Stop folder when running out of disk space (fixes #2057)

& tweaks by calmh

lib/osutil/osutil.go

@@ -16,6 +16,7 @@ import (
 	"runtime"
 	"strings"
 
+	"github.com/calmh/du"
 	"github.com/syncthing/syncthing/lib/sync"
 )
 
@@ -210,3 +211,13 @@ func init() {
 func IsWindowsExecutable(path string) bool {
 	return execExts[strings.ToLower(filepath.Ext(path))]
 }
+
+func DiskFreeBytes(path string) (free int64, err error) {
+	u, err := du.Get(path)
+	return u.FreeBytes, err
+}
+
+func DiskFreePercentage(path string) (freePct float64, err error) {
+	u, err := du.Get(path)
+	return (float64(u.FreeBytes) / float64(u.TotalBytes)) * 100, err
+}

lib/osutil/osutil_test.go

@@ -164,3 +164,18 @@ func TestInWritableDirWindowsRename(t *testing.T) {
 		}
 	}
 }
+
+func TestDiskUsage(t *testing.T) {
+	free, err := osutil.DiskFreePercentage(".")
+	if err != nil {
+		if runtime.GOOS == "netbsd" ||
+			runtime.GOOS == "openbsd" ||
+			runtime.GOOS == "solaris" {
+			t.Skip()
+		}
+		t.Errorf("Unexpected error: %s", err)
+	}
+	if free < 1 {
+		t.Error("Disk is full?", free)
+	}
+}