Fix read console input on windows with codepage support

src/crystal/system/win32/file_descriptor.cr

@@ -11,7 +11,22 @@ module Crystal::System::FileDescriptor
   @system_blocking = true
 
   private def unbuffered_read(slice : Bytes)
-    if system_blocking?
+    handle = windows_handle
+    if LibC.GetConsoleMode(handle, nil) != 0
+      u16buffer = Slice(UInt16).new(slice.size)
+      chars_read = LibC::DWORD.new(0)
+      if 0 == LibC.ReadConsoleW(handle, u16buffer, u16buffer.size, pointerof(chars_read), nil)
+        raise IO::Error.from_winerror("Error reading from console")
+      end
+
+      appender = slice.to_unsafe.appender
+      String.each_utf16_char(u16buffer[0, chars_read]) do |char|
+        char.each_byte do |byte|
+          appender << byte
+        end
+      end
+      chars_read
+    elsif system_blocking?
       bytes_read = LibC._read(fd, slice, slice.size)
       if bytes_read == -1
         if Errno.value == Errno::EBADF
@@ -22,7 +37,6 @@ module Crystal::System::FileDescriptor
       end
       bytes_read
     else
-      handle = windows_handle
       overlapped_operation(handle, "ReadFile", read_timeout) do |overlapped|
         ret = LibC.ReadFile(handle, slice, slice.size, out byte_count, overlapped)
         {ret, byte_count}

src/lib_c/x86_64-windows-msvc/c/consoleapi.cr

@@ -14,6 +14,14 @@ lib LibC
   fun GetConsoleCP : DWORD
   fun GetConsoleOutputCP : DWORD
 
+  fun ReadConsoleW(
+    hConsoleInput : HANDLE,
+    lpBuffer : Void*,
+    nNumberOfCharsToRead : DWORD,
+    lpNumberOfCharsRead : DWORD*,
+    pInputControl : Void*
+  ) : BOOL
+
   CTRL_C_EVENT     = 0
   CTRL_BREAK_EVENT = 1
 

src/string/utf16.cr

@@ -128,8 +128,10 @@ class String
     {string, pointer + 1}
   end
 
+  # :nodoc:
+  #
   # Yields each decoded char in the given slice.
-  private def self.each_utf16_char(slice : Slice(UInt16), &)
+  def self.each_utf16_char(slice : Slice(UInt16), &)
     i = 0
     while i < slice.size
       byte = slice[i].to_i
@@ -153,8 +155,10 @@ class String
     end
   end
 
+  # :nodoc:
+  #
   # Yields each decoded char in the given pointer, stopping at the first null byte.
-  private def self.each_utf16_char(pointer : Pointer(UInt16), &) : Pointer(UInt16)
+  def self.each_utf16_char(pointer : Pointer(UInt16), &) : Pointer(UInt16)
     loop do
       byte = pointer.value.to_i
       break if byte == 0