add message Image get support

client.go

@@ -349,3 +349,13 @@ func (c *Client) WebWxVerifyUser(storage WechatStorage, info RecommendInfo, veri
 	req.Header.Add("Content-Type", jsonContentType)
 	return c.Do(req)
 }
+
+func (c *Client) WebWxGetMsgImg(msg *Message, info LoginInfo) (*http.Response, error) {
+	path, _ := url.Parse(webWxGetMsgImgUrl)
+	params := url.Values{}
+	params.Add("MsgID", msg.MsgId)
+	params.Add("skey", info.SKey)
+	params.Add("type", "slave")
+	path.RawQuery = params.Encode()
+	return c.Get(path.String())
+}

global.go

@@ -29,6 +29,7 @@ const (
 	webWxVerifyUserUrl      = "https://wx2.qq.com/cgi-bin/mmwebwx-bin/webwxverifyuser"
 	syncCheckUrl            = "https://webpush.wx2.qq.com/cgi-bin/mmwebwx-bin/synccheck"
 	webWxUpLoadMediaUrl     = "https://file.wx2.qq.com/cgi-bin/mmwebwx-bin/webwxuploadmedia"
+	webWxGetMsgImgUrl          = "https://wx2.qq.com/cgi-bin/mmwebwx-bin/webwxgetmsgimg"
 
 	jsonContentType = "application/json; charset=utf-8"
 )

message.go

@@ -3,6 +3,7 @@ package openwechat
 import (
 	"context"
 	"errors"
+	"net/http"
 	"os"
 	"strings"
 	"sync"
@@ -170,6 +171,17 @@ func (m *Message) IsSystem() bool {
 	return m.MsgType == 10000
 }
 
+func (m *Message) IsNotify() bool {
+	return m.MsgType == 51 && m.StatusNotifyCode != 0
+}
+
+func (m *Message) GetMsgImageResponse() (*http.Response, error) {
+	if !m.IsPicture() {
+		return nil, errors.New("Picture type message required")
+	}
+	return m.Bot.Caller.Client.WebWxGetMsgImg(m, m.Bot.storage.GetLoginInfo())
+}
+
 // 用在多个messageHandler之间传递信息
 func (m *Message) Set(key string, value interface{}) {
 	m.mu.Lock()
@@ -194,9 +206,7 @@ func (m *Message) init(bot *Bot) {
 		m.Content = strings.Join(data[1:], "")
 		m.senderInGroupUserName = data[0]
 		receiver, err := m.Receiver()
-		if err != nil {
-			return
-		}
+		if err == nil {
 			displayName := receiver.DisplayName
 			if displayName == "" {
 				displayName = receiver.NickName
@@ -209,6 +219,7 @@ func (m *Message) init(bot *Bot) {
 			}
 		}
 	}
+}
 
 //func (m *Message) Agree() error {
 //	if !m.IsFriendAdd() {