busboy not firing finish event

This answer might help someone who wants to consume the file...

Make sure to pass control back to express by calling next() in the finish method after consuming the file e.g.

app.use(function(req: Request, res: ServerResponse, next:any) {
let bb = new busboy({ headers: req.headers });
let fileData: any = null;
const fieldArray: any = [];
let dataLength: number;
const extractFields =  (name: string, val: any, data: any) => {
  if (Array.isArray(data[name])) {
    data[name].push(val);
  } else if (data[name]) {
    data[name] = [data[name], val];
  } else {
    data[name] = val;
  }
};
bb.on('field', function(fieldname: string, val:any, fieldnameTruncated: boolean, valTruncated: boolean, encoding: string, mimetype: string) {
  // extract fields to add to req body for later processing
  extractFields(fieldname, val, fieldArray);
  console.log('Field [' + fieldname + ']: value: ' + val);

});

bb.on('file', function(fieldname: string, file: NodeJS.ReadableStream , filename: string, encoding: string, mimetype: string) {
  file.on('data', function(data) {
    console.log('File [' + fieldname + '] got ' + data.length + ' bytes');
    // Process buffer to save complete file to add to the req for access later
    if (fileData === null) {
      fileData = data;
    } else {
      fileData = Buffer.concat([fileData, data]);
    }
  });
  file.on('end', function() {
    console.log('File [' + fieldname + '] Finished');
  });
});

bb.on('finish', function() {
  req.body = fieldArray
  req.body.files = {file: fileData};
  console.log('Done parsing form!');
  next(); // <- Allows processing to continue and avoids request hanging
});

bb.on('close', () => {
console.log('Event closed')
});
// what does this do? Send the readable request stream to busboy which is a writeable stream. The above code dictates to the writeable
// how to respond when certain events are fired during the pipe.
req.pipe(bb);
});

You need to consume the file stream somehow. For testing purposes you can ignore the data by adding file.resume(); inside the file event handler.