Make goss compile on windows. (#2)

I've extracted the unix-only part to file_unix.go and windows part to file_windows.go. I haven't found an easy way to support owners/groups on windows, so I've left it empty.

TODO: figure out how to write and run integration tests on windows, but probably not this pr.

system/file.go

@@ -9,7 +9,6 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
-	"syscall"
 
 	"github.com/aelsabbahy/goss/util"
 	"github.com/opencontainers/runc/libcontainer/user"
@@ -84,22 +83,6 @@ func (f *DefFile) Contains() (io.Reader, error) {
 	return fh, nil
 }
 
-func (f *DefFile) Mode() (string, error) {
-	if err := f.setup(); err != nil {
-		return "", err
-	}
-
-	fi, err := os.Lstat(f.realPath)
-	if err != nil {
-		return "", err
-	}
-
-	sys := fi.Sys()
-	stat := sys.(*syscall.Stat_t)
-	mode := fmt.Sprintf("%04o", (stat.Mode & 07777))
-	return mode, nil
-}
-
 func (f *DefFile) Size() (int, error) {
 	if err := f.setup(); err != nil {
 		return 0, err
@@ -145,42 +128,6 @@ func (f *DefFile) Filetype() (string, error) {
 	return "file", nil
 }
 
-func (f *DefFile) Owner() (string, error) {
-	if err := f.setup(); err != nil {
-		return "", err
-	}
-
-	fi, err := os.Lstat(f.realPath)
-	if err != nil {
-		return "", err
-	}
-
-	uidS := fmt.Sprint(fi.Sys().(*syscall.Stat_t).Uid)
-	uid, err := strconv.Atoi(uidS)
-	if err != nil {
-		return "", err
-	}
-	return getUserForUid(uid)
-}
-
-func (f *DefFile) Group() (string, error) {
-	if err := f.setup(); err != nil {
-		return "", err
-	}
-
-	fi, err := os.Lstat(f.realPath)
-	if err != nil {
-		return "", err
-	}
-
-	gidS := fmt.Sprint(fi.Sys().(*syscall.Stat_t).Gid)
-	gid, err := strconv.Atoi(gidS)
-	if err != nil {
-		return "", err
-	}
-	return getGroupForGid(gid)
-}
-
 func (f *DefFile) LinkedTo() (string, error) {
 	if err := f.setup(); err != nil {
 		return "", err

system/file_unix.go

@@ -0,0 +1,62 @@
+// +build !windows
+
+package system
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"syscall"
+)
+
+func (f *DefFile) Mode() (string, error) {
+	if err := f.setup(); err != nil {
+		return "", err
+	}
+
+	fi, err := os.Lstat(f.realPath)
+	if err != nil {
+		return "", err
+	}
+
+	sys := fi.Sys()
+	stat := sys.(*syscall.Stat_t)
+	mode := fmt.Sprintf("%04o", (stat.Mode & 07777))
+	return mode, nil
+}
+
+func (f *DefFile) Owner() (string, error) {
+	if err := f.setup(); err != nil {
+		return "", err
+	}
+
+	fi, err := os.Lstat(f.realPath)
+	if err != nil {
+		return "", err
+	}
+
+	uidS := fmt.Sprint(fi.Sys().(*syscall.Stat_t).Uid)
+	uid, err := strconv.Atoi(uidS)
+	if err != nil {
+		return "", err
+	}
+	return getUserForUid(uid)
+}
+
+func (f *DefFile) Group() (string, error) {
+	if err := f.setup(); err != nil {
+		return "", err
+	}
+
+	fi, err := os.Lstat(f.realPath)
+	if err != nil {
+		return "", err
+	}
+
+	gidS := fmt.Sprint(fi.Sys().(*syscall.Stat_t).Gid)
+	gid, err := strconv.Atoi(gidS)
+	if err != nil {
+		return "", err
+	}
+	return getGroupForGid(gid)
+}

system/file_windows.go

@@ -0,0 +1,31 @@
+package system
+
+import (
+	"fmt"
+	"os"
+)
+
+// Mode returns golang file mode. This method is cross-platform, but we are keeping unix-specific implementation
+// in file_unix.go for backwards compatibility.
+func (f *DefFile) Mode() (string, error) {
+	if err := f.setup(); err != nil {
+		return "", err
+	}
+
+	fi, err := os.Lstat(f.realPath)
+	if err != nil {
+		return "", err
+	}
+
+	mode := fmt.Sprintf("%04o", (fi.Mode() & 07777))
+	return mode, nil
+}
+
+// TODO(ENG-1522): owner and group are not defined for windows in standard library, find out whether we can support it.
+func (f *DefFile) Owner() (string, error) {
+	return "", nil
+}
+
+func (f *DefFile) Group() (string, error) {
+	return "", nil
+}