system: separate link Op implementation

This Op would still be useful after replacing the Tmpfiles interface, so isolate it here.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/system/link.go

@@ -0,0 +1,53 @@
+package system
+
+import (
+	"fmt"
+	"os"
+
+	"git.gensokyo.uk/security/fortify/internal/fmsg"
+)
+
+// Link registers an Op that links dst to src.
+func (sys *I) Link(oldname, newname string) *I { return sys.LinkFileType(Process, oldname, newname) }
+
+// LinkFileType registers a file linking Op labelled with type et.
+func (sys *I) LinkFileType(et Enablement, oldname, newname string) *I {
+	sys.lock.Lock()
+	defer sys.lock.Unlock()
+
+	sys.ops = append(sys.ops, &Hardlink{et, newname, oldname})
+
+	return sys
+}
+
+type Hardlink struct {
+	et       Enablement
+	dst, src string
+}
+
+func (l *Hardlink) Type() Enablement { return l.et }
+
+func (l *Hardlink) apply(_ *I) error {
+	fmsg.VPrintln("linking ", l)
+	return fmsg.WrapErrorSuffix(os.Link(l.src, l.dst),
+		fmt.Sprintf("cannot link %q:", l.dst))
+}
+
+func (l *Hardlink) revert(_ *I, ec *Criteria) error {
+	if ec.hasType(l) {
+		fmsg.VPrintf("removing hard link %q", l.dst)
+		return fmsg.WrapErrorSuffix(os.Remove(l.dst),
+			fmt.Sprintf("cannot remove hard link %q:", l.dst))
+	} else {
+		fmsg.VPrintf("skipping hard link %q", l.dst)
+		return nil
+	}
+}
+
+func (l *Hardlink) Is(o Op) bool {
+	l0, ok := o.(*Hardlink)
+	return ok && l0 != nil && *l == *l0
+}
+
+func (l *Hardlink) Path() string   { return l.src }
+func (l *Hardlink) String() string { return fmt.Sprintf("%q from %q", l.dst, l.src) }

internal/system/tmpfiles.go

@@ -27,24 +27,8 @@ func (sys *I) CopyFileType(et Enablement, dst, src string) *I {
 	return sys
 }
 
-// Link registers an Op that links dst to src.
-func (sys *I) Link(oldname, newname string) *I {
-	return sys.LinkFileType(Process, oldname, newname)
-}
-
-// LinkFileType registers a file linking Op labelled with type et.
-func (sys *I) LinkFileType(et Enablement, oldname, newname string) *I {
-	sys.lock.Lock()
-	defer sys.lock.Unlock()
-
-	sys.ops = append(sys.ops, &Tmpfile{et, tmpfileLink, newname, oldname})
-
-	return sys
-}
-
 const (
 	tmpfileCopy uint8 = iota
-	tmpfileLink
 )
 
 type Tmpfile struct {
@@ -63,10 +47,6 @@ func (t *Tmpfile) apply(_ *I) error {
 		fmsg.VPrintln("publishing tmpfile", t)
 		return fmsg.WrapErrorSuffix(copyFile(t.dst, t.src),
 			fmt.Sprintf("cannot copy tmpfile %q:", t.dst))
-	case tmpfileLink:
-		fmsg.VPrintln("linking tmpfile", t)
-		return fmsg.WrapErrorSuffix(os.Link(t.src, t.dst),
-			fmt.Sprintf("cannot link tmpfile %q:", t.dst))
 	default:
 		panic("invalid tmpfile method " + strconv.Itoa(int(t.method)))
 	}
@@ -94,8 +74,6 @@ func (t *Tmpfile) String() string {
 	switch t.method {
 	case tmpfileCopy:
 		return fmt.Sprintf("%q from %q", t.dst, t.src)
-	case tmpfileLink:
-		return fmt.Sprintf("%q from %q", t.dst, t.src)
 	default:
 		panic("invalid tmpfile method " + strconv.Itoa(int(t.method)))
 	}

internal/system/tmpfiles_test.go

@@ -57,7 +57,7 @@ func TestLink(t *testing.T) {
 			sys := New(150)
 			sys.Link(tc.src, tc.dst)
 			(&tcOp{Process, tc.src}).test(t, sys.ops, []Op{
-				&Tmpfile{Process, tmpfileLink, tc.dst, tc.src},
+				&Hardlink{Process, tc.dst, tc.src},
 			}, "Link")
 		})
 	}
@@ -76,7 +76,7 @@ func TestLinkFileType(t *testing.T) {
 			sys := New(150)
 			sys.LinkFileType(tc.et, tc.path, tc.dst)
 			tc.test(t, sys.ops, []Op{
-				&Tmpfile{tc.et, tmpfileLink, tc.dst, tc.path},
+				&Hardlink{tc.et, tc.dst, tc.path},
 			}, "LinkFileType")
 		})
 	}
@@ -101,10 +101,6 @@ func TestTmpfile_String(t *testing.T) {
 	}{
 		{tmpfileCopy, "/tmp/fortify.1971/4b6bdc9182fb2f1d3a965c5fa8b9b66e/pulse-cookie", "/home/ophestra/xdg/config/pulse/cookie",
 			`"/tmp/fortify.1971/4b6bdc9182fb2f1d3a965c5fa8b9b66e/pulse-cookie" from "/home/ophestra/xdg/config/pulse/cookie"`},
-		{tmpfileLink, "/run/user/1971/fortify/4b6bdc9182fb2f1d3a965c5fa8b9b66e/wayland", "/run/user/1971/wayland-0",
-			`"/run/user/1971/fortify/4b6bdc9182fb2f1d3a965c5fa8b9b66e/wayland" from "/run/user/1971/wayland-0"`},
-		{tmpfileLink, "/run/user/1971/fortify/4b6bdc9182fb2f1d3a965c5fa8b9b66e/pulse", "/run/user/1971/pulse/native",
-			`"/run/user/1971/fortify/4b6bdc9182fb2f1d3a965c5fa8b9b66e/pulse" from "/run/user/1971/pulse/native"`},
 	}
 
 	for _, tc := range testCases {