bird/lib/cbor-parser.c

/*
 *	BIRD CBOR parser
 *
 *	(c) 2024 Maria Matejka <mq@jmq.cz>
 *
 *	Can be freely distributed and used under the terms of the GNU GPL.
 */

#include "lib/birdlib.h"
#include "lib/cbor.h"

struct cbor_parser_context *
cbor_parser_new(pool *p, uint stack_max_depth)
{
  linpool *lp = lp_new(p);
  struct cbor_parser_context *ctx = lp_allocz(
      lp, sizeof *ctx + (stack_max_depth + 1) * sizeof ctx->stack_countdown[0]);

  ctx->lp = lp;
  ctx->flush = lp_save(lp);

  ctx->type = 0xff;
  ctx->stack_countdown[0] = 1;
  ctx->stack_max = stack_max_depth;

  return ctx;
}

void cbor_parser_reset(struct cbor_parser_context *ctx)
{
  lp_restore(ctx->lp, ctx->flush);
  ctx->flush = lp_save(ctx->lp);

  ctx->type = 0xff;
  ctx->target_buf = NULL;
  ctx->target_len = 0;
  ctx->error = NULL;
  ctx->partial_state = CPE_TYPE;
  ctx->partial_countdown = 0;
  ctx->stack_pos = 0;
  ctx->stack_countdown[0] = 1;
}

#define CBOR_PARSER_ERROR(...) do {		\
  ctx->error = lp_sprintf(ctx->lp, __VA_ARGS__);\
  return CPR_ERROR;				\
} while (0)

enum cbor_parse_result
cbor_parse_byte(struct cbor_parser_context *ctx, const byte bp)
{
  ctx->tflags = 0;

  switch (ctx->partial_state)
  {
    case CPE_EXIT:
      CBOR_PARSER_ERROR("Trailing byte %02x", bp);

    case CPE_ITEM_DONE:
      bug("You have to check cbor_parse_block_end() before running cbor_parse_byte()");

    case CPE_TYPE:
      /* Split the byte to type and value */
      ctx->type = bp >> 5;
      ctx->value = bp & 0x1f;

      if (ctx->type == 7)
      {
	if (ctx->value < 20)
	  CBOR_PARSER_ERROR("Unknown simple value %u", ctx->value);
	else if (ctx->value < 24)
	  ; /* false, true, null, undefined */
	else if (ctx->value < 28)
	{
	  /* Need more data */
	  ctx->partial_state = CPE_READ_INT;
	  ctx->partial_countdown = (1 << (ctx->value - 24));
	  ctx->value = 0;
	  break;
	}
	else if (ctx->value == 31)
	  ; /* break-stop */
	else
	  CBOR_PARSER_ERROR("Unknown simple value %u", ctx->value);
      }
      else
      {
	if (ctx->value < 24)
	  ; /* Immediate value, fall through */
	else if (ctx->value < 28)
	{
	  /* Need more data */
	  ctx->partial_state = CPE_READ_INT;
	  ctx->partial_countdown = (1 << (ctx->value - 24));
	  ctx->value = 0;
	  break;
	}
	else if ((ctx->value == 31) && (ctx->type >= 2) && (ctx->type <= 5))
	  /* Indefinite length, fall through */
	  ctx->tflags |= CPT_VARLEN;
	else
	  CBOR_PARSER_ERROR("Garbled additional value %u for type %u", ctx->value, ctx->type);
      }
      /* fall through */

    case CPE_READ_INT:
      if (ctx->partial_state == CPE_READ_INT)
      {
	/* Reading a network order integer */
	ctx->value <<= 8;
	ctx->value |= bp;
	if (--ctx->partial_countdown)
	  break;
      }
      /* fall through */

    case CPE_COMPLETE_INT:
      /* Some types are completely parsed, some not yet */
      switch (ctx->type)
      {
	case 0:
	case 1:
	case 7:
	  ctx->partial_state = CPE_ITEM_DONE;
	  break;

	case 2:
	case 3:
	  ctx->partial_state = CPE_READ_BYTE;
	  ctx->partial_countdown = ctx->value;
	  break;

	case 4:
	case 5:
	  if (++ctx->stack_pos >= ctx->stack_max)
	    CBOR_PARSER_ERROR("Stack too deep");

	  /* set array/map size;
	   * once for arrays, twice for maps;
	   * ~0 for indefinite, plus one for the array/map head itself */
	  ctx->stack_countdown[ctx->stack_pos] = (ctx->tflags & CPT_VARLEN) ? ~0ULL :
	    (ctx->value * (ctx->type - 3)) ;
	  ctx->partial_state = CPE_TYPE;
	  break;
      }

      /* Process the value */
      return CPR_MAJOR;

    case CPE_READ_BYTE:
      *ctx->target_buf = bp;
      ctx->target_buf++;
      if (--ctx->target_len)
	break;

      ctx->target_buf = NULL;
      ctx->partial_state = CPE_ITEM_DONE;
      return CPR_STR_END;
  }

  return CPR_MORE;
}

bool
cbor_parse_block_end(struct cbor_parser_context *ctx)
{
  if (ctx->partial_state != CPE_ITEM_DONE)
    return false;

  if (--ctx->stack_countdown[ctx->stack_pos])
  {
    ctx->partial_state = CPE_TYPE;
    return false;
  }

  if (!ctx->stack_pos--)
    ctx->partial_state = CPE_EXIT;

  return true;
}