Base64编码/解码导致输出损坏

Question

I'm trying to write some convenience wrapper funcs that base64 encodes and decodes byte slices. (Can't understand why this is not conveniently provided in the stdlib.)

However this code (in playground):

func b64encode(b []byte) []byte {
    encodedData := &bytes.Buffer{}
    encoder := base64.NewEncoder(base64.URLEncoding, encodedData)
    defer encoder.Close()
    encoder.Write(b)
    return encodedData.Bytes()
}

func b64decode(b []byte) ([]byte, error) {
    dec := base64.NewDecoder(base64.URLEncoding, bytes.NewReader(b))
    buf := &bytes.Buffer{}
    _, err := io.Copy(buf, dec)
    if err != nil {
        return nil, err
    }
    return buf.Bytes(), nil
}


func main() {
    b := []byte("hello")
    e := b64encode(b)
    d, err := b64decode(e)
    if err != nil {
        log.Fatalf("could not decode: %s", err)
    }
    fmt.Println(string(d))
}

generates truncated output when I try to print it:

hel

What's going on?

Answer 1

The defer executes when the function ends. That is AFTER the return statement has been evaluated.

The following works: https://play.golang.org/p/sYn-W6fZh1

func b64encode(b []byte) []byte {
    encodedData := &bytes.Buffer{}
    encoder := base64.NewEncoder(base64.URLEncoding, encodedData)
    encoder.Write(b)
    encoder.Close()
    return encodedData.Bytes()
}

---

That being said, if it really is all in memory, you can avoid creating an encoder entirely. Instead, you can do something like:

func b64encode(b []byte) []byte {
    ret := make([]byte, base64.URLEncoding.EncodedLen(len(b)))
    base64.URLEncoding.Encode(ret, b)
    return ret
}

An added benefit of doing it this way it it is more efficient since it only needs to allocate once. It also allows you to no longer ignore errors in the Write and Close methods.