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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

            
              <div class="container">
  
  <div class="text">
    使用 Javascript 识别文件 MIME TYPE 类型
  </div>
  
  <div class="demo-contain">
    <section class="output-contain output-contain--extension">
      <h2>1. 使用 e.target.files[0].type 来获取文件类型(Read file type using e.target.files[0].type)</h2>
      <input type="file" class="control-extension"/>
      <div class="output">
        <dl>
          <dt>File Type: </dt><dd class=""></dd>
        </dl>
      </div>
    </section>
    
    <section class="output-contain output-contain--mn">
      <h2>2. 通过 FileReader.readAsArrayBuffer 来读取文件二进制数据,从而匹配文件类型。(Read file type using file signature/magic number)</h2>
      <input type="file" class="control-magic-number" />
      <div class="output">
        <dl>
          <dt>&bull;&nbsp;Bytes (decimal): </dt>
          <dd class="bytes-decimal"></dd>
        </dl>
        <dl>
          <dt>&bull;&nbsp;Bytes (hex): </dt>
          <dd class="bytes-hex"></dd>
        </dl>
        <dl>
          <dt>&bull;&nbsp;File MIME TYPE: </dt>
          <dd class="file-type"></dd>
        </dl>
      </div>
    </section>
    
    <section class="file-signatures__contain">
      <table>
        <thead>
          <tr>
            <th>file extension</th>
            <th>file signature</th>
          </tr>
        </thead>
        <tbody>
          <!-- JPG/JPEG -->
          <tr>
            <td rowspan="4">image/jpeg</td>
            <td>FF D8 FF E0</td>
          </tr>
          <tr>
            <td>FF D8 FF E1</td>
          </tr>
          <tr>
            <td>FF D8 FF E2</td>
          </tr>
          <tr>
            <td>FF D8 FF E3</td>
          </tr>
          <!-- PNG -->
          <tr>
            <td>image/png</td>
            <td>89 50 4E 47 0D 0A 1A 0A</td>
          </tr>
          <!-- GIF -->
          <tr>
            <td rowspan="2">image/gif</td>
            <td>47 49 46 38 37 61</td>
          </tr>
          <tr>
            <td>47 49 46 38 39 61</td>
          </tr>
          <!-- AVI -->
          <tr>
            <td>video/avi</td>
            <td>52 49 46 46 00 00 00 00 41 56 49 20</td>
          </tr>
        </tbody>
      </table>
      
      <div class="text text-info">
        如果想要测试 avi 文件,需要相对较小的样本(比如这里:<a href="http://www.engr.colostate.edu/me/facil/dynamics/avis.htm">High Speed Camera Sample AVI's</a>)。原因是,比如说你从硬盘的哪个角落翻出一部电影来,1 个 G,2 个 G,以至于几个 G,通过  input[type="file"] 来提取文件流,需要对文件 (BLOB) 进行裁切(slice)操作,不然基本就炸。
      </div>  
    </section>
  </div>
</div>
            
          
!
            
              html {
  font-size: 14px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, Helvetica, Arial, sans-serif, "Apple Color Emoji";
}

.container {
  width: 85%;
  max-width: 720px;
  background: #f1f2f3;
  margin: .65rem auto;
  padding: .65rem;
  border-radius: 4px;
}

.text {
  font-size: .95rem;
  line-height: 1.25;
  margin-bottom: .65rem;
  color: #000000;
  margin: .65rem;
  
  &.text-info {
    font-size: .85rem; 
    color: #646566;
    
    &:before {
      content: '*';
      color: red;
    }
    a:link, 
    a:hover,
    a:visited,
    a:active,
    a:focus {
      color: #0066cc;
    }
  }
}

.demo-contain {
  > .output-contain {
    padding: .65rem;
  }
  > .output-contain > h2 {
    margin: .325rem 0;
    font-weight: bold;
    font-size: 1rem;
  }
  > .output-contain > div.output {
    margin: .325rem 0;
  }
  > .output-contain > input[type="file"] {
    margin: .325rem 0;
  }
  > .output-contain > div.output > dl {
    display: flex;
    align-items: center;
    flex-flow: row wrap;
    margin-bottom: .325rem;
  }
  > .output-contain > div.output > dl dt,
  > .output-contain > div.output > dl dd {
    white-space: nowrap;
  }
  > .output-contain > div.output > dl dt {
     flex-basis: 30%;
  }
  > .output-contain > div.output > dl dd {
     flex-basis: 60%;
  }
}

.file-signatures__contain {
  width: 100%;
  > table {
    width: 100%;
    border: 1px solid #a3a4a5;
  }
  > table th,
  > table td {
    box-sizing: border-box;
    padding: .35rem 0;
    border: 1px solid #a3a4a5;
  }
  table th {
    background: #454647;
    color: #ffffff;
  }
  > table td {
    background: #f3f4f5;
    vertical-align: middle;
    text-align: center;
  }
}
            
          
!
            
              ;((win, doc, $) => {
  'use strict'
  
  let $outputE = $('section.output-contain--extension .output')
    , $outputMN = $('section.output-contain--mn .output')
    // control to read MIME TYPE using file extension
    , $controlE = $('input.control-extension')
    // control to read MIME TYPE using MAGIC NUMBER
    , $controlMN = $('input.control-magic-number')
    // decimal bytes output 
    , $bytesDecimal = $('.bytes-decimal', $outputMN)
    // hex bytes output
    , $bytesHex = $('.bytes-hex', $outputMN)
    , $fileType = $('.file-type', $outputMN)
  
  $controlE.on('change', (e) => { 
    $('dl dd', $outputE).text(e.target.files[0].type) 
  }) 
  
  const handleFileTYpe = (view) => {
    let first4Bytes = view.getUint32(0, false);
    let first4BytesHex = Number(first4Bytes).toString(16).toUpperCase()
    
    var count = 0 
    while (count < 4) {
      var int8 = view.getUint8(count, false)
      count++
    }
    
    // show the decimal value of bytes
    $bytesDecimal.text(first4Bytes)
    // show the hex value of bytes
    $bytesHex.text(first4BytesHex)
    
    switch (first4BytesHex) {
      case 'FFD8FFE0':
      case 'FFD8FFE1':
      case 'FFD8FFE2':
      case 'FFD8FFE3':
        $fileType.text('image/jpeg'); break;
      case '89504E47':
        $fileType.text('image/png'); break;
      case '47494638':
        $fileType.text('image/gif'); break;
      case '52494646':
        $fileType.text('video/avi'); break;
      default:
        $fileType.text('undefined'); break;
    }
  }
  
  const handleFileType = (file) => {
    let FR = new FileReader()
    FR.onload = (e)  => {
      let af = e.target.result
        , view = new DataView(af);
      
      /* for testing purpose START */
      let uint8 = new Uint8Array(af)
        , bytesFromUint8 = uint8.subarray(0, 4);
      
      let uint16 = new Uint16Array(af)
        , bytesFromUint16 = uint16.subarray(0, 2);
      
      let uint32 = new Uint32Array(af)
        , bytesFromUint32 = uint32.subarray(0, 1);
      
      console.log('uint8: ', bytesFromUint8.reduce((hex, decimal) => hex + Number(decimal).toString(16) + ' ', ' '))
      console.log('uint16: ', bytesFromUint16.reduce((hex, decimal) => hex + Number(decimal).toString(16) + ' ', ' '))
      console.log('uint32: ', bytesFromUint32.reduce((hex, decimal) => hex + Number(decimal).toString(16) + ' ', ' '))
      /* for testing purpose END */
      
      handleFileTYpe(view);
    }
    FR.readAsArrayBuffer(file)
  }
  
  $controlMN.on('change', (e) => { 
    handleFileType(e.target.files[0])
  })
  
})(window, document, jQuery)
            
          
!
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