如何在HummusJS中将流从请求修改为新的响应流 [英] How to modify a stream from request to a new response stream in HummusJS

问题描述

我需要使用HummusJS将png注入到PDF中.

I need to inject a png into a PDF using HummusJS.

在我的API的生产版本中，我将收到一个包含base64的发布请求，该请求将转换为二进制阅读器流. (在下面的示例中，我正在使用从本地文件读取的测试.)

In the production version of my API, I'll be receiving a post request containing a base64 that I'll convert to binary reader stream. (In the example below, I'm using a test read from a local file.)

这是我的测试输入流(在创建"对象工厂中定义):

Here's my test input stream (which is defined in a "create" object factory):

hummusReadStreamObject (filePath) {
  let fileData = fs.readFileSync(filePath).toString('hex');
  let result = []
  for (var i = 0; i < fileData.length; i+=2) {
    result.push('0x'+fileData[i]+''+fileData[i+1])
  }
  return new hummus.PDFRStreamForBuffer(result)
},

我生成一个PNG(我已经确认，PNG已写入且有效)，然后在流的最终"事件期间执行修改

I generate a PNG (I have confirmed, the PNG is written and valid) and then perform modification during the stream's "finally" event

png.on('finish', function () {
    create.modifiedPDFResponseStream({
      pngFileName,
      readStream: create.hummusReadStreamObject('/foo/file/path'),
      res
    })
  })

modifiedPDFResponseStream现在可以拉入png并应该将其附加到文件中:

the modifiedPDFResponseStream now pulls in the png and is supposed to append it to the file:

modifiedPDFResponseStream ({ pngFileName, readStream, res }) {
  const writeStream = new hummus.PDFStreamForResponse(res)
  const pdfWriter = hummus.createWriterToModify(
    readStream,
    writeStream,
    { log: `path/to/error.txt` })
  debugger
  const pageModifier = new hummus.PDFPageModifier(pdfWriter,0);
  if (pngFileName) {
    const ctx = pageModifier.startContext().getContext()
    ctx.drawImage(2, 2, `./path/to/${pngFileName}`)
    pageModifier.endContext().writePage()
    pdfWriter.end()
  }
}

我认为我已经接近解决方案，错误日志不会报告任何问题，但是在通过Chrome进行调试时，我收到以下异常:

I sense that I'm close to a solution, the error logs do not report any problems, but i receive the following exception when debugging via Chrome:

events.js:183 Uncaught Error: write after end
at write_ (_http_outgoing.js:622:15)
at ServerResponse.write (_http_outgoing.js:617:10)
at PDFStreamForResponse.write

问题与在.png的.on('finish', ...)事件期间填充流有关吗?如果是这样，我是否可以采用一种同步方法来缓解此问题?

is the issue something to do with the fact that the stream is being populated during the .png's .on('finish', ...) event? If so, is there a synchronous approach I could take that would mitigate this problem?

推荐答案

受@JAM在"等待所有流完成-流式传输文件目录"

我解决了这个问题，方法是让.pngWriteStream方法返回一个promise，并让writestream在完成时解析:

I solved this issue by having the .pngWriteStream method return a promise and having the writestream resolve on finish:

return new Promise((resolve, reject) => {
      try {
        writeStream.on('finish', resolve)
      } catch (e) {
        $.logger.error(e.message)
        reject()
      }

因此代替:

const png = create.pngWriteStream({ ... })
png.on('finish', function () {
  create.modifiedPDFResponseStream({
    pngFileName,
    readStream: create.hummusReadStreamObject('/foo/file/path'),
    res
  })
})

我在等待诺言的解决

const png = await create.pngWriteStream({
    fileName: pngFileName,
    value: '123456789' })

并且img文件可用于hummus.js写入pdf！

and the img file is available for hummus.js to write to the pdf!

create.modifiedPDFResponseStream({
    pngFileName,
    readStream: create.hummusReadStreamObject('/foo/file/path'),
    writeStream: new hummus.PDFStreamForResponse(res)
  })

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