static int mailimf_field_parse(const char * message, size_t length,
			       size_t * indx,
			       struct mailimf_field ** result)
{
  size_t cur_token;
  int type;
  struct mailimf_return * return_path;
  struct mailimf_orig_date * resent_date;
  struct mailimf_from * resent_from;
  struct mailimf_sender * resent_sender;
  struct mailimf_to* resent_to;
  struct mailimf_cc * resent_cc;
  struct mailimf_bcc * resent_bcc;
  struct mailimf_message_id * resent_msg_id;
  struct mailimf_orig_date * orig_date;
  struct mailimf_from * from;
  struct mailimf_sender * sender;
  struct mailimf_reply_to * reply_to;
  struct mailimf_to * to;
  struct mailimf_cc * cc;
  struct mailimf_bcc * bcc;
  struct mailimf_message_id * message_id;
  struct mailimf_in_reply_to * in_reply_to;
  struct mailimf_references * references;
  struct mailimf_subject * subject;
  struct mailimf_comments * comments;
  struct mailimf_keywords * keywords;
  struct mailimf_optional_field * optional_field;
  struct mailimf_field * field;
  int guessed_type;
  int r;
  int res;
  
  cur_token = * indx;

  return_path = NULL;
  resent_date = NULL;
  resent_from = NULL;
  resent_sender = NULL;
  resent_to = NULL;
  resent_cc = NULL;
  resent_bcc = NULL;
  resent_msg_id = NULL;
  orig_date = NULL;
  from = NULL;
  sender = NULL;
  reply_to = NULL;
  to = NULL;
  cc = NULL;
  bcc = NULL;
  message_id = NULL;
  in_reply_to = NULL;
  references = NULL;
  subject = NULL;
  comments = NULL;
  keywords = NULL;
  optional_field = NULL;

  guessed_type = guess_header_type(message, length, cur_token);
  type = MAILIMF_FIELD_NONE;

  switch (guessed_type) {
  case MAILIMF_FIELD_ORIG_DATE:
    r = mailimf_orig_date_parse(message, length, &cur_token,
				&orig_date);
    if (r == MAILIMF_NO_ERROR)
      type = MAILIMF_FIELD_ORIG_DATE;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_FROM:
    r = mailimf_from_parse(message, length, &cur_token,
			   &from);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_SENDER:
    r = mailimf_sender_parse(message, length, &cur_token,
			     &sender);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_REPLY_TO:
    r = mailimf_reply_to_parse(message, length, &cur_token,
			       &reply_to);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_TO:
    r = mailimf_to_parse(message, length, &cur_token,
			 &to);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_CC:
    r = mailimf_cc_parse(message, length, &cur_token,
			 &cc);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_BCC:
    r = mailimf_bcc_parse(message, length, &cur_token,
			  &bcc);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_MESSAGE_ID:
    r = mailimf_message_id_parse(message, length, &cur_token,
				 &message_id);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_IN_REPLY_TO:
    r = mailimf_in_reply_to_parse(message, length, &cur_token,
				  &in_reply_to);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_REFERENCES:
    r = mailimf_references_parse(message, length, &cur_token,
				 &references);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_SUBJECT:
    r = mailimf_subject_parse(message, length, &cur_token,
			      &subject);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_COMMENTS:
    r = mailimf_comments_parse(message, length, &cur_token,
			       &comments);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_KEYWORDS:
    r = mailimf_keywords_parse(message, length, &cur_token,
			       &keywords);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RETURN_PATH:
    r = mailimf_return_parse(message, length, &cur_token,
        &return_path);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RESENT_DATE:
    r = mailimf_resent_date_parse(message, length, &cur_token,
				  &resent_date);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RESENT_FROM:
    r = mailimf_resent_from_parse(message, length, &cur_token,
				  &resent_from);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RESENT_SENDER:
    r = mailimf_resent_sender_parse(message, length, &cur_token,
				    &resent_sender);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RESENT_TO:
    r = mailimf_resent_to_parse(message, length, &cur_token,
				&resent_to);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RESENT_CC:
    r= mailimf_resent_cc_parse(message, length, &cur_token,
			       &resent_cc);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RESENT_BCC:
    r = mailimf_resent_bcc_parse(message, length, &cur_token,
				 &resent_bcc);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  case MAILIMF_FIELD_RESENT_MSG_ID:
    r = mailimf_resent_msg_id_parse(message, length, &cur_token,
				    &resent_msg_id);
    if (r == MAILIMF_NO_ERROR)
      type = guessed_type;
    else if (r == MAILIMF_ERROR_PARSE) {
      /* do nothing */
    }
    else {
      res = r;
      goto err;
    }
    break;
  }

  if (type == MAILIMF_FIELD_NONE) {
    r = mailimf_optional_field_parse(message, length, &cur_token,
        &optional_field);
    if (r != MAILIMF_NO_ERROR) {
      res = r;
      goto err;
    }

    type = MAILIMF_FIELD_OPTIONAL_FIELD;
  }

  field = mailimf_field_new(type, return_path, resent_date,
      resent_from, resent_sender, resent_to, resent_cc, resent_bcc,
      resent_msg_id, orig_date, from, sender, reply_to, to,
      cc, bcc, message_id, in_reply_to, references,
      subject, comments, keywords, optional_field);
  if (field == NULL) {
    res = MAILIMF_ERROR_MEMORY;
    goto free_field;
  }

  * result = field;
  * indx = cur_token;

  return MAILIMF_NO_ERROR;

 free_field:
  if (return_path != NULL)
    mailimf_return_free(return_path);
  if (resent_date != NULL)
    mailimf_orig_date_free(resent_date);
  if (resent_from != NULL)
    mailimf_from_free(resent_from);
  if (resent_sender != NULL)
    mailimf_sender_free(resent_sender);
  if (resent_to != NULL)
    mailimf_to_free(resent_to);
  if (resent_cc != NULL)
    mailimf_cc_free(resent_cc);
  if (resent_bcc != NULL)
    mailimf_bcc_free(resent_bcc);
  if (resent_msg_id != NULL)
    mailimf_message_id_free(resent_msg_id);
  if (orig_date != NULL)
    mailimf_orig_date_free(orig_date);
  if (from != NULL)
    mailimf_from_free(from);
  if (sender != NULL)
    mailimf_sender_free(sender);
  if (reply_to != NULL)
    mailimf_reply_to_free(reply_to);
  if (to != NULL)
    mailimf_to_free(to);
  if (cc != NULL)
    mailimf_cc_free(cc);
  if (bcc != NULL)
    mailimf_bcc_free(bcc);
  if (message_id != NULL)
    mailimf_message_id_free(message_id);
  if (in_reply_to != NULL)
    mailimf_in_reply_to_free(in_reply_to);
  if (references != NULL)
    mailimf_references_free(references);
  if (subject != NULL)
    mailimf_subject_free(subject);
  if (comments != NULL)
    mailimf_comments_free(comments);
  if (keywords != NULL)
    mailimf_keywords_free(keywords);
  if (optional_field != NULL)
    mailimf_optional_field_free(optional_field);
 err:
  return res;
}

The product dereferences a pointer that it expects to be valid but is NULL.