解压后如何取回原来的字符串 - Zlib

Posted 2023-02-22

【中文标题】解压后如何取回原来的字符串 - Zlib

【英文标题】：How to get back the original string after decompressing - Zlib

【发布时间】：2014-11-20 12:03:50

【问题描述】：

我正在尝试使用Zlib 压缩和解压缩字符串。这是我用来压缩和解压缩的JS 文件。

压缩代码：

compress_string = function () 

   var string = document.getElementById("input_value").value;

   var deflate = new Zlib.Deflate(string);
   var compressed = deflate.compress();

   var b64encoded = btoa(String.fromCharCode.apply(null, compressed));

   var elem = document.getElementById("input_value");
   elem.value = b64encoded;

   var elemLabel = document.getElementById("zlsize");
   elemLabel.value = ("Size of sample is: " + string.length) + " " + ("Compressed Value: " + b64encoded + " Size: " + b64encoded.length);

压缩后，我将压缩值设置回input_value 文本字段。

解压码：

decompress_string = function () 

   var string = document.getElementById("input_value").value;

   var compressData = new Uint8Array(atob(string).split("").map(function(c)  return c.charCodeAt(0); ))

   var inflate = new Zlib.Inflate(compressData);
   var plain = inflate.decompress();

   var elem = document.getElementById("input_value");
   elem.value = btoa(plain);

   var elemLabel = document.getElementById("zlsize");
   elemLabel.value = ("Size of compressed string is: " + string.length) + " " + ("Decompressed Value: " + plain + " Size: " + plain.length);

我正在尝试压缩以下示例字符串：

<xml><username>myusername</username><password>mypassword</password></xml>

样本大小为：73

压缩值： eJxNibEJAAAMg/7/OjoEdCjGAoAnmqg6fF8T7QMfCxxR

尺寸：44

当尝试解压上述压缩字符串时，我得到一个Uint8Array 的对象，如下所示：

压缩字符串的大小为：44

解压值： [object Uint8Array]

尺寸：70

尝试使用btoa() 将对象Uint8Array 转换为字符串时，输出如下：

W29iamVjdCBVaW50OEFycmF5XQ==

问题： 如何获取原始字符串？

【参考方案1】：

你的问题是文本编码。

Uint8Array 是某事物的二进制表示，字符串可以写成多种格式。您需要坚持一个，并使用它进行转换。

在这个例子中我选择了 UTF-8，使用这个library

function compress(input)
    var binaryconverter = new TextEncoder('utf-8');
    var binary = binaryconverter.encode(input);
    var deflate = new Zlib.Deflate(binary);
    var compressed = deflate.compress();
    return btoa(String.fromCharCode.apply(null, compressed));


function decompress(b64encoded)
    var compressed = new Uint8Array(atob(b64encoded).split("").map(function(c)return c.charCodeAt(0);));
    var inflate = new Zlib.Inflate(compressed);
    var binary = inflate.decompress();
    var binaryconverter = new TextDecoder('utf-8');
    return binaryconverter.decode(binary);


var input = '<xml><username>myusername</username><password>mypassword</password></xml>';
var b64encoded = compress(input);
var output = decompress(b64encoded);
alert(output);

因此，在编码时，我首先将字符串转换为 UTF-8 格式文本的二进制表示，然后使用 ZLib 进行压缩，然后再次将其转换为 base64 字符串以便于传输。

要解压缩，你做相反的事情：首先解码 base64 字符串，然后 ZLib 进行膨胀，最后我们再次使用 UTF-8 将二进制转换为字符串

【讨论】：

库只需要encoding.js，因为我们只使用UTF-8。

【参考方案2】：

文档zlib.js 似乎建议plain（输入）类型为Array.<number> or Uint8Array

    // plain = Array.<number> or Uint8Array
    var deflate = new Zlib.Deflate(plain);
    var compressed = deflate.compress();

在 OP 处，var string 似乎是类型 string，请参阅

   var string = document.getElementById("input_value").value;
   var deflate = new Zlib.Deflate(string);

要从压缩的base64 格式化字符串中检索text 值，如下；首先，将var string映射到.charCodeAt()number，返回代表文本字符的numbers数组；第二，将.charCodeAt()数字推送到映射数组；第三，在charCodeAt()值数组中的每个项目上调用window.btoa(encodeURIComponent(escape(compressed[i])))，推送到同一个映射数组；第四，在for循环中解码base64encoded字符串，在解压Uint8Array时调用String.fromCharCode(plain[i])，返回原始输入string。

试试

var elem = document.getElementById("input_value")
    , elemLabel = document.getElementById("zlsize")
    , compress = document.getElementById("compress")
    , decompress = document.getElementById("decompress")
    , b64map = []
    , _b64encoded
    , b64encoded
    , _string
    , string
    , _plain
    , compressData;

    function compress_string () 
        string = elem.value;
        _string = [].slice.call(string).map(function (value, key) 
            return value.charCodeAt(0)
        );
        var deflate = new Zlib.Deflate(_string);
        var compressed = deflate.compress();
        for (var i = 0; i < compressed.length; i++) 
            b64map.push([compressed[i]
                , window.btoa(encodeURIComponent(escape(compressed[i])))])
        ;
        _b64encoded = b64map.map(function (value, key) 
            return value[1]
        );
        b64encoded = _b64encoded.join("");
        elem.value = b64encoded;
        elemLabel.innerText = ("Size of sample is: " 
                              + string.length) + " " + ("Compressed Value: " 
                              + b64encoded + " Size: " + b64encoded.length)
    ;

    function decompress_string () 
        string = elem.value;
        elem.value = "";
        compressData = _b64encoded.map(function (value, key)                       
            return new RegExp(value).test(string) ? b64map[key][0] : null
        );

        compressData = new Uint8Array(compressData);
        var inflate = new Zlib.Inflate(compressData);

        var plain = inflate.decompress();
        b64map = b64encoded = [];
        _plain = "";
        for (var i = 0; i < plain.length; i++) 
            _plain += String.fromCharCode(plain[i])
        ;
        elem.value = _plain;
        elemLabel.innerText = ("Size of compressed string is: " 
                              + elem.value.length) + " " 
                              + ("Decompressed Value: " + _plain + " Size: " 
                              + _plain.length);
    ;

    compress.addEventListener("click", compress_string);
    decompress.addEventListener("click", decompress_string);

jsfiddle http://jsfiddle.net/guest271314/ov6nwLak/

$.getScript("https://raw.githubusercontent.com/imaya/zlib.js/master/bin/zlib.min.js")

var elem = document.getElementById("input_value")
    , elemLabel = document.getElementById("zlsize")
    , compress = document.getElementById("compress")
    , decompress = document.getElementById("decompress")
    , b64map = []
    , _b64encoded
    , b64encoded
    , _string
    , string
    , _plain
    , compressData;
    elem.value = "<xml><username>myusername</username><password>mypassword</password></xml>";
    function compress_string () 
        string = elem.value;
        _string = [].slice.call(string).map(function (value, key) 
            return value.charCodeAt(0)
        );
        var deflate = new Zlib.Deflate(_string);
        var compressed = deflate.compress();
        for (var i = 0; i < compressed.length; i++) 
            b64map.push([compressed[i]
                , window.btoa(encodeURIComponent(escape(compressed[i])))])
        ;
        _b64encoded = b64map.map(function (value, key) 
            return value[1]
        );
        b64encoded = _b64encoded.join("");
        elem.value = b64encoded;
        elemLabel.innerText = ("Size of sample is: " 
                              + string.length) + " " + ("Compressed Value: " 
                              + b64encoded + " Size: " + b64encoded.length)
    ;
    
    function decompress_string () 
        string = elem.value;
        elem.value = "";
        compressData = _b64encoded.map(function (value, key)                       
            return new RegExp(value).test(string) ? b64map[key][0] : null
        );
        
        compressData = new Uint8Array(compressData);
        var inflate = new Zlib.Inflate(compressData);
    
        var plain = inflate.decompress();
        b64map = b64encoded = [];
        _plain = "";
        for (var i = 0; i < plain.length; i++) 
            _plain += String.fromCharCode(plain[i])
        ;
        elem.value = _plain;
        elemLabel.innerText = ("Size of compressed string is: " 
                              + elem.value.length) + " " 
                              + ("Decompressed Value: " + _plain + " Size: " +         
                              _plain.length);
    ;
    
    compress.addEventListener("click", compress_string);
    decompress.addEventListener("click", decompress_string);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>




<input type="text" id="input_value" />
<button id="compress">compress</button>
<button id="decompress">decompress</button>
<br />
<label id="zlsize"></label>