NodeJS base64圖像編碼/解碼不起作用

Question

我一直在嘗試處理將保存的圖像發送到nodeJS（以及快速框架）到數據庫，並且遇到了一些麻煩。忽略所有的Web處理，我認爲我已經將問題縮小到了base64編碼在節點中發生的方式。我相信下面的簡單示例應該可以工作，但輸出圖像總是被損壞。

加載到圖像（2）中的示例（1）保存if（image_orig）的副本以確認節點可以正確讀取文件。這總是有效的。 （3）我把圖像和base64編碼其內容，（4）然後解碼它。最終輸出圖像（image_decoded）始終損壞。

幫助！ （node.js的0.6.0在OSX獅子）

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

我想你是誤會了編碼參數位的使用。如果你打算指定編碼'二進制'，那麼你需要一直這樣做。但是，你真的不需要它。你似乎混淆了Buffer和二進制字符串的用法。

// 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) {}); 
}); 

下一個示例將工作，但因爲改變不需要所有的時間編碼效率非常低，但我只是想表明它是清楚的。如果你真的想要一個特定的編碼，你需要確保你是一致的。每個函數都有一個編碼參數。

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) {}); 
}); 

這是正確的做法。保持一切爲緩衝區，除非你使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

稍微好一點的解決方法是將刪除所有MIME類型可能：

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'); 
}); 

這是除了@埃爾韋的答案。