Resolve #2017

[yhirose]

No description provided.

[ngxson]

This is great, thanks a lot for the rapid response!

I implemented it this PR and it just works.

Do you think it's better to add an example in README? I'd suggest this:

// If the handler takes time to finish, you can also poll the connection state

svr.Get("/task", [&](const Request& req, Response& res) {
  const char * result = nullptr;
  process.run(); // for example, starting an external process
  while (result == nullptr) {
    sleep(1);
    if (req.is_connection_closed()) {
      process.kill(); // kill the process
      return;
    }
    result = process.stdout(); // != nullptr if the process finishes
  }
  res.set_content(result, "text/plain");
});

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Btw, not related to this, but I got this warning when compiling the file:

httplib.h:2576:2: warning: extra ';' outside of a function is incompatible with C++98 [-Wc++98-compat-extra-semi]

Would you mind to also remove this semicolon, so it can be compiled with -Werror? Thanks again.

[yhirose]

@ngxson I have updated the code and README according to your suggestions. Thanks for your fine contribution!