🔢 Parse `nmap -p` style port range list string input into a linked list..

portrange.c

/*
 * Parse `nmap -p` style port range list string input into a linked list..
 *
 * Written By: Derek Callaway [decal (AT) sdf {D0T} org]
 * Compile As: gcc -O2 -Wall -pedantic -o portrange portrange.c
 * Updated On: Fri Apr 27 01:14:29 DST 2018
 */

#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
#include<sysexits.h>
#include<string.h>
#include<ctype.h>
#include<error.h>
#include<errno.h>
#include<assert.h>

/* Undefining this causes assert(3) to perform conditional testing */
#define NDEBUG 1

/* This line is required for output */
static const bool is_debug = 1;

/* Port number ranges linked list; single port has equal lo and hi values */
typedef struct port_numbers {
  unsigned short portlo;
  unsigned short porthi;
  struct port_numbers *nextpn;
} PORT_NUMBERS, *PPORT_NUMBERS, **PPPORT_NUMBERS;

/* Count the total number of ports */
size_t count_ports(const PPORT_NUMBERS pnums) {
  register PPORT_NUMBERS pport = pnums;
  register size_t count = -1;
  
  assert(pnums);

  for(pport = pnums;pport;pport = pport->nextpn) {
    count += pport->porthi - pport->portlo;

    count++;
  }

  return count;
}

/* Exit if a library function gives an erroneous return value */
static void fatal(const char *s) {
  perror(s);

  exit(EXIT_FAILURE);
}

/* Primary parsing function of port range list string input */
PORT_NUMBERS *parse_ports(const char *portstr) {
  const char *current_range = portstr;
  char *endptr = NULL;
  long int rangestart = 0, rangeend = 0;

  assert(portstr);

  PORT_NUMBERS *portp = calloc(1, sizeof *portp);

  if(!portp)
    error_at_line(1, errno, __FILE__, __LINE__, "calloc: %s", strerror(errno));

  PORT_NUMBERS *pnret = portp;

  do {
        while(*current_range && isspace((int) (unsigned char) *current_range))
      current_range++;

    if(isdigit((int) (unsigned char) *current_range)) {
      rangestart = strtol(current_range, &endptr, 10);

      if(rangestart == ERANGE)
        error_at_line(1, errno, __FILE__, __LINE__, "strtol: %s", strerror(errno));

      if (rangestart < 0 || rangestart > 65535)
        fatal("Parse error: Ports must be between 0 and 65535 inclusive");

      current_range = endptr;

      while(isspace((int)(unsigned char)*current_range))
        current_range++;
    } else
      fatal("Parse error: An example of proper portlist form is \"21-25,53,80\"");

    /* Now I have a rangestart, time to go after rangeend */
    if (!*current_range || *current_range == ',') {
      /* Single port specification */
      rangeend = rangestart;
    } else if (*current_range == '-') {
      current_range++;

      if (isdigit((int) (unsigned char) *current_range)) {
        rangeend = strtol(current_range, &endptr, 10);

        if(rangeend == ERANGE)
          error_at_line(1, errno, __FILE__, __LINE__, "strtol: %s", strerror(errno));

        if (rangeend < 0 || rangeend > 65535 || rangeend < rangestart)
          fatal("Parse error: Ports must be between 0 and 65535 inclusive");
        current_range = endptr;
      } else
        fatal("Parse error: An example of proper portlist form is \"21-25,53,80\"");
    } else
      fatal("Parse error: An example of proper portlist form is \"21-25,53,80\"");

    /* Now I have a rangestart and a rangeend, so I can add these ports */
    portp->portlo = (unsigned short)rangestart;

    while(rangestart <= rangeend)
      rangestart++;

    portp->porthi = (unsigned short)rangeend;
    portp->nextpn = calloc(1, sizeof *(portp->nextpn));

    if(!portp->nextpn)
      error_at_line(1, errno, __FILE__, __LINE__, "calloc: %s", strerror(errno));

    portp = portp->nextpn;

    /* Find the next range */
    while(isspace((int) (unsigned char) *current_range))
      current_range++;

    if (*current_range && *current_range != ',')
      fatal("Parse error: An example of proper portlist form is \"21-25,53,80\"");

    if (*current_range == ',')
      current_range++;
  } while(current_range && *current_range);

  return pnret;
}

/* Program entry point */
int main(int argc, char *argv[], char *envp[]) {
  register size_t acnt = 0;

  /* Show usage when lacking arguments */
  if(argc < 2) {
    fprintf(stderr, "usage: %s PORTSTR\n", *argv);
    fputs("  PORTSTR  port range string\n", stderr);

    exit(EX_USAGE);
  }

  /* Pass command-line argument to parsing function */
  PORT_NUMBERS *const pnms = parse_ports(argv[1]);

  register const PORT_NUMBERS *pptr = pnms;

  /* Display results */
  while(pptr) {
    if(is_debug)
      fprintf(stderr, "portlo: %hu porthi: %hu\n", pptr->portlo, pptr->porthi);

    pptr = pptr->nextpn;
  }

  acnt += count_ports(pnms);

  if(is_debug)
    fprintf(stderr, "count: %lu\n", acnt);

  /* Exit process gracefully */
  exit(EXIT_SUCCESS);
}