UnityWebRequest.downloadHandler returning null, while getting response from Node Server

Question

I am creating a Registration Scene on Unity. On the backend I have NodeJS server with MongoDB. Registration is successful and data is saved on Mongo too.

This is my NodeJS api for register

api.post('/register', (req,res) => {
Account.register(new Account({username: req.body.username}), req.body.password, function(err, account){
  console.log("acc: "+account);
  if(err){
    if (err.name == "UserExistsError") {
      console.log("User Exists");
      return res.status(409).send(err);
    }else {
      console.log("User Error 500");
      return res.status(500).send(err);
    }
  }else {
    let newUser = new User();
    newUser.accountid = account._id;
    newUser.name = req.body.fullname;
    newUser.gender = req.body.gender;
    newUser.role = req.body.role;
    newUser.country = req.body.country;
    newUser.coins = req.body.coins;
    newUser.save(err => {
      if(err){
        console.log(err);
        return res.send(err);
      }else{
        console.log('user saved');
        res.json({ message: 'User saved' });
      }
    });
    passport.authenticate(
      'local', {
        session: false
      })(req,res, () => {
         res.json({ registermsg: 'Successfully created new account'});
      });
  }
});
});

And this is my POST co-routine in Unity C#

IEnumerator Post(string b) {

    byte[] bytes = System.Text.Encoding.ASCII.GetBytes(b);

    using (UnityWebRequest www = new UnityWebRequest(BASE_URL, UnityWebRequest.kHttpVerbPOST)) {
        UploadHandlerRaw uH = new UploadHandlerRaw(bytes);
        www.uploadHandler = uH;
        www.SetRequestHeader("Content-Type", "application/json");
        yield return www.Send();

        if (www.isError) {
            Debug.Log(www.error);
        } else {
            lbltext.text = "User Registered";
            Debug.Log(www.ToString());
            Debug.Log(www.downloadHandler.text);
        }
    }
}

I am trying to Debug.Log(www.downloadHandler.text); but I get NullReferenceException.

I'd like to ask, is the way I am using to return response in my api correct? If yes, how can I use that response in Unity side.

Solution

UnityWebRequest.Post, UnityWebRequest.Get and other UnityWebRequest functions that creates new instance of UnityWebRequest, will automatically have DownloadHandlerBuffer attached to it.

Now, if you create new instance of UnityWebRequest with the UnityWebRequest constructor, DownloadHandler is not attached to that new instance. You have to manually do that with DownloadHandlerBuffer.

IEnumerator Post(string b)
{

    byte[] bytes = System.Text.Encoding.ASCII.GetBytes(b);

    using (UnityWebRequest www = new UnityWebRequest(BASE_URL, UnityWebRequest.kHttpVerbPOST))
    {
        UploadHandlerRaw uH = new UploadHandlerRaw(bytes);
        DownloadHandlerBuffer dH = new DownloadHandlerBuffer();

        www.uploadHandler = uH;
        www.downloadHandler = dH;
        www.SetRequestHeader("Content-Type", "application/json");
        yield return www.Send();

        if (www.isError)
        {
            Debug.Log(www.error);
        }
        else
        {
            lbltext.text = "User Registered";
            Debug.Log(www.ToString());
            Debug.Log(www.downloadHandler.text);
        }
    }
}

Comments

[Luzan Baral]

Thanks, I was confused on using DownloadHandlerBuffer. But now I get Can't send headers after they are set. I read lot's of question but could not make my code work as per them.

[Programmer]

I was planning to rename the title to "UnityWebRequest.downloadHandler returning null". That will help many people that will run into this problem. It would be nice to create a new question for your new header problem. Better if you describe what that problem is.

[Luzan Baral]

Okay, I'll change the question.

[Programmer]

Maybe this? Will be away for hours and can't reply until I return.

[Luzan Baral]

Okay, I'm also going through other Q&As related to same problem. Thanks again.

[Luzan Baral]

I fixed the code by changing the nested structure of the code in my Node API, and updated code in my question.

[Evorlor]

Why don't they have it attach automatically?

[Evorlor]

I know this is probably a question for someone at Unity, but maybe you'll know. Why is it not attached when using a null constructor? Is there any benefit to leaving it as null?

[Programmer]

@Evorlor I don't know what "null constructor" is and I only talked about constructor not "null constructor". When you create new instance of UnityWebRequest with its constructor like you would normally do, DownloadHandlerBuffer is not attached. If you create new instance of UnityWebRequest with the UnityWebRequest.Post or UnityWebRequest.Get functions, those functions will automatically attach DownloadHandlerBuffer to it because 90% of the time, people need to access the data from server in a Get/Post request.

[Programmer]

If you just want to make a request but don't care about the data sent by the data, why would you want DownloadHandlerBuffer to be attached to UnityWebRequest? If you want to stream or access the data while it's still being received, why would you want Unity to attach DownloadHandlerBuffer? It's totally useless here and DownloadHandlerScript is needed instead of DownloadHandlerBuffer.

[Programmer]

If you want to efficiently download a texture, why should Unity attach DownloadHandlerBuffer when DownloadHandlerTexture is needed and here and used to decompression texture on a worker Thread? It's not attached because creating new instance of UnityWebRequest means that you are doing something custom so you've got to write more code. Unity wants to give you control . I am sure there are many other reasons.

[Programmer]

By attaching DownloadHandlerBuffer when it's not needed, you are unnecessary allocating memory on the heap and making it run unnecessary processing on the native(C++) side. So memory space + cpu time = wasted.