refactor: collect docker-options file helpers in functions.go

Moves `copyPhaseFile` and `removePhaseFile` next to the other phase-file helpers so the package keeps a single home for filesystem plumbing.

plugins/docker-options/functions.go

@@ -2,6 +2,7 @@ package dockeroptions
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"strings"
@@ -13,6 +14,39 @@ func getPhaseFilePath(appName string, phase string) string {
 	return filepath.Join(common.AppRoot(appName), "DOCKER_OPTIONS_"+strings.ToUpper(phase))
 }
 
+func copyPhaseFile(srcApp string, dstApp string, phase string) error {
+	srcPath := getPhaseFilePath(srcApp, phase)
+	if !common.FileExists(srcPath) {
+		return nil
+	}
+
+	src, err := os.Open(srcPath)
+	if err != nil {
+		return fmt.Errorf("Unable to open docker options phase file %s.%s: %s", srcApp, phase, err.Error())
+	}
+	defer src.Close()
+
+	dstPath := getPhaseFilePath(dstApp, phase)
+	dst, err := os.OpenFile(dstPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return fmt.Errorf("Unable to create docker options phase file %s.%s: %s", dstApp, phase, err.Error())
+	}
+	defer dst.Close()
+
+	if _, err := io.Copy(dst, src); err != nil {
+		return fmt.Errorf("Unable to copy docker options phase file %s.%s to %s.%s: %s", srcApp, phase, dstApp, phase, err.Error())
+	}
+
+	return nil
+}
+
+func removePhaseFile(appName string, phase string) error {
+	if err := os.Remove(getPhaseFilePath(appName, phase)); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	return nil
+}
+
 func touchPhaseFile(appName string, phase string) error {
 	phaseFilePath := getPhaseFilePath(appName, phase)