javascript - Pdf.js:使用 base64 文件源而不是 url 呈现 pdf 文件

Question

我正在尝试使用 pdf.js 从 pdf 渲染页面

通常，使用 url，我可以这样做:

PDFJS.getDocument("http://www.server.com/file.pdf").then(function getPdfHelloWorld(pdf) {
  //
  // Fetch the first page
  //
  pdf.getPage(1).then(function getPageHelloWorld(page) {
    var scale = 1.5;
    var viewport = page.getViewport(scale);

    //
    // Prepare canvas using PDF page dimensions
    //
    var canvas = document.getElementById('the-canvas');
    var context = canvas.getContext('2d');
    canvas.height = viewport.height;
    canvas.width = viewport.width;

    //
    // Render PDF page into canvas context
    //
    page.render({canvasContext: context, viewport: viewport});
  });
});

但在这种情况下，我的文件是 base64 而不是 url:

data:application/pdf;base64,JVBERi0xLjUKJdDUxdgKNSAwIG9iaiA8PAovTGVuZ3RoIDE2NjUgICAgICAKL0ZpbHRlciAvRmxhdGVEZWNvZGUKPj4Kc3RyZWFtCnjarVhLc9s2...

如何做到这一点？

Answer 1

来自源代码 http://mozilla.github.com/pdf.js/build/pdf.js

/**
 * This is the main entry point for loading a PDF and interacting with it.
 * NOTE: If a URL is used to fetch the PDF data a standard XMLHttpRequest(XHR)
 * is used, which means it must follow the same origin rules that any XHR does
 * e.g. No cross domain requests without CORS.
 *
 * @param {string|TypedAray|object} source Can be an url to where a PDF is
 * located, a typed array (Uint8Array) already populated with data or
 * and parameter object with the following possible fields:
 *  - url   - The URL of the PDF.
 *  - data  - A typed array with PDF data.
 *  - httpHeaders - Basic authentication headers.
 *  - password - For decrypting password-protected PDFs.
 *
 * @return {Promise} A promise that is resolved with {PDFDocumentProxy} object.
 */

因此，标准的 XMLHttpRequest(XHR) 用于检索文档。 问题在于 XMLHttpRequests 不支持数据:uris(例如 data:application/pdf;base64,JVBERi0xLjUK...)。

但是有可能将类型化的 Javascript 数组传递给函数。 您唯一需要做的就是将 base64 字符串转换为 Uint8Array。您可以使用位于 https://gist.github.com/1032746 的此功能

var BASE64_MARKER = ';base64,';

function convertDataURIToBinary(dataURI) {
  var base64Index = dataURI.indexOf(BASE64_MARKER) + BASE64_MARKER.length;
  var base64 = dataURI.substring(base64Index);
  var raw = window.atob(base64);
  var rawLength = raw.length;
  var array = new Uint8Array(new ArrayBuffer(rawLength));

  for(var i = 0; i < rawLength; i++) {
    array[i] = raw.charCodeAt(i);
  }
  return array;
}

tl;dr

var pdfAsDataUri = "data:application/pdf;base64,JVBERi0xLjUK..."; // shortened
var pdfAsArray = convertDataURIToBinary(pdfAsDataUri);
PDFJS.getDocument(pdfAsArray)