（节点：23）UnhandledPromiseRejectionWarning：错误[ERR_HTTP_HEADERS_SENT]：将标头发送到客户端后无法设置标头

Question

我正在创建一个应用程序，当我尝试上载图像时，它在控制台中显示此错误：（节点：23）UnhandledPromiseRejectionWarning：错误[ERR_HTTP_HEADERS_SENT]：将标头发送到客户端后无法设置标头。 我该怎么解决？

我的提取：

let formData = new FormData();
formData.append('arquivo', document.querySelector('input[name="arquivo"]').files[0])
formData.append('candy', candy)
formData.append('theme', document.getElementById('candytheme').value)

fetch('https://nodemae.herokuapp.com/candy', { method: 'post', headers: {'x-auth-token': window.sessionStorage.getItem('token') }, body: formData}).then

我的服务器端：

async store(req, res) {
    let candy= req.body.candy;
    let name= uniqid(doce+'-')+'.jpg';
    let route= `/img/${doce}/`;
    let theme= req.body.theme;
    let sampleFile = req.files.arquivo;
    sampleFile.mv(`./public${route}${name}`, function(err){
        if (err) {
            return res.send(err)
        }
    });
    const candy = await Candy.create({
        name: name,
        candy: candy,
        route: route,
        theme: theme
    });

    return res.json(candy);
},

返回res.json（candy）;返回以下内容：{“ errno”：-2，“ code”：“ ENOENT”，“ syscall”：“ open”，“ path”：“ ./ public / img / paomel / paomel-q6zynjrg8w45y.jpg”}

Answer 1

由于此回调函数而出现此错误

 sampleFile.mv(`./public${caminho}${nome}`, function(err){
    if (err) {
        return res.send(err)
    }
});

您的代码在同步运行时从res.json(candy);发送响应，但是当激发异步回调时，您将得到err和`return res.send（err）

解决方案

尝试此代码

async store(req, res)
{
try {
    let doce = req.body.doce;
    let nome = uniqid(doce+'-')+'.jpg';
    let caminho = `/img/${doce}/`;
    let tema = req.body.tema;
    let sampleFile = req.files.arquivo;
    await sampleFile.mv(`./public${caminho}${nome}`)
    const candy = await Candy.create({
            nome: nome,
            doce: doce,
            caminho: caminho,
            tema: tema
        });

        return res.json(candy);
    });
}catch (err) {
    return res.send(err)
}}

Answer 2

执行sampleFile时发生错误。代码的其他部分需要等待sampleFile完成。因此，您有两个错误："errno":-2,"code":"ENOENT","syscall":"open","path":"./public/img/paomel/paomel-q6zynjrg8w45y.jpg"（因为它找不到文件）和第二个错误Cannot set headers after they are sent to the client...（因为您的代码无法处理错误，并遵循最后的return res.json(candy);尝试：< / p>

async store(req, res) {
  let candy= req.body.candy;
  let name= uniqid(doce+'-')+'.jpg';
  let route= `/img/${doce}/`;
  let theme= req.body.theme;
  let sampleFile = req.files.arquivo;
  sampleFile.mv(`./public${route}${name}`, async function(err) {
      if (err) {
        res.send(err)
      } else {
        const candy = await Candy.create({
          name: name,
          candy: candy,
          route: route,
          theme: theme
        });

        res.json(candy);
     }
   });
}

您也可以使用then，而不使用async和await：

store(req, res) {
  let candy= req.body.candy;
  let name= uniqid(doce+'-')+'.jpg';
  let route= `/img/${doce}/`;
  let theme= req.body.theme;
  let sampleFile = req.files.arquivo;
  sampleFile.mv(`./public${route}${name}`, function(err) {
      if (err) {
        res.send(err)
      } else {

        Candy.create({
          name: name,
          candy: candy,
          route: route,
          theme: theme
        })
        .then(function(candy) {
          res.json(candy);
        })
        .catch(function(err) {
          console.log(err);
        });  
     }
   });
}

尝试在此处/public${route}${name}使用绝对路径进行文件上传，因为fileupload软件包不使用相对路径。