Golang archive/zip producing corrupt zip files - go

Question

I wrote a small utility in Go to zip a folder. It seems to work in many cases, but every now and then it produces a zip file that is coming up as corrupt when I open it in an unzip app (they all seem to complain about it).
Here is the code:
const (
singleFileByteLimit = 107374182400 // 1 GB
chunkSize = 1024 // 1 KB
)
// ZipFolder zips the given folder to the a zip file
// with the given name
func ZipFolder(srcFolder string, destFile string) error {
z := &zipper{
srcFolder: srcFolder,
destFile: destFile,
}
return z.zipFolder()
}
// We need a struct internally because the filepath WalkFunc
// doesn't allow custom params. So we save them here so it can
// access them
type zipper struct {
srcFolder string
destFile string
writer *zip.Writer
}
// internal function to zip a folder
func (z *zipper) zipFolder() error {
// create zip file
zipFile, err := os.Create(z.destFile)
if err != nil {
return err
}
defer zipFile.Close()
// create zip writer
z.writer = zip.NewWriter(zipFile)
// traverse the source folder
err = filepath.Walk(z.srcFolder, z.zipFile)
if err != nil {
return nil
}
// close the zip file
err = z.writer.Close()
if err != nil {
return err
}
return nil
}
// internal function to zip a file, called by filepath.Walk on each file
func (z *zipper) zipFile(path string, f os.FileInfo, err error) error {
// only zip files (directories are created by the files inside of them)
// TODO allow creating folder when no files are inside
if !f.IsDir() && f.Size() > 0 {
// open file
file, err := os.Open(path)
if err != nil {
return err
}
defer file.Close()
// create new file in zip
fileName := strings.TrimPrefix(path, z.srcFolder+"/")
w, err := z.writer.Create(fileName)
if err != nil {
return err
}
// copy contents of the file to the zip writer
err = copyContents(file, w)
if err != nil {
return err
}
}
return nil
}
func copyContents(r io.Reader, w io.Writer) error {
var size int64
for {
b := make([]byte, chunkSize)
// we limit the size to avoid zip bombs
size += chunkSize
if size > singleFileByteLimit {
return errors.New("file too large, please contact us for assitance")
}
// read chunk into memory
length, err := r.Read(b)
if err == io.EOF {
break
} else if err != nil {
return err
}
// write chunk to zip file
_, err = w.Write(b[:length])
if err != nil {
return err
}
}
return nil
}

Answer 1

Reading through your code, I fixed things that didn't look right. Try the following:
const (
singleFileByteLimit = 107374182400 // 1 GB
chunkSize = 4096 // 4 KB
)
func copyContents(r io.Reader, w io.Writer) error {
var size int64
b := make([]byte, chunkSize)
for {
// we limit the size to avoid zip bombs
size += chunkSize
if size > singleFileByteLimit {
return errors.New("file too large, please contact us for assistance")
}
// read chunk into memory
length, err := r.Read(b[:cap(b)])
if err != nil {
if err != io.EOF {
return err
}
if length == 0 {
break
}
}
// write chunk to zip file
_, err = w.Write(b[:length])
if err != nil {
return err
}
}
return nil
}
// We need a struct internally because the filepath WalkFunc
// doesn't allow custom params. So we save them here so it can
// access them
type zipper struct {
srcFolder string
destFile string
writer *zip.Writer
}
// internal function to zip a file, called by filepath.Walk on each file
func (z *zipper) zipFile(path string, f os.FileInfo, err error) error {
if err != nil {
return err
}
// only zip files (directories are created by the files inside of them)
// TODO allow creating folder when no files are inside
if !f.Mode().IsRegular() || f.Size() == 0 {
return nil
}
// open file
file, err := os.Open(path)
if err != nil {
return err
}
defer file.Close()
// create new file in zip
fileName := strings.TrimPrefix(path, z.srcFolder+"/")
w, err := z.writer.Create(fileName)
if err != nil {
return err
}
// copy contents of the file to the zip writer
err = copyContents(file, w)
if err != nil {
return err
}
return nil
}
// internal function to zip a folder
func (z *zipper) zipFolder() error {
// create zip file
zipFile, err := os.Create(z.destFile)
if err != nil {
return err
}
defer zipFile.Close()
// create zip writer
z.writer = zip.NewWriter(zipFile)
err = filepath.Walk(z.srcFolder, z.zipFile)
if err != nil {
return nil
}
// close the zip file
err = z.writer.Close()
if err != nil {
return err
}
return nil
}
// ZipFolder zips the given folder to the a zip file
// with the given name
func ZipFolder(srcFolder string, destFile string) error {
z := &zipper{
srcFolder: srcFolder,
destFile: destFile,
}
return z.zipFolder()
}