putFile POST request sends an empty body

I have implemented discovery, getFileInfo, getFile and putFile in my own WOPI host. All are working fine except putFile.
When I change my document it is routed to my putFile function, but the body which is expected to have the file content, is empty!

Can anybody help why that happened?

 route('POST', '/wopi/files/:fileId/contents', (req, res) => {
    console.log('*********putFile routed*********')
    if (req.body) {
      console.dir( req.body)
    } else {
      console.log('Not possible to get the file content.');

If you turn debugging up to ‘trace’ - what do the logs say about posting the file on save ? =) there is very verbose loolwsd.log logging indeed if you turn it to maximum.

Thank you for your reply.

I checked the loggs, It says that it successfully upload the file contents. the logs are exactly the same as logs produced via example project which its putFile has content in its body.

So should I do something in my project to make it work?

Actually the problem solved, it was about using body-parser in my wopi host code.