NodeJS base64 图像编码/解码不太工作 [英] NodeJS base64 image encoding/decoding not quite working

问题描述

我一直在尝试处理将发布到 nodeJS(和 express 框架)的图像保存到数据库，并且遇到了一些麻烦.忽略所有的 web 处理，我认为我已经将问题缩小到 base64 编码在 node.js 中发生的方式.我相信下面这个过于简单的例子应该可以工作，但输出图像总是被破坏.

I've been trying to handle saving images POSTed to nodeJS (and the express framework) to a database, and have been having some trouble. Ignoring all the web processing, I think that I've narrowed down the problem to the way base64 encoding is happening in node. I believe that the oversimplified example below should work, but the output image is always corrupted.

示例 (1) 加载图像 (2) 保存 if (image_orig) 的副本，以确认节点可以正确读取文件.这总是有效的.(3) 我获取图像并对其内容进行 base64 编码，(4) 然后对其进行解码.最终输出图像 (image_decoded) 总是损坏的.

The example (1) loads in an image (2) saves a copy of if (image_orig) to confirm that node can read the file properly. This always works. (3) I take the image and base64 encode its contents, (4) then decode it. The final output image (image_decoded) is always corrupted.

帮助！(OSX Lion 上的 node.js 0.6.0)

Help! (node.js 0.6.0 on OSX Lion)

console.log("starting");
process.chdir(__dirname);

var fs = require("fs");

var image_origial = "image.jpg";
fs.readFile(image_origial, function(err, original_data){
    fs.writeFile('image_orig.jpg', original_data, function(err) {});
    var base64Image = new Buffer(original_data, 'binary').toString('base64');
    var decodedImage = new Buffer(base64Image, 'base64').toString('binary');
    fs.writeFile('image_decoded.jpg', decodedImage, function(err) {});
});

推荐答案

我觉得你对 encoding 参数的用法有点误解了.如果您要指定编码二进制"，那么您需要始终如一地执行此操作.但实际上你根本不需要它.您似乎混淆了 Buffer 与二进制字符串的用法.

I think you are misunderstanding the usage of the encoding argument a bit. If you are going to specify encoding 'binary', then you need to do it consistently. But really you don't need it at all. You seem to be confusing the usage of Buffer vs binary strings.

// This tells node to load the file into a Buffer 'original_data' because you
// have not specified an encoding for the returned values. If you provided an
// encoding, then original_data would be a string with that encoding.
fs.readFile(image_origial, function(err, original_data){

    // This tells node to take that buffer, and write it to the new filename.
    // Again no encoding is provided, so it will assume a Buffer or utf8 string.
    fs.writeFile('image_orig.jpg', original_data, function(err) {});

    // This tells node to create a new buffer from the old buffer, which means
    // it will iterate over original_data copying the bytes one at a time. But
    // they will be identical buffers. It will ignore the 'binary' argument
    // since the object you are passing isn't a string.
    // Then it encodes the content of that Buffer to base64, which is fine.
    var base64Image = new Buffer(original_data, 'binary').toString('base64');

    // Here you decode the base64 to a buffer, which is fine, but then you
    // convert the buffer into a string with encoding 'binary'. This means that
    // it is a string object whose code points are bytes of the buffer.
    var decodedImage = new Buffer(base64Image, 'base64').toString('binary');

    // Here you try to write that String object to a file. Since the argument you
    // have given is a string and you have not given an encoding argument for the
    // write command, then it will assume that 'utf8' is the encoding. It will try to
    // decode your binary string into a utf8 encoded buffer, and write that buffer.
    // This will cause it to fail because that encoding conversion is wrong.
    // Really through, 'binary' is just wrong to use. Buffers are already binary.
    fs.writeFile('image_decoded.jpg', decodedImage, function(err) {});
});

下一个示例将起作用，但效率非常低，因为不需要一直更改编码，但我只是想清楚地表明它.如果你真的想要有一个特定的编码，你需要确保你是一致的.这些函数中的每一个都有一个编码参数.

This next example will work but is very inefficient because changing encodings all the time isn't needed, but I just want to show it to be clear. If you really DID want to have a specific encoding, you need to make sure you are consistent. Every one of those functions has an encoding argument.

fs.readFile(image_origial, 'binary', function(err, original_data){
    fs.writeFile('image_orig.jpg', original_data, 'binary', function(err) {});
    var base64Image = new Buffer(original_data, 'binary').toString('base64');
    var decodedImage = new Buffer(base64Image, 'base64').toString('binary');
    fs.writeFile('image_decoded.jpg', decodedImage, 'binary', function(err) {});
});

这是正确的做法.将所有内容都保存为 Buffer，除非您将其设为 base64.

This is the right way to do it. Keep everything as a Buffer, except when you make it base64.

fs.readFile(image_origial, function(err, original_data){
    fs.writeFile('image_orig.jpg', original_data, function(err) {});
    var base64Image = original_data.toString('base64');
    var decodedImage = new Buffer(base64Image, 'base64');
    fs.writeFile('image_decoded.jpg', decodedImage, function(err) {});
});

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