求指点微信公众号如何群发消息

初学go，网上看到了关于微信公众号发送消息的代码，想将其改成群发试试，读过关于微信的开发者文章，群发只要改其中的touser，但努力了半天还是不会，望有大神指点。 这里贴出网上的代码，若有侵权，还望海涵。 package main import ( "bytes" "encoding/json" "fmt" "io/ioutil" "log" "net/http" "strings" ) const ( appID = "" appSecret = "" accessTokenFetchUrl = "https://api.weixin.qq.com/cgi-bin/token" customServicePostUrl = "https://api.weixin.qq.com/cgi-bin/message/custom/send" ) type AccessTokenResponse struct { AccessToken string `json:"access_token"` ExpiresIn float64 `json:"expires_in"` } type AccessTokenErrorResponse struct { Errcode float64 Errmsg string } type CustomServiceMsg struct { ToUser string `json:"touser"` MsgType string `json:"msgtype"` Text TextMsgContent `json:"text"` } type TextMsgContent struct { Content string `json:"content"` } func fetchAccessToken() (string, float64, error) { requestLine := strings.Join([]string{accessTokenFetchUrl, "?grant_type=client_credential&appid=", appID, "&secret=", appSecret}, "") resp, err := http.Get(requestLine) if err != nil || resp.StatusCode != http.StatusOK { return "", 0.0, err } defer resp.Body.Close() body, err := ioutil.ReadAll(resp.Body) if err != nil { return "", 0.0, err } fmt.Println(string(body)) if bytes.Contains(body, []byte("access_token")) { fmt.Println("return ok") atr := AccessTokenResponse{} err = json.Unmarshal(body, &atr) if err != nil { return "", 0.0, err } return atr.AccessToken, atr.ExpiresIn, nil } else { fmt.Println("return err") ater := AccessTokenErrorResponse{} err = json.Unmarshal(body, &ater) if err != nil { return "", 0.0, err } return "", 0.0, fmt.Errorf("%s", ater.Errmsg) } } func pushCustomMsg(accessToken, toUser, msg string) error { csMsg := &CustomServiceMsg{ ToUser: toUser, MsgType: "text", Text: TextMsgContent{Content: msg}, } body, err := json.MarshalIndent(csMsg, " ", " ") if err != nil { return err } fmt.Println(string(body)) postReq, err := http.NewRequest("POST", strings.Join([]string{customServicePostUrl, "?access_token=", accessToken}, ""), bytes.NewReader(body)) if err != nil { return err } postReq.Header.Set("Content-Type", "application/json; encoding=utf-8") client := &http.Client{} resp, err := client.Do(postReq) if err != nil { return err } resp.Body.Close() return nil } func main() { accessToken, expiresIn, err := fetchAccessToken() if err != nil { log.Println("Get access_token error:", err) return } fmt.Println(accessToken, expiresIn) openID := "oBQcwuAbKpiSAbbvd_DEZg7q27QI" msg := "你好" err = pushCustomMsg(accessToken, openID, msg) if err != nil { log.Println("Push custom service message err:", err) return } }