connect to host … : Unknown error for WSAEHOSTUNREACH / WSAENETUNREACH (no errno mapping) #2482

Summary

When the TCP connect fails because the host or network is unreachable (for example, Wi-Fi drops), ssh prints

ssh: connect to host 192.168.0.63 port 22: Unknown error

instead of a meaningful message. Tools that parse ssh's output to decide whether a failure is transient can't classify it. VS Code Remote-SSH, for example, treats it as a permanent error and stops reconnecting.

Steps to reproduce

1. ssh -F NUL -o BatchMode=yes x@240.0.0.1 (no route) → ssh: connect to host 240.0.0.1 port 22: Unknown error, instantly.
2. Or, with Wi-Fi disconnected (netsh wlan disconnect), ssh <LAN host> → same Unknown error. .NET reports the same connect as SocketError.HostUnreachable (10065).

Expected

No route to host / Network is unreachable (or at least a message naming the Winsock error).

Actual

Unknown error.

Cause

contrib/win32/win32compat/socketio.c, errno_from_WSAError() maps only a handful of WSA codes. Everything else falls to

default:
    return wsaerrno - 10000;

So WSAEHOSTUNREACH (10065) becomes errno 65 and WSAENETUNREACH (10051) becomes 51. w32_strerror() in misc.c only has strings for EADDRINUSE..EWOULDBLOCK (100–140), so strerror_s returns "Unknown error" for those values.

Suggested fix: add explicit cases:

• WSAENETDOWN → ENETDOWN
• WSAENETUNREACH → ENETUNREACH
• WSAEHOSTUNREACH → EHOSTUNREACH
• WSAEADDRNOTAVAIL → EADDRNOTAVAIL

Optionally, use the POSIX/glibc wording in _sys_errlist_ext ("No route to host", "Network is unreachable"); the current "Host is unreachable" and "Network unreachable" differ from what other platforms print and from what scripts match.

Version

• OpenSSH_for_Windows_9.5p1, LibreSSL 3.8.2 (Windows 10 Pro 22H2 19045, built-in)
• Same code in v10.4.0.0 (socketio.c unchanged).