Re: [boost] [system] - system_message and gai_strerror function

From: Christopher Kohlhoff (chris_at_[hidden])
Date: 2006-06-26 09:37:19

Oliver.Kowalke_at_[hidden] wrote:
> the system_message function is implemented with ::strerror.
> How to handle systems erros related like EAI_NONAME (host not
> found), EAI_MEMORY (allocation failure) etc.? This erros
> occure in the context of getaddrinfo (related to network
> address and service translation) and requier ::gai_strerror in
> system_message.

And there's also the error EAI_SYSTEM, which means that the
actual error value is to be found in errno instead.

This is the issue I raised a while back, where I suggested that
maybe we need support for implementation-defined error
categories, or "errorspaces". I'm not sure what the best
solution is, but it's a problem that needs to be solved for
asio.

I'm definitely in favour of having a single error_code type used
across all system functions to allow the simpler composition of
higher-level system operations. For example:

- A connect_host/async_connect_host function as suggested by
  Cory would need to use a resolver (which raises
  getaddrinfo-sourced errors) followed by a socket (which raises
  errno errors).

- A hypothetical transmit_file/async_transmit_file function
  could have errors resulting from filesystem access or from
  socket operations.

There's also the problem of the error asio::error::eof, which
corresponds to a real error on Windows, but is synthesised on
POSIX platforms.

Cheers,
Chris