PHP无法通过Golang解压缩gzip数据

Why can't decompress gzip data by Go in my PHP demo, but PHP gzip data to Go is successful? I need post gzip JSON data from Go to PHP API service.

Test result

 -> |  php   |  go 
---------------------
php |  ok    |  ok
go  |  fail  |  ok

PHP code

class GzipDemo
{
    public function gzen($data, $file){
       $json_data = json_encode($data);
       $gz_data = gzencode($json_data,9);
       file_put_contents($file,$gz_data);
    }

    public function gzdn($file){
       $data = file_get_contents($file);
        $unpacked = gzdecode($data);
        if ($unpacked === FALSE)
        {
            print("failed:".$file."
");
        }else{
             print($file. " result Data :".$unpacked ."
");
        }
    }
}

$demo = new GzipDemo();
$file="phpgzip.txt";
$demo->gzen("data",$file);
$demo->gzdn($file);
$demo->gzdn("gogzip.txt");

This result: PHP to PHP okay. Go to PHP fail.

Go code

package main

import (
    "bytes"
    "compress/gzip"
    "encoding/json"
    "fmt"
    "io/ioutil"
    "os"
)

func main() {
    gzen("data", "gogzip.txt")
    gden("gogzip.txt")
    gden("phpgzip.txt")
}
func gzen(data string, file string) {
    b, _ := json.Marshal(data)
    buffer := new(bytes.Buffer)
    w, _ := gzip.NewWriterLevel(buffer, gzip.BestCompression)
    defer w.Close()
    w.Write(b)
    w.Flush()
    ioutil.WriteFile(file, buffer.Bytes(), os.ModePerm)
}
func gden(file string) {
    b, _ := ioutil.ReadFile(file)
    buffer := new(bytes.Buffer)
    buffer.Write(b)
    r, _ := gzip.NewReader(buffer)
    defer r.close()
    data, _ := ioutil.ReadAll(r)
    fmt.Println(file, " result Data:", string(data))
}

This result: Go to Go okay. PHP to Go okay.