Golang archive/zip producing corrupt zip files

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) // travers…

Accepted Answer

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()
}
```

Golang archive/zip producing corrupt zip files

Solution

Problem