Curl error 65: neccessary data rewind wasn't possible

We are having quite a lot of trouble with Editor and PC build sending POST WebRequests on our server. At random times it throws this error CURL error 65. I tried searching a lot but no solution to be found for us.

EDIT : The CURL issue happens only on PC build and Unity editor. (Webgl , android unafected)
We also tried removing the Uploadhandler which prevented crashing but this is not a solutions since we cant upload any data on server this way.

 

I am getting same. It doesn't even stack trace. I wish there was some way to get more info. Just jumping on the thread for notifications.

 

We are using default settings for apache.
Amazon Linux 2
Apache/2.4.46 - Aug 24 2020 18:54:20
This is the best info I can provide for now since our server guy is not present atm.
If there is any more info you need please ask.
Project in unity is running 2020.3.13f version

 

I am fairly sure this is related to using Photon Chat. I don't know their specifics!

 

I am getting same error sometimes - 2019 LTS, simple web requests, only gets errors in the editor
The error is really unhelpful...

 

unity 2020.3.17f1

Curl error 65: necessary data rewind wasn't possible

 

What is the root of the error in Unity though? - it gives no indication of its cause

 

OK but it is no good for Unity to post such error messages. You could post "WebRequest error: Resend failed", or "server error: Curl 65...". As it is, it is not a human readable error. I only know it may be to do with server communication due to this thread!

 

I was facing this issue as well, in Unity 2021.1.13f1 using the POST method of web service call.
One thing, I have noticed was when I was calling the same web service again after a few seconds, I was getting this error message within the Unity Editor.

Here you have exact screenshots:




Here is the actual code that is executing:

Code (CSharp):

1.     public void FetchLevelGameQuestions()
2.     {
3.         StartCoroutine(FetchLevelGameQuestionsEnumerator());
4.     }
5.  
6.     IEnumerator FetchLevelGameQuestionsEnumerator()
7.     {
8.  
9.         WWWForm form = new WWWForm();
10.         //form.headers[HEADER_AUTHORIZATION] = AdhocStorage.userProfile.accessToken;
11.         form.AddField(PARAM_LEVEL_ID, GameManager.Instance.SelectedLevelId);
12.         form.AddField(PARAM_GAME_ID, GameManager.Instance.SelectedGameId);
13.  
14.  
15.         using (UnityWebRequest webRequest = UnityWebRequest.Post(GameConstants.HOOPSENGLISH_BASE_URL + GameConstants.WEB_LIST_QUESTIONS_URI, form))
16.         {
17.             webRequest.SetRequestHeader(HEADER_AUTHORIZATION, AdhocStorage.userProfile.accessToken);
18.  
19.             // Request and wait for the desired page.
20.             yield return webRequest.SendWebRequest();
21.  
22.             switch (webRequest.result)
23.             {
24.                 case UnityWebRequest.Result.ConnectionError:
25.                 case UnityWebRequest.Result.DataProcessingError:
26.                     Debug.LogError("Error: " + webRequest.error);
27.                     break;
28.                 case UnityWebRequest.Result.ProtocolError:
29.                     Debug.LogError("HTTP Error: " + webRequest.error);
30.                     break;
31.                 case UnityWebRequest.Result.Success:
32.                     Debug.Log("\nReceived: " + webRequest.downloadHandler.text);
33.                     //ParsingUserProfile(webRequest.downloadHandler.text);
34.                     ParseGameQuestions(webRequest.downloadHandler.text);
35.                     break;
36.             }
37.         }
38.     }
39.  

Please help me to sort out this because my game can't able execute the same web service again.
If you need anything from my side then let me know.

 

I have also just started getting this error and not sure why in the editor.
Curl error 65: necessary data rewind wasn't possible

 

Got this moments ago with 2021.2.12f1.
Curl error 65: necessary data rewind wasn't possible

happened once on editor game start, and then webrequests worked again

 

If you can recreate consistently - make a bug for Unity.
They seem unaware of the cause of this (it is an error from some (third-party?) http api which should not be thrown) and want examples of how to get - it is to do with web connections to an apache server maybe. You also get errors for aborting web requests in 2019 (stopped in later versions thankfully), so seems bad practice to me in how http errors are managed.

 

I am not sure if the devs are still following this or not but it seems to be a problem with their code somewhere. If I use a program like fiddler anywhere and connect through that then I have NEVER got the curl error message. However if I use my normal internet here in Thailand then I get the message sometimes, It seems to happen after you send a webrequest it returns and then you send another one in 3-4 seconds, If you wait longer then this then it does not seem to happen.

Basically a quick fix for anyone with this problem is to do this

Code (CSharp):

1. if (www.result == UnityWebRequest.Result.Success)
2. {
3.     //it worked and no curl error
4. }
5. else
6. {
7.     if (instance.retries < 1)
8.     {
9.         instance.retries++;
10.         // redo web request
11.     }
12.     else
13.     {
14.         //it failed twice, only happens during a server error with the script.
15.     }
16. }

 

Try to check if the JSON is valid.

Code (CSharp):

1. private IEnumerator GetJSONData()
2. {
3.     string data;
4.  
5.     using UnityWebRequest unityWebRequest = UnityWebRequest.Get("URL");
6.     yield return unityWebRequest.SendWebRequest();
7.  
8.     if (unityWebRequest.result == UnityWebRequest.Result.Success)
9.         data = unityWebRequest.downloadHandler.text;
10.     else
11.         data = unityWebRequest.error;
12.  
13.     if ((data.TrimStart().StartsWith("{") && data.TrimEnd().EndsWith("}")) ||
14.      (data.TrimStart().StartsWith("[") && data.TrimEnd().EndsWith("]")))
15.     {
16.         Debug.Log("it's a JSON");
17.     }
18.     else
19.     {
20.         Debug.Log("it's not a JSON");
21.     }
22. }

 

I know this thread is a little old, but I just received similar messages today after integrating Playfab just a couple days ago.

Curl error 56: Receiving data failed with unitytls error code 1048578
Failed to send session data. Error: /Event/WriteEvents: Unknown Error
Curl error 65: necessary data rewind wasn't possible
Failed to send session data. Error: /Event/WriteEvents: Unknown Error

Uploaded a bug report: https://fogbugz.unity3d.com/default.asp?1424036_6br6rorjf8ft439q

 

If the free libcurl (https://curl.se/libcurl/) is the basis for all UnityWebRequest it should probably be mentioned in the docs. But as said - errors from that library should not produce errors directly like this - they should be fed up to the result from UnityWebRequest to be dealt with by the developer.

 

Still I was facing similar error multiple times when I call custom web services related to project.

 

Same issue happening to me.

 

Did you fix this error?how ?

 

Having the same problem. In my game, players can search for other players in the game from the game server (wordpress database). If you do too many searches fairly quickly then it throws Curl Errors 65 and 52

 

there is no fix to this (been having this problem for 3 years now) just check if UnityWebRequest.Result.Success is true and if not then run a function that will run the web request again. I have a web game that uses a server backend and this has worked everytime, It seems only the first webrequest will fail sometimes but the 2nd one always goes through.

Obviously add in some code so that it will only resend the webrequest once if it fails and not loop continuously.