ossp/firewall_parser.c

//
// Created by akp on 05/10/23.
//
#pragma once

#include "firewall_types.c"
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

enum ParseState {
    ParseState_ip1,
    ParseState_ip2,
    ParseState_port1,
    ParseState_port2,
};

// parse_ip parses an IP address line starting at startptr. Returns the ending
// position of the pointer in line. Returns NULL on failure.
char *parse_ip(char *startptr, struct IP *ip) {
    char *endptr = startptr;

    for (int i = 0; i < 4; i += 1) {
        long n = strtol(endptr, &endptr, 10);
        if (n > UCHAR_MAX || n < 0)
            return NULL;

        ip->val[i] = n;

        if (i != 3) {
            if (*endptr != '.' || *(endptr + 1) == '\0') {
                return NULL;
            } else {
                endptr += 1;
            }
        }
    }

    endptr += 1;

    return endptr;
}

// parse_port parses a port starting at startptr. Returns the ending position of
// the pointer in line. Returns NULL on failure.
char *parse_port(char *startptr, Port *port) {
    char *end;
    long n = strtol(startptr, &end, 10);
    if (n > USHRT_MAX || n < 0)
        return NULL;
    *port = n;
    return end;
}

// parse_rule parses a rule out a string, line. The result is saved to result,
// which must be allocated by the caller. The return value is the ending
// position of the rule in the string.
char *parse_rule(char line[], struct Rule *result) {
    enum ParseState state = ParseState_ip1;

    result->ip.end = NULL;
    result->port.end = NULL;

    int ptr = 0;
    for (;;) {
        switch (state) {
        case ParseState_ip1: {
            char *end = parse_ip(line + ptr, &result->ip.start);
            if (end == NULL) {
                goto fail;
            }
            ptr = (int)(end - line);

            switch (line[ptr - 1]) {
            case '-':
                state = ParseState_ip2;
                break;
            case ' ':
                state = ParseState_port1;
                break;
            default:
                goto fail;
            }

            break;
        }
        case ParseState_ip2: {
            result->ip.end = (struct IP *)malloc(sizeof(struct IP));

            char *end = parse_ip(line + ptr, result->ip.end);
            if (end == NULL) {
                goto fail;
            }
            ptr = (int)(end - line);

            state = ParseState_port1;
            break;
        }
        case ParseState_port1: {
            char *end = parse_port(line + ptr, &result->port.start);
            if (end == NULL) {
                goto fail;
            }
            ptr = (int)(end - line);

            if (line[ptr] == '-') {
                ptr += 1;
                state = ParseState_port2;
            } else {
                goto finished_parsing;
            }

            break;
        }
        case ParseState_port2: {
            result->port.end = (Port *)malloc(sizeof(Port));

            char *end = parse_port(line + ptr, result->port.end);
            if (end == NULL) {
                goto fail;
            }
            ptr = (int)(end - line);

            goto finished_parsing;
        }
        }
    }

finished_parsing:

    if (result->ip.end != NULL) {
        if (compare_ip(&result->ip.start, result->ip.end) == 1) {
            goto fail;
        }
    }

    if (result->port.end != NULL) {
        if (akpa_numcmp(result->port.start, *result->port.end) == 1) {
            goto fail;
        }
    }

    return line + ptr;

fail:
    return NULL;
}

#define MAX_RULES 128

// parse_file parses a set of rules from the file named fname. The memory used
// by the return value should be freed by the caller. If the return value is
// NULL, an error was encoutered and echo'd.
struct Rule **parse_file(char fname[], size_t *num_parsed_rules) {
    int is_stdin = strcmp(fname, "--") == 0;

    FILE *fp = NULL;

    if (is_stdin == 1) {
        fp = stdin;
    } else {
        fp = fopen(fname, "r");
        if (fp == NULL) {
            perror("Read input file");
            return NULL;
        }
    }

    struct Rule **parsed_rules = malloc(sizeof(struct Rule *) * MAX_RULES);
    *num_parsed_rules = 0;

    char *line = NULL;
    size_t line_size = 0;
    while (getline(&line, &line_size, fp) != -1) {
        if (*num_parsed_rules == MAX_RULES) {
            fprintf(stderr, "Too many rules\n");
            return NULL;
        }
        struct Rule *rule = (struct Rule *)malloc(sizeof(struct Rule));
        char *endptr = parse_rule(line, rule);
        if (endptr == NULL || *endptr != '\n') {
            fprintf(stderr, "Ill formed rule: %s\n", line);
            return NULL;
        }
        parsed_rules[*num_parsed_rules] = rule;
        (*num_parsed_rules) += 1;
    }
    if (!feof(fp)) { // When we get here, getline has always returned -1 but may
                     // or may not have reached EOF.
        // If it hasn't reached EOF, an error was thrown.
        perror("Read line");
        return NULL;
    }
    free(line);

    if (is_stdin != 1) {
        if (fclose(fp) != 0) {
            perror("Close input file");
            return NULL;
        }
    }

    return parsed_rules;
}