Node.js/Loopback生成PDF保存至路径后，如何实现自动下载？

Hey Ahmed, let's sort out how to trigger an automatic download right after your PDF finishes generating in LoopBack! Here's a step-by-step fix with modified code:

Step 1: Update the PDF Generator to Return a Promise #

First, we need to make your pdfGenerator function asynchronous so we can wait for the PDF to fully write to disk before triggering the download. Wrap it in a Promise:

// generatorPdf.js
module.exports = {
  pdfGenerator: function(data, pathfile) {
    return new Promise((resolve, reject) => {
      var fonts = {
        Roboto: {
          normal: 'server/pdfgenerator/fonts/Roboto-Regular.ttf',
          bold: 'server/pdfgenerator/fonts/Roboto-Medium.ttf',
          italics: 'server/pdfgenerator/fonts/Roboto-Italic.ttf',
          bolditalics: 'server/pdfgenerator/fonts/Roboto-MediumItalic.ttf'
        }
      };
      var datePaiements = '';
      var dateFinPaiements = '';
      
      if (data.abonnement[0].datePaiement != null)
        datePaiements = new Date(data.abonnement[0].datePaiement.toString());
      
      if (datePaiements !== '') {
        dateFinPaiements = ('0' + datePaiements.getDate()).slice(-2) + '/' + ('0' + (datePaiements.getMonth() + 1)).slice(-2) + '/' + (datePaiements.getFullYear() + 1);
        datePaiements = ('0' + datePaiements.getDate()).slice(-2) + '/' + ('0' + (datePaiements.getMonth() + 1)).slice(-2) + '/' + datePaiements.getFullYear();
      }
      
      var dateFacture = new Date(data.abonnement[0].timestampCreation.toString());
      dateFacture = ('0' + dateFacture.getDate()).slice(-2) + '/' + ('0' + (dateFacture.getMonth() + 1)).slice(-2) + '/' + dateFacture.getFullYear();
      
      var PdfPrinter = require('pdfmake/src/printer');
      var printer = new PdfPrinter(fonts);
      var fs = require('fs');
      
      var dd = {
        content: [/* Your existing content here */],
        footer: {/* Your existing footer here */}
      };
      
      try {
        var pdfDoc = printer.createPdfKitDocument(dd);
        
        // Handle existing file deletion before writing
        const writePdfStream = () => {
          pdfDoc.pipe(fs.createWriteStream(pathfile))
            .on('finish', () => resolve(pathfile)) // Resolve when PDF is ready
            .on('error', (err) => reject(err));
          pdfDoc.end(); // Don't forget to end the PDF stream!
        };
        
        if (fs.existsSync(pathfile)) {
          fs.unlink(pathfile, (err) => {
            if (err) reject(err);
            else writePdfStream();
          });
        } else {
          writePdfStream();
        }
      } catch (e) {
        console.error(e);
        reject(e);
      }
    });
  }
};

Step 2: Modify the LoopBack Remote Method to Trigger Download #

Now, update your remote method to wait for the PDF to generate, then use Express's res.download() to prompt the browser to download the file:

// Your LoopBack remote method
cm_abonnements.getAbonnementById = async (options, req, res) => {
  const token = options && options.accessToken;
  const userId = token && token.userId;
  
  try {
    if (!userId) {
      return res.status(401).send('Unauthorized access');
    }
    
    let dataComedien = await app.models.cm_comediens.getComedienByUser(userId);
    let argAbn = {};
    
    // Parse form data with promise wrapper
    await new Promise((resolve, reject) => {
      const form = new formidable.IncomingForm();
      form.parse(req, (err, fields) => {
        if (err) reject(err);
        argAbn.idAbonnement = fields.key;
        resolve();
      });
    });
    
    let dataFac = await cm_abonnements.find({
      where: {
        and: [
          { idAbonnement: argAbn.idAbonnement },
          { idComedien: dataComedien.idComedien }
        ]
      }
    });
    
    if (!dataFac.length) {
      return res.status(404).send('Invoice not found');
    }
    
    // Prepare PDF file details
    var data = { abonnement: dataFac };
    var str_date = new Date(dataFac[0].timestampCreation.toString());
    var nameFile = `Fac_${dataFac[0].idFacture}_${str_date.getFullYear()}-${('0' + (str_date.getMonth() + 1)).slice(-2)}-${('0' + str_date.getDate()).slice(-2)}.pdf`;
    var path = `public/upload/Comediens/${dataComedien.idComedien}/factures/${nameFile}`;
    
    // Wait for PDF to finish generating
    await createPdf.pdfGenerator(data, path);
    
    // Trigger browser download
    res.download(path, nameFile, (err) => {
      if (err) {
        console.error(err);
        res.status(500).send('Failed to initiate PDF download');
      }
      // Optional: Delete the file after download if you don't need to keep it
      // fs.unlink(path, (unlinkErr) => { if (unlinkErr) console.error(unlinkErr); });
    });
  } catch (e) {
    console.error(e);
    res.status(500).send('Error generating invoice PDF');
  }
};

cm_abonnements.remoteMethod(
  'getAbonnementById', {
    http: { verb: 'POST' },
    description: 'Retrieve invoice details and trigger PDF download',
    accepts: [
      { arg: "options", type: "object", http: "optionsFromRequest" },
      { arg: 'req', type: 'object', http: { source: 'req' }},
      { arg: 'res', type: 'object', http: { source: 'res' }}
    ]
    // Remove the `returns` config since we're sending a file, not JSON
  }
);

Key Changes Explained: #

• Promise Wrapper for PDF Generation: Ensures we wait until the PDF is fully written to disk before trying to download it.
• res.download(): Sets the correct HTTP headers (Content-Disposition) to tell the browser to download the file instead of displaying it.
• Error Handling: Added proper error responses for unauthorized access, missing invoices, and generation/download failures.
• Stream Cleanup: Made sure to call pdfDoc.end() to finalize the PDF stream (this was missing in your original code!).

内容的提问来源于stack exchange，提问作者Ahmed