Can't cancel an async request v1.12.0 ... v1.14.1

[baderouaich]

Description

This syntax doesn't compile anymore in v1.12.0 and up:

#include <iostream>
#include <cpr/cpr.h>

int main() {
  // Launch a long async GET request...
  cpr::Session session{};
  session.SetUrl(cpr::Url{"https://ash-speed.hetzner.com/1GB.bin"});
  cpr::AsyncResponse future = session.GetAsync();

  // Wait 1s  
  std::this_thread::sleep_for(std::chrono::seconds(1));

  // Cancel request after 1s
  if (not future.IsCancelled()) {
    std::cout << "Cancelling..." << std::endl;
    cpr::CancellationResult cr = future.Cancel();
    switch (cr) {
      case cpr::CancellationResult::failure:
        std::cout << "failure" << std::endl;
        break;
      case cpr::CancellationResult::success:
        std::cout << "success" << std::endl;
        break;
      case cpr::CancellationResult::invalid_operation:
        std::cout << "invalid_operation" << std::endl;
        break;
    }
  }
}

Compile error

/home/libcpr_cancelable/main.cpp: In function ‘int main()’:
/home/libcpr_cancelable/main.cpp:11:18: error: ‘using cpr::AsyncResponse = class cpr::AsyncWrapper<cpr::Response>’ {aka ‘class cpr::AsyncWrapper<cpr::Response>’} has no member named ‘IsCancelled’
   11 |   if (not future.IsCancelled()) {
      |                  ^~~~~~~~~~~
/home/libcpr_cancelable/main.cpp:13:41: error: ‘using cpr::AsyncResponse = class cpr::AsyncWrapper<cpr::Response>’ {aka ‘class cpr::AsyncWrapper<cpr::Response>’} has no member named ‘Cancel’
   13 |     cpr::CancellationResult cr = future.Cancel();
      |                                         ^~~~~~

Did the api change recently? if so what will be the new way of cancelling async requests? Thank you.

Example/How to Reproduce

1. Create a cpr::Session
2. Set option cpr::Url("https://ash-speed.hetzner.com/1GB.bin") to slow down the response
3. Perform an async GET request
4. Cancel the async request after ~1s
5. Compile and see compilation error

Possible Fix

No response

Where did you get it from?

GitHub (branch e.g. master)

Additional Context/Your Environment

• OS: Ubuntu
• Version: 24.04.1 LTS

[COM8]

@baderouaich thanks for reporting. Yes, this changed I'm not sure exactly why. It looks like the default of cpr::async changed to isCancellable = false.
A workaround would be using multi async.
The docs are here: https://docs.libcpr.dev/advanced-usage.html#asynchronous-requests

[Anohkka]

My PR is likely the reason why the example code no longer builds: #1206
The example code also fails at runtime on 1.11.3 with bad_weak_ptr, which can be fixed with

-  cpr::Session session{};
-  session.SetUrl(cpr::Url{"https://ash-speed.hetzner.com/1GB.bin"});
-  cpr::AsyncResponse future = session.GetAsync();
+  auto session = std::make_shared<cpr::Session>();
+  session->SetUrl(cpr::Url{"https://ash-speed.hetzner.com/1GB.bin"});
+  cpr::AsyncResponse future = session->GetAsync();

It looks like the default of cpr::async changed to isCancellable = false.

That was already the default. The difference is that functions related to cancellation are no longer present when isCancellable = false, which makes it more clear when something can't be cancelled, exactly to prevent this type of misunderstanding. AsyncResponse is and was a typedef for AsyncWrapper<cpr::Response, false>, so it wasn't ever cancellable. You could call Cancel() on it, but it always returned CancellationResult::invalid_operation.

[COM8]

Thanks @Anohkka!

In my eyes we should investigate how it is possible to make all requests cancelable.

I don't have time for it right now. In case someone is interested in this - I would be happy about a MR!