Merge pull request #16 from hellofresh/minor/RDEV-966-copy-stream-ins…

…tead

[SelfUpdate] Copy bytes from the stream instead of loading them all into the memory

apply.go

@@ -3,12 +3,12 @@ package updater
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 )
 
-// Apply performs an update of the current executable (or opts.TargetFile, if set) with the contents of the given io.Reader.
+// Apply performs an update of the current executable (or opts.TargetFile, if set) with the contents of the given
+// io.Reader.
 //
 // Apply performs the following actions to ensure a safe cross-platform update:
 //   - Creates a new file, /path/to/.target.new with the TargetMode with the contents of the updated file
@@ -19,10 +19,10 @@ import (
 //   - If the final rename fails, attempts to roll back by renaming /path/to/.target.old
 //     back to /path/to/target.
 //
-// If the roll back operation fails, the file system is left in an inconsistent state where
-// there is no new executable file and the old executable file could not be be moved to its original location. In this
-// case you should notify the user of the bad news and ask them to recover manually. Applications can determine whether
-// the rollback failed by calling RollbackError, see the documentation on that function for additional detail.
+// If the rollback operation fails, the file system is left in an inconsistent state where there is no new executable
+// file and the old executable file could not be be moved to its original location. In this case you should notify the
+// user of the bad news and ask them to recover manually. Applications can determine whether the rollback failed by
+// calling RollbackError, see the documentation on that function for additional detail.
 func Apply(update io.Reader, targetPath string, targetMode os.FileMode) error {
 	if targetPath == "" {
 		executablePath, executableMode, err := executableInfo()
@@ -42,41 +42,35 @@ func Apply(update io.Reader, targetPath string, targetMode os.FileMode) error {
 		targetMode = targetStats.Mode()
 	}
 
-	// get the directory the executable exists in
+	// Get the directory the executable exists in.
 	updateDir := filepath.Dir(targetPath)
 	filename := filepath.Base(targetPath)
 
-	// define paths to use
+	// Define paths to use.
 	newPath := filepath.Join(updateDir, fmt.Sprintf(".%s.new", filename))
 	oldPath := filepath.Join(updateDir, fmt.Sprintf(".%s.old", filename))
 
-	// Read updated binary information
-	newBytes, err := ioutil.ReadAll(update)
-	if err != nil {
-		return err
-	}
-
-	// Copy the contents of newbinary to a new executable file
-	if err := ioutil.WriteFile(newPath, newBytes, targetMode); err != nil {
+	// Copy the new executable to a new file.
+	if err := copyToFile(update, newPath, targetMode); err != nil {
 		return err
 	}
 
-	// delete any existing old exec file
+	// Delete any existing old exec file.
 	os.Remove(oldPath)
 
 	// move the existing executable to a new file in the same directory
 	if err := os.Rename(targetPath, oldPath); err != nil {
 		return err
 	}
 
-	// move the new executable in to become the new program
+	// Move the new executable in to become the new program.
 	if err := os.Rename(newPath, targetPath); err != nil {
-		// move unsuccessful
+		// Move unsuccessful.
+		//
+		// The filesystem is now in a bad state. We have successfully moved the existing binary to a new location, but
+		// we couldn't move the new binary to take its place. That means there is no file where the current executable
+		// binary used to be!
 		//
-		// The filesystem is now in a bad state. We have successfully
-		// moved the existing binary to a new location, but we couldn't move the new
-		// binary to take its place. That means there is no file where the current executable binary
-		// used to be!
 		// Try to rollback by restoring the old binary to its original path.
 		rollbackErr := os.Rename(oldPath, targetPath)
 		if rollbackErr != nil {
@@ -86,20 +80,34 @@ func Apply(update io.Reader, targetPath string, targetMode os.FileMode) error {
 		return err
 	}
 
-	// remove the old binary
-	err = os.Remove(oldPath)
-	if err != nil {
-		// windows has trouble with removing old binaries, so hide it instead
+	// Remove the old binary.
+	if err := os.Remove(oldPath); err != nil {
+		// Windows has trouble with removing old binaries, so hide it instead.
 		_ = hideFile(oldPath)
 	}
 
 	return nil
 }
 
-// RollbackErr represents an error occurred during rollback operation
+// RollbackErr represents an error occurred during rollback operation.
 type RollbackErr struct {
-	// error the original error
+	// error the original error.
 	error
-	// RollbackErr the error encountered while rolling back
+	// RollbackErr the error encountered while rolling back.
 	RollbackErr error
 }
+
+func copyToFile(src io.Reader, dst string, mode os.FileMode) error {
+	f, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, mode)
+	if err != nil {
+		return err
+	}
+
+	defer f.Close()
+
+	if _, err = io.Copy(f, src); err != nil {
+		return err
+	}
+
+	return f.Sync()
+}