDiskSpace(path string) (float64, error) {
+// AvailableDiskSpaceRatio returns ratio of available disk space to total
+// capacity for solaris.
+func AvailableDiskSpaceRatio(path string) (float64, error) {
 	s := unix.Statvfs_t{}
 	err := unix.Statvfs(path, &s)
 	if err != nil {
@@ -15,3 +15,15 @@ func AvailableDiskSpace(path string) (float64, error) {
 	// free blocks.
 	return float64(s.Bfree) / float64(s.Blocks), nil
 }
+
+// AvailableDiskSpace returns the available disk space in bytes of the given
+// file system for solaris.
+func AvailableDiskSpace(path string) (uint64, error) {
+	s := unix.Statvfs_t{}
+	err := unix.Statvfs(path, &s)
+	if err != nil {
+		return 0, err
+	}
+
+	return s.Bavail * uint64(s.Bsize), nil
+}

healthcheck/diskcheck_windows.go

@@ -2,16 +2,30 @@ package healthcheck
 
 import "golang.org/x/sys/windows"
 
-// AvailableDiskSpace returns ratio of available disk space to total capacity
-// for windows.
-func AvailableDiskSpace(path string) (float64, error) {
+// AvailableDiskSpaceRatio returns ratio of available disk space to total
+// capacity for windows.
+func AvailableDiskSpaceRatio(path string) (float64, error) {
 	var free, total, avail uint64
 
 	pathPtr, err := windows.UTF16PtrFromString(path)
 	if err != nil {
-		panic(err)
+		return 0, err
 	}
 	err = windows.GetDiskFreeSpaceEx(pathPtr, &free, &total, &avail)
 
 	return float64(avail) / float64(total), nil
 }
+
+// AvailableDiskSpace returns the available disk space in bytes of the given
+// file system for windows.
+func AvailableDiskSpace(path string) (uint64, error) {
+	var free, total, avail uint64
+
+	pathPtr, err := windows.UTF16PtrFromString(path)
+	if err != nil {
+		return 0, err
+	}
+	err = windows.GetDiskFreeSpaceEx(pathPtr, &free, &total, &avail)
+
+	return avail, nil
+}

server.go

@@ -1302,7 +1302,9 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 	diskCheck := healthcheck.NewObservation(
 		"disk space",
 		func() error {
-			free, err := healthcheck.AvailableDiskSpace(cfg.LndDir)
+			free, err := healthcheck.AvailableDiskSpaceRatio(
+				cfg.LndDir,
+			)
 			if err != nil {
 				return err
 			}