#include <stdio.h>
#include <string.h>
#include <unistd.h>

struct string {
  char   *s;
  size_t  size;
  size_t  len;
};

void
string_append(struct string *str, char c)
{
  if (str->len < str->size) {
    str->s[str->len++] = c;
  }
}

int
string_cmp(struct string *a, char *b, size_t blen)
{
  if (a->len > blen) {
    return 1;
  } else if (a->len < blen) {
    return -1;
  } else {
    return memcmp(a->s, b, blen);
  }
}

void
string_cpy(struct string *dst, struct string *src)
{
  if (dst->size < src->len) {
    dst->len = dst->size;
  } else {
    dst->len = src->len;
  }
  memcpy(dst->s, src->s, dst->len);
}

char
tonum(int c)
{
  if ((c >= '0') && (c <= '9')) {
    return c - '0';
  }
  if ((c >= 'a') && (c <= 'f')) {
    return 10 + c - 'a';
  }
  if ((c >= 'A') && (c <= 'F')) {
    return 10 + c - 'A';
  }
  return 0;
}

char
read_hex(FILE *f)
{
  int  a   = fgetc(f);
  int  b   = fgetc(f);

  return tonum(a)*16 + tonum(b);
}

/* Read a key or a value.  Since & and = aren't supposed to appear
   outside of boundaries, we can use the same function for both.
*/
int
read_item(FILE *f, struct string *str)
{
  int c;

  while (1) {
    c = fgetc(f);
    switch (c) {
      case EOF:
        return 0;
        break;
      case '=':
      case '&':
        return 1;
        break;
      case '%':
        string_append(str, read_hex(f));
        break;
      default:
        string_append(str, c);
        break;
    }
  }
}

int
read_pair(FILE *f, struct string *key, struct string *val)
{
  if (! read_item(f, key)) {
    return 0;
  }
  return read_item(f, val);
}

#define new_string(name, size)                  \
  char _##name[size];                           \
  struct string name = {_##name, size, 0 }

int
main(int argc, char *argv[])
{
  int sensor[10][4];

  new_string(key, 20);
  new_string(val, 8192);
  new_string(name, 20);
  new_string(author, 20);

  printf("Content-type: text/plain\n\n");

  while (! feof(stdin)) {
    read_pair(stdin, &key, &val);
    write(1, key.s, key.len);
    write(1, "=", 1);
    write(1, val.s, val.len);
    write(1, "\n", 1);
  }

  return 0;
}