title: zip a folder of files with golang creates a broken zip
body: <p>how do I zip files in a folder with sub-directories correctly.</p>
  
  <p>I have a local folder with following structure:</p>
  
  <pre><code>folder/hello/
  folder/hello/world/
  folder/hello/world/helloword.txt
  folder/index.txt
  </code></pre>
  
  <p>this is my code: </p>
  
  <pre><code>package main
  
  import (
      "archive/zip"
      "fmt"
      "io"
      "os"
      "path/filepath"
  )
  
  func main() {
  
      files, err := listFiles("./folder")
      if err != nil {
          panic(err)
      }
  
      zipMe(files, "test.zip")
  
      for _, f := range files {
          fmt.Println(f)
      }
      fmt.Println("Done!")
  }
  
  func listFiles(root string) ([]string, error) {
      var files []string
  
      err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
          files = append(files, path)
          return nil
      })
      if err != nil {
          return nil, err
      }
      return files, nil
  
  }
  
  func zipMe(filepaths []string, target string) error {
  
      flags := os.O_WRONLY | os.O_CREATE | os.O_TRUNC
      file, err := os.OpenFile(target, flags, 0644)
  
      if err != nil {
          return fmt.Errorf("Failed to open zip for writing: %s", err)
      }
      defer file.Close()
  
      zipw := zip.NewWriter(file)
      defer zipw.Close()
  
      for _, filename := range filepaths {
          if err := addFileToZip(filename, zipw); err != nil {
              return fmt.Errorf("Failed to add file %s to zip: %s", filename, err)
          }
      }
      return nil
  
  }
  
  func addFileToZip(filename string, zipw *zip.Writer) error {
      file, err := os.Open(filename)
  
      if err != nil {
          return fmt.Errorf("Error opening file %s: %s", filename, err)
      }
      defer file.Close()
  
      wr, err := zipw.Create(filename)
      if err != nil {
  
          return fmt.Errorf("Error adding file; '%s' to zip : %s", filename, err)
      }
  
      if _, err := io.Copy(wr, file); err != nil {
          return fmt.Errorf("Error writing %s to zip: %s", filename, err)
      }
  
      return nil
  }
  </code></pre>
  
  <p>This creates a broken zip which can not be extracted (I am running on mac os but this should not make a difference).
  I also tried several other examples from stackoverflow and links found through google, but I do always get a broken zip. I get a zip with 135 bytes when I extract it I get 1 binary file with 0 bytes). </p>
  
  <p>It would be great if someone could help me to find out what I am missing here.</p>
  
  <p>Thx</p>