windowsGetReadResult

Simple wrapper around GetOverlappedResult to determine the result of a ReadFile operation. If !allow_aborted, then aborted is never returned (OPERATION_ABORTED is considered unexpected).

The ReadFile documentation states that the number of bytes read by an overlapped ReadFile must be determined using GetOverlappedResult, even if the operation immediately returns data: "Use NULL for [lpNumberOfBytesRead] if this is an asynchronous operation to avoid potentially erroneous results." "If hFile was opened with FILE_FLAG_OVERLAPPED, the following conditions are in effect: [...] The lpNumberOfBytesRead parameter should be set to NULL. Use the GetOverlappedResult function to get the actual number of bytes read." See: https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-readfile

Source

Implementation

fn windowsGetReadResult(
    handle: windows.HANDLE,
    overlapped: *windows.OVERLAPPED,
    allow_aborted: bool,
) !union(enum) {
    success: u32,
    closed,
    aborted,
} {
    var num_bytes_read: u32 = undefined;
    if (0 == windows.kernel32.GetOverlappedResult(
        handle,
        overlapped,
        &num_bytes_read,
        0,
    )) switch (windows.GetLastError()) {
        .BROKEN_PIPE => return .closed,
        .OPERATION_ABORTED => |err| if (allow_aborted) {
            return .aborted;
        } else {
            return windows.unexpectedError(err);
        },
        else => |err| return windows.unexpectedError(err),
    };
    return .{ .success = num_bytes_read };
}