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//
// Mono.Net.Dns.DnsUtil
//
// Authors:
// Gonzalo Paniagua Javier (gonzalo.mono@gmail.com)
//
// Copyright 2011 Gonzalo Paniagua Javier
//
// 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.
//
using System;
using System.Collections.Generic;
using System.Text;
namespace Mono.Net.Dns {
static class DnsUtil {
// RFC 2181 - Section 11
public static bool IsValidDnsName (string name)
{
if (name == null)
return false;
int len = name.Length;
if (len > 255)
return false;
int part_length = 0;
for (int i = 0; i < len; i++) {
char c = name [i];
if (c == '.') {
if (i == 0 && len > 1)
return false; // Can't begin with a dot unless it's "."
if (i > 0 && part_length == 0)
return false; // No ".." allowed
part_length = 0;
continue;
}
part_length++;
if (part_length > 63)
return false;
}
return true;
}
public static int GetEncodedLength (string name)
{
if (!IsValidDnsName (name))
return -1;
if (name == String.Empty)
return 1;
int len = name.Length;
if (name [len - 1] == '.')
return len + 1; // (length + label + ... + \0)
return len + 2; // need 1 more for the second to last label length
}
public static int GetNameLength (byte [] buffer)
{
return GetNameLength (buffer, 0);
}
public static int GetNameLength (byte [] buffer, int offset)
{
if (buffer == null)
throw new ArgumentNullException ("buffer");
if (offset < 0 || offset >= buffer.Length)
throw new ArgumentOutOfRangeException ("offset");
int i = 0;
int len = 0;
while (len < 256) {
i = buffer [offset++];
if (i == 0)
return len > 0 ? --len : 0;
int ptr = i & 0x0C0;
if (ptr == 0x0C0) {
i = ((ptr & 0x3F) << 8) + buffer[offset++];
offset = i;
continue;
} else if (ptr >= 0x40) {
return -2; // Invalid ptr
}
len += i + 1;
offset += i;
}
return -1; // Invalid length
}
public static string ReadName (byte [] buffer, ref int offset)
{
if (buffer == null)
throw new ArgumentNullException ("buffer");
if (offset < 0 || offset >= buffer.Length)
throw new ArgumentOutOfRangeException ("offset");
StringBuilder sb = new StringBuilder (32);
int i = 0;
bool no_ptr = true;
int off = offset;
while (sb.Length < 256) {
i = buffer [off++];
if (no_ptr) offset++;
if (i == 0) {
if (sb.Length > 0)
sb.Length--;
return sb.ToString ();
}
int ptr = i & 0x0C0;
if (ptr == 0x0C0) {
i = ((ptr & 0x3F) << 8) + buffer [off];
if (no_ptr) offset++;
no_ptr = false;
off = i;
continue;
} else if (i >= 0x40) {
return null; // Invalid ptr
}
for (int k = 0; k < i; k++)
sb.Append ((char) buffer [off + k]);
sb.Append ('.');
off += i;
if (no_ptr) offset += i;
}
return null; // never reached
}
}
}
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