我正在尝试使用XMLHttpRequest(使用最新的Webkit)下载二进制文件,并使用以下简单功能对base64的内容进行编码:
XMLHttpRequest
function getBinary(file){ var xhr = new XMLHttpRequest(); xhr.open("GET", file, false); xhr.overrideMimeType("text/plain; charset=x-user-defined"); xhr.send(null); return xhr.responseText; } function base64encode(binary) { return btoa(unescape(encodeURIComponent(binary))); } var binary = getBinary('http://some.tld/sample.pdf'); var base64encoded = base64encode(binary);
附带说明一下,以上所有内容都是标准Javascript内容,包括btoa()和encodeURIComponent()
btoa()
encodeURIComponent()
这工作非常顺利,我什至可以使用Javascript解码base64内容:
function base64decode(base64) { return decodeURIComponent(escape(atob(base64))); } var decodedBinary = base64decode(base64encoded); decodedBinary === binary // true
现在,我想使用Python解码base64编码的内容,该内容使用一些JSON字符串来获取base64encoded字符串值。天真的,这就是我的工作:
base64encoded
import urllib import base64 # ... retrieving of base64 encoded string through JSON base64 = "77+9UE5HDQ……………oaCgA=" source_contents = urllib.unquote(base64.b64decode(base64)) destination_file = open(destination, 'wb') destination_file.write(source_contents) destination_file.close()
但是生成的文件无效,看起来该操作已被UTF-8,编码或其他尚不清楚的东西弄乱了。
如果在将UTF-8内容放入目标文件之前尝试对其进行解码,则会引发错误:
import urllib import base64 # ... retrieving of base64 encoded string through JSON base64 = "77+9UE5HDQ……………oaCgA=" source_contents = urllib.unquote(base64.b64decode(base64)).decode('utf-8') destination_file = open(destination, 'wb') destination_file.write(source_contents) destination_file.close() $ python test.py // ... UnicodeEncodeError: 'ascii' codec can't encode character u'\ufffd' in position 0: ordinal not in range(128)
附带说明一下,这是同一文件的两种文本表示形式的屏幕截图;左:原件;右:从base64解码的字符串创建的一个
尝试重新创建文件时,是否存在已知的技巧来规避编码问题?您将如何实现自己?
任何帮助或暗示非常感谢:)
所以我对自己回答-对此感到抱歉-但我认为这对于像我一样迷路的人可能有用;)
所以,你必须使用ArrayBuffer和设置responseType您的属性XMLHttpRequest对象实例的arraybuffer检索字节的原始数组,可以转换为使用下列方便的功能的base64(发现那里,笔者可以在这里祝福):
responseType
arraybuffer
function base64ArrayBuffer(arrayBuffer) { var base64 = '' var encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/' var bytes = new Uint8Array(arrayBuffer) var byteLength = bytes.byteLength var byteRemainder = byteLength % 3 var mainLength = byteLength - byteRemainder var a, b, c, d var chunk // Main loop deals with bytes in chunks of 3 for (var i = 0; i < mainLength; i = i + 3) { // Combine the three bytes into a single integer chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2] // Use bitmasks to extract 6-bit segments from the triplet a = (chunk & 16515072) >> 18 // 16515072 = (2^6 - 1) << 18 b = (chunk & 258048) >> 12 // 258048 = (2^6 - 1) << 12 c = (chunk & 4032) >> 6 // 4032 = (2^6 - 1) << 6 d = chunk & 63 // 63 = 2^6 - 1 // Convert the raw binary segments to the appropriate ASCII encoding base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d] } // Deal with the remaining bytes and padding if (byteRemainder == 1) { chunk = bytes[mainLength] a = (chunk & 252) >> 2 // 252 = (2^6 - 1) << 2 // Set the 4 least significant bits to zero b = (chunk & 3) << 4 // 3 = 2^2 - 1 base64 += encodings[a] + encodings[b] + '==' } else if (byteRemainder == 2) { chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1] a = (chunk & 64512) >> 10 // 64512 = (2^6 - 1) << 10 b = (chunk & 1008) >> 4 // 1008 = (2^6 - 1) << 4 // Set the 2 least significant bits to zero c = (chunk & 15) << 2 // 15 = 2^4 - 1 base64 += encodings[a] + encodings[b] + encodings[c] + '=' } return base64 }
所以这是一个工作代码:
var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://some.tld/favicon.png', false); xhr.responseType = 'arraybuffer'; xhr.onload = function(e) { console.log(base64ArrayBuffer(e.currentTarget.response)); }; xhr.send();
这将记录一个表示二进制文件内容的 有效 base64编码的字符串。
编辑: 对于无法访问ArrayBuffer且btoa()编码字符失败的旧版浏览器,这是获取任何二进制文件的base64编码版本的另一种方法:
ArrayBuffer
function getBinary(file){ var xhr = new XMLHttpRequest(); xhr.open("GET", file, false); xhr.overrideMimeType("text/plain; charset=x-user-defined"); xhr.send(null); return xhr.responseText; } function base64Encode(str) { var CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; var out = "", i = 0, len = str.length, c1, c2, c3; while (i < len) { c1 = str.charCodeAt(i++) & 0xff; if (i == len) { out += CHARS.charAt(c1 >> 2); out += CHARS.charAt((c1 & 0x3) << 4); out += "=="; break; } c2 = str.charCodeAt(i++); if (i == len) { out += CHARS.charAt(c1 >> 2); out += CHARS.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4)); out += CHARS.charAt((c2 & 0xF) << 2); out += "="; break; } c3 = str.charCodeAt(i++); out += CHARS.charAt(c1 >> 2); out += CHARS.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)); out += CHARS.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6)); out += CHARS.charAt(c3 & 0x3F); } return out; } console.log(base64Encode(getBinary('http://www.google.fr/images/srpr/logo3w.png')));
希望这能对我有所帮助。