So, what did you see instead? What is the failure you'd like to report?

See the chop_write function:

When a CURLOPT_WRITEFUNCTION callback called, the return size was stored in wrote variable. This function checks if the returned value was CURL_WRITEFUNC_PAUSE. If the special CURL_WRITEFUNC_ERROR return negative value is returned, a generic CURLE_WRITE_ERROR. Get the specific CURLE_ABORTED_BY_CALLBACK error is better in order to distinguish a non-error-condition status from a generic-error status when aborting curl session.

Probably this report should be a suggestion to have a CURL_WRITEFUNC_ABORT special returned value, right?

I still don't understand. Your callback returns CURL_WRITEFUNC_ERROR.

What are you saying is returned and what are you saying you think should have been returned?

Yes, literally if the CURLOPT_WRITEFUNCTION callback needs to return a abort, now only CURL_WRITEFUNC_ERROR can used. Then, if this special value was returned, the curl sessions ends with CURLE_WRITE_ERROR final code. This is the same final code if callbacks get an error (not memory or something like this)... in this case, by returning a amount that differs from the amount passed by curl, is enough.

So, my suggestion is: return CURLE_ABORTED_BY_CALLBACK when callback returns CURL_WRITEFUNC_ERROR, or better, make a new CURL_WRITEFUNC_ABORT special return value to use in callbacks in order to get the curl session final code CURLE_ABORTED_BY_CALLBACK.

Yes, maybe CURLE_ABORTED_BY_CALLBACK would be slightly more logical to use, but I am reluctant to change this now that it has been in use like this since 7.87.0. Applications and users have already adapted to this return code and I fear that changing it now might cause more problems than simply accepting defeat and better documenting the current state.

Thanks @bagder , please, consider to add a new CURL_WRITEFUNC_ABORT special return value for Callbacks in order to get a CURLE_ABORTED_BY_CALLBACK response code from curl session!

consider to add a new CURL_WRITEFUNC_ABORT special return value for Callbacks in order to get a CURLE_ABORTED_BY_CALLBACK response code from curl session!

I like this idea!