如何将PDF发送至Watson的文档转换服务而无需先将其写入磁盘？

Question

我试图使用watson-developer-cloud node.js库将this document (http://www.redbooks.ibm.com/redbooks/pdfs/ga195486.pdf)转换为Watson文档转换服务中的单元。

在实际的程序（不是这个测试程序）中，我正在检索文档并将其转换，而不是先写入磁盘。我之前已经使用过其他文档，但最新版本的库（v 1.7.0）似乎已经发生了变化，它不再以我使用它的方式工作。但即使在我开始使用最新版本之前，这个特定的文档也不会转换。

我正在使用的带注释的测试代码如下。我尝试了几种方法来实现这一点，其中的变体都在var opts = {以下。您必须一次取消注释其中之一以查看结果。

'use strict'; 
var bluemix = require('./bluemix'); 
var extend=require('util')._extend; 
var fs=require('fs'); 
var watson=require('watson-developer-cloud'); 
var streams = require('memory-streams'); 

var dcCredentials = extend({ 
    url: '<url>', 
    version: 'v1', 
    username: '<username>', 
    password: '<password>' 
}, bluemix.getServiceCreds('document_conversion')); // VCAP_SERVICES 
var document_conversion = watson.document_conversion(dcCredentials); 

var bookpdf=getBook('ga195486.pdf'); 
convert(bookpdf); 

function getBook(filename) 
    { 
    var bl=fs.readFileSync(filename,'utf8'); 
    return bl; 
    } 

function convert(content) 
    { 
    var opts={ //uncomment ONE of these 
//  file: new Buffer(content), //See message #1 below 
//  file: {value: new Buffer(content), options: {}}, //see message #2 below 
//  file: {value: new Buffer(content), options: {contentType: "application/pdf"}}, //This used to work. See message #2 (again) below 
//  file: new streams.ReadableStream(content),//see message #3 below 
     conversion_target: "ANSWER_UNITS", 
     content_type:'application/pdf' 
     }; 
    document_conversion.convert(opts, 
     function (err, response) 
     { 
     if (err) 
      { 
      console.log("Error converting doc: ", err); 
      } 
     else if (response.answer_units.length==0) 
      { 
      var msg="No answer units"; 
      console.log(msg,response); 
      } 
     else 
      { 
      console.log('Works!'); 
      console.dir(response); 
      } 
     } 
    ); 
    } 

//Message #1: This returns: 
// No answer units { source_document_id: '', 
// timestamp: '2016-05-23T16:18:23.825Z', 
// media_type_detected: 'application/pdf', 
// metadata: [], 
// answer_units: [], 
// warnings: 
// [ { phase: 'pdf', 
//  warning_id: 'empty_input_to_converter', 
//  description: 'The input provided to the converter phase is empty or doesn\'t contain text that can be converted.' }, 
//  { phase: 'normalized_html', 
//  warning_id: 'empty_input_to_converter', 
//  description: 'The input HTML document has no body content.' }, 
//  { phase: 'answer_units', 
//  warning_id: 'empty_input_to_converter', 
//  description: 'The input provided to the converter phase is empty or doesn\'t contain text that can be converted.' } ] } 


//Message #2: These return: 
///home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/node_modules/combined-stream/node_modules/delayed-stream/lib/delayed_stream.js:33 
// source.on('error', function() {}); 
// 
//TypeError: source.on is not a function 
// at Function.DelayedStream.create (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/node_modules/combined-stream/node_modules/delayed-stream/lib/delayed_stream.js:33:10) 
// at FormData.CombinedStream.append (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/node_modules/combined-stream/lib/combined_stream.js:43:37) 
// at FormData.append (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/node_modules/form-data/lib/form_data.js:68:3) 
// at appendFormValue (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/request.js:339:21) 
// at Request.init (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/request.js:352:11) 
// at new Request (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/request.js:142:8) 
// at request (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/node_modules/request/index.js:55:10) 
// at createRequest (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/lib/requestwrapper.js:134:10) 
// at DocumentConversion.convert (/home/david/git/ccb-contentbridge/node_modules/watson-developer-cloud/services/document_conversion/v1.js:134:10) 
// at convert (/home/david/git/ccb-contentbridge/testRedbooks.js:35:24) 


//Message #3: This returns and then it hangs there: 
//Error converting doc: { code: 400, error: 'Error in the web application' } 

有人能告诉我我做错了什么吗？

Answer 1

该特定文件大于文档转换服务当前可处理的文件。不幸的是，我现在还没有很好的信息来说明现在的限制，但团队意识到这一点并正在寻求改进。

如果你能提供一个以前工作过的例子，但打破了node.js库的v1.7.0，我会看看它，希望能够提供更好的信息。

哦，并在您的fs.readfileSync()呼叫中指定'utf8'可能会导致您遇到的一些麻烦。

Answer 2

看起来Doc Con的限制是50 MB per this而且我们的文档比那个小...肯定是其他一些问题。