142 lines
3.3 KiB
C#
142 lines
3.3 KiB
C#
//
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// Mono.Net.Dns.DnsUtil
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//
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// Authors:
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// Gonzalo Paniagua Javier (gonzalo.mono@gmail.com)
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//
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// Copyright 2011 Gonzalo Paniagua Javier
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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using System;
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using System.Collections.Generic;
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using System.Text;
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namespace Mono.Net.Dns {
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static class DnsUtil {
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// RFC 2181 - Section 11
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public static bool IsValidDnsName (string name)
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{
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if (name == null)
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return false;
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int len = name.Length;
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if (len > 255)
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return false;
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int part_length = 0;
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for (int i = 0; i < len; i++) {
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char c = name [i];
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if (c == '.') {
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if (i == 0 && len > 1)
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return false; // Can't begin with a dot unless it's "."
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if (i > 0 && part_length == 0)
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return false; // No ".." allowed
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part_length = 0;
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continue;
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}
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part_length++;
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if (part_length > 63)
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return false;
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}
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return true;
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}
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public static int GetEncodedLength (string name)
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{
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if (!IsValidDnsName (name))
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return -1;
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if (name == String.Empty)
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return 1;
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int len = name.Length;
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if (name [len - 1] == '.')
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return len + 1; // (length + label + ... + \0)
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return len + 2; // need 1 more for the second to last label length
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}
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public static int GetNameLength (byte [] buffer)
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{
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return GetNameLength (buffer, 0);
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}
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public static int GetNameLength (byte [] buffer, int offset)
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{
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if (buffer == null)
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throw new ArgumentNullException ("buffer");
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if (offset < 0 || offset >= buffer.Length)
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throw new ArgumentOutOfRangeException ("offset");
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int i = 0;
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int len = 0;
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while (len < 256) {
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i = buffer [offset++];
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if (i == 0)
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return len > 0 ? --len : 0;
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int ptr = i & 0x0C0;
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if (ptr == 0x0C0) {
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i = ((ptr & 0x3F) << 8) + buffer[offset++];
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offset = i;
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continue;
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} else if (ptr >= 0x40) {
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return -2; // Invalid ptr
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}
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len += i + 1;
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offset += i;
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}
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return -1; // Invalid length
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}
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public static string ReadName (byte [] buffer, ref int offset)
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{
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if (buffer == null)
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throw new ArgumentNullException ("buffer");
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if (offset < 0 || offset >= buffer.Length)
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throw new ArgumentOutOfRangeException ("offset");
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StringBuilder sb = new StringBuilder (32);
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int i = 0;
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bool no_ptr = true;
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int off = offset;
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while (sb.Length < 256) {
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i = buffer [off++];
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if (no_ptr) offset++;
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if (i == 0) {
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if (sb.Length > 0)
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sb.Length--;
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return sb.ToString ();
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}
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int ptr = i & 0x0C0;
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if (ptr == 0x0C0) {
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i = ((ptr & 0x3F) << 8) + buffer [off];
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if (no_ptr) offset++;
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no_ptr = false;
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off = i;
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continue;
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} else if (i >= 0x40) {
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return null; // Invalid ptr
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}
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for (int k = 0; k < i; k++)
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sb.Append ((char) buffer [off + k]);
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sb.Append ('.');
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off += i;
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if (no_ptr) offset += i;
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}
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return null; // never reached
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}
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}
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}
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