如何在循环中“等待”异步函数的承诺/通过 Postmark API 发送带有附件的电子邮件

如何解决如何在循环中“等待”异步函数的承诺/通过 Postmark API 发送带有附件的电子邮件

我想通过 Postmark API 从我的快递服务器发送邮件。 我在我的快速服务器上收到一个具有以下 json 负载的后请求：

{
    "mail": {
        "from": "[e-mail]","to": "[e-mail]","subject": "Test mit Datei","textBody": "Test mit Datei","replyTo": "[e-mail]","files": [
            {
                "name": "filename.pdf","url": "https://sharelink.de"
            }
        ]
    }
}  

我需要遍历 files 数组并下载每个文件并将其转换为 base64，然后使用名称和内容类型在一个对象中保护结果，我可以通过 Postmark API 发送该对象。 就像在发送邮件但没有文件的那一刻一样。我认为这是因为 sendEmail 函数没有等待 encode2base64 函数完成。因此它发送一个空数组。但我不知道如何在这种情况下设置 await 语法。

这是我目前的代码：

    // Execution
    const from = req.body.mail.from;
    const to = req.body.mail.to;
    const subject = req.body.mail.subject;
    const htmlBody = req.body.mail.htmlBody;
    const textBody = req.body.mail.textBody;
    const replyTo = req.body.mail.replyTo;
    const files = req.body.mail.files;
    sendEmail(from,to,subject,htmlBody,textBody,replyTo,files)
    .catch((err)=>{
                    res.send({"error": err.message});
     })
    .then((response)=>{
                console.log("prom response ",response.data );
     res.send( response.data );
     })
    //==========================================
    //===== SEND EMAIL WITH POSTMARK API =======
    //==========================================
    /*  FOR THE API THE ATTACHMENTS MUST BE IN THE FOLLOWING FORMAT
    "Attachments": [{
                        Name: text(filename),Content: 'BASE64 ENCODED FILE',ContentType: "application/octet-stream"
                    }]
            */
    async function sendEmail( from,files ){
      var attachments = [];
      if ( files ) {
        console.log("============ EMAIL WITH FILES ==============")
        
        for (i in files ){
          var fileName = files[i].name;
          var shareLink = files[i].url;
          console.log("fileName",fileName );
          console.log("url: ",shareLink );
          encodeFile2Base64( shareLink )
          .catch((err)=>{
            console.log(err)
            })
          .then((response)=>{
              const encoded = new Buffer.from(response.data).toString('base64');
              attachments.push({
                "Name": fileName,"Content": encoded,"ContentType": "application/octet-stream"
              })
              
            })
    
      }}
      var config = {
        method: 'post',url: 'https://api.postmarkapp.com/email',headers: {'Content-Type': 'application/json','Accept':'application/json','X- Postmark-Server-Token': process.env.POSTMARK_KEY},data:{
                "From": from,"To": to,"Subject": subject,"HtmlBody": htmlBody,"TextBody": textBody,"ReplyTo": replyTo,"Attachments": attachments
            }
      };
      const promSendMail = axios(config);
      const resMailSent = await promSendMail;
      return resMailSent
    }
    //==========================================
    
    //==========================================
    //======== ENCODE TO BASE64 ================
    //==========================================
    async function encodeFile2Base64(url){
      var config = {
        method: 'get',url : url,headers : { responseType: 'arraybuffer' }
      };
      const prom = axios( config );
      const data = await prom;
      return data
    }

我需要将整个循环包装成一个异步函数吗？或者我应该首先创建附件对象，然后对 Postmark 进行 API 调用？但无论如何我都需要等待。

解决方法

如果您希望使用 async / await，您需要将循环包装在一个异步函数中。

sendEmail 函数必须返回一个 Promise，理想情况下应该在发送失败时拒绝。

您可以使用一些模拟发送代码在概念上对此进行测试，以便了解逻辑/基本原理。

您可以使用 for...of、for...in、for 循环。只是不要使用 Array.forEach，这不会很好地与 await 配合使用！

例如：

// Send successfully exept for email #2 (simulate an error)
function sendEmail(from,to,subject,body) {
    return new Promise((resolve,reject) => setTimeout(from === 'from2' ? reject: resolve,1000,from === 'from2' ? "send failure ?" : "send success ?"));
}


let emails = Array.from( {length: 5},(v,k) => ({ from: 'from' + k,to: "to" + k,subject: "subject" + k,body: "body" + k}));

async function sendEmails(emails,stopOnError) {
    for(let i = 0; i < emails.length; i++) {
        try { 
            console.log(`Sending email ${i+1} of ${emails.length}...`);
            let result = await sendEmail(emails[i].from,emails[i].to,emails[i].subject,emails[i].body);
            console.log("result:",result);
        } catch (error) {
            console.error(`sendEmails: error occurred at email #${i}:`,error);
            if (stopOnError) throw error
        }
    }
}

// Don't stop if we get an error,change to true to abandon sending on error
sendEmails(emails,false);