Windows Chrome extension native messaging can only receive the first response - windows

Question

I am trying to use native messaging to send some data to my native windows application. It works well with the runtime.sendNativeMessage() method. When I am trying to use long lived connections which uses a port, it also can pass data from chrome to my app. However, chrome extension can only receive the first response from my app. I am sure that the port is still open because my app can still receive data from chrome. Following are my code:
Chrome Extension Script:
var port = chrome.runtime.connectNative('com.mydomain.app1');
port.onMessage.addListener(function(msg) {
console.log("Received from port:", msg);
});
port.onDisconnect.addListener(function() {
console.log("Disconnected");
});
chrome.tabs.onUpdated.addListener(
function(tabId, changeInfo, tab) {
var param = {};
param['url'] = tab.url;
port.postMessage( param);
}
}
My windows app in c++:
int _tmain(int argc, _TCHAR* argv[])
{
while( true )
{
//read the first four bytes (=> Length)
unsigned int length = 0;
for (int i = 0; i < 4; i++)
{
char c;
if( ( c=getchar()) != EOF)
length += c<<i*8;
else return 0;
}
//read the json-message
std::string msg = "";
for (int i = 0; i < length; i++)
{
msg += getchar();
}
//.... do something
//send a response message
std::string message = "{\"text\": \"This is a response message\"}";
unsigned int len = message.length();
// We need to send the 4 bytes 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 << message.c_str();
std::cout.flush();
}
}
Notice that the last line "std::cout.flush();", if I comment it out, even the first response won't be shown in chrome. I just couldn't figure out how chrome reads from the app's stdout.

Answer 1

Try with automatic flushing - std::cout.setf( std::ios_base::unitbuf )
Also, the way you read/write the input/output messages length is incorrect and will fail on long messages.
This code works well for me:
int main(int argc, char* argv[])
{
std::cout.setf( std::ios_base::unitbuf );
while (true)
{
unsigned int ch, inMsgLen = 0, outMsgLen = 0;
std::string input = "", response = "";
// Read 4 bytes for data length
std::cin.read((char*)&inMsgLen, 4);
if (inMsgLen == 0)
{
break;
}
else
{
// Loop getchar to pull in the message until we reach the total length provided.
for (int i=0; i < inMsgLen; i++)
{
ch = getchar();
input += ch;
}
}
response.append("{\"echo\":").append(input).append("}");
outMsgLen = response.length();
// Send 4 bytes of data length
std::cout.write((char*)&outMsgLen, 4);
// Send the data
std::cout << response;
}
return 0;
}