chromium/chrome/browser/extensions/api/messaging/native_messaging_test_echo_host.cc

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This is a simple Native Message Host application. It echoes any messages
// it receives.
#include <windows.h>

#include <string.h>

#include "base/files/file.h"

int main(int argc, char* argv[]) {
  base::File read_stream = base::File(GetStdHandle(STD_INPUT_HANDLE));
  base::File write_stream = base::File(GetStdHandle(STD_OUTPUT_HANDLE));

  uint32_t message_len = 0;

  // Read and echo messages in a loop.
  while (true) {
    // Read the message's length prefix.
    size_t bytes_read = read_stream.ReadAtCurrentPos(
        reinterpret_cast<char*>(&message_len), sizeof(message_len));

    // If stdin was closed, the host should exit.
    if (bytes_read != sizeof(message_len)) {
      break;
    }

    // Read the message body.
    std::string message_body(message_len, '\0');
    bytes_read =
        read_stream.ReadAtCurrentPos(std::data(message_body), message_len);

    // Bail if we failed to read the entire message.
    if (bytes_read != message_len) {
      break;
    }

    // Reply by echoing the message length and body.
    write_stream.WriteAtCurrentPos(reinterpret_cast<char*>(&message_len),
                                   sizeof(message_len));
    write_stream.WriteAtCurrentPos(message_body.data(), message_len);
  }
}