suggest.c

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/* suggest.c --- Suggest client mechanism to use, from a set of mechanisms.
 * Copyright (C) 2002-2025 Simon Josefsson
 *
 * This file is part of GNU SASL Library.
 *
 * GNU SASL Library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * GNU SASL Library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with GNU SASL Library; if not, see
 * <https://www.gnu.org/licenses/>.
 *
 */
 
#include <config.h>
#include "internal.h"
 
/*
 * _GSASL_VALID_MECHANISM_CHARACTERS:
 *
 * A zero-terminated character array, or string, with all ASCII
 * characters that may be used within a SASL mechanism name.
 **/
static const char *_GSASL_VALID_MECHANISM_CHARACTERS =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_";
 
int
gsasl_mechanism_name_p (const char *mech)
{
  size_t l;
 
  if (mech == NULL)
    return 0;
 
  l = strlen (mech);
 
  if (l < GSASL_MIN_MECHANISM_SIZE)
    return 0;
 
  if (l > GSASL_MAX_MECHANISM_SIZE)
    return 0;
 
  while (*mech)
    if (strchr (_GSASL_VALID_MECHANISM_CHARACTERS, *mech++) == NULL)
      return 0;
 
  return 1;
}
 
const char *
gsasl_client_suggest_mechanism (Gsasl *ctx, const char *mechlist)
{
  size_t mechlist_len, target_mech, i;
 
  mechlist_len = mechlist ? strlen (mechlist) : 0;
  target_mech = ctx->n_client_mechs;    /* ~ no target */
 
  for (i = 0; i < mechlist_len;)
    {
      size_t len;
 
      len = strspn (mechlist + i, _GSASL_VALID_MECHANISM_CHARACTERS);
      if (!len)
        ++i;
      else
        {
          size_t j;
 
          /* Assumption: the mechs array is sorted by preference
           * from low security to high security. */
          for (j = (target_mech < ctx->n_client_mechs ? target_mech + 1 : 0);
               j < ctx->n_client_mechs; ++j)
            {
              if ((strlen (ctx->client_mechs[j].name) == len)
                  && (strncmp (ctx->client_mechs[j].name, mechlist + i,
                               len) == 0))
                {
                  Gsasl_session *sctx;
 
                  if (gsasl_client_start (ctx, ctx->client_mechs[j].name,
                                          &sctx) == GSASL_OK)
                    {
                      gsasl_finish (sctx);
                      target_mech = j;
                    }
 
                  break;
                }
            }
          i += len + 1;
        }
    }
 
  return target_mech < ctx->n_client_mechs ?
    ctx->client_mechs[target_mech].name : NULL;
}