NodeJS base64图像编码/解码不太合适

Question

我一直在尝试将发布到nodeJS(和快速框架)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了base64编码在节点中发生的方式.我相信下面的过度简化示例应该可以工作,但输出图像总是被破坏.

示例(1)加载图像(2)保存if(image_orig)的副本以确认该节点可以正确读取文件.这总是有效的.(3)我拍摄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)总是被破坏.

救命!(OSX Lion上的node.js 0.6.0)

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) {});
});

Answer 1

我认为你误解了编码参数的用法.如果要指定编码'binary',则需要一致地执行.但实际上你根本不需要它.您似乎混淆了Buffer与二进制字符串的使用.

// 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,但我只想表明它是清楚的.如果你真的想要拥有特定的编码,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.

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) {});
});

这是正确的方法.将所有内容保留为缓冲区,除非您将其设置为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) {});
});

Answer 2

稍微好一点的解决方案是删除所有可能的mime类型:

var buff = new Buffer(req.body.imageFile
    .replace(/^data:image\/(png|gif|jpeg);base64,/,''), 'base64');
fs.writeFile('/file/path/', buff, function (err) {
    console.log('done');
});

这是@Herve答案的补充.