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node.js - Node JS https 检查下载的图像是否 100% 完成

问题描述

我的应用程序使用 NodeJS https 模块实现了图像下载功能。下载很好，但有时（没有明确原因），下载的图像不完整/包含灰色区域

const fs = require('fs'), https = require('https');
// ...
        return new Promise(async (res) => {
            // ...
            // assume var url = 'https://example.com/image.jpg'
            let file = fs.createWriteStream('./image.jpg');
            await https.get(url, async (response) => {
                response.pipe(file).on("finish", () => res(true))
            }).on("error", err => res(err.stack))
        })

2 示例：100%，失败

正如您在上面看到的（以及图像的描述），失败的图像没有引发任何错误（ .on('err'... failed to catch anything)

在调用 Promise 的 resolve() 之前，如何检查/验证下载的图像是否 100% 完成？

标签： node.jsimagedownloadimagedownload

解决方案

我想我找到了。因此，对于任何与我有相同问题的人，我想在这里分享我的答案

我不得不切换到 node-fetch，所以如果您正在寻找 http 解决方案，那么我很抱歉，但我不知道如何。

const fs = require('fs'), fetch= require('https');
var w_size: number = 0 // file size from URL

await (async (url: string) => {
    return new Promise<Buffer>(resolve =>
        resolve(fetch(url)
            .then((r) => { /* get file size from header */ w_size = parseInt(r.headers.get('content-length') || '0'); return r })
            .then(res => res.arrayBuffer())
            .then(buff => Buffer.from(buff)))
    )
})(url).then(async (buffer) => {
    console.log('Writing');
    await fs.writeFileSync(downloadedFilePath, buffer);
    if (w_size) { // if w_size == 0 (means failed to get ['content-length'] from headers), jump to else
        var getPercent = fs.statSync(downloadedFilePath).size;
        if (Math.round((getPercent / w_size) * 100) < 99) { // minimum of 99 percent complete, or if you want to be strict, use <= 99 to make sure it's 100%
            // Partial download (download failed)
            console.log(`Error:\nBuffer end before whole file finished downloading (partial download)`)
            throw new Error('Partial download detected')
        }
        else {...} // Download success
    }
    else {...} // default behavior if failed to get w_size from URL (means original / meant-to-be size is unknown)
})

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