在 node.js 中解码 Base64 字符串

2022-01-21 00:00:00 node.js decoding base64 javascript

我正在尝试解码表示存储在数据库中的图像的 base64 字符串.我尝试了 SO 上提供的许多库和解决方案，但我仍然无法正确解码图像.特别是，使用以下代码:

I'm trying to decode a base64 string representing an image stored in a db. I tried many libraries and solutions provided on SO, but I'm still unable to decode the image correctly. In particular, using the following code:

var img = new Buffer(b64, 'base64').toString('ascii');

我得到了一个类似的二进制表示，除了第一个字节.这是 base64 字符串的初始部分:

I get a similar binary representation, except for the first bytes. This is the initial part of the base64 string:

/9j/4RxVRXhpZgAASUkqAAgAAAANADIBAgAUAAAAqgAAACWIBAABAAAAiwYAABABAgAIAAAAvgAA

这里是原始图像的前 50 个字节:

Here are the first 50 bytes of the original image:

ffd8ffe11c5545786966000049492a00080000000d003201020014000000aa00000025880400010000008b06000010010200

这是我用 javascript 得到的字符串的前 50 个字节:

And here are the first 50 bytes of the string I get with javascript:

7f587f611c5545786966000049492a00080000000d0032010200140000002a00000025080400010000000b06000010010200

你可以看到，这两个字符串是相同的，除了前 3 个字节和中间的几个字节.
有人可以帮我理解为什么会发生这种情况以及如何解决吗?谢谢

How you can see, the two strings are identical except for the fisrt 3 bytes and some few bytes in the middle.
Can somebody help me understand why this is happening and how to solve it? Thanks

推荐答案

问题是您正在尝试将二进制数据转换为 ASCII，这很可能意味着数据丢失，因为 ASCII 仅包含值 0x00-0x7F.所以当转换发生时，所有大于 0x7F 的字节都被限制为 0x7F.

The problem is that you're trying to convert binary data to ASCII, which most likely than not, will mean loss of data since ASCII only consists of values 0x00-0x7F. So when the conversion takes place, all bytes > 0x7F are capped at 0x7F.

如果您改为这样做，您可以看到数据与原始图像的前 50 个字节匹配:

If you do this instead, you can see the data matches your first 50 bytes of the original image:

console.log(Buffer.from(b64, 'base64').toString('hex'));

但是如果你想保持二进制数据完整，只需将它作为一个Buffer实例而不调用.toString()，因为许多处理二进制数据的函数都可以处理Buffers(例如fs 核心模块).

But if you want to keep the binary data intact, just keep it as a Buffer instance without calling .toString(), as many functions that work with binary data can deal with Buffers (e.g. fs core module).

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