CODEWITHSUNDEEP
qtsocketstcp
Nyaruko
Nyaruko

Reputation: 4459

Qt: Use tcp socket to get google map image?

For some reason I need to use a blocking call to perform image accessing from google's server. However, QNetworkAccessManager seems to be async, though there are many work arounds, like calling a eventLoop.exec(); many people online suggested me not to do so.

So I am trying to use TCP socekt. I want to access the image here:

http://mt1.google.com/vt/lyrs=y&x=0&y=0&z=0

And here is my code:

socket = new QTcpSocket(this);

    socket->connectToHost("mt1.google.com", 80, QIODevice::ReadWrite);

    if(socket->waitForConnected(5000))
    {
        qDebug() << "Connected!";

        // send
        socket->write("/vt/lyrs=y&x=0&y=0&z=0");
        socket->waitForBytesWritten(1000);
        socket->waitForReadyRead(3000);

        qDebug() << "Reading: " << socket->bytesAvailable();

        // get the data
        qDebug() << socket->readAll();

        // close the connection
        socket->close();
    }
    else
    {
        qDebug() << "Not connected!";
    }

But it seems to working at all? What should I write through the tcp socket to get the image?

Upvotes: 0

Views: 273

Answers (1)

Murat Şeker
Murat Şeker

Reputation: 1711

TCP provides only the transport mechanism. Since you are trying to communicate with a web server, you should compose HTTP messages.

Replace the line 

socket->write("/vt/lyrs=y&x=0&y=0&z=0");

with

socket->write("GET /vt/lyrs=y&x=0&y=0&z=0 HTTP/1.1\r\nHost: mt1.google.com\r\nUser-Agent: TestAgent\r\n\r\n");

And you should get the following response :

HTTP/1.1 200 OK
Date: Sun, 14 Jun 2015 14:24:40 GMT
Expires: Sun, 14 Jun 2015 14:24:40 GMT
Cache-Control: private, max-age=3600
Access-Control-Allow-Origin: *
Content-Type: image/jpeg
X-Content-Type-Options: nosniff
Server: paintfe
Content-Length: 10790
X-XSS-Protection: 1; mode=block
X-Frame-Options: SAMEORIGIN
Alternate-Protocol: 80:quic,p=0

IMAGEDATA

Parse the response and extract the IMAGEDATA part.

EDIT : TCP delivers the response divided into chunks. With this approach, you will not be able to receive the whole response since you are trying to receive it in one go.

You should examine the Content-Length header and wait until receiveing the specified amount of bytes.

Upvotes: 1

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