如何生成校验和在不溢出RAM的情况下将非常大的文件转换为Javascript中的64位？ [英] How to generate checksum & convert to 64 bit in Javascript for very large files without overflowing RAM?

问题描述

问题：

1. 如何正确生成校验和，这是唯一的，一致的，独立的浏览器？另外，我想将SHA256 / MD5校验和字符串转换为64位。

1. How to generate a checksum correctly, which is unique, consistent independent of browsers? Also, I would like to convert a SHA256/MD5 checksum string to 64-bit.

如何在不占用大量RAM的情况下正确读取文件以生成校验和？即我们如何处理1 GB的文件而不会损害RAM

How to properly read a file without huge RAM requirement to generate checksum? i.e. how do we deal with 1 GB file without compromising RAM

例如是否可以在不将文件加载到内存的情况下读取文件？（请参见答案）

此项目看起来很有希望，但也无法使它起作用

This project seems promising, but couldn't get it worked either.

我的意图是逐步/递增地在X MB块中生成校验和。这可能有助于避免一次使用过多的RAM。

以下代码无法正常工作：

My intention is to generate the checksum progressively/incrementally in chunks of X MBs. This may help to avoid using too much RAM at a time.
Following is the code, which is not working as expected:

let SIZE_CHECKSUM = 10 * Math.pow(1024, 2); // 10 MB; But can be 1 MB too
async function GetChecksum (file: File):
Promise<string>
{
  let hashAlgorithm: CryptoJS.lib.IHasher<Object> = CryptoJS.algo.SHA256.create();
  let totalChunks: number = Math.ceil(file.size / SIZE_CHECKSUM);
  for (let chunkCount = 0, start = 0, end = 0; chunkCount < totalChunks; ++chunkCount)
  {
    end = Math.min(start + SIZE_CHECKSUM, file.size);
    let resultChunk: string = await (new Response(file.slice(start, end)).text());
    hashAlgorithm.update(resultChunk);
    start = chunkCount * SIZE_CHECKSUM;
  }
  let long: bigInt.BigInteger = bigInt.fromArray(hashAlgorithm.finalize().words, 16, false);
  if(long.compareTo(bigInt.zero) < 0)
    long = long.add(bigInt.one.shiftLeft(64));
  return long.toString();
}

在不同的浏览器中显示不同的结果。

It shows different results in different browsers.

推荐答案

下面的代码行中有一个逻辑问题：

There is a logical issue in the code at below line:

start = chunkCount * SIZE_CHECKSUM;  // <--- bug

变量 start 初始化为0，然后在第一次迭代中再次重置为0 ，这是不对的。

以下是使用以下方法获取32字节SHA5校验和的方法：问题中提到的同一库： emn178 / js-sha256 。

The variable start is initialized to 0 and then again reset to 0 in the 1st iteration, which is not right.
Following is the way to get a 32 bytes SHA5 checksum with the same library mentioned in the question: "emn178/js-sha256".

该库不提供Typescript接口，但是我们可以定义如下：

That library doesn't provide a Typescript interface, but we can define trivially as following:

// Sha256.d.ts  (also name the corresponding JS file as "Sha256.js")
declare class Sha256 {
  update (data: ArrayBuffer): Sha256;
  hex (): string;
}

declare var sha256: any;
declare interface sha256 {
  create (): Sha256;
}

然后按以下方式使用它：

Then use it as following:

import "./external/Sha256"

async function GetChecksum (file: File):
Promise<string>
{
  let algorithm = sha256.create(); 
  for(let chunkCount = 0, totalChunks = Math.ceil(file.size / SIZE_CHECKSUM); 
      chunkCount < totalChunks;
      ++chunkCount)
  {
    let start = chunkCount * SIZE_CHECKSUM, end = Math.min(start + SIZE_CHECKSUM, file.size); 
    algorithm.update(await (new Response(file.slice(start, end)).arrayBuffer()));
  }
  return algorithm.hex();
}

以上代码在我的所有浏览器中针对任何块大小生成相同的校验和。

Above code generates same checksums in all my browsers for any chunk size.

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