refactor: consolidate copyFile implementations into shared util.CopyFile

Eliminated 3 duplicate copyFile() implementations across the codebase:
- composer.go (io.Copy, no permission handling)
- supply.go (io.Copy + explicit os.Chmod)
- finalize.go (ReadFile + WriteFile with mode)

Created unified util.CopyFile() that:
- Preserves file permissions by copying source file mode
- Uses os.ReadFile/WriteFile pattern (simplest and most robust)
- Replaces all 3 local implementations

Files modified:
- src/php/util/util.go: Added CopyFile() function
- src/php/extensions/composer/composer.go: Removed copyFile(), updated call site
- src/php/supply/supply.go: Removed copyFile(), updated call site
- src/php/finalize/finalize.go: Removed copyFile(), updated call site, added util import

Result: ~50 lines of duplicate code eliminated
All tests passing: 144 specs across 8 test suites

Author: ramonskie

src/php/extensions/composer/composer.go

@@ -912,7 +912,7 @@ func (e *ComposerExtension) setupPHPConfig(ctx *extensions.Context) error {
 	// Copy processed php.ini to TMPDIR for Composer to use
 	// This matches the Python buildpack behavior where PHPRC points to TMPDIR
 	tmpPhpIniPath := filepath.Join(e.tmpDir, "php.ini")
-	if err := e.copyFile(phpIniPath, tmpPhpIniPath); err != nil {
+	if err := util.CopyFile(phpIniPath, tmpPhpIniPath); err != nil {
 		return fmt.Errorf("failed to copy php.ini to TMPDIR: %w", err)
 	}
 
@@ -1174,24 +1174,6 @@ func (e *ComposerExtension) ServiceEnvironment(ctx *extensions.Context) (map[str
 	return nil, nil
 }
 
-// copyFile copies a file from src to dst
-func (e *ComposerExtension) copyFile(src, dst string) error {
-	sourceFile, err := os.Open(src)
-	if err != nil {
-		return err
-	}
-	defer sourceFile.Close()
-
-	destFile, err := os.Create(dst)
-	if err != nil {
-		return err
-	}
-	defer destFile.Close()
-
-	_, err = io.Copy(destFile, sourceFile)
-	return err
-}
-
 func (e *ComposerExtension) loadUserExtensions(ctx *extensions.Context) error {
 	return extensions.LoadUserExtensions(ctx, e.buildDir)
 }

src/php/finalize/finalize.go

@@ -9,6 +9,7 @@ import (
 	"github.com/cloudfoundry/libbuildpack"
 	"github.com/cloudfoundry/php-buildpack/src/php/extensions"
 	"github.com/cloudfoundry/php-buildpack/src/php/options"
+	"github.com/cloudfoundry/php-buildpack/src/php/util"
 )
 
 // Stager interface abstracts buildpack staging operations
@@ -231,7 +232,7 @@ func (f *Finalizer) CreateStartScript() error {
 	}
 	rewriteSrc := filepath.Join(bpDir, "bin", "rewrite")
 	rewriteDst := filepath.Join(bpBinDir, "rewrite")
-	if err := copyFile(rewriteSrc, rewriteDst); err != nil {
+	if err := util.CopyFile(rewriteSrc, rewriteDst); err != nil {
 		return fmt.Errorf("could not copy rewrite binary: %v", err)
 	}
 	f.Log.Debug("Copied rewrite binary to .bp/bin")
@@ -351,24 +352,6 @@ func (f *Finalizer) CreatePHPRuntimeDirectories() error {
 	return nil
 }
 
-// copyFile copies a file from src to dst with the same permissions
-func copyFile(src, dst string) error {
-	// Read source file
-	data, err := os.ReadFile(src)
-	if err != nil {
-		return err
-	}
-
-	// Get source file info for permissions
-	srcInfo, err := os.Stat(src)
-	if err != nil {
-		return err
-	}
-
-	// Write destination file with same permissions
-	return os.WriteFile(dst, data, srcInfo.Mode())
-}
-
 // generateHTTPDStartScript generates a start script for Apache HTTPD with PHP-FPM
 func (f *Finalizer) generateHTTPDStartScript(depsIdx string, opts *options.Options) string {
 	// Load options to get WEBDIR and other config values

src/php/supply/supply.go

@@ -775,36 +775,10 @@ func (s *Supplier) copyUserConfigs(srcDir, destDir string) error {
 
 		// If it's a file, copy it
 		s.Log.Debug("Copying user config: %s -> %s", path, destPath)
-		return s.copyFile(path, destPath)
+		return util.CopyFile(path, destPath)
 	})
 }
 
-// copyFile copies a single file from src to dest
-func (s *Supplier) copyFile(src, dest string) error {
-	sourceFile, err := os.Open(src)
-	if err != nil {
-		return err
-	}
-	defer sourceFile.Close()
-
-	destFile, err := os.Create(dest)
-	if err != nil {
-		return err
-	}
-	defer destFile.Close()
-
-	if _, err := io.Copy(destFile, sourceFile); err != nil {
-		return err
-	}
-
-	// Copy file permissions
-	sourceInfo, err := os.Stat(src)
-	if err != nil {
-		return err
-	}
-	return os.Chmod(dest, sourceInfo.Mode())
-}
-
 // ProcessPhpFpmConfForTesting exposes processPhpFpmConf for testing purposes
 func (s *Supplier) ProcessPhpFpmConfForTesting(phpFpmConfPath, phpEtcDir string) error {
 	return s.processPhpFpmConf(phpFpmConfPath, phpEtcDir)

src/php/util/util.go

@@ -85,3 +85,18 @@ func CompareVersions(v1, v2 string) int {
 
 	return 0
 }
+
+// CopyFile copies a file from src to dst preserving file permissions
+func CopyFile(src, dst string) error {
+	data, err := os.ReadFile(src)
+	if err != nil {
+		return err
+	}
+
+	srcInfo, err := os.Stat(src)
+	if err != nil {
+		return err
+	}
+
+	return os.WriteFile(dst, data, srcInfo.Mode())
+}