Nodejs等待镜像将被下载

Question

我不明白为什么这个函数在图像下载和保存之前就退出了
在退出之前，我需要等待图像将被保存。

function downloadImagefromRemote(url_immagine, filename) {
console.log('[2] Salvo l'immagine remota in locale');
const downloadFile = async (fileUrl, downloadFolder, filename) => {
// Get the file name
const fileName = path.basename(fileUrl);
// The path of the downloaded file on our machine
const localFilePath = path.resolve(__dirname, downloadFolder, filename);
try {
const response = await axios({ // <----- here jump out
method: "GET",
url: fileUrl,
responseType: "stream",
});
await response.data.pipe(fs.createWriteStream(localFilePath));
console.log("Successfully downloaded file!");
} catch (err) {
throw new Error(err);
}
};
const IMAGE_URL = 'https://www.kindacode.com/wp-content/uploads/2021/01/test.jpg';
let rel_path = __dirname + '/../../public/images/';
downloadFile(IMAGE_URL, rel_path, filename);
}

Answer 1

主要问题是使用

axios({...})

您需要指定

url: imgUrl

更一般地说：

• 避免不必要的嵌套函数
• 清理未使用和不必要的参数

这里是一个功能示例：

'use strict'
const fs = require('fs')
const path = require('path')
const axios = require('axios')
async function downloadImage(imgUrl, saveRelPath, saveName) {
const _path = path.resolve(__dirname, saveRelPath, saveName)
const writer = fs.createWriteStream(_path)
const response = await axios({
url: imgUrl,
method: 'GET',
responseType: 'stream',
})
response.data.pipe(writer)
return new Promise((resolve, reject) => {
writer.on('finish', resolve)
writer.on('error', reject)
})
}
async function anotherFunction() {
const IMG_URL = 'https://www.kindacode.com/wp-content/uploads/2021/01/test.jpg'
const REL_PATH = '.'
const NAME = 'test.jpg'
console.log('Get and save image')
await downloadImage(IMG_URL, REL_PATH, NAME)
console.log('Image saving done, other stuff here')
}
anotherFunction()

编辑：作为对的回应

I can't understand why this function exit before image is downloaded and saved

流水不回承诺，所以你不能等它。您通过管道将流导入EventEmitter的写入流，因此应该使用侦听器。

Answer 2

您可以尝试一下，它应该会起作用。关于pipeline((的解释，请参阅这个答案Promise在编写文件之前完成。我承诺你的流能够在流处理结束后立即解决(注意，我不知道你代码的其他部分，比如如果axios不返回流，它就不会工作(

const { pipeline } = require('stream')
async function downloadImagefromRemote(url_immagine, filename) {
console.log('[2] Salvo l'immagine remota in locale');
const downloadFile = (fileUrl, downloadFolder, filename) => {
return new Promise(async(resolve, reject) => {
// Get the file name
const fileName = path.basename(fileUrl);
// The path of the downloaded file on our machine
const localFilePath = path.resolve(__dirname, downloadFolder, filename);
try {
const response = await axios({ // <----- here jump out
method: "GET",
url: fileUrl,
responseType: "stream",
});
pipeline(
response.data,
fs.createWriteStream(localFilePath),
e => {
if(e) reject(e)
else resolve("Successfully downloaded file!")
}
)  
} catch (err) {
reject(Error(err))
}
})    
};
const IMAGE_URL = 'https://www.kindacode.com/wp-content/uploads/2021/01/test.jpg';
let rel_path = __dirname + '/../../public/images/';
try{
const confirmDownload = await downloadFile(IMAGE_URL, rel_path, filename);
console.log(confirmDownload)
} catch(e) {
console.log('catched err:', e)
}
}