/*
 * Copyright ©2026 Soham Pardeshi. All rights reserved.
 * Permission is hereby granted to students registered for University of
 * Washington CSE 333 for use solely during Summer Quarter 2026 for
 * purposes of the course. No other use, copying, distribution, or
 * modification is permitted without prior written consent. Copyrights
 * for third-party components of this work must be honored. Instructors
 * interested in reusing these course materials should contact the author.
 */

/* WARNING! Don't just blindly copy code -- check to see if you need to make
 * any tweaks to do exactly what you want it to.
 * You should also NOT assume that this sample code has perfect style.
 */

#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#include <iostream>

void Usage(char* progname);
void PrintOut(int fd, struct sockaddr* addr, size_t addrlen);
void PrintReverseDNS(struct sockaddr* addr, size_t addrlen);
void PrintServerSide(int client_fd, int sock_family);
int  Listen(char* portnum, int* sock_family);
void HandleClient(int c_fd, struct sockaddr* addr, size_t addrlen,
                  int sock_family);

int main(int argc, char** argv) {
  // Expect the port number as a command line argument.
  if (argc != 2) {
    Usage(argv[0]);
  }

  int sock_family;
  int listen_fd = Listen(argv[1], &sock_family);
  if (listen_fd <= 0) {
    // We failed to bind/listen to a socket.  Quit with failure.
    std::cerr << "Couldn't bind to any addresses." << std::endl;
    return EXIT_FAILURE;
  }

  // Loop forever, accepting a connection from a client and doing
  // an echo trick to it.
  while (1) {
    struct sockaddr_storage caddr;
    socklen_t caddr_len = sizeof(caddr);
    int client_fd = accept(listen_fd,
                           reinterpret_cast<struct sockaddr*>(&caddr),
                           &caddr_len);
    if (client_fd < 0) {
      if ((errno == EINTR) || (errno == EAGAIN) || (errno == EWOULDBLOCK))
        continue;
      std::cerr << "Failure on accept: " << strerror(errno) << std::endl;
      break;
    }

    HandleClient(client_fd,
                 reinterpret_cast<struct sockaddr*>(&caddr),
                 caddr_len,
                 sock_family);
  }

  // Close up shop.
  close(listen_fd);
  return EXIT_SUCCESS;
}

void Usage(char* progname) {
  std::cerr << "usage: " << progname << " port" << std::endl;
  exit(EXIT_FAILURE);
}

void PrintOut(int fd, struct sockaddr* addr, size_t addrlen) {
  std::cout << "Socket [" << fd << "] is bound to:" << std::endl;
  if (addr->sa_family == AF_INET) {
    // Print out the IPV4 address and port

    char astring[INET_ADDRSTRLEN];
    struct sockaddr_in* in4 = reinterpret_cast<struct sockaddr_in*>(addr);
    inet_ntop(AF_INET, &(in4->sin_addr), astring, INET_ADDRSTRLEN);
    std::cout << " IPv4 address " << astring;
    std::cout << " and port " << ntohs(in4->sin_port) << std::endl;

  } else if (addr->sa_family == AF_INET6) {
    // Print out the IPV6 address and port

    char astring[INET6_ADDRSTRLEN];
    struct sockaddr_in6* in6 = reinterpret_cast<struct sockaddr_in6*>(addr);
    inet_ntop(AF_INET6, &(in6->sin6_addr), astring, INET6_ADDRSTRLEN);
    std::cout << " IPv6 address " << astring;
    std::cout << " and port " << ntohs(in6->sin6_port) << std::endl;

  } else {
    std::cout << " ???? address and port ????" << std::endl;
  }
}

void PrintReverseDNS(struct sockaddr* addr, size_t addrlen) {
  char hostname[1024];  // ought to be big enough.
  if (getnameinfo(addr, addrlen, hostname, 1024, nullptr, 0, 0) != 0) {
    sprintf(hostname, "[reverse DNS failed]");
  }
  std::cout << " DNS name: " << hostname << std::endl;
}

void PrintServerSide(int client_fd, int sock_family) {
  char hname[1024];
  hname[0] = '\0';

  std::cout << "Server side interface is ";
  if (sock_family == AF_INET) {
    // The server is using an IPv4 address.
    struct sockaddr_in srvr;
    socklen_t srvrlen = sizeof(srvr);
    char addrbuf[INET_ADDRSTRLEN];
    getsockname(client_fd,
                reinterpret_cast<struct sockaddr*>(&srvr),
                &srvrlen);
    inet_ntop(AF_INET, &srvr.sin_addr, addrbuf, INET_ADDRSTRLEN);
    std::cout << addrbuf;
    // Get the server's dns name, or return it's IP address as
    // a substitute if the dns lookup fails.
    getnameinfo(reinterpret_cast<struct sockaddr*>(&srvr),
                srvrlen, hname, 1024, nullptr, 0, 0);
    std::cout << " [" << hname << "]" << std::endl;
  } else {
    // The server is using an IPv6 address.
    struct sockaddr_in6 srvr;
    socklen_t srvrlen = sizeof(srvr);
    char addrbuf[INET6_ADDRSTRLEN];
    getsockname(client_fd,
                reinterpret_cast<struct sockaddr*>(&srvr),
                &srvrlen);
    inet_ntop(AF_INET6, &srvr.sin6_addr, addrbuf, INET6_ADDRSTRLEN);
    std::cout << addrbuf;
    // Get the server's dns name, or return it's IP address as
    // a substitute if the dns lookup fails.
    getnameinfo(reinterpret_cast<struct sockaddr*>(&srvr),
                srvrlen, hname, 1024, nullptr, 0, 0);
    std::cout << " [" << hname << "]" << std::endl;
  }
}

int Listen(char* portnum, int* sock_family) {
  // Populate the "hints" addrinfo structure for getaddrinfo().
  // ("man addrinfo")
  struct addrinfo hints;
  memset(&hints, 0, sizeof(struct addrinfo));
  hints.ai_family = AF_INET6;       // IPv6 (also handles IPv4 clients)
  hints.ai_socktype = SOCK_STREAM;  // stream
  hints.ai_flags = AI_PASSIVE;      // use wildcard "in6addr_any" address
  hints.ai_flags |= AI_V4MAPPED;    // use v4-mapped v6 if no v6 found
  hints.ai_protocol = IPPROTO_TCP;  // tcp protocol
  hints.ai_canonname = nullptr;
  hints.ai_addr = nullptr;
  hints.ai_next = nullptr;

  // Use argv[1] as the string representation of our portnumber to
  // pass in to getaddrinfo().  getaddrinfo() returns a list of
  // address structures via the output parameter "result".
  struct addrinfo* result;
  int res = getaddrinfo(nullptr, portnum, &hints, &result);

  // Did addrinfo() fail?
  if (res != 0) {
    std::cerr << "getaddrinfo() failed: ";
    std::cerr << gai_strerror(res) << std::endl;
    return -1;
  }

  // Loop through the returned address structures until we are able
  // to create a socket and bind to one.  The address structures are
  // linked in a list through the "ai_next" field of result.
  int listen_fd = -1;
  for (struct addrinfo* rp = result; rp != nullptr; rp = rp->ai_next) {
    listen_fd = socket(rp->ai_family,
                       rp->ai_socktype,
                       rp->ai_protocol);
    if (listen_fd == -1) {
      // Creating this socket failed.  So, loop to the next returned
      // result and try again.
      std::cerr << "socket() failed: " << strerror(errno) << std::endl;
      listen_fd = -1;
      continue;
    }

    // Configure the socket; we're setting a socket "option."  In
    // particular, we set "SO_REUSEADDR", which tells the TCP stack
    // so make the port we bind to available again as soon as we
    // exit, rather than waiting for a few tens of seconds to recycle it.
    int optval = 1;
    setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR,
               &optval, sizeof(optval));

    // Try binding the socket to the address and port number returned
    // by getaddrinfo().
    if (bind(listen_fd, rp->ai_addr, rp->ai_addrlen) == 0) {
      // Bind worked!  Print out the information about what
      // we bound to.
      PrintOut(listen_fd, rp->ai_addr, rp->ai_addrlen);

      // Return to the caller the address family.
      *sock_family = rp->ai_family;
      break;
    }

    // The bind failed.  Close the socket, then loop back around and
    // try the next address/port returned by getaddrinfo().
    close(listen_fd);
    listen_fd = -1;
  }

  // Free the structure returned by getaddrinfo().
  freeaddrinfo(result);

  // If we failed to bind, return failure.
  if (listen_fd == -1)
    return listen_fd;

  // Success. Tell the OS that we want this to be a listening socket.
  if (listen(listen_fd, SOMAXCONN) != 0) {
    std::cerr << "Failed to mark socket as listening: ";
    std::cerr << strerror(errno) << std::endl;
    close(listen_fd);
    return -1;
  }

  // Return to the client the listening file descriptor.
  return listen_fd;
}

void HandleClient(int c_fd, struct sockaddr* addr, size_t addrlen,
                  int sock_family) {
  // Print out information about the client.
  std::cout << std::endl;
  std::cout << "New client connection" << std::endl;
  PrintOut(c_fd, addr, addrlen);
  PrintReverseDNS(addr, addrlen);
  PrintServerSide(c_fd, sock_family);

  // Loop, reading data and echo'ing it back, until the client
  // closes the connection.
  while (1) {
    char clientbuf[1024];
    ssize_t res = read(c_fd, clientbuf, 1023);
    if (res == 0) {
      std::cout << " [The client disconnected.]" << std::endl;
      break;
    }

    if (res == -1) {
      if ((errno == EAGAIN) || (errno == EINTR))
        continue;

      std::cout << " [Error on client socket: ";
      std::cout << strerror(errno) << "]" << std::endl;
      break;
    }
    clientbuf[res] = '\0';
    std::cout << " the client sent: " << clientbuf;

    // Really should do this in a loop in case of EAGAIN, EINTR,
    // or short write, but I'm lazy.  Don't be like me. ;)
    write(c_fd, "You typed: ", strlen("You typed: "));
    write(c_fd, clientbuf, strlen(clientbuf));
  }

  close(c_fd);
}