Update frame after each iteration - c++

Question

I am currently coding a port-scanner in Qt(C++) for Mac. The process of checking if a certain port is open or not works completely fine. But if the port range which the user wants to check is too big, every port will be checked but the output happens only after this process.
The program actually should check for example port 1 and output the result. After that it should check the next and output and so on...
void MainWindow::checkPort(int portmin, int portmax, string ip) {
int dif = portmax - portmin;
if (dif <= 0)
return;
unsigned int open = 0;
unsigned int closed = 0;
int checked = 0;
sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(ip.c_str());
for (int i = portmin; i <= portmax; i++) {
int s = socket(AF_INET, SOCK_STREAM, 0);
addr.sin_port = htons(i);
int con = ::connect(s, reinterpret_cast<sockaddr*>(&addr), sizeof(sockaddr));
if (con == 0){
ui->textEdit->setTextColor(Qt::green);
ui->textEdit->append("Port " + QString::number(i) + " open.");
open++;
}
if (con == -1) {
ui->textEdit->setTextColor(Qt::red);
ui->textEdit->append("Port " + QString::number(i) + " closed.");
closed++;
}
::close(con);
::close(s);
checked++;
}
Have you got any advise how I could have an output after each iteration?

Answer 1

Perhaps something like this:
//...
bool tooManyPorts = dif > 10000; // Set flag to true if port range is too big (for example more than 10 000 ports
//
QString msgs = "";
for (int i = portmin; i <= portmax; i++) {
int s = socket(AF_INET, SOCK_STREAM, 0);
addr.sin_port = htons(i);
if (con == 0){
if (tooManyPorts) {
QString("<font color='green'>Port " + QString::number(i) + " open.</font><br/>");
}
else {
ui->textEdit->setTextColor(Qt::green);
ui->textEdit->append("Port " + QString::number(i) + " open.");
}
open++;
}
if (con == -1) {
if (tooManyPorts) {
msgs += QString("<font color='red'>Port " + QString::number(i) + " closed.</font><br/>");
}
else {
ui->textEdit->setTextColor(Qt::red);
ui->textEdit->append("Port " + QString::number(i) + " closed.");
}
closed++;
}
// ...
}
if(tooManyPorts) {
ui->textEdit->append(msgs); // Add all iteration messages to text edit
}
Note the usage of HTML for the formatting part.
This adds all the output to your field AFTER the loop. To get it to work for each iteration just set msgs = ... and not msgs += ... in the loop and then move the if(tooManyPorts) ... at the end of your for but not outside. Frankly I have difficulty understanding whether you don't want the first version (AFTER the loop) since right now you are adding your output to your text field in each iteration step.

Answer 2

The simplest solution is to run the whole scanning job concurrently using the thread pool. The inter-thread communication is done safely via the signal-slot mechanism:
// https://github.com/KubaO/stackoverflown/tree/master/questions/async-portscan-39469180
#include <QtWidgets>
#include <QtConcurrent>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <unistd.h>
class Scanner : public QObject {
Q_OBJECT
bool running = false, stop = false;
int open = 0, closed = 0, total = 0;
void scan() {
running = true;
sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
for (int i = 1; i < 65536 && !stop; ++i) {
auto s = socket(AF_INET, SOCK_STREAM, 0);
addr.sin_port = htons(i);
auto con = ::connect(s, reinterpret_cast<sockaddr*>(&addr), sizeof(sockaddr));
emit hasResult(i, con == 0);
con == 0 ? ++open : ++closed;
++total;
::close(s);
}
emit done();
running = false;
}
public:
~Scanner() {
stop = true;
while (running);
}
Q_SIGNAL void hasResult(int port, bool open);
Q_SIGNAL void done();
Q_SLOT void start() {
QtConcurrent::run(this, &Scanner::scan);
}
};
int main(int argc, char ** argv) {
using Q = QObject;
QApplication app{argc, argv};
QWidget ui;
QVBoxLayout layout{&ui};
QTextBrowser log;
QProgressBar bar;
QPushButton scan{"Scan localhost"};
layout.addWidget(&log);
layout.addWidget(&bar);
layout.addWidget(&scan);
bar.setRange(1, 65535);
ui.show();
Scanner scanner;
Q::connect(&scan, &QPushButton::clicked, &scanner, [&]{
scan.setEnabled(false);
scanner.start();
});
Q::connect(&scanner, &Scanner::hasResult, &log, [&](int port, bool isOpen){
bar.setValue(port);
if (!isOpen) return;
auto color = isOpen ? QStringLiteral("green") : QStringLiteral("red");
auto state = isOpen ? QStringLiteral("open") : QStringLiteral("closed");
log.append(QStringLiteral("<font color=\"%1\">Port %2 is %3.</font><br/>").
arg(color).arg(port).arg(state));
});
Q::connect(&scanner, &Scanner::done, &scan, [&]{
bar.reset();
scan.setEnabled(true);
});
return app.exec();
}
#include "main.moc"