Proper handling async IO for WIN32

Even given OVERLAPPED, functions like ReadFile/WriteFile
still MAY complete before they return. In that case,
we should not call GetOverlappedResult, and should respect
the numberOfBytes output from the original IO function.

Author: hsfzxjy

libc/calls/ntspawn.c

@@ -68,7 +68,7 @@ static textwindows ssize_t ntspawn_read(intptr_t fh, char *buf, size_t len) {
   uint32_t got;
   struct NtOverlapped overlap = {.hEvent = CreateEvent(0, 0, 0, 0)};
   ok = overlap.hEvent &&
-       (ReadFile(fh, buf, len, 0, &overlap) ||
+       (ReadFile(fh, buf, len, &got, &overlap) ||
         GetLastError() == kNtErrorIoPending) &&
        GetOverlappedResult(fh, &overlap, &got, true);
   if (overlap.hEvent)

libc/calls/readwrite-nt.c

@@ -93,7 +93,8 @@ sys_readwrite_nt(int fd, void *data, size_t size, ssize_t offset,
 
     // initiate asynchronous i/o operation with win32
     struct NtOverlapped overlap = {.hEvent = event, .Pointer = offset};
-    bool32 ok = ReadOrWriteFile(handle, data, size, 0, &overlap);
+    uint32_t exchanged = 0;
+    bool32 ok = ReadOrWriteFile(handle, data, size, &exchanged, &overlap);
     if (!ok && GetLastError() == kNtErrorIoPending) {
       if (f->flags & _O_NONBLOCK) {
         // immediately back out of blocking i/o if non-blocking
@@ -135,11 +136,8 @@ sys_readwrite_nt(int fd, void *data, size_t size, ssize_t offset,
           CancelIoEx(handle, &overlap);
         }
       }
-      ok = true;
-    }
-    uint32_t exchanged = 0;
-    if (ok)
       ok = GetOverlappedResult(handle, &overlap, &exchanged, true);
+    }
     uint32_t io_error = GetLastError();
     CloseHandle(event);
 

libc/calls/winexec.c

@@ -81,7 +81,7 @@ textwindows int IsWindowsExecutable(int64_t handle, const char16_t *path) {
   BLOCK_SIGNALS;
   struct NtOverlapped overlap = {.hEvent = CreateEvent(0, 0, 0, 0)};
   ok = overlap.hEvent &&
-       (ReadFile(handle, buf, 2, 0, &overlap) ||
+       (ReadFile(handle, buf, 2, &got, &overlap) ||
         GetLastError() == kNtErrorIoPending) &&
        GetOverlappedResult(handle, &overlap, &got, true);
   CloseHandle(overlap.hEvent);

libc/intrin/kprintf.greg.c

@@ -362,8 +362,7 @@ ABI void klog(const char *b, size_t n) {
       struct NtOverlapped overlap = {.hEvent = ev};
       ok = !!__imp_WriteFile(h, b, n, 0, &overlap);
       if (!ok && __imp_GetLastError() == kNtErrorIoPending)
-        ok = true;
-      ok &= !!__imp_GetOverlappedResult(h, &overlap, &wrote, true);
+        ok = !!__imp_GetOverlappedResult(h, &overlap, &wrote, true);
       if (!ok)
         __klog_handle = 0;
       __imp_CloseHandle(ev);