socket-error-symbol for interrupted-error is always EINTR even if errno was originally EAGAIN

[Anton Kovalenko]

DEFINE-SOCKET-CONDITION expansions in sockets.lisp add :initform to defined conditions, writing appropriate sockint:* errno symbol to the SYMBOL slot (with SOCKET-ERROR-SYMBOL as reader). This SOCKET-ERROR-SYMBOL is used in the :report clause of the socket-error condition, supposedly representing an original errno value.

It goes wrong when there is a single condition for multiple errnos, like interrupted-error for EINTR and EAGAIN. Interrupted-error gets redefined, and the last redefinition's initform wins, providing the same socket-error-symbol for all kinds of interrupted-error.

While debugging an usocket issue https://github.com/usocket/usocket/issues/106, I've got WSAEWOULDBLOCK from Winsock (on connect() with a non-blocking socket), that got translated to EAGAIN by constants-win32.lisp. The error message I got is this:

Socket error in "connect": EINTR (NIL)

Due to redefinition of interrupted-error condition, I had no chance to see the original EAGAIN.

I'd propose a change in (defun socket-error ...) that would provide a :symbol argument to the newly-created condition, looked up by errno-to-symbol mapping (a new *symbols-for-errno* alist should probably be added).