bm.c

/* START OF THIS CODE WAS OBTAINED FROM
  
https://www.cs.cmu.edu/afs/cs/academic/class/15213-f99/www/class26/udpserver.c
*/

/* 
 * udpserver.c - A simple UDP echo server 
 * usage: udpserver <port>
 */

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

#include "bm.h"

typedef unsigned char byte;

const byte DHCP_OP_BOOTREQUEST = 1;
const byte DHCP_OP_BOOTREPLY = 2;
const byte DHCP_FLAGS_BROADCAST[2] = { 0x80, 0x00 };

struct DHCP_DISCOVERY_MESSAGE {
  byte Op;
  byte Htype;
  byte Hlen;
  byte Hops;
  byte XID[4];
  byte Sec[2];
  byte Flags[2];
  byte CIAddr[4];
  byte YIAddr[4];
  byte SIAddr[4];
  byte GIAddr[4];
  byte CHAddr[16];
  byte SName[64];
  byte File[128];
  byte Options[];
};

const byte DHCP_OPTIONS_MAGIC[4] = { 99, 130, 83, 99 };
const byte DHCP_OPTION_PAD_CODE = 0x00;
const byte DHCP_OPTION_END_CODE = 0xff;

struct DHCP_OPTION {
  byte Code;
  byte Len;
  byte Data[];
};


const byte TFTP_OPCODE_RD_REQ[2] = { 0x01, 0x00 };
const byte TFTP_OPCODE_WR_REQ[2] = { 0x02, 0x00 };
const byte TFTP_OPCODE_DATA[2]   = { 0x03, 0x00 };
const byte TFTP_OPCODE_ACK[2]    = { 0x04, 0x00 };
const byte TFTP_OPCODE_ERROR[2]  = { 0x05, 0x00 };

struct TFTP_ERROR {
  const byte ErrorCode[2];
  char  ErrorString[80];
} TFPT_ERRORS[] = {
  { { 0x0, 0x0 }, "Not defined, see error message (if any)." },
  { { 0x1, 0x0 }, "File not found." },
  { { 0x2, 0x0 }, "Access violation"},
  { { 0x3, 0x0 }, "Disk full or allocation exceeded" },
  { { 0x4, 0x0 }, "Illegal TFTP operation" },
  { { 0x5, 0x0 }, "Unknown transfer ID" },
  { { 0x6, 0x0 }, "File already exists" },
  { { 0x7, 0x0 }, "No such user" }
};

struct TFTP_HEADER {
  byte OpCode[2];
};

struct TFTP_REQUEST_PACKET {
  struct TFTP_HEADER Header;
  byte   FileModeOptions[];
  // byte FileName[]; 0 terminated byte array
  // byte Mode[]; 0 terminated byte array
  // byte Options[]; 0 terminated byte array
};

struct TFTP_DATA_PACKET {
  struct TFTP_HEADER Header;
  byte BlockNumber[2];
  byte Data[];
};

struct TFTP_ACK_PACKET {
  struct TFTP_HEADER Header;
  byte BlockNumber[2];
};

struct TFTP_ERROR_PACKET {
  struct TFTP_HEADER Header;
  byte Error[2];
  byte ErrMsg[];
};

struct TFTP_OPTION_ACK_PACKET {
  struct TFTP_HEADER Header;
  byte Options[];
};



/*
 * error - wrapper for perror
 *. WARNING WILL NEED TO PROVIDE THIS IF YOU ARE 
 *. PORTING
 */
void
error(char *msg) {
  perror(msg);
  exit(1);
}


void
asciiDump(unsigned char *s, int len)
{
  unsigned char c;
  for (int i=0; i<len; i++) {
    c=s[i];
    if (c>=' ' && c<='~') printf("%c", c);
    else printf(".");
  }
}

int 
hexDump(unsigned char *start, int bytes) 
{
  int j;
  for (j=0; j<bytes;) {
    int offset=j*16;
    int end=((bytes-j) < 16) ? bytes-j : 16;
    printf("%08x:  ", offset);
    for (int i=0;i<end;i++) {
      printf("%02x  ", start[offset+i]);
    }
    for (int i=end;i<16;i++) printf("    ");
    printf("|");
    for (int i=0;i<end;i++) {
      unsigned char c=start[offset+i];
      if (c>=' ' && c<='~') printf("%c", c);
      else printf(".");
    }
    printf("|\n");
    j+=end;
  }
  return j;
}

/*
  There are several special addresses: INADDR_LOOPBACK (127.0.0.1) always refers to the local
  host via  the  loopback  device;  INADDR_ANY  (0.0.0.0)  means  any  address  for  binding;
  INADDR_BROADCAST  (255.255.255.255)  means  any  host  and  has  the same effect on bind as
  INADDR_ANY for historical reasons.
*/
int
openUDPSocket(uint32_t myaddr, unsigned short portno, int broadcast)
{
  int sockfd;
  int optval = 1;
  struct sockaddr_in addr;
  
  sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  if (sockfd < 0) 
    error("ERROR opening socket");

  if (broadcast) {
    /* Set socket to allow broadcast */
    if (setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, (void *)&optval, 
		   sizeof(optval)) < 0)
      error("setsockopt(SO_BROADCAST) failed");
  }
  
  /* setsockopt: Handy debugging trick that lets 
   * us rerun the server immediately after we kill it; 
   * otherwise we have to wait about 20 secs. 
   * Eliminates "ERROR on binding: Address already in use" error. 
   */
  setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, 
	     (const void *)&optval , sizeof(int));

  /*
   * build the server's Internet address
   */
  bzero((char *) &addr, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_addr.s_addr = htonl(myaddr);
  addr.sin_port = htons(portno);

  /* 
   * bind: associate the parent socket with a port 
   */
  if (bind(sockfd, (struct sockaddr *) &addr, 
	   sizeof(addr)) < 0) 
    error("ERROR on binding");

  return sockfd;
}

int
processDHCPOption(struct DHCP_OPTION *o)
{
  
  if (o->Code == DHCP_OPTION_PAD_CODE){printf("\tCode: 0x00 Pad\n"); return 1;}
  if (o->Code == DHCP_OPTION_END_CODE){printf("\tCode: 0xff End\n"); return -1;}
  printf("\tCode: 0x%02x\n\tLen: %d\n", o->Code, o->Len);
  hexDump(o->Data, o->Len);
  return (sizeof(struct DHCP_OPTION) + o->Len);
}

int
processDHCPMessage(byte *buf, int len)
{
  struct DHCP_DISCOVERY_MESSAGE *m;

  if (len < sizeof(struct DHCP_DISCOVERY_MESSAGE)) return 0;
  m = (struct DHCP_DISCOVERY_MESSAGE *) buf;

  printf(">>>> DHCP PACKET: buf:%p len:%d\n", m, len);
  printf("Op: 0x%02x\nHtype: 0x%02x\nHlen: %d\nHops: 0x%02x\n",
	 m->Op, m->Htype, m->Hlen, m->Hops);
  printf("XID: %02x%02x%02x%02x\nSec: %02x%02x\nFlags: %02x%02x\n",
	 m->XID[0],m->XID[1],m->XID[2],m->XID[3],
	 m->Sec[0],m->Sec[1],
	 m->Flags[0],m->Flags[1]);
  printf("CIAddr: %02x%02x%02x%02x\n",
	 m->CIAddr[0],m->CIAddr[1],m->CIAddr[2],m->CIAddr[3]);
  printf("YIAddr: %02x%02x%02x%02x\n",
	 m->YIAddr[0],m->YIAddr[1],m->YIAddr[2],m->YIAddr[3]);
  printf("SIAddr: %02x%02x%02x%02x\n",
	 m->SIAddr[0],m->SIAddr[1],m->SIAddr[2],m->SIAddr[3]);
  printf("GIAddr: %02x%02x%02x%02x\n",
	 m->GIAddr[0],m->GIAddr[1],m->GIAddr[2],m->GIAddr[3]);
  printf("CHAddr: %02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x\n",
	 m->CHAddr[0],m->CHAddr[1],m->CHAddr[2],m->CHAddr[3],
	 m->CHAddr[4],m->CHAddr[5],m->CHAddr[6],m->CHAddr[7],
	 m->CHAddr[8],m->CHAddr[9],m->CHAddr[10],m->CHAddr[11],
	 m->CHAddr[12],m->CHAddr[13],m->CHAddr[14],m->CHAddr[15]);
  printf("SName: ");
  asciiDump(m->SName, sizeof(m->SName));
  printf("\nFile: ");
  asciiDump(m->File, sizeof(m->File));
  printf("\n");
  
  len = len - sizeof(struct DHCP_DISCOVERY_MESSAGE);
  
  if (len > 4
      && m->Options[0] == DHCP_OPTIONS_MAGIC[0]
      && m->Options[1] == DHCP_OPTIONS_MAGIC[1]
      && m->Options[2] == DHCP_OPTIONS_MAGIC[2]
      && m->Options[3] == DHCP_OPTIONS_MAGIC[3]) {
    len = len - 4;
    int n = 4;
    struct DHCP_OPTION *o = (struct DHCP_OPTION *)(&m->Options[n]);
    printf("Options:\n");
    while (len && (n=processDHCPOption(o))) {
      if (n < 0) break;
      len = len - n;
      o = (struct DHCP_OPTION *) ((byte *)o + n);
    }
  }
  printf("<<<< DHCP PACKET\n");
#if 0
    /* 
     * sendto: echo the input back to the client 
     */
    n = sendto(bcastReplyfd, buf, strlen(buf), 0, 
	       (struct sockaddr *) &clientaddr, clientlen);
    if (n < 0) 
      error("ERROR in sendto");
#endif

  return 1;
}