How to operate the Koa2 WeChat public account to achieve message management

Receive messages

When an ordinary WeChat user sends a message to a public account, the WeChat server will POST the XML data packet of the message to the URL filled in by the developer .

2.1 Receive common message data format

The structure of XML is basically fixed, and different message types are slightly different.

When a user sends a text message, the XML data format received by the WeChat public account is as follows:

<xml>
 <ToUserName><![CDATA[toUser]]></ToUserName>
 <FromUserName><![CDATA[fromUser]]></FromUserName>
 <CreateTime>createTime</CreateTime>
 <MsgType><![CDATA[text]]></MsgType>
 <Content><![CDATA[this is a test]]></Content>
 <MsgId>1234567890123456</MsgId>
</xml>

When a user sends a picture message, the XML data format received by the WeChat public account is as follows ：

<xml> 
 <ToUserName><![CDATA[toUser]]></ToUserName>
 <FromUserName><![CDATA[fromUser]]></FromUserName>
 <CreateTime>1348831860</CreateTime> 
 <MsgType><![CDATA[image]]></MsgType> 
 <PicUrl><![CDATA[this is a url]]></PicUrl>
 <MediaId><![CDATA[media_id]]></MediaId> 
 <MsgId>1234567890123456</MsgId>
</xml>

For the structure of other message message types, please refer to [WeChat Public Platform Development Documents]

For the processing of POST request, koa2 does not encapsulate the method of obtaining parameters, which is required By parsing the native node.js request object request in the context context by itself. We will use the row-body module to get the data.

2.2 Let’s optimize the previous code first

The code in this section follows the code implemented in the previous session, with slight changes based on the previous session. .

'use strict'
const Koa = require('koa')
const app = new Koa()
const crypto = require('crypto')
// 将配置文件独立到config.js
const config = require('./config')
app.use(async ctx => {
 // GET 验证服务器
 if (ctx.method === 'GET') {
  const { signature, timestamp, nonce, echostr } = ctx.query
  const TOKEN = config.wechat.token
  let hash = crypto.createHash('sha1')
  const arr = [TOKEN, timestamp, nonce].sort()
  hash.update(arr.join(''))
  const shasum = hash.digest('hex')
  if (shasum === signature) {
   return ctx.body = echostr
  }
  ctx.status = 401
  ctx.body = 'Invalid signature'
 } else if (ctx.method === 'POST') { // POST接收数据
  // TODO
 }
});
app.listen(7001);

Here we only verified whether the signature value is legal in GET. In fact, we should also verify the signature in POST.

Write signature verification as a function

function getSignature (timestamp, nonce, token) {
 let hash = crypto.createHash('sha1')
 const arr = [token, timestamp, nonce].sort()
 hash.update(arr.join(''))
 return hash.digest('hex')
}

Optimize the code and add verification to POST

...
app.use(async ctx => {
 const { signature, timestamp, nonce, echostr } = ctx.query
 const TOKEN = config.wechat.token
 if (ctx.method === 'GET') {
  if (signature === getSignature(timestamp, nonce, TOKEN)) {
   return ctx.body = echostr
  }
  ctx.status = 401
  ctx.body = 'Invalid signature'
 }else if (ctx.method === 'POST') {
  if (signature !== getSignature(timestamp, nonce, TOKEN)) {
   ctx.status = 401
   return ctx.body = 'Invalid signature'
  }
  // TODO
 }
});
...

Up to this point we have not started to implement the function of accepting XML data packets, but It is the code before modification. This is to demonstrate the actual development process. Writing any code is not a one-step process, and good code can only be modified.

2.3 Receive XML data packets for ordinary messages from public accounts

Now let’s get to the point of this section, accept XML data packets and convert them to JSON

$ npm install raw-body --save

...
const getRawBody = require('raw-body')
...
// TODO
// 取原始数据
const xml = await getRawBody(ctx.req, {
 length: ctx.request.length,
 limit: '1mb',
 encoding: ctx.request.charset || 'utf-8'
});
console.log(xml)
return ctx.body = 'success' // 直接回复success，微信服务器不会对此作任何处理

Send a text message to your test account, you can see the following data printed out on the command line

<xml>
 <ToUserName><![CDATA[gh_9d2d49e7e006]]></ToUserName>
 <FromUserName><![CDATA[oBp2T0wK8lM4vIkmMTJfFpk6Owlo]]></FromUserName>
 <CreateTime>1516940059</CreateTime>
 <MsgType><![CDATA[text]]></MsgType>
 <Content><![CDATA[JavaScript之禅]]></Content>
 <MsgId>6515207943908059832</MsgId>
</xml>

Congratulations, you can now receive XML data.

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