Bencode to JSON converter

be2json.c

/* converts Bencoded data on stdin to JSON on stdout */

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

int pos = 0;
int c;
char stack[1024], *sp = stack;

void die() {
    fflush(stdout);
    fprintf(stderr, "\nparse error at position %d: ", pos);
    if (c == EOF) 
        fputs("got EOF\n", stderr);
    else
        fprintf(stderr, "found '%c'\n", (char)c);
    exit (1);
}

static inline int chomp() {
    pos++;
    c = getchar();
    return c != EOF;
}

static inline void dump_int() {
    int st = 0;

    while (chomp()) {
        if (isdigit(c)) {
            st = 2;
            putchar(c);
        } else if (c == 'e' && st == 2) {
            return;
        } else if (c == '-' && st == 0) {
            st = 1;
            putchar(c);
        } else {
            die();
        }
    }
}


static inline void dump_str(int len) {
    int st = 0;

    len -= '0';
    putchar('"');
    while (chomp()) {
        if (st == 0) {
            if (isdigit(c)) {
                len = 10 * len + c - '0';
            } else if (c == ':') {
                st = 1;
                if (len == 0) break;
            } else die();
        } else {
            len--;
            if (c == '"' || c == '\\') {
                putchar('\\');
            }
            putchar(c);
            if (len == 0) break;
        }
    }
    if (len > 0) die();
    putchar('"');
}

static void struct_hlp() {
    switch (*sp) {
        case 'd':
            *sp = 'e';
            break;
        case 'e':
            putchar(':');
            *sp = 'f';
            break;
        case 'f':
            putchar(',');
            *sp = 'e';
            break;
        case 'l':
            *sp = 'm';
            break;
        case 'm':
            putchar(',');
            break;
    }
}

static inline void push(char ch) {
    if (sp >= stack + sizeof(stack) - 1) {
        fputs("stack overflow\n", stderr);
        die();
    }
    *++sp = ch;
}

int main(int ac, char *av[]) {
    *sp = 'i';
    while (chomp()) {
        switch((char)c) {
            case 'd':
                struct_hlp();
                putchar('{');
                push((char) c);
                break;
            case 'l':
                struct_hlp();
                putchar('[');
                push((char) c);
                break;
            case 'i':
                struct_hlp();
                dump_int();
                break;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                struct_hlp();
                dump_str(c);
                break;
            case 'e':
                if (*sp == 'l' || *sp == 'm') {
                    putchar(']');
                    sp--;
                } else if (*sp == 'd' || *sp == 'f') {
                    putchar('}');
                    sp--;
                } else die();
                if (sp < stack) die();
                break;
            case '\n':
                break;
            default:
                die();
                break;
        }
    }
    if (sp != stack) die();
    putchar('\n');
    return 0;
}