hop-2012/sexpio.c

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

#include <assert.h>

#include <ucontext.h>

#include "cmsg_private.h"
#include "ref.h"
#include "sexp.h"
#include "harness.h"
#include "sexpio.h"

/* TODO: limit size of individual simple strings */
/* TODO: limit nesting of sexps */

static sexp_t *read_simple_string(IOHandle *h, cmsg_bytes_t buf) {
  int i = 0;
  sexp_t *result;

  while (1) {
    buf = iohandle_readwait(h, buf.len + 1);
    if (h->error_kind) return NULL;
    /* Don't reset i to zero: avoids scanning the beginning of the
       number repeatedly */

    while (i < buf.len) {
      if (i > 10) {
	/* More than ten digits of length prefix. We're unlikely to be
	   able to cope with anything that large. */
	h->error_kind = SEXP_ERROR_OVERFLOW;
	return NULL;
      }
      if (buf.bytes[i] == ':') {
	size_t count;
	buf.bytes[i] = '\0';
	count = atoi((char *) buf.bytes);
	iohandle_drain(h, i + 1);
	buf = iohandle_readwait(h, count);
	buf.len = count;
	result = sexp_bytes(buf);
	iohandle_drain(h, count);
	return result;
      }

      if (!isdigit(buf.bytes[i])) {
	h->error_kind = SEXP_ERROR_SYNTAX;
	return NULL;
      }

      i++;
    }
  }
}

#define CHECKH \
  if (h->error_kind) goto error;

#define READ1					\
  buf = iohandle_readwait(h, 1);		\
  CHECKH;

sexp_t *sexp_read(IOHandle *h) {
  cmsg_bytes_t buf;
  sexp_t *stack = NULL; /* held */
  sexp_t *hint = NULL; /* held */
  sexp_t *body = NULL; /* held */
  sexp_t *accumulator = NULL; /* not held */

  while (1) {
    READ1;
    switch (buf.bytes[0]) {
      case '[': {
	iohandle_drain(h, 1);
	hint = INCREF(read_simple_string(h, EMPTY_BYTES));
	CHECKH;
	READ1;
	if (buf.bytes[0] != ']') {
	  h->error_kind = SEXP_ERROR_SYNTAX;
	  goto error;
	}
	iohandle_drain(h, 1);
	body = INCREF(read_simple_string(h, EMPTY_BYTES));
	CHECKH;
	accumulator = sexp_display_hint(hint, body);
	DECREF(hint, sexp_destructor); /* these could be UNGRABs */
	DECREF(body, sexp_destructor);
	break;
      }

      case '(':
	iohandle_drain(h, 1);
	sexp_push(stack, sexp_cons(NULL, NULL));
	continue;

      case ')': {
	sexp_t *current;
	if (stack == NULL) {
	  h->error_kind = SEXP_ERROR_SYNTAX;
	  goto error;
	}
	current = sexp_pop(stack);
	iohandle_drain(h, 1);
	accumulator = INCREF(sexp_head(current));
	DECREF(current, sexp_destructor);
	UNGRAB(accumulator);
	break;
      }

      default:
	if (isspace(buf.bytes[0])) {
	  iohandle_drain(h, 1);
	  continue;
	}
	buf.len = 1; /* needed to avoid reading too much in read_simple_string */
	accumulator = read_simple_string(h, buf);
	if (h->error_kind) goto error;
	break;
    }

    if (stack == NULL) {
      return accumulator;
    } else {
      sexp_t *current = sexp_head(stack); /* not held */
      sexp_t *cell = sexp_cons(accumulator, NULL);
      if (sexp_tail(current) == NULL) {
	sexp_sethead(current, cell);
      } else {
	sexp_settail(sexp_tail(current), cell);
      }
      sexp_settail(current, cell);
    }
  }

 error:
  DECREF(stack, sexp_destructor);
  DECREF(hint, sexp_destructor);
  DECREF(body, sexp_destructor);
  return NULL;
}

void write_simple_string(IOHandle *h, sexp_t *x) {
  cmsg_bytes_t data = sexp_data(x);
  char lenstr[16];
  snprintf(lenstr, sizeof(lenstr), "%u:", (unsigned int) data.len);
  lenstr[sizeof(lenstr) - 1] = '\0';
  iohandle_write(h, cmsg_cstring_bytes(lenstr));
  iohandle_write(h, data);
}

unsigned short sexp_write(IOHandle *h, sexp_t *x) {
  sexp_t *stack = NULL; /* held */
  sexp_t *current = x;

 write1:
  if (current == NULL) {
    iohandle_write(h, cmsg_cstring_bytes("()"));
  } else {
    switch (current->kind) {
      case SEXP_BYTES:
      case SEXP_SLICE:
	write_simple_string(h, current);
	break;

      case SEXP_DISPLAY_HINT:
	iohandle_write(h, cmsg_cstring_bytes("["));
	write_simple_string(h, sexp_hint(current));
	iohandle_write(h, cmsg_cstring_bytes("]"));
	write_simple_string(h, sexp_body(current));
	break;

      case SEXP_PAIR:
	iohandle_write(h, cmsg_cstring_bytes("("));
	sexp_push(stack, current);
	break;

      default:
	die("Unknown sexp kind %d in sexp_write\n", current->kind);
    }
  }

 check_stack:
  if (stack == NULL) {
    return 0;
  }

  {
    sexp_t *cell = sexp_head(stack);
    if (cell == NULL) {
      iohandle_write(h, cmsg_cstring_bytes(")"));
      sexp_pop(stack); /* no need to worry about incref/decref: it's NULL! */
      goto check_stack;
    }

    if (sexp_pairp(cell)) {
      current = sexp_head(cell);
      sexp_sethead(stack, sexp_tail(cell));
      goto write1;
    }

    return SEXP_ERROR_SYNTAX;
  }
}