A proof of concept auto-update mechanism

autoupdate.cpp

// Auto-update proof of concept
//  embedding the update step into the
//  current and new executables ahead of
//  time, we don't need any extra scripts.
//  It works by calling the new executable
//   to rename the old one, and call the
//   old one to rename the new one, execute
//   it and exit. Finally the renamed new
//   one removes the old one and runs normally.
// Process:
// self.new.exe -u1 self
//  mv self{,.old}.exe
//  self.old.exe -u2 new
//   mv self.{new,}.exe
//   self.exe -u3 self.old.exe
//    rm self.old.exe

#include <iostream>
#include <string>
#include <fstream>
#include <cstdio>
#include <unistd.h>

unsigned int backoff = 100;
unsigned int max_tries = 3;

int safe_rename(char *old_f, char *new_f) {
  int status = rename(old_f, new_f);
  int t = 1;

  while(status != 0 && max_tries > t++) {
    usleep(backoff);
    status = rename(old_f, new_f);
  }

  return status;
}

int safe_remove(char *f) {
  int status = remove(f);
  int t = 1;

  while(status != 0 && max_tries > t++) {
    usleep(backoff);
    status = remove(f);
  }

  return status;
}

int main(int argc, char *argv[]) {
  char *self = argv[0];
  if(argc > 1) {
    char *arg = argv[1];
    if(*arg == '-') {
      ++arg;
      if(*arg == '-') {
        ++arg;
        // --
      }
      else if(*arg == 'u') {
        ++arg;
        // -u
        if(*arg == '1') {
          std::string farg = std::string(argv[2]);
          farg = farg.substr(0, farg.length()-4);

          safe_rename((farg+".exe").c_str(), (farg+".old.exe").c_str());

          char *args[] = { const_cast<char*>((farg+".old.exe").c_str()), const_cast<char*>("-u2"), self, NULL };
          char *environ[] = { NULL };
          return execve((farg+".old.exe").c_str(), args, environ);
        }
        else if(*arg == '2') {
          std::string farg = std::string(argv[2]);
          farg = farg.substr(0, farg.length()-8);

          safe_rename((farg+".new.exe").c_str(), (farg+".exe").c_str());

          char *args[] = { const_cast<char*>((farg+".exe").c_str()), const_cast<char*>("-u3"), self, NULL };
          char *environ[] = { NULL };
          return execve((farg+".exe").c_str(), args, environ);
        }
        else if(*arg == '3') {
          safe_remove(argv[2]);
        }
      }
      else if(*arg == '\0') {
        // self.exe -
      }
    }
  }
  std::cout << "Normal Runtime" << std::endl;
  return 0;
}