refactor(unit): Separate UnitDestination from PlaceUnit

initialize/config.go

@@ -133,9 +133,9 @@ func Apply(cfg CloudConfig, env *Environment) error {
 
 		for _, unit := range cfg.Coreos.Units {
 			if unit.Content != "" {
-				log.Printf("Writing unit %s to filesystem", unit.Name)
+				dst := system.UnitDestination(&unit, env.Root())
-				dst, err := system.PlaceUnit(&unit, env.Root())
+				log.Printf("Writing unit %s to filesystem at path %s", unit.Name, dst)
-				if err != nil {
+				if err := system.PlaceUnit(&unit, dst); err != nil {
 					return err
 				}
 				log.Printf("Placed unit %s at %s", unit.Name, dst)

system/systemd.go

@@ -42,20 +42,27 @@ func (u *Unit) Group() (group string) {
 
 type Script []byte
 
-func PlaceUnit(u *Unit, root string) (string, error) {
+// UnitDestination builds the appropriate absolte file path for
+// the given unit. The root argument indicates the effective base
+// directory of the system (similar to a chroot).
+func UnitDestination(u *Unit, root string) string {
 	dir := "etc"
 	if u.Runtime {
 		dir = "run"
 	}
 
-	dst := path.Join(root, dir, "systemd", u.Group())
+	return path.Join(root, dir, "systemd", u.Group(), u.Name)
-	if _, err := os.Stat(dst); os.IsNotExist(err) {
-		if err := os.MkdirAll(dst, os.FileMode(0755)); err != nil {
-			return "", err
-		}
 }
 
-	dst = path.Join(dst, u.Name)
+// PlaceUnit writes a unit file at the provided destination, creating
+// parent directories as necessary.
+func PlaceUnit(u *Unit, dst string) error {
+	dir := filepath.Dir(dst)
+	if _, err := os.Stat(dir); os.IsNotExist(err) {
+		if err := os.MkdirAll(dir, os.FileMode(0755)); err != nil {
+			return err
+		}
+	}
 
 	file := File{
 		Path: dst,
@@ -65,10 +72,10 @@ func PlaceUnit(u *Unit, root string) (string, error) {
 
 	err := WriteFile(&file)
 	if err != nil {
-		return "", err
+		return err
 	}
 
-	return dst, nil
+	return nil
 }
 
 func EnableUnitFile(file string, runtime bool) error {

system/systemd_test.go

@@ -26,12 +26,17 @@ Address=10.209.171.177/19
 	}
 	defer syscall.Rmdir(dir)
 
-	if _, err := PlaceUnit(&u, dir); err != nil {
+	dst := UnitDestination(&u, dir)
+	expectDst := path.Join(dir, "run", "systemd", "network", "50-eth0.network")
+	if dst != expectDst {
+		t.Fatalf("UnitDestination returned %s, expected %s", dst, expectDst)
+	}
+
+	if err := PlaceUnit(&u, dst); err != nil {
 		t.Fatalf("PlaceUnit failed: %v", err)
 	}
 
-	fullPath := path.Join(dir, "run", "systemd", "network", "50-eth0.network")
+	fi, err := os.Stat(dst)
-	fi, err := os.Stat(fullPath)
 	if err != nil {
 		t.Fatalf("Unable to stat file: %v", err)
 	}
@@ -40,19 +45,19 @@ Address=10.209.171.177/19
 		t.Errorf("File has incorrect mode: %v", fi.Mode())
 	}
 
-	contents, err := ioutil.ReadFile(fullPath)
+	contents, err := ioutil.ReadFile(dst)
 	if err != nil {
 		t.Fatalf("Unable to read expected file: %v", err)
 	}
 
-	expect := `[Match]
+	expectContents := `[Match]
 Name=eth47
 
 [Network]
 Address=10.209.171.177/19
 `
-	if string(contents) != expect {
+	if string(contents) != expectContents {
-		t.Fatalf("File has incorrect contents '%s'.\nExpected '%s'", string(contents), expect)
+		t.Fatalf("File has incorrect contents '%s'.\nExpected '%s'", string(contents), expectContents)
 	}
 }
 
@@ -72,12 +77,17 @@ Where=/media/state
 	}
 	defer syscall.Rmdir(dir)
 
-	if _, err := PlaceUnit(&u, dir); err != nil {
+	dst := UnitDestination(&u, dir)
+	expectDst := path.Join(dir, "etc", "systemd", "system", "media-state.mount")
+	if dst != expectDst {
+		t.Fatalf("UnitDestination returned %s, expected %s", dst, expectDst)
+	}
+
+	if err := PlaceUnit(&u, dst); err != nil {
 		t.Fatalf("PlaceUnit failed: %v", err)
 	}
 
-	fullPath := path.Join(dir, "etc", "systemd", "system", "media-state.mount")
+	fi, err := os.Stat(dst)
-	fi, err := os.Stat(fullPath)
 	if err != nil {
 		t.Fatalf("Unable to stat file: %v", err)
 	}
@@ -86,17 +96,17 @@ Where=/media/state
 		t.Errorf("File has incorrect mode: %v", fi.Mode())
 	}
 
-	contents, err := ioutil.ReadFile(fullPath)
+	contents, err := ioutil.ReadFile(dst)
 	if err != nil {
 		t.Fatalf("Unable to read expected file: %v", err)
 	}
 
-	expect := `[Mount]
+	expectContents := `[Mount]
 What=/dev/sdb1
 Where=/media/state
 `
-	if string(contents) != expect {
+	if string(contents) != expectContents {
-		t.Fatalf("File has incorrect contents '%s'.\nExpected '%s'", string(contents), expect)
+		t.Fatalf("File has incorrect contents '%s'.\nExpected '%s'", string(contents), expectContents)
 	}
 }