how to append files into a exists zip file without full read it into the memory?

[james-tech]

hello,
how to append files into a exists zip file without full read it into the memory?
I want to append files into a big zip file, and count not read the whole file into the memory.
I according to your write_test.go as demo, and wrote the follow code, but unfortunately , it seems not work.
the zip file didn't take any change after I run my program, could you be pleasure to help me.
thank you very much!

package main

import (
    "bytes"
    //  "archive/zip"
    "io/ioutil"
    "log"
    "os"
    "path/filepath"

    "github.com/juju/zip"
)

func main() {
    if err := AppendToZip(`dev/META-INF`, `dev/a.apk`); err != nil {
        panic(err)
    }
}

func AppendToZip(src, zipfile string) error {

    var err error

    r, err := zip.OpenReader(zipfile)

    if err != nil {
        panic(err)
    }
    defer r.Close()

    abuf := new(bytes.Buffer)
    aw := r.Append(abuf)
    defer aw.Close()

    err = filepath.Walk(src, func(path string, info os.FileInfo, err error) error {

        log.Println(path)
        var file []byte
        if err != nil {
            return filepath.SkipDir
        }
        header, err := zip.FileInfoHeader(info)
        if err != nil {
            return filepath.SkipDir
        }

        header.Name, _ = filepath.Rel(filepath.Dir(src), path)
        log.Println("header.Name is: " + header.Name)

        if !info.IsDir() {
            w, err := aw.CreateHeader(header)
            if err != nil {
                log.Panic("create header fail!")
                return err
            }
            log.Println("trace is not dir")

            header.Method = zip.Deflate

            file, err = ioutil.ReadFile(path)
            if err != nil {
                panic(err)
                return filepath.SkipDir
            }
            log.Println("file len is : ", len(file))

            _, err = w.Write(file)
            if err != nil {
                log.Panic("write file content fail!")
                return err
            }
        }

        return nil
    })
    return err
}

$ cksum a.apk
1171332196 34649113 a.apk

$ ./doit
2016/05/07 02:27:43 dev/META-INF
2016/05/07 02:27:43 header.Name is: META-INF
2016/05/07 02:27:43 dev/META-INF/channel_123_456
2016/05/07 02:27:43 header.Name is: META-INF/channel_123_456
2016/05/07 02:27:43 trace is not dir
2016/05/07 02:27:43 file len is :  0

$ cksum a.apk
1171332196 34649113 a.apk