Read content of posted .txt file with Azure function NodeJS

Question

I want to know the content from a.txt file I upload via the JSON response with an Azure function. I'm able to read the filename and type, but also want to convert the file to a string in my JSON response. But currently the response in data stays empty:

{
  "name": "20200429112846_-_IB_records.txt",
  "type": "text/plain",
  "data": ""
}

My code is:

var multipart = require("parse-multipart");

module.exports = function (context, request) {   
    // encode body to base64 string
    var bodyBuffer = Buffer.from(request.body);

    var boundary = multipart.getBoundary(request.headers['content-type']);
    // parse the body
    var parts = multipart.Parse(bodyBuffer, boundary);

    var fileContent = "";

    var fileBuffer = Buffer.from(parts[0].data);

    var fs = require('fs');

    fs.readFile(fileBuffer, 'utf8', function(err, data) {
        if (err) throw err;
        fileContent = data;
    });

    context.res = { body : { name : parts[0].filename, type: parts[0].type, data: fileContent}}; 
    context.done();  
};

Anyone got an idea?

Answer 1

fs.readFile operates asynchronously, so

context.res = { body : { name : parts[0].filename, type: parts[0].type, data: fileContent}}; 
context.done();  

is executed before the file has actually been read. One way to solve this is to put the context -stuff in the readFile callback:

 fs.readFile(fileBuffer, 'utf8', function(err, data) {
        if (err) throw err;
        fileContent = data;
        context.res = { body : { name : parts[0].filename, type: parts[0].type, data: fileContent}}; 
        context.done();  
    });