Image shows up corrupted on localhost - c++

Question

I'm horribly new to c++ and programming in general. I'm simply trying to read a picture using opencv and display it on web server using boost asio. This is an initial step before I do this for all frames from a video. The following is my code -
#include <iostream>
#include <string>
#include <boost/asio.hpp>
#include <thread>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/core/core.hpp>
using boost::asio::ip::tcp;
using namespace std;
using namespace cv;
int main(){
try{
boost::asio::io_service io_service;
tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), 1112));
for (;;){
tcp::socket socket(io_service);
acceptor.accept(socket);
boost::system::error_code ignored_error;
cv::Mat frame = cv::imread("x.jpg");
vector<uchar> buff;
vector<int> param = vector<int>(2);
param[0]=cv::IMWRITE_JPEG_QUALITY;
param[1]=95;
imencode(".jpg",frame,buff,param);
const char mess[] = "axaxaxaxasaaaaaaaaaaxax";
std::string content(buff.begin(), buff.end());
boost::asio::write(socket, boost::asio::buffer(content), boost::asio::transfer_all(), ignored_error);
// boost::asio::write(socket, boost::asio::buffer(mess), boost::asio::transfer_all(), ignored_error);
}
}
catch(std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}
now sending the message works just fine but when i try to send the image via content or buff, it shows up as gibberish. I feel like it's because I'm not sending any information about the picture prior to sending the picture. But I can't figure out how to do that.
Or maybe I'm entirely wrong. Any help/advice would be appreciated. Cheers!

Answer 1

I've simplified the code a little:
#include <iostream>
#include <string>
#include <boost/asio.hpp>
#include <opencv2/opencv.hpp>
using boost::asio::ip::tcp;
int main(){
try{
boost::asio::io_service io_service;
tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), 1112));
for (;;){
tcp::socket socket(io_service);
acceptor.accept(socket);
cv::Mat frame = cv::imread("x.jpg");
std::vector<uchar> buff;
imencode(".jpg", frame, buff, std::vector<int> { cv::IMWRITE_JPEG_QUALITY, 95 });
boost::system::error_code err;
auto bytes_transferred = boost::asio::write(socket, boost::asio::buffer(buff), boost::asio::transfer_all(), err);
std::cout << "Written: " << bytes_transferred << " (" << err.message() << ")\n";
}
}
catch(std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}
(specifically, don't use using namespace unneccessarily, not copying into a std::string unneccessarily, and not ignoring the error code unnecessarily)
Compiled it with
g++ test.cpp -L/usr/local/lib -pedantic -Wall -Wextra -pthread -lope^Cv_{core,imgproc,imgcodecs} -lboost_{system,thread} -o test.exe
Copied a sampe jpeg as x.jpg, running it in a terminal:
./test.exe
Then using netcat to read the result:
netcat localhost 1112 > verify.jpg
The server process will print the same message each time:
Written: 6130 (Success)
(6130 bytes happens to be the 95% re-encoded size of the test image I chose). The resulting image (verify.jpg) looks fine in my image viewer.
Conclusion
I think the code is probably fine (but check with the improvements above) and you might have been testing the result incorrectly.