/*
 * Copyright 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "../domain_registry.h"

#include <string.h>

#include "tsk_assert.h"
#include "string_util.h"
#include "trie_search.h"

/* RFCs 1035 and 1123 specify a max hostname length of 255 bytes. */
static const size_t kMaxHostnameLen = 255;

/* strdup() is not part of ANSI C89 so we define our own. */
static char* StrDup(const char* s) {
  const size_t len = strlen(s);
  char* s2 = malloc(len + 1);
  if (s2 == NULL) {
    return NULL;
  }
  memcpy(s2, s, len);
  s2[len] = 0;
  return s2;
}

/* strnlen() is not part of ANSI C89 so we define our own. */
static size_t StrnLen(const char* s, size_t max) {
  const char* end = s + max;
  const char* i;
  for (i = s; i < end; ++i) {
    if (*i == 0) break;
  }
  return (size_t) (i - s);
}

static int IsStringASCII(const char* s) {
  const char* it = s;
  for (; *it != 0; ++it) {
    unsigned const char unsigned_char = (unsigned char)*it;
    if (unsigned_char > 0x7f) {
      return 0;
    }
  }
  return 1;
}

static int IsValidHostname(const char* hostname) {
  /*
   * http://www.ietf.org/rfc/rfc1035.txt (DNS) and
   * http://tools.ietf.org/html/rfc1123 (Internet host requirements)
   * specify a maximum hostname length of 255 characters. To make sure
   * string comparisons, etc are bounded elsewhere in the codebase, we
   * enforce the 255 character limit here. There are various other
   * hostname constraints specified in the RFCs (63 bytes per
   * hostname-part, etc) but we do not enforce those here since doing
   * so would not change correctness of the overall implementation,
   * and it's possible that hostnames used in other contexts
   * (e.g. outside of DNS) would not be subject to the 63-byte
   * hostname-part limit. So we let the DNS layer enforce its policy,
   * and enforce only the maximum hostname length here.
   */
  if (StrnLen(hostname, kMaxHostnameLen + 1) > kMaxHostnameLen) {
    return 0;
  }

  /*
   * All hostnames must contain only ASCII characters. If a hostname
   * is passed in that contains non-ASCII (e.g. an IDN that hasn't been
   * converted to ASCII via punycode) we want to reject it outright.
   */
  if (IsStringASCII(hostname) == 0) {
    return 0;
  }

  return 1;
}

/*
 * Get a pointer to the beginning of the valid registry. If rule_part
 * is an exception component, this will seek past the
 * rule_part. Otherwise this will simply return the component itself.
 */
static const char* GetDomainRegistryStr(const char* rule_part,
                                        const char* component) {
  if (IsExceptionComponent(rule_part)) {
    return component + strlen(component) + 1;
  } else {
    return component;
  }
}

/*
 * Iterates the hostname-parts between start and end in reverse order,
 * separated by the character specified by sep. For instance if the
 * string between start and end is "foo\0bar\0com" and sep is the null
 * character, we will return a pointer to "com", then "bar", then
 * "foo".
 */
static const char* GetNextHostnamePartImpl(const char* start,
                                           const char* end,
                                           char sep,
                                           void** ctx) {
  const char* last;
  const char* i;

  if (*ctx == NULL) {
    *ctx = (void*) end;

    /*
     * Special case: a single trailing dot indicates a fully-qualified
     * domain name. Skip over it.
     */
    if (end > start && *(end - 1) == sep) {
      *ctx = (void*) (end - 1);
    }
  }
  last = *ctx;
  if (start > last) return NULL;
  for (i = last - 1; i >= start; --i) {
    if (*i == sep) {
      *ctx = (void*) i;
      return i + 1;
    }
  }
  if (last != start && *start != 0) {
    /*
     * Special case: If we didn't find a match, but the context
     * indicates that we haven't visited the first component yet, and
     * there is a non-NULL first component, then visit the first
     * component.
     */
    *ctx = (void*) start;
    return start;
  }
  return NULL;
}

static const char* GetNextHostnamePart(const char* start,
                                       const char* end,
                                       char sep,
                                       void** ctx) {
  const char* hostname_part = GetNextHostnamePartImpl(start, end, sep, ctx);
  if (IsInvalidComponent(hostname_part)) {
    return NULL;
  }
  return hostname_part;
}

/*
 * Iterate over all hostname-parts between value and value_end, where
 * the hostname-parts are separated by character sep.
 */
static const char* GetRegistryForHostname(const char* value,
                                          const char* value_end,
                                          const char sep) {
  void *ctx = NULL;
  const struct TrieNode* current = NULL;
  const char* component = NULL;
  const char* last_valid = NULL;

  /*
   * Iterate over the hostname components one at a time, e.g. if value
   * is foo.com, we will first visit component com, then component foo.
   */
  while ((component =
          GetNextHostnamePart(value, value_end, sep, &ctx)) != NULL) {
    const char* leaf_node;

    current = FindRegistryNode(component, current);
    if (current == NULL) {
      break;
    }
    if (current->is_terminal == 1) {
      last_valid = GetDomainRegistryStr(
          GetHostnamePart(current->string_table_offset), component);
    } else {
      last_valid = NULL;
    }
    if (HasLeafChildren(current)) {
      /*
       * The child nodes are in the leaf node table, so perform a
       * search in that table.
       */
      component = GetNextHostnamePart(value, value_end, sep, &ctx);
      if (component == NULL) {
        break;
      }
      leaf_node = FindRegistryLeafNode(component, current);
      if (leaf_node == NULL) {
        break;
      }
      return GetDomainRegistryStr(leaf_node, component);
    }
  }

  return last_valid;
}

static size_t GetRegistryLengthImpl(
    const char* value,
    const char* value_end,
    const char sep,
    int allow_unknown_registries) {
  const char* registry;
  size_t match_len;

  while (*value == sep && value < value_end) {
    /* Skip over leading separators. */
    ++value;
  }
  registry = GetRegistryForHostname(value, value_end, sep);
  if (registry == NULL) {
    /*
     * Didn't find a match. If unknown registries are allowed, see if
     * the root hostname part is not in the table. If so, consider it to be a
     * valid registry, and return its length.
     */
    if (allow_unknown_registries != 0) {
      void* ctx = NULL;
      const char* root_hostname_part =
          GetNextHostnamePart(value, value_end, sep, &ctx);
      /*
       * See if the root hostname-part is in the table. If it's not in
       * the table, then consider the unknown registry to be a valid
       * registry.
       */
      if (root_hostname_part != NULL &&
          FindRegistryNode(root_hostname_part, NULL) == NULL) {
        registry = root_hostname_part;
      }
    }
    if (registry == NULL) {
      return 0;
    }
  }
  if (registry < value || registry >= value_end) {
    /* Error cases. */
    DCHECK(registry >= value);
    DCHECK(registry < value_end);
    return 0;
  }
  match_len = (size_t) (value_end - registry);
  return match_len;
}

size_t GetRegistryLength(const char* hostname) {
  const char* buf_end;
  char* buf;
  size_t registry_length;

  if (hostname == NULL) {
    return 0;
  }
  if (IsValidHostname(hostname) == 0) {
    return 0;
  }

  /*
   * Replace dots between hostname parts with the null byte. This
   * allows us to index directly into the string and refer to each
   * hostname-part as if it were its own null-terminated string.
   */
  buf = StrDup(hostname);
  if (buf == NULL) {
    return 0;
  }
  ReplaceChar(buf, '.', '\0');

  buf_end = buf + strlen(hostname);
  DCHECK(*buf_end == 0);

  /* Normalize the input by converting all characters to lowercase. */
  ToLowerASCII(buf, buf_end);
  registry_length = GetRegistryLengthImpl(buf, buf_end, '\0', 0);
  free(buf);
  return registry_length;
}

size_t GetRegistryLengthAllowUnknownRegistries(const char* hostname) {
  const char* buf_end;
  char* buf;
  size_t registry_length;

  if (hostname == NULL) {
    return 0;
  }
  if (IsValidHostname(hostname) == 0) {
    return 0;
  }

  /*
   * Replace dots between hostname parts with the null byte. This
   * allows us to index directly into the string and refer to each
   * hostname-part as if it were its own null-terminated string.
   */
  buf = StrDup(hostname);
  if (buf == NULL) {
    return 0;
  }
  ReplaceChar(buf, '.', '\0');

  buf_end = buf + strlen(hostname);
  DCHECK(*buf_end == 0);

  /* Normalize the input by converting all characters to lowercase. */
  ToLowerASCII(buf, buf_end);
  registry_length = GetRegistryLengthImpl(buf, buf_end, '\0', 1);
  free(buf);
  return registry_length;
}