Native Messaging host not able to send 1 MB data

Question

I am using the native-host in C++, when i send base64 from the native app to chrome extension(Native messaging) with size base64 < 1M, the program is still running. but when i send base64 from the native app to chrome extension (Native messaging) with size base64 >1M, the program is error "Error when communicating with the native messaging host" my code below

int _tmain(int argc, _TCHAR* argv[])
{
    std::cout.setf( std::ios_base::unitbuf );
    unsigned int c, t=0;
    inp="";
    t=0;
    // Sum the first 4 chars from stdin (the length of the message passed).
    for (int i = 0; i <= 3; i++) {
        //t += getchar();
        t += std::pow(256.0f, i) * getchar();
    }
    // Loop getchar to pull in the message until we reach the total
    //  length provided.
    for (int i=0; i < t; i++) {
        c = getchar();
        inp += c;
    }

    unsigned int len =  inp.length();
    // We need to send the 4 btyes of length information
    std::cout << char(((len>>0) & 0xFF))
              << char(((len>>8) & 0xFF))
              << char(((len>>16) & 0xFF))
              << char(((len>>24) & 0xFF));
    // Now we can output our message
    std::cout << inp;
    return 0;
}

Answer 1

Native messaging hosts cannot send a message with more than 1024*1024 bytes. From

https://cs.chromium.org/file%3Anative_message_process_host.cc%20kMaximumMessageSize:

// Maximum message size in bytes for messages received from Native Messaging
// hosts. Message size is limited mainly to prevent Chrome from crashing when
// native application misbehaves (e.g. starts writing garbage to the pipe).
const size_t kMaximumMessageSize = 1024 * 1024;

To work around this problem, you have to split the message sent from the native messaging host to your extension/app in chunks of less than 1MB.
In your native messaging host, you could create a loop that repeatedly outputs the 32-bit message length (max 1MB) followed by a chunk of the message.
In your app/extension, use chrome.runtime.connectNative instead of chrome.runtime.sendNativeMessage to open a port that lasts longer than one message (if you use sendNativeMessage, the port will be closed after receiving one reply, which causes the native messaging host to terminate).