【C言語】疑似DHCPクライアント・サーバ

悩んでいる人

C言語で疑似DHCPクライアント・サーバを教えて！

こういった悩みにお答えします．

本記事の信頼性

リアルタイムシステムの研究歴12年．
東大教員の時に，英語でOS（Linuxカーネル）の授業．
2012年9月～2013年8月にアメリカのノースカロライナ大学チャペルヒル校（UNC）コンピュータサイエンス学部で客員研究員として勤務．C言語でリアルタイムLinuxの研究開発．
プログラミング歴15年以上，習得している言語: C/C++，Python，Solidity/Vyper，Java，Ruby，Go，Rust，D，HTML/CSS/JS/PHP，MATLAB，Verse（UEFN）, Assembler (x64，ARM)．
東大教員の時に，C++言語で開発した「LLVMコンパイラの拡張」，C言語で開発した独自のリアルタイムOS「Mcube Kernel」をGitHubにオープンソースとして公開．
2020年1月～現在はアメリカのノースカロライナ州チャペルヒルにあるGuarantee Happiness LLCのCTOとしてECサイト開発やWeb/SNSマーケティングの業務．2022年6月～現在はアメリカのノースカロライナ州チャペルヒルにあるJapanese Tar Heel, Inc.のCEO兼CTO．
最近は自然言語処理AIとイーサリアムに関する有益な情報発信に従事．

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こういった私から学べます．

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私のキャパシティもあり，一定数に達したら終了しますので，今すぐ追加しましょう！

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: 元東大教員がおすすめするC言語を学べるオンラインプログラミングスクール5社

こういった悩みにお答えします．こういった私が解説していきます．私が大学の授業で初めてC言語を勉強した時は全然できませんでしたが，先生やTA，友人に相談しながら一生懸命C言語を勉強してできるようにな ...

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疑似DHCPクライアント・サーバ

C言語で疑似DHCPクライアント・サーバを紹介します．

本記事は以下の内容を理解していることを前提とします．

: 【C言語】INETドメイン/UNIXドメインソケット通信によるネットワークプログラミング【TCP，UDP】

こういった悩みにお答えします．こういった私から学べます． C言語のINETドメイン/UNIXドメインソケット通信によるネットワークプログラミング本記事では，C言語のINETドメイン/UNIXドメイ ...

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: 【C言語】select/pselect/poll/ppoll/epoll関数の違い

こういった悩みにお答えします．こういった私から学べます． C言語のselect/pselect/poll/ppoll/epoll関数の違いを紹介します． select/pselect関数 [cray ...

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擬似DHCPでIPアドレスを割り当て，解法等の管理をするプログラムです．

15秒ごとにIPアドレスの更新手続きを行います．

更新に失敗した場合，新しいIPアドレスの要求を行います．

上記の手順を状態遷移で実装します．

疑似DHCPクライアントの状態遷移は以下になります．

疑似DHCPサーバの状態遷移は以下になります．

疑似DHCPクライアント・サーバのコード

疑似DHCPクライアント・サーバのコード一式はこちらからダウンロードして下さい．

コード一式は以下になります．

Makefile：makeのビルドファイル
common.h，common.c：疑似DHCPクライアント・サーバの共通ファイル
config.txt：疑似DHCPサーバのIPアドレスとネットマスクの設定ファイル
mydhcp_client.c：疑似DHCPクライアントのファイル
mydhcp_server.c：疑似DHCPサーバのファイル

以下の手順で解凍とmakeでビルドします．

$ unzip mydhcp.zip
$ cd mydhcp
$ make
gcc -Wall   -c -o mydhcp_client.o mydhcp_client.c
gcc -Wall   -c -o common.o common.c
gcc -o mydhcp_client mydhcp_client.c common.c -Wall 
gcc -Wall   -c -o mydhcp_server.o mydhcp_server.c
gcc -o mydhcp_server mydhcp_server.c common.c -Wall

$ unzip mydhcp.zip

$ cd mydhcp

$ make

gcc -Wall -c -o mydhcp_client.o mydhcp_client.c

gcc -Wall -c -o common.o common.c

gcc -o mydhcp_client mydhcp_client.c common.c -Wall

gcc -Wall -c -o mydhcp_server.o mydhcp_server.c

gcc -o mydhcp_server mydhcp_server.c common.c -Wall

common.h，common.c，mydhcp_client.c，mydhcp_server.cは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#ifndef __COMMON_H__
#define __COMMON_H__

#define PORT 65432

#define BUFSIZE 128
#define NETSIZE 32

enum states {
  STAT_WAIT_DISCOVER = 1,
  STAT_WAIT_OFFER = 2,
  STAT_WAIT_REQUEST = 3,
  REPLY = 4,
  RELEASE = 5,
  STAT_WAIT_ACK = 6,
  DHCPDISCOVER = 7,
  DHCPOFFER = 8,
  DHCPREQUEST = 9,
  DHCPACK = 10,
  STAT_BOUND = 11
};

enum time {
  USETIME_SEC = 30,
  USETIME_USEC = 0
};

typedef struct message {
  uint8_t type;
  uint8_t code;
  uint16_t time_to_live;
  uint8_t ip[NETSIZE];
  uint8_t netmask[NETSIZE];
} message;

typedef struct command_table {
  char *cmd;
  void (*func)(void);
} table;

void command(int n, char pBuf[], table *cmd_tbl);

#define EXIT_STR "exit"

#endif /* __COMMON_H__ */

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#ifndef __COMMON_H__

#define __COMMON_H__

#define PORT 65432

#define BUFSIZE 128

#define NETSIZE 32

enum states {

STAT_WAIT_DISCOVER = 1,

STAT_WAIT_OFFER = 2,

STAT_WAIT_REQUEST = 3,

REPLY = 4,

RELEASE = 5,

STAT_WAIT_ACK = 6,

DHCPDISCOVER = 7,

DHCPOFFER = 8,

DHCPREQUEST = 9,

DHCPACK = 10,

STAT_BOUND = 11

};

enum time {

USETIME_SEC = 30,

USETIME_USEC = 0

};

typedef struct message {

uint8_t type;

uint8_t code;

uint16_t time_to_live;

uint8_t ip[NETSIZE];

uint8_t netmask[NETSIZE];

} message;

typedef struct command_table {

char *cmd;

void (*func)(void);

} table;

void command(int n, char pBuf[], table *cmd_tbl);

#define EXIT_STR "exit"

#endif /* __COMMON_H__ */

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include "common.h"

int search_keytab(int n, char s[], table *cmd_tbl)
{
  int cond;
  int low, mid, high;
  low = 0;
  high = n - 1;

  while (low <= high) {
    mid = (low + high) / 2;

    if ((cond = strcmp(s, cmd_tbl[mid].cmd)) < 0) {
      high = mid - 1;
    } else if (cond > 0) {
      low = mid + 1;
    } else {
      return mid;
    }
  }

  return -1;
}

void command(int n, char pBuf[], table *cmd_tbl)
{
  int key;

  if ((key = search_keytab(n, pBuf, cmd_tbl)) < 0 || key > n - 1) {
    fprintf(stderr, "Error: %s is unknown command\n", pBuf);
  } else {
    (cmd_tbl[key].func)();
  }
}

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <string.h>

#include <inttypes.h>

#include "common.h"

int search_keytab(int n, char s[], table *cmd_tbl)

{

int cond;

int low, mid, high;

low = 0;

high = n - 1;

while (low <= high) {

mid = (low + high) / 2;

if ((cond = strcmp(s, cmd_tbl[mid].cmd)) < 0) {

high = mid - 1;

} else if (cond > 0) {

low = mid + 1;

} else {

return mid;

}

return -1;

}

void command(int n, char pBuf[], table *cmd_tbl)

{

int key;

if ((key = search_keytab(n, pBuf, cmd_tbl)) < 0 || key > n - 1) {

fprintf(stderr, "Error: %s is unknown command\n", pBuf);

} else {

(cmd_tbl[key].func)();

}

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <time.h>
#include <signal.h>
#include <limits.h>
#include "common.h"


void func_exit(void);
void func_release(void);
void func_timeout(void);


table cmd_tbl[] = {
  {.cmd = "exit", .func = func_exit},
  {.cmd = "re", .func = func_release},
  {.cmd = "to", .func = func_timeout}
};


#define NKEYS (sizeof cmd_tbl / sizeof cmd_tbl[0])
#define DEBUG(s) puts(s)

message msg;
int msg_num = sizeof(message);
int sock;
int alrmflag = 0;
int status;
struct sockaddr_in serverAddr;
struct itimerval *itv;
struct timeval tv, to;
struct itimerval value, ivalue, ovalue;

void sigint_handler(int signal)
{
  printf("\nrelease client\n");
  msg.type = RELEASE;
  msg.netmask[0] = '\0';

  if (sendto(sock, &msg, sizeof(message), 0,
             (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
    perror("sendto");
    exit(9);
  }

  exit(0);
}

void sigalrm_handler(int signal)
{
  alrmflag++;
}

void func_exit(void)
{
  /* do nothing but go to exit. */
}

void func_timeout(void)
{
  if (status == STAT_BOUND) {
    gettimeofday(&tv, NULL);
    printf("CurrentTime: %s", ctime((time_t *) &tv));
    printf("TimeoutTime: %s", ctime((time_t *) &to));
  } else {
    fprintf(stderr, "Error: haven't allocated IP address yet.\n");
  }
}

void func_release(void)
{
  printf("\nrelease IP address %s\n", msg.ip);
  msg.type = RELEASE;
  msg.netmask[0] = '\0';

  if (sendto(sock, &msg, sizeof(message), 0,
             (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
    perror("sendto");
    exit(10);
  }

  setitimer(ITIMER_REAL, &ovalue, NULL);
  sleep(1);
  msg.type = DHCPDISCOVER;
  msg.code = 0;

  if (sendto(sock, &msg, sizeof(message), 0,
             (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
    perror("sendto");
    exit(7);
  }

  status = STAT_WAIT_OFFER;
  printf("\tstatus: STAT_WAIT_OFFER\n");
}


int main(int argc, char *argv[])
{
  int msgtype;
  struct sockaddr_in clientAddr;
  int addrLen;
  int n;
  struct hostent *pServerHostEnt;
  char pBuf[BUFSIZE];
  fd_set fds, readfds;

  if (argc != 2) {
    fprintf(stderr, "Error: %s [hostname]\n", argv[0]);
    exit(1);
  }

  if ((pServerHostEnt = (struct hostent *) gethostbyname(argv[1])) == NULL) {
    perror("gethostbyname");
    exit(2);
  }

  memset((char *) &serverAddr, 0, sizeof(serverAddr));
  serverAddr.sin_family = AF_INET;
  memmove((char *) &serverAddr.sin_addr, (void *) pServerHostEnt->h_addr,
          pServerHostEnt->h_length);
  serverAddr.sin_port = htons(PORT);

  if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
    perror("socket");
    exit(3);
  }

  memset((char *) &clientAddr, 0, sizeof(clientAddr));

  clientAddr.sin_family = AF_INET;
  clientAddr.sin_addr.s_addr = htonl(INADDR_ANY);
  clientAddr.sin_port = htons(0);

  if (bind(sock, (struct sockaddr *) &clientAddr, sizeof(clientAddr)) < 0) {
    perror("bind");
    exit(4);
  }

  signal(SIGINT, sigint_handler);
  signal(SIGALRM, sigalrm_handler);

  msg.type = DHCPDISCOVER;
  msg.code = 0;
  msg.time_to_live = 0;

  if (sendto(sock, &msg, sizeof(message), 0,
             (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
    perror("sendto");
    exit(5);
  }

  FD_ZERO(&readfds);
  FD_SET(0, &readfds);
  FD_SET(sock, &readfds);

  status = STAT_WAIT_OFFER;
  printf("\tstatus: STAT_WAIT_OFFER\n");

  value.it_value.tv_usec = USETIME_USEC;
  value.it_value.tv_sec = USETIME_SEC / 2;
  value.it_interval.tv_usec = USETIME_USEC;
  value.it_interval.tv_sec = USETIME_SEC / 2;

  ivalue.it_value.tv_usec = USETIME_USEC;
  ivalue.it_value.tv_sec = USETIME_SEC;
  ivalue.it_interval.tv_usec = USETIME_USEC;
  ivalue.it_interval.tv_sec = USETIME_SEC;

  setitimer(ITIMER_REAL, &ivalue, &ovalue);

  while (true) {
    memcpy(&fds, &readfds, sizeof(fd_set));

    if (select(sock + 1, &fds, NULL, NULL, NULL) < 0) {
      if (alrmflag > 0) {
        if (alrmflag == 1 && status == STAT_BOUND) {
          printf("Request continue IP address %s\n", msg.ip);
          setitimer(ITIMER_REAL, &value, NULL);
          msg.type = DHCPREQUEST;
          msg.code = 11;
          printf("send msgtype: DHCPREQUEST\n");

          if (sendto(sock, &msg, sizeof(message), 0,
                     (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
            perror("sendto");
            exit(6);
          }

          continue;
        } else {
          alrmflag = 0;
          printf("Timeout\n");
          msg.type = DHCPDISCOVER;
          msg.code = 0;
          msg.ip[0] = '\0';
          msg.netmask[0] = '\0';
          msg.time_to_live = 0;
          printf("send msgtype: DHCPDISCOVER\n");

          if (sendto(sock, &msg, sizeof(message), 0,
                     (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
            perror("sendto");
            exit(7);
          }

          setitimer(ITIMER_REAL, &ovalue, NULL);
          setitimer(ITIMER_REAL, &ivalue, NULL);
          status = STAT_WAIT_OFFER;
          printf("\tstatus: STAT_WAIT_OFFER\n");
          continue;
        }
      } else {
        perror("select");
        exit(8);
      }
    }

    if (FD_ISSET(0, &fds)) {
      if ((n = read(0, pBuf, BUFSIZE)) > 0) {
        pBuf[n - 1] = '\0';
        printf("Execute command: %s\n", pBuf);
        command(NKEYS, pBuf, cmd_tbl);

        if (!strncmp(pBuf, EXIT_STR, strlen(EXIT_STR))) {
          break;
        }
      }

      continue;
    }

    if (FD_ISSET(sock, &fds)) {
      if ((n = recvfrom(sock, &msg, sizeof(message), 0,
                        (struct sockaddr *) &clientAddr, (socklen_t *) &addrLen)) < 0) {
        perror("recvfrom");
        break;
      }
    }

    if (alrmflag == 1) {
      if (msg.code == 12) {
        alrmflag = 0;
        gettimeofday(&tv, NULL);
        printf("Success contniue IP address %s\n", msg.ip);
        printf("CurrentTime: %s", ctime((time_t *) &tv));
        to.tv_sec = tv.tv_sec + msg.time_to_live;
        to.tv_usec = tv.tv_usec;
        printf("TimeoutTime: %s", ctime((time_t *) &to));
        setitimer(ITIMER_REAL, &ovalue, NULL);
        setitimer(ITIMER_REAL, &value, NULL);
        continue;
      } else {
        alrmflag = 0;
        fprintf(stderr, "Error: failure continue IP address %s\n", msg.ip);
        msg.type = DHCPDISCOVER;
        msg.code = 0;
        msg.ip[0] = '\0';
        msg.netmask[0] = '\0';
        msg.time_to_live = 0;
        printf("send msgtype: DHCPDISCOVER\n");

        if (sendto(sock, &msg, sizeof(message), 0,
                   (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
          perror("sendto");
          exit(9);
        }

        setitimer(ITIMER_REAL, &ovalue, NULL);
        setitimer(ITIMER_REAL, &ivalue, NULL);
        status = STAT_WAIT_OFFER;
        printf("\tstatus: STAT_WAIT_OFFER\n");
        continue;
      }
    }

    printf("Server IP: %s\n", inet_ntoa(serverAddr.sin_addr));

    msgtype = msg.type;

    switch (status) {
    case STAT_WAIT_OFFER:
      if (msgtype == DHCPOFFER) {
        printf("receive msgtype: DHCPOFFER\n");

        if (msg.code == 0) {
          msg.type = DHCPREQUEST;
          msg.code = 10;
          printf("send msgtype: DHCPREQUEST\n");

          if (sendto(sock, &msg, sizeof(message), 0,
                     (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
            perror("sendto");
            exit(10);
          }

          printf("\tstatus: STAT_WAIT_ACK\n");
          status = STAT_WAIT_ACK;
        } else if (msg.code == 129) {
          fprintf(stderr, "Error: failed IP address\n");
        } else {
          fprintf(stderr, "Error: unexpected message received: code = %d\n", msg.code);
        }
      } else {
        fprintf(stderr, "Error: receive %d, not %d\n", msgtype, DHCPOFFER);
      }

      break;

    case STAT_WAIT_ACK:
      if (msgtype == DHCPACK) {
        printf("receive msgtype: DHCPACK\n");

        if (msg.code == 0) {
          printf("IP: %s netmask: %s\n", msg.ip, msg.netmask);
          gettimeofday(&tv, NULL);
          printf("CurrentTime: %s", ctime((time_t *) &tv));
          to.tv_sec = tv.tv_sec + msg.time_to_live;
          to.tv_usec = tv.tv_usec + USETIME_USEC;
          printf("TimeoutTime: %s", ctime((time_t *) &to));
          setitimer(ITIMER_REAL, &ovalue, NULL);
          setitimer(ITIMER_REAL, &value, NULL);
          status = STAT_BOUND;
          printf("\tstatus: STAT_BOUND\n");
        } else if (msg.code == 130) {
          fprintf(stderr, "Error: failed IP address\n");
        } else {
          fprintf(stderr, "Error: unexpected message received\n");
        }
      } else {
        fprintf(stderr, "Error: receive %d not %d\n", msgtype, DHCPACK);
      }

      break;

    case STAT_BOUND:
      printf("\tstatus: STAT_BOUND\n");
      break;

    default:
      fprintf(stderr, "Error: undefined status\n");
      msg.type = DHCPDISCOVER;
      msg.code = 0;
      printf("send msgtype: DHCPDISCOVER\n");

      if (sendto(sock, &msg, sizeof(message), 0,
                 (struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {
        perror("sendto");
        exit(11);
      }

      setitimer(ITIMER_REAL, &ovalue, NULL);
      status = STAT_WAIT_OFFER;
      printf("\tSTAT_WAIT_OFFER\n");
      break;
    }
  }

  FD_CLR(0, &readfds);

  if (close(sock) == -1) {
    perror("close");
    exit(12);
  }

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <stdbool.h>

#include <sys/time.h>

#include <sys/socket.h>

#include <sys/select.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <unistd.h>

#include <netdb.h>

#include <time.h>

#include <signal.h>

#include <limits.h>

#include "common.h"

void func_exit(void);

void func_release(void);

void func_timeout(void);

table cmd_tbl[] = {

{.cmd = "exit", .func = func_exit},

{.cmd = "re", .func = func_release},

{.cmd = "to", .func = func_timeout}

};

#define NKEYS (sizeof cmd_tbl / sizeof cmd_tbl[0])

#define DEBUG(s) puts(s)

message msg;

int msg_num = sizeof(message);

int sock;

int alrmflag = 0;

int status;

struct sockaddr_in serverAddr;

struct itimerval *itv;

struct timeval tv, to;

struct itimerval value, ivalue, ovalue;

void sigint_handler(int signal)

{

printf("\nrelease client\n");

msg.type = RELEASE;

msg.netmask[0] = '\0';

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(9);

}

exit(0);

}

void sigalrm_handler(int signal)

{

alrmflag++;

}

void func_exit(void)

{

/* do nothing but go to exit. */

}

void func_timeout(void)

{

if (status == STAT_BOUND) {

gettimeofday(&tv, NULL);

printf("CurrentTime: %s", ctime((time_t *) &tv));

printf("TimeoutTime: %s", ctime((time_t *) &to));

} else {

fprintf(stderr, "Error: haven't allocated IP address yet.\n");

}

void func_release(void)

{

printf("\nrelease IP address %s\n", msg.ip);

msg.type = RELEASE;

msg.netmask[0] = '\0';

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(10);

}

setitimer(ITIMER_REAL, &ovalue, NULL);

sleep(1);

msg.type = DHCPDISCOVER;

msg.code = 0;

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(7);

}

status = STAT_WAIT_OFFER;

printf("\tstatus: STAT_WAIT_OFFER\n");

}

int main(int argc, char *argv[])

{

int msgtype;

struct sockaddr_in clientAddr;

int addrLen;

int n;

struct hostent *pServerHostEnt;

char pBuf[BUFSIZE];

fd_set fds, readfds;

if (argc != 2) {

fprintf(stderr, "Error: %s [hostname]\n", argv[0]);

exit(1);

}

if ((pServerHostEnt = (struct hostent *) gethostbyname(argv[1])) == NULL) {

perror("gethostbyname");

exit(2);

}

memset((char *) &serverAddr, 0, sizeof(serverAddr));

serverAddr.sin_family = AF_INET;

memmove((char *) &serverAddr.sin_addr, (void *) pServerHostEnt->h_addr,

pServerHostEnt->h_length);

serverAddr.sin_port = htons(PORT);

if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {

perror("socket");

exit(3);

}

memset((char *) &clientAddr, 0, sizeof(clientAddr));

clientAddr.sin_family = AF_INET;

clientAddr.sin_addr.s_addr = htonl(INADDR_ANY);

clientAddr.sin_port = htons(0);

if (bind(sock, (struct sockaddr *) &clientAddr, sizeof(clientAddr)) < 0) {

perror("bind");

exit(4);

}

signal(SIGINT, sigint_handler);

signal(SIGALRM, sigalrm_handler);

msg.type = DHCPDISCOVER;

msg.code = 0;

msg.time_to_live = 0;

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(5);

}

FD_ZERO(&readfds);

FD_SET(0, &readfds);

FD_SET(sock, &readfds);

status = STAT_WAIT_OFFER;

printf("\tstatus: STAT_WAIT_OFFER\n");

value.it_value.tv_usec = USETIME_USEC;

value.it_value.tv_sec = USETIME_SEC / 2;

value.it_interval.tv_usec = USETIME_USEC;

value.it_interval.tv_sec = USETIME_SEC / 2;

ivalue.it_value.tv_usec = USETIME_USEC;

ivalue.it_value.tv_sec = USETIME_SEC;

ivalue.it_interval.tv_usec = USETIME_USEC;

ivalue.it_interval.tv_sec = USETIME_SEC;

setitimer(ITIMER_REAL, &ivalue, &ovalue);

while (true) {

memcpy(&fds, &readfds, sizeof(fd_set));

if (select(sock + 1, &fds, NULL, NULL, NULL) < 0) {

if (alrmflag > 0) {

if (alrmflag == 1 && status == STAT_BOUND) {

printf("Request continue IP address %s\n", msg.ip);

setitimer(ITIMER_REAL, &value, NULL);

msg.type = DHCPREQUEST;

msg.code = 11;

printf("send msgtype: DHCPREQUEST\n");

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(6);

}

continue;

} else {

alrmflag = 0;

printf("Timeout\n");

msg.type = DHCPDISCOVER;

msg.code = 0;

msg.ip[0] = '\0';

msg.netmask[0] = '\0';

msg.time_to_live = 0;

printf("send msgtype: DHCPDISCOVER\n");

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(7);

}

setitimer(ITIMER_REAL, &ovalue, NULL);

setitimer(ITIMER_REAL, &ivalue, NULL);

status = STAT_WAIT_OFFER;

printf("\tstatus: STAT_WAIT_OFFER\n");

continue;

}

} else {

perror("select");

exit(8);

}

if (FD_ISSET(0, &fds)) {

if ((n = read(0, pBuf, BUFSIZE)) > 0) {

pBuf[n - 1] = '\0';

printf("Execute command: %s\n", pBuf);

command(NKEYS, pBuf, cmd_tbl);

if (!strncmp(pBuf, EXIT_STR, strlen(EXIT_STR))) {

break;

}

continue;

}

if (FD_ISSET(sock, &fds)) {

if ((n = recvfrom(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &clientAddr, (socklen_t *) &addrLen)) < 0) {

perror("recvfrom");

break;

}

if (alrmflag == 1) {

if (msg.code == 12) {

alrmflag = 0;

gettimeofday(&tv, NULL);

printf("Success contniue IP address %s\n", msg.ip);

printf("CurrentTime: %s", ctime((time_t *) &tv));

to.tv_sec = tv.tv_sec + msg.time_to_live;

to.tv_usec = tv.tv_usec;

printf("TimeoutTime: %s", ctime((time_t *) &to));

setitimer(ITIMER_REAL, &ovalue, NULL);

setitimer(ITIMER_REAL, &value, NULL);

continue;

} else {

alrmflag = 0;

fprintf(stderr, "Error: failure continue IP address %s\n", msg.ip);

msg.type = DHCPDISCOVER;

msg.code = 0;

msg.ip[0] = '\0';

msg.netmask[0] = '\0';

msg.time_to_live = 0;

printf("send msgtype: DHCPDISCOVER\n");

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(9);

}

setitimer(ITIMER_REAL, &ovalue, NULL);

setitimer(ITIMER_REAL, &ivalue, NULL);

status = STAT_WAIT_OFFER;

printf("\tstatus: STAT_WAIT_OFFER\n");

continue;

}

printf("Server IP: %s\n", inet_ntoa(serverAddr.sin_addr));

msgtype = msg.type;

switch (status) {

case STAT_WAIT_OFFER:

if (msgtype == DHCPOFFER) {

printf("receive msgtype: DHCPOFFER\n");

if (msg.code == 0) {

msg.type = DHCPREQUEST;

msg.code = 10;

printf("send msgtype: DHCPREQUEST\n");

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(10);

}

printf("\tstatus: STAT_WAIT_ACK\n");

status = STAT_WAIT_ACK;

} else if (msg.code == 129) {

fprintf(stderr, "Error: failed IP address\n");

} else {

fprintf(stderr, "Error: unexpected message received: code = %d\n", msg.code);

}

} else {

fprintf(stderr, "Error: receive %d, not %d\n", msgtype, DHCPOFFER);

}

break;

case STAT_WAIT_ACK:

if (msgtype == DHCPACK) {

printf("receive msgtype: DHCPACK\n");

if (msg.code == 0) {

printf("IP: %s netmask: %s\n", msg.ip, msg.netmask);

gettimeofday(&tv, NULL);

printf("CurrentTime: %s", ctime((time_t *) &tv));

to.tv_sec = tv.tv_sec + msg.time_to_live;

to.tv_usec = tv.tv_usec + USETIME_USEC;

printf("TimeoutTime: %s", ctime((time_t *) &to));

setitimer(ITIMER_REAL, &ovalue, NULL);

setitimer(ITIMER_REAL, &value, NULL);

status = STAT_BOUND;

printf("\tstatus: STAT_BOUND\n");

} else if (msg.code == 130) {

fprintf(stderr, "Error: failed IP address\n");

} else {

fprintf(stderr, "Error: unexpected message received\n");

}

} else {

fprintf(stderr, "Error: receive %d not %d\n", msgtype, DHCPACK);

}

break;

case STAT_BOUND:

printf("\tstatus: STAT_BOUND\n");

break;

default:

fprintf(stderr, "Error: undefined status\n");

msg.type = DHCPDISCOVER;

msg.code = 0;

printf("send msgtype: DHCPDISCOVER\n");

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &serverAddr, sizeof(serverAddr)) != msg_num) {

perror("sendto");

exit(11);

}

setitimer(ITIMER_REAL, &ovalue, NULL);

status = STAT_WAIT_OFFER;

printf("\tSTAT_WAIT_OFFER\n");

break;

}

FD_CLR(0, &readfds);

if (close(sock) == -1) {

perror("close");

exit(12);

}

return 0;

}

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctype.h>
#include <time.h>
#include <signal.h>
#include <limits.h>
#include "common.h"


typedef struct address {
  struct address *bp;
  struct address *fp;
  int port;
  uint8_t ip[NETSIZE];
  uint8_t netmask[NETSIZE];
} address;


void func_exit(void);
void func_ip(void);
void func_timeout(void);
void func_use(void);

table cmd_tbl[] = {
  {.cmd = "exit", .func = func_exit},
  {.cmd = "ip", .func = func_ip},
  {.cmd = "to", .func = func_timeout},
  {.cmd = "use", .func = func_use}
};


#define NKEYS (sizeof(cmd_tbl) / sizeof(cmd_tbl[0]))
#define DEBUG(s) puts(s)

address head;
address use;
struct timeval tv, to;
struct itimerval value, ovalue;

int alrmflag = 0;

void insert_bottom(address *h, address *p)
{
  p->fp = h;
  p->bp = h->bp;
  h->bp->fp = p;
  h->bp = p;
}

void init_config(char *argv)
{
  FILE *fp;
  char line[BUFSIZE];
  int i, j;
  char tmp[NETSIZE];
  char tmp2[NETSIZE];
  address *p;
  address *ptr;

  head.fp = head.bp = &head;
  use.fp = NULL;

  if ((fp = fopen(argv, "r")) == NULL) {
    fprintf(stderr, "Error: cannot open %s\n", argv);
    exit(2);
  }

  while (fgets(line, sizeof line, fp) != NULL) {
    i = 0;

    while (isspace(line[i]) && line[i] != '\n') {
      i++;
    }

    if (line[i] == '\n') {
      continue;
    }

    j = 0;

    while (!isspace(line[i]) && line[i] != '\n') {
      tmp[j++] = line[i++];
    }

    tmp[j] = '\0';

    while (isspace(line[i]) && line[i] != '\n') {
      i++;
    }

    if (line[i] == '\n') {
      continue;
    }

    j = 0;

    while (!isspace(line[i]) && line[i] != '\n') {
      tmp2[j++] = line[i++];
    }

    tmp2[j] = '\0';

    if ((ptr = (address *) malloc(sizeof(address))) == NULL) {
      fprintf(stderr, "Error: cannot allocate memory %zu\n", sizeof(address));
      exit(3);
    }

    ptr->port = -1;
    strcpy((char *) ptr->ip, (char *) tmp);
    strcpy((char *) ptr->netmask, (char *) tmp2);
    insert_bottom(&head, ptr);
  }

  for (p = head.fp; p != &head; p = p->fp) {
    printf("ip = %s net = %s\n", p->ip, p->netmask);
  }

  if (fclose(fp) == EOF) {
    fprintf(stderr, "Error: cannot close file %s\n", argv);
    exit(4);
  }
}

void exit_config(void)
{
  address *p = head.fp, *prev;

  while (p != &head) {
    printf("ip = %s net = %s\n", p->ip, p->netmask);
    prev = p;
    p = p->fp;
    free(prev);
  }
}


void insert_use(address *p)
{
  address *ap;

  if (use.fp == NULL) {
    use.fp = p;
  } else {
    for (ap = use.fp; ap->fp != NULL; ap = ap->fp)
      ;

    ap->fp = p;
  }
}

void delete_use(int port)
{
  address *ap = &use, *p;

  for (; ap->fp != NULL && ap->fp->port != port; ap = ap->fp)
    ;

  if (ap->fp == NULL) {
    fprintf(stderr, "Error: cannot delete_use() with port %d\n", port);
  } else {
    printf("delete_use() with port %d\n", port);
    p = ap->fp;
    ap->fp = p->fp;
    p->port = -1;
    insert_bottom(&head, p);
  }
}

address *delete_top(address *h)
{
  h->bp->fp = h->fp;
  h->fp->bp = h->bp;
  h->fp = h->bp = NULL;
  return h;
}

void func_exit(void)
{
  /* do nothing but go to exit. */
}

void func_ip(void)
{
  address *ap = head.fp;
  int i;

  for (i = 0, ap = head.fp; ap != &head; i++, ap = ap->fp) {
    printf("IP: %s Netmask: %s\n", ap->ip, ap->netmask);
  }

  if (i == 0) {
    printf("No allocatable IP address\n");
  }
}

void func_timeout(void)
{
  gettimeofday(&tv, NULL);
  printf("CurrentTime: %s\n", ctime((time_t *) &tv));
  printf("TimeoutTime: %s\n", ctime((time_t *) &to));
}

void func_use(void)
{
  address *ap;
  int i;

  for (i = 0, ap = use.fp; ap != NULL; i++, ap = ap->fp) {
    printf("IP: %s Netmask: %s\n", ap->ip, ap->netmask);
  }

  if (i == 0) {
    printf("No allocatable IP address\n");
  }
}

void sigalrm_handler(int signal)
{
  alrmflag++;
}

int allocate_ip(void)
{
  address *ap = &head;

  if (ap->fp == &head) {
    return 0;
  } else {
    return 1;
  }
}

int search_port(int port)
{
  address *ap;

  for (ap = head.fp; ap != &head; ap = ap->fp) {
    if (ap->port == port) {
      return 1;
    }
  }

  return 0;
}

int main(int argc, char *argv[])
{
  int sock;
  int port;
  int status;
  int msgtype;
  struct sockaddr_in serverAddr;
  struct sockaddr_in clientAddr;
  int addrLen, n;
  char pBuf[BUFSIZE];

  fd_set fds, readfds;
  message msg;
  address *add;

  if (argc != 2) {
    fprintf(stderr, "Error: %s [config_file]\n", argv[0]);
    exit(1);
  }

  init_config(argv[1]);

  if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
    perror("socket");
    exit(2);
  }

  memset((char *) &serverAddr, 0, sizeof(serverAddr));

  serverAddr.sin_family = AF_INET;
  serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
  serverAddr.sin_port = htons(PORT);

  if (bind(sock, (struct sockaddr *) &serverAddr, sizeof(serverAddr)) < 0) {
    perror("bind");
    exit(3);
  }

  FD_ZERO(&readfds);
  FD_SET(0, &readfds);
  FD_SET(sock, &readfds);

  status = STAT_WAIT_DISCOVER;
  printf("\tstatus: STAT_WAIT_DISCOVER\n");

  signal(SIGALRM, sigalrm_handler);

  value.it_value.tv_usec = USETIME_USEC;
  value.it_value.tv_sec = USETIME_SEC;
  value.it_interval.tv_usec = USETIME_USEC;
  value.it_interval.tv_sec = USETIME_SEC;

  setitimer(ITIMER_REAL, NULL, &ovalue);

  while (true) {
    memcpy(&fds, &readfds, sizeof(fd_set));

    addrLen = sizeof(clientAddr);

    if (select(INT_MAX, &fds, NULL, NULL, NULL) < 0) {
      if (alrmflag > 0) {
        alrmflag = 0;
        printf("Timeout\n");
        setitimer(ITIMER_REAL, &ovalue, NULL);
        delete_use(port);
        status = STAT_WAIT_DISCOVER;
        printf("\tstatus: STAT_WAIT_DISCOVER\n");
      } else {
        perror("select");
        exit(4);
      }
    }

    if (FD_ISSET(0, &fds)) {
      if ((n = read(0, pBuf, BUFSIZE)) > 0) {
        pBuf[n - 1] = '\0';
        printf("Execute command: %s\n", pBuf);
        command(NKEYS, pBuf, cmd_tbl);

        if (!strncmp(pBuf, EXIT_STR, strlen(EXIT_STR))) {
          break;
        }
      }

      continue;
    }

    if (FD_ISSET(sock, &fds)) {
      if ((n = recvfrom(sock, &msg, sizeof(message), 0,
                        (struct sockaddr *) &clientAddr,
                        (socklen_t *) &addrLen)) < 0) {
        perror("recvfrom");
        break;
      }
    } else {
      fprintf(stderr, "Error: unexpected message received\n");
      continue;
    }

    port = ntohs(clientAddr.sin_port);
    printf("Client IP: %s\n", inet_ntoa(clientAddr.sin_addr));
    printf("port %d\n", port);
    msgtype = msg.type;

    if (msgtype == RELEASE) {
      delete_use(port);
      msg.ip[0] = '\0';
      setitimer(ITIMER_REAL, &ovalue, NULL);
      continue;
    }

    if (msg.code == 11) {
      status = STAT_WAIT_REQUEST;
      printf("\tstatus: STAT_WAIT_REQUEST\n");
    }

    switch (status) {
    case STAT_WAIT_DISCOVER:
      if (msgtype == DHCPDISCOVER) {
        printf("receive msgtype: DHCPDISCOVER\n");

        if (allocate_ip()) {
          printf("find IP address %s\n", head.fp->ip);
          msg.type = DHCPOFFER;
          msg.code = 0;
          printf("send msgtype: DHCPOFFER\n");
        } else {
          fprintf(stderr, "Error: empty IP address\n");
          msg.code = 129;
        }

        if (sendto(sock, &msg, n, 0, (struct sockaddr *) &clientAddr, addrLen) != n) {
          perror("sendto");
          exit(5);
        }

        status = STAT_WAIT_REQUEST;
        printf("\tstatus: STAT_WAIT_REQUEST\n");
      } else {
        fprintf(stderr, "Error: receive %d not %d\n", msgtype, DHCPDISCOVER);
      }

      break;

    case STAT_WAIT_REQUEST:
      if (msgtype == DHCPREQUEST) {
        printf("receive msgtype: DHCPREQUEST\n");

        if (msg.code == 10 && allocate_ip()) {
          add = delete_top(head.fp);
          add->port = port;
          insert_use(add);
          strcpy((char *) msg.ip, (char *) add->ip);
          strcpy((char *) msg.netmask, (char *) add->netmask);
          msg.type = DHCPACK;
          msg.code = 0;
          msg.time_to_live = USETIME_SEC;
          printf("Client IP address %s\n", inet_ntoa(clientAddr.sin_addr));
          printf("allocated IP address %s\n", add->ip);
          printf("allocated Netmask %s\n", add->netmask);
          gettimeofday(&tv, NULL);
          printf("CurrentTime: %s", ctime((time_t *) &tv));
          to.tv_sec = tv.tv_sec + msg.time_to_live;
          to.tv_usec = tv.tv_usec + USETIME_USEC;
          printf("TimeoutTime: %s", ctime((time_t *) &to));
          setitimer(ITIMER_REAL, &value, NULL);
          printf("send msgtype: DHCPACK\n");
        } else if (msg.code == 11) {
          msg.code = 12;
          printf("Client IP address %s\n", inet_ntoa(clientAddr.sin_addr));
          printf("continue IP address %s\n", add->ip);
          printf("continue Netmask %s\n", add->netmask);
          gettimeofday(&tv, NULL);
          printf("CurrentTime: %s", ctime((time_t *) &tv));
          to.tv_sec = tv.tv_sec + msg.time_to_live;
          to.tv_usec = tv.tv_usec + USETIME_USEC;
          printf("TimeoutTime: %s", ctime((time_t *) &to));
          setitimer(ITIMER_REAL, &value, NULL);
          printf("Success continue IP address\n");
        } else {
          fprintf(stderr, "Error: cannot allocate IP address\n");
          msg.code = 130;
        }

        if (sendto(sock, &msg, sizeof(message), 0,
                   (struct sockaddr *) &clientAddr, sizeof(serverAddr)) != n) {
          perror("sendto");
          exit(6);
        }

        status = STAT_WAIT_DISCOVER;
        printf("\tstatus: STAT_WAIT_DISCOVER\n");
      } else {
        fprintf(stderr, "Error: receive %d not %d\n", msgtype, DHCPREQUEST);
        status = STAT_WAIT_DISCOVER;
        printf("\tstatus: STAT_WAIT_DISCOVER\n");
      }

      break;

    }
  }

  if (close(sock) == -1) {
    perror("close");
    exit(7);
  }

  exit_config();

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <stdbool.h>

#include <sys/types.h>

#include <sys/time.h>

#include <sys/socket.h>

#include <sys/select.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <unistd.h>

#include <ctype.h>

#include <time.h>

#include <signal.h>

#include <limits.h>

#include "common.h"

typedef struct address {

struct address *bp;

struct address *fp;

int port;

uint8_t ip[NETSIZE];

uint8_t netmask[NETSIZE];

} address;

void func_exit(void);

void func_ip(void);

void func_timeout(void);

void func_use(void);

table cmd_tbl[] = {

{.cmd = "exit", .func = func_exit},

{.cmd = "ip", .func = func_ip},

{.cmd = "to", .func = func_timeout},

{.cmd = "use", .func = func_use}

};

#define NKEYS (sizeof(cmd_tbl) / sizeof(cmd_tbl[0]))

#define DEBUG(s) puts(s)

address head;

address use;

struct timeval tv, to;

struct itimerval value, ovalue;

int alrmflag = 0;

void insert_bottom(address *h, address *p)

{

p->fp = h;

p->bp = h->bp;

h->bp->fp = p;

h->bp = p;

}

void init_config(char *argv)

{

FILE *fp;

char line[BUFSIZE];

int i, j;

char tmp[NETSIZE];

char tmp2[NETSIZE];

address *p;

address *ptr;

head.fp = head.bp = &head;

use.fp = NULL;

if ((fp = fopen(argv, "r")) == NULL) {

fprintf(stderr, "Error: cannot open %s\n", argv);

exit(2);

}

while (fgets(line, sizeof line, fp) != NULL) {

i = 0;

while (isspace(line[i]) && line[i] != '\n') {

i++;

}

if (line[i] == '\n') {

continue;

}

j = 0;

while (!isspace(line[i]) && line[i] != '\n') {

tmp[j++] = line[i++];

}

tmp[j] = '\0';

while (isspace(line[i]) && line[i] != '\n') {

i++;

}

if (line[i] == '\n') {

continue;

}

j = 0;

while (!isspace(line[i]) && line[i] != '\n') {

tmp2[j++] = line[i++];

}

tmp2[j] = '\0';

if ((ptr = (address *) malloc(sizeof(address))) == NULL) {

fprintf(stderr, "Error: cannot allocate memory %zu\n", sizeof(address));

exit(3);

}

ptr->port = -1;

strcpy((char *) ptr->ip, (char *) tmp);

strcpy((char *) ptr->netmask, (char *) tmp2);

insert_bottom(&head, ptr);

}

for (p = head.fp; p != &head; p = p->fp) {

printf("ip = %s net = %s\n", p->ip, p->netmask);

}

if (fclose(fp) == EOF) {

fprintf(stderr, "Error: cannot close file %s\n", argv);

exit(4);

}

void exit_config(void)

{

address *p = head.fp, *prev;

while (p != &head) {

printf("ip = %s net = %s\n", p->ip, p->netmask);

prev = p;

p = p->fp;

free(prev);

}

void insert_use(address *p)

{

address *ap;

if (use.fp == NULL) {

use.fp = p;

} else {

for (ap = use.fp; ap->fp != NULL; ap = ap->fp)

;

ap->fp = p;

}

void delete_use(int port)

{

address *ap = &use, *p;

for (; ap->fp != NULL && ap->fp->port != port; ap = ap->fp)

;

if (ap->fp == NULL) {

fprintf(stderr, "Error: cannot delete_use() with port %d\n", port);

} else {

printf("delete_use() with port %d\n", port);

p = ap->fp;

ap->fp = p->fp;

p->port = -1;

insert_bottom(&head, p);

}

address *delete_top(address *h)

{

h->bp->fp = h->fp;

h->fp->bp = h->bp;

h->fp = h->bp = NULL;

return h;

}

void func_exit(void)

{

/* do nothing but go to exit. */

}

void func_ip(void)

{

address *ap = head.fp;

int i;

for (i = 0, ap = head.fp; ap != &head; i++, ap = ap->fp) {

printf("IP: %s Netmask: %s\n", ap->ip, ap->netmask);

}

if (i == 0) {

printf("No allocatable IP address\n");

}

void func_timeout(void)

{

gettimeofday(&tv, NULL);

printf("CurrentTime: %s\n", ctime((time_t *) &tv));

printf("TimeoutTime: %s\n", ctime((time_t *) &to));

}

void func_use(void)

{

address *ap;

int i;

for (i = 0, ap = use.fp; ap != NULL; i++, ap = ap->fp) {

printf("IP: %s Netmask: %s\n", ap->ip, ap->netmask);

}

if (i == 0) {

printf("No allocatable IP address\n");

}

void sigalrm_handler(int signal)

{

alrmflag++;

}

int allocate_ip(void)

{

address *ap = &head;

if (ap->fp == &head) {

return 0;

} else {

return 1;

}

int search_port(int port)

{

address *ap;

for (ap = head.fp; ap != &head; ap = ap->fp) {

if (ap->port == port) {

return 1;

}

return 0;

}

int main(int argc, char *argv[])

{

int sock;

int port;

int status;

int msgtype;

struct sockaddr_in serverAddr;

struct sockaddr_in clientAddr;

int addrLen, n;

char pBuf[BUFSIZE];

fd_set fds, readfds;

message msg;

address *add;

if (argc != 2) {

fprintf(stderr, "Error: %s [config_file]\n", argv[0]);

exit(1);

}

init_config(argv[1]);

if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {

perror("socket");

exit(2);

}

memset((char *) &serverAddr, 0, sizeof(serverAddr));

serverAddr.sin_family = AF_INET;

serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);

serverAddr.sin_port = htons(PORT);

if (bind(sock, (struct sockaddr *) &serverAddr, sizeof(serverAddr)) < 0) {

perror("bind");

exit(3);

}

FD_ZERO(&readfds);

FD_SET(0, &readfds);

FD_SET(sock, &readfds);

status = STAT_WAIT_DISCOVER;

printf("\tstatus: STAT_WAIT_DISCOVER\n");

signal(SIGALRM, sigalrm_handler);

value.it_value.tv_usec = USETIME_USEC;

value.it_value.tv_sec = USETIME_SEC;

value.it_interval.tv_usec = USETIME_USEC;

value.it_interval.tv_sec = USETIME_SEC;

setitimer(ITIMER_REAL, NULL, &ovalue);

while (true) {

memcpy(&fds, &readfds, sizeof(fd_set));

addrLen = sizeof(clientAddr);

if (select(INT_MAX, &fds, NULL, NULL, NULL) < 0) {

if (alrmflag > 0) {

alrmflag = 0;

printf("Timeout\n");

setitimer(ITIMER_REAL, &ovalue, NULL);

delete_use(port);

status = STAT_WAIT_DISCOVER;

printf("\tstatus: STAT_WAIT_DISCOVER\n");

} else {

perror("select");

exit(4);

}

if (FD_ISSET(0, &fds)) {

if ((n = read(0, pBuf, BUFSIZE)) > 0) {

pBuf[n - 1] = '\0';

printf("Execute command: %s\n", pBuf);

command(NKEYS, pBuf, cmd_tbl);

if (!strncmp(pBuf, EXIT_STR, strlen(EXIT_STR))) {

break;

}

continue;

}

if (FD_ISSET(sock, &fds)) {

if ((n = recvfrom(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &clientAddr,

(socklen_t *) &addrLen)) < 0) {

perror("recvfrom");

break;

}

} else {

fprintf(stderr, "Error: unexpected message received\n");

continue;

}

port = ntohs(clientAddr.sin_port);

printf("Client IP: %s\n", inet_ntoa(clientAddr.sin_addr));

printf("port %d\n", port);

msgtype = msg.type;

if (msgtype == RELEASE) {

delete_use(port);

msg.ip[0] = '\0';

setitimer(ITIMER_REAL, &ovalue, NULL);

continue;

}

if (msg.code == 11) {

status = STAT_WAIT_REQUEST;

printf("\tstatus: STAT_WAIT_REQUEST\n");

}

switch (status) {

case STAT_WAIT_DISCOVER:

if (msgtype == DHCPDISCOVER) {

printf("receive msgtype: DHCPDISCOVER\n");

if (allocate_ip()) {

printf("find IP address %s\n", head.fp->ip);

msg.type = DHCPOFFER;

msg.code = 0;

printf("send msgtype: DHCPOFFER\n");

} else {

fprintf(stderr, "Error: empty IP address\n");

msg.code = 129;

}

if (sendto(sock, &msg, n, 0, (struct sockaddr *) &clientAddr, addrLen) != n) {

perror("sendto");

exit(5);

}

status = STAT_WAIT_REQUEST;

printf("\tstatus: STAT_WAIT_REQUEST\n");

} else {

fprintf(stderr, "Error: receive %d not %d\n", msgtype, DHCPDISCOVER);

}

break;

case STAT_WAIT_REQUEST:

if (msgtype == DHCPREQUEST) {

printf("receive msgtype: DHCPREQUEST\n");

if (msg.code == 10 && allocate_ip()) {

add = delete_top(head.fp);

add->port = port;

insert_use(add);

strcpy((char *) msg.ip, (char *) add->ip);

strcpy((char *) msg.netmask, (char *) add->netmask);

msg.type = DHCPACK;

msg.code = 0;

msg.time_to_live = USETIME_SEC;

printf("Client IP address %s\n", inet_ntoa(clientAddr.sin_addr));

printf("allocated IP address %s\n", add->ip);

printf("allocated Netmask %s\n", add->netmask);

gettimeofday(&tv, NULL);

printf("CurrentTime: %s", ctime((time_t *) &tv));

to.tv_sec = tv.tv_sec + msg.time_to_live;

to.tv_usec = tv.tv_usec + USETIME_USEC;

printf("TimeoutTime: %s", ctime((time_t *) &to));

setitimer(ITIMER_REAL, &value, NULL);

printf("send msgtype: DHCPACK\n");

} else if (msg.code == 11) {

msg.code = 12;

printf("Client IP address %s\n", inet_ntoa(clientAddr.sin_addr));

printf("continue IP address %s\n", add->ip);

printf("continue Netmask %s\n", add->netmask);

gettimeofday(&tv, NULL);

printf("CurrentTime: %s", ctime((time_t *) &tv));

to.tv_sec = tv.tv_sec + msg.time_to_live;

to.tv_usec = tv.tv_usec + USETIME_USEC;

printf("TimeoutTime: %s", ctime((time_t *) &to));

setitimer(ITIMER_REAL, &value, NULL);

printf("Success continue IP address\n");

} else {

fprintf(stderr, "Error: cannot allocate IP address\n");

msg.code = 130;

}

if (sendto(sock, &msg, sizeof(message), 0,

(struct sockaddr *) &clientAddr, sizeof(serverAddr)) != n) {

perror("sendto");

exit(6);

}

status = STAT_WAIT_DISCOVER;

printf("\tstatus: STAT_WAIT_DISCOVER\n");

} else {

fprintf(stderr, "Error: receive %d not %d\n", msgtype, DHCPREQUEST);

status = STAT_WAIT_DISCOVER;

printf("\tstatus: STAT_WAIT_DISCOVER\n");

}

break;

}

if (close(sock) == -1) {

perror("close");

exit(7);

}

exit_config();

return 0;

}

疑似DHCPクライアント・サーバの実行方法

疑似DHCPクライアント・サーバの実行方法を紹介します．

クライアント・サーバはそれぞれ実行中に以下のコマンドを実行できます．

クライアント
- quit：クライアントの実行をIPアドレスを解放せずに終了する
- re：IPアドレスを解放する
- to：現在の時刻とタイムアウト時刻を表示する
サーバ
- ip：割り当て可能なIPアドレスを先頭から順に表示する
- to：現在の時刻とタイムアウト時刻を表示する
- use：現在使用しているIPアドレスを表示する

config.txtの中身は以下になります．

$ cat config.txt 
192.168.10.1    255.255.252.0
192.168.10.2    255.255.252.0
192.168.10.3    255.255.252.0
192.168.10.4    255.255.252.0
192.168.10.5    255.255.252.0

$ cat config.txt

192.168.10.1 255.255.252.0

192.168.10.2 255.255.252.0

192.168.10.3 255.255.252.0

192.168.10.4 255.255.252.0

192.168.10.5 255.255.252.0

疑似DHCPクライアント・サーバの実行方法は以下になります．

まずはサーバを引数config.txtをつけて実行します．

$ ./mydhcp_server config.txt 
ip = 192.168.10.1 net = 255.255.252.0
ip = 192.168.10.2 net = 255.255.252.0
ip = 192.168.10.3 net = 255.255.252.0
ip = 192.168.10.4 net = 255.255.252.0
ip = 192.168.10.5 net = 255.255.252.0
        status: STAT_WAIT_DISCOVER

$ ./mydhcp_server config.txt

ip = 192.168.10.1 net = 255.255.252.0

ip = 192.168.10.2 net = 255.255.252.0

ip = 192.168.10.3 net = 255.255.252.0

ip = 192.168.10.4 net = 255.255.252.0

ip = 192.168.10.5 net = 255.255.252.0

status: STAT_WAIT_DISCOVER

次に，クライアントを引数localhostをつけて実行します．

そうするとクライアントがDHCPのアドレス192.168.10.1を取得します．

$ ./mydhcp_client localhost
        status: STAT_WAIT_OFFER
Server IP: 127.0.0.1
receive msgtype: DHCPOFFER
send msgtype: DHCPREQUEST
        status: STAT_WAIT_ACK
Server IP: 127.0.0.1
receive msgtype: DHCPACK
IP: 192.168.10.1 netmask: 255.255.252.0
CurrentTime: Mon Jul 11 19:58:05 2022
TimeoutTime: Mon Jul 11 19:58:35 2022
        status: STAT_BOUND
Request continue IP address 192.168.10.1
send msgtype: DHCPREQUEST
Success contniue IP address 192.168.10.1
CurrentTime: Mon Jul 11 19:58:20 2022
TimeoutTime: Mon Jul 11 19:58:50 2022
...

$ ./mydhcp_client localhost

status: STAT_WAIT_OFFER

Server IP: 127.0.0.1

receive msgtype: DHCPOFFER

send msgtype: DHCPREQUEST

status: STAT_WAIT_ACK

Server IP: 127.0.0.1

receive msgtype: DHCPACK

IP: 192.168.10.1 netmask: 255.255.252.0

CurrentTime: Mon Jul 11 19:58:05 2022

TimeoutTime: Mon Jul 11 19:58:35 2022

status: STAT_BOUND

Request continue IP address 192.168.10.1

send msgtype: DHCPREQUEST

Success contniue IP address 192.168.10.1

CurrentTime: Mon Jul 11 19:58:20 2022

TimeoutTime: Mon Jul 11 19:58:50 2022

...

サーバはクライアントに192.168.10.1のIPアドレス，255.255.252.0のネットマスクを割り当てたことがわかります．

$ ./mydhcp_server config.txt
ip = 192.168.10.1 net = 255.255.252.0
ip = 192.168.10.2 net = 255.255.252.0
ip = 192.168.10.3 net = 255.255.252.0
ip = 192.168.10.4 net = 255.255.252.0
ip = 192.168.10.5 net = 255.255.252.0
        status: STAT_WAIT_DISCOVER
Client IP: 127.0.0.1
port 55420
receive msgtype: DHCPDISCOVER
find IP address 192.168.10.1
send msgtype: DHCPOFFER
        status: STAT_WAIT_REQUEST
Client IP: 127.0.0.1
port 55420
receive msgtype: DHCPREQUEST
Client IP address 127.0.0.1
allocated IP address 192.168.10.1
allocated Netmask 255.255.252.0
CurrentTime: Mon Jul 11 20:01:43 2022
TimeoutTime: Mon Jul 11 20:02:13 2022
send msgtype: DHCPACK
        status: STAT_WAIT_DISCOVER

$ ./mydhcp_server config.txt

ip = 192.168.10.1 net = 255.255.252.0

ip = 192.168.10.2 net = 255.255.252.0

ip = 192.168.10.3 net = 255.255.252.0

ip = 192.168.10.4 net = 255.255.252.0

ip = 192.168.10.5 net = 255.255.252.0

status: STAT_WAIT_DISCOVER

Client IP: 127.0.0.1

port 55420

receive msgtype: DHCPDISCOVER

find IP address 192.168.10.1

send msgtype: DHCPOFFER

status: STAT_WAIT_REQUEST

Client IP: 127.0.0.1

port 55420

receive msgtype: DHCPREQUEST

Client IP address 127.0.0.1

allocated IP address 192.168.10.1

allocated Netmask 255.255.252.0

CurrentTime: Mon Jul 11 20:01:43 2022

TimeoutTime: Mon Jul 11 20:02:13 2022

send msgtype: DHCPACK

status: STAT_WAIT_DISCOVER

まとめ

C言語で疑似DHCPクライアント・サーバを紹介しました．

疑似DHCPのコードを読んでDHCPの理解を深めましょう！

挑戦したいあなたは，独自機能を追加してみましょう！

C言語を独学で習得することは難しいです．

私にC言語の無料相談をしたいあなたは，公式LINE「ChishiroのC言語」の友だち追加をお願い致します．

私のキャパシティもあり，一定数に達したら終了しますので，今すぐ追加しましょう！

: 元東大教員がおすすめするC言語を学べるオンラインプログラミングスクール5社

こういった悩みにお答えします．こういった私が解説していきます．私が大学の授業で初めてC言語を勉強した時は全然できませんでしたが，先生やTA，友人に相談しながら一生懸命C言語を勉強してできるようにな ...

続きを見る

【C言語】疑似DHCPクライアント・サーバ

元東大教員がおすすめするC言語を学べるオンラインプログラミングスクール5社

疑似DHCPクライアント・サーバ

【C言語】INETドメイン/UNIXドメインソケット通信によるネットワークプログラミング【TCP，UDP】

【C言語】select/pselect/poll/ppoll/epoll関数の違い

疑似DHCPクライアント・サーバのコード

疑似DHCPクライアント・サーバの実行方法

まとめ

元東大教員がおすすめするC言語を学べるオンラインプログラミングスクール5社