fix(host): use ioctlsocket(FIONREAD) fallback for read-readiness on Windows

select() on Windows fails to report read-readiness on connected
sockets (both TCP and UDP), even when data is sitting in the receive
buffer. This causes blocking urllib calls without a timeout to hang
indefinitely — the guest's poll loop never sees POLLIN.

Add ioctlsocket(FIONREAD) as a fallback in both handle_net_poll and
hl_sleep_poll_sockets: if select() misses read-readiness, check
whether the socket has bytes pending in its receive buffer.

Signed-off-by: danbugs <danilochiarlone@gmail.com>

Author: danbugs

host/src/lib.rs

@@ -1706,7 +1706,8 @@ fn handle_net_poll(
     use serde_json::json;
     use std::os::windows::io::AsRawSocket;
     use windows_sys::Win32::Networking::WinSock::{
-        __WSAFDIsSet, select, FD_SET, FD_SETSIZE, SOCKET, SOCKET_ERROR, TIMEVAL,
+        __WSAFDIsSet, ioctlsocket, select, FD_SET, FD_SETSIZE, FIONREAD, SOCKET, SOCKET_ERROR,
+        TIMEVAL,
     };
 
     const POSIX_POLLIN: i16 = 0x0001;
@@ -1819,6 +1820,17 @@ fn handle_net_poll(
         if unsafe { __WSAFDIsSet(e.raw, &mut readfds) } != 0 {
             revents |= POSIX_POLLIN;
         }
+        // Fallback: select() on Windows can miss read-readiness on
+        // connected sockets. Use ioctlsocket(FIONREAD) to check if
+        // bytes are waiting in the receive buffer.
+        if e.want_read && revents & POSIX_POLLIN == 0 {
+            let mut bytes_available: u32 = 0;
+            if unsafe { ioctlsocket(e.raw, FIONREAD, &mut bytes_available) } == 0
+                && bytes_available > 0
+            {
+                revents |= POSIX_POLLIN;
+            }
+        }
         if unsafe { __WSAFDIsSet(e.raw, &mut writefds) } != 0 {
             revents |= POSIX_POLLOUT;
         }
@@ -1892,7 +1904,7 @@ fn hl_sleep_poll_sockets(
     use serde_json::json;
     use std::os::windows::io::AsRawSocket;
     use windows_sys::Win32::Networking::WinSock::{
-        select, FD_SET, FD_SETSIZE, SOCKET, SOCKET_ERROR, TIMEVAL,
+        ioctlsocket, select, FD_SET, FD_SETSIZE, FIONREAD, SOCKET, SOCKET_ERROR, TIMEVAL,
     };
 
     let tbl = table.lock().unwrap();
@@ -1937,7 +1949,19 @@ fn hl_sleep_poll_sockets(
         return Err(anyhow!("hl_sleep select() failed: {err}"));
     }
 
-    let ready = ret > 0;
+    // select() on Windows can miss read-readiness on connected sockets.
+    // Fall back to ioctlsocket(FIONREAD) to detect pending data.
+    let mut ready = ret > 0;
+    if !ready {
+        for &s in &raw_sockets {
+            let mut bytes_available: u32 = 0;
+            if unsafe { ioctlsocket(s, FIONREAD, &mut bytes_available) } == 0 && bytes_available > 0
+            {
+                ready = true;
+                break;
+            }
+        }
+    }
     Ok(json!({"socket_ready": ready}))
 }