How to decode chunked data in node js? - node.js

Question

I am receiving a PDF file from a node server (it is running jsreport in this server) and i need to download this PDF in the client (i am using react in the client) but the problem is that when i download the file, it comes all blank and the title some strange symbols. After a lot of tests and researchs, i found that the problem may be that the file is coming enconded as chunked (i can see that in the headers of the response) and i need to decode do become a file again.
So, how to decode this chunked string to a file again?
In the client i am just downloading the file that comes in the responde:
handleGerarRelatorioButtonClick(){
axios.post(`${REQUEST_URL}/relatorios`, this.state.selectedExam).then((response) => {
fileDownload(response.data, this.state.selectedExam.cliente.nome.replace(' ', '_') + ".pdf");
});
}
In my server, i am making a request to my jsreport that is other node server and it returns the report as a PDF:
app.post('/relatorios', (request, response) => {
var exame = new Exame(request.body);
var pdf = '';
var body = {
"template": {
"shortid": "S1C9birB-",
"data": exame
}
};
var options = {
hostname: 'localhost',
port: 5488,
path: '/api/report',
method: 'POST',
headers: {
'Content-Type': 'application/json'
}
};
var bodyparts = [];
var bodylength = 0;
var post = http.request(options, (res) => {
res.on('data', (chunk) => {
bodyparts.push(chunk);
bodylength += chunk.length;
});
res.on('end', () => {
var pdf = new Buffer(bodylength);
var pdfPos = 0;
for(var i=0;i<bodyparts.length;i++){
bodyparts[i].copy(pdf, pdfPos, 0, bodyparts[i].length);
pdfPos += bodyparts[i].length;
}
response.setHeader('Content-Type', 'application/pdf');
response.setHeader('Content-disposition', exame._id + '.pdf');
response.setHeader('Content-Length', bodylength);
response.end(Buffer.from(pdf));
});
});
post.write(JSON.stringify(body));
post.end();
});
I am sure that my report is being rendered as expected because if i make a request from postman, it returns the PDF just fine.

Answer 1

Your solution is simply relaying data chunks but you are not telling your front end what to expect of these chunks or how to assemble them. At a minimum you should be setting the the Content-Type response header to application/pdf and to be complete should also be sending the Content-disposition as well as Content-Length. You may need to collect the PDF from your 3rd party source into a buffer and then send that buffer to your client if you are not able to set headers and pipe to response successfully.
[edit] - I'm not familiar with jsreport but it is possible (and likely) that the response they send is a buffer. If that is the case you could use something like this in place of your response to the client:
myGetPDFFunction(params, (err, res) => {
if (err) {
//handle it
} else {
response.writeHead(200, {
'Content-Type': 'application/pdf',
'Content-Length': [your buffer's content length]
});
response.end(Buffer.from([the res PDF buffer]));
}
}
What you haven't shown is the request made to obtain that PDF, so I couldn't be more specific at this time. You should look into the documentation of jsreport to see what it sends in its response, and you can also read up on buffers here
This is rough pseudo code but the point is to respond with the PDF buffer after setting the headers to their proper values.