获取资源，计算哈希，返回承诺 [英] fetch resource, compute hash, return promise

问题描述

我想在浏览器扩展程序中使用获取API 下载资源并计算其哈希值.以下作品(通过 crypto rel ="nofollow">浏览)

I would like to use the Fetch API in a browser extension to download a resource and compute a hash thereof. The following works (using crypto through Browserify)

fetch(url).then(function(response) {
  return response.blob();
}).then(function(data) {
  var a = new FileReader();
  a.readAsBinaryString(data);
  a.onloadend = function() {
    var hash = crypto.createHash(hashType);
    hash.update(a.result, 'binary');
    return hash.digest('hex');
  };
})

，但缺点是我必须等待a.onloadend，而要嵌入它的上下文需要返回Promise.同样，首先获取整个Blob，然后将其读取到FileReader，然后再将其转储到createHash，似乎很奇怪.

but has the disadvantage that I have to wait for a.onloadend while the context in which I'd like to embed it requires a Promise to be returned. Also, it seems quite weird to first fetch the entire blob, then read it into a FileReader just to dump it into createHash afterwards.

有任何提示吗?

推荐答案

密码hash.update方法也需要一个缓冲区，因此无需通过FileReader绕行.随便

fetch(url).then(function(response) {
    return response.arrayBuffer();
}).then(function(arrayBuffer) {
    var buffer = require('buffer')(new Uint8Array(arrayBuffer));
    var hash = require('crypto').createHash(hashType);
    hash.update(buffer, 'binary');
    return hash.digest('hex');
})

如果这不起作用，则可以轻松实现 a FileReader:

If that doesn't work, you can easily promisify a FileReader:

function getResult(reader) {
    return new Promise(function(resolve, reject) {
        reader.onload = function() {
            resolve(this.result);
        };
        reader.onerror = reader.onabort = reject;
    });
}

并像这样使用它:

fetch(url).then(function(response) {
    return response.blob();
}).then(function(data) {
    var a = new FileReader();
    a.readAsBinaryString(data);
    return getResult(a);
}).then(function(result) {
    var hash = crypto.createHash(hashType);
    hash.update(result, 'binary');
    return hash.digest('hex');
})

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