I'm trying to create a Node server that generates a PDF on-the-fly using PDFKit. The PDF is generated based on parameters from a POST request (via Express). One of the parameters specifies an image URL, which the server downloads and injects into the PDF.
Right now, I have the following structure:
// Get dependencies
var express = require('express'),
http = require('http'),
fs = require('fs'),
pdfDocument = require('pdfkit');
// Get express started.
var app = express();
// Use JSON in POST body
app.use(express.json());
// Setup POST response
app.post('/post_pdf', function(req, res) {
// Get the PDF initialized
var doc = new pdfDocument();
// Set some headers
res.statusCode = 200;
res.setHeader('Content-type', 'application/pdf');
res.setHeader('Access-Control-Allow-Origin', '*');
// Header to force download
res.setHeader('Content-disposition', 'attachment; filename=Untitled.pdf');
// Pipe generated PDF into response
doc.pipe(res);
/**
* Generate PDF contents
*/
// Prepare write stream for image
var image = fs.createWriteStream('image.jpeg');
// Download image
http.get("http://dummyimage.com/640.jpeg", function(response) {
// Pipe response into image write stream
// (because PDFKit needs to read from a saved file)
response.pipe(image).on('close', function() {
// Read data back, make sure there are no errors
fs.readFile('image.jpeg', function(err, data) {
if (err) throw err;
/**
* Use `data` to get image info (width, height, etc.)
* ------------------
* Inject image
*/
// Close document and response
doc.end();
res.end();
return;
})
});
});
});
I have two questions:
In debugging this issue, I discovered several things:
PDFKit does not need to read info from a file. It will also accept a Buffer
doc.image(myBuffer); // You don't have to use a path string
When piping a file directly into the response, a manual call to response.end()
will cause problems if the file has already been closed
doc.pipe(res); // Pipe document directly into the response
doc.end(); // When called, this ends the file and the response
// res.end(); <-- DON'T call res.end()
// The response was already closed by doc.end()
return;
Request is a super-useful NodeJS library that can flatten the callback tree
var express = require('express'),
request = require('request'),
pdfDocument = require('pdfkit');
// Start Express
var app = express();
// Use JSON in POST body
app.use(express.json());
// Setup POST response
app.post('/post_pdf', function(req, res) {
// Create PDF
var doc = new pdfDocument();
// Write headers
res.writeHead(200, {
'Content-Type': 'application/pdf',
'Access-Control-Allow-Origin': '*',
'Content-Disposition': 'attachment; filename=Untitled.pdf'
});
// Pipe generated PDF into response
doc.pipe(res);
// Process image
request({
url: 'http://dummyimage.com/640.jpeg',
encoding: null // Prevents Request from converting response to string
}, function(err, response, body) {
if (err) throw err;
// Inject image
doc.image(body); // `body` is a Buffer because we told Request
// to not make it a string
doc.end(); // Close document and, by extension, response
return;
});
});