342 lines
12 KiB
C#
342 lines
12 KiB
C#
// Copyright (c) .NET Foundation. All rights reserved.
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// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
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using System;
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using System.Diagnostics;
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using System.Text;
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namespace Microsoft.AspNetCore.HttpSys.Internal
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{
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// We don't use the cooked URL because http.sys unescapes all percent-encoded values. However,
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// we also can't just use the raw Uri, since http.sys supports not only UTF-8, but also ANSI/DBCS and
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// Unicode code points. System.Uri only supports UTF-8.
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// The purpose of this class is to decode all UTF-8 percent encoded characters, with the
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// exception of %2F ('/'), which is left encoded
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internal static class RequestUriBuilder
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{
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private static readonly Encoding UTF8 = new UTF8Encoding(
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encoderShouldEmitUTF8Identifier: false,
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throwOnInvalidBytes: true);
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public static string DecodeAndUnescapePath(Span<byte> rawUrlBytes)
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{
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Debug.Assert(rawUrlBytes.Length != 0, "Length of the URL cannot be zero.");
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var rawPath = RawUrlHelper.GetPath(rawUrlBytes);
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if (rawPath.Length == 0)
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{
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return "/";
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}
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var unescapedPath = Unescape(rawPath);
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var length = PathNormalizer.RemoveDotSegments(unescapedPath);
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return UTF8.GetString(unescapedPath.Slice(0, length));
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}
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/// <summary>
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/// Unescape a given path string in place. The given path string may contain escaped char.
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/// </summary>
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/// <param name="rawPath">The raw path string to be unescaped</param>
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/// <returns>The unescaped path string</returns>
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private static Span<byte> Unescape(Span<byte> rawPath)
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{
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// the slot to read the input
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var reader = 0;
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// the slot to write the unescaped byte
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var writer = 0;
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// the end of the path
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var end = rawPath.Length;
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while (true)
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{
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if (reader == end)
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{
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break;
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}
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if (rawPath[reader] == '%')
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{
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var decodeReader = reader;
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// If decoding process succeeds, the writer iterator will be moved
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// to the next write-ready location. On the other hand if the scanned
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// percent-encodings cannot be interpreted as sequence of UTF-8 octets,
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// these bytes should be copied to output as is.
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// The decodeReader iterator is always moved to the first byte not yet
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// be scanned after the process. A failed decoding means the chars
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// between the reader and decodeReader can be copied to output untouched.
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if (!DecodeCore(ref decodeReader, ref writer, end, rawPath))
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{
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Copy(reader, decodeReader, ref writer, rawPath);
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}
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reader = decodeReader;
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}
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else
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{
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rawPath[writer++] = rawPath[reader++];
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}
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}
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return rawPath.Slice(0, writer);
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}
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/// <summary>
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/// Unescape the percent-encodings
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/// </summary>
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/// <param name="reader">The iterator point to the first % char</param>
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/// <param name="writer">The place to write to</param>
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/// <param name="end">The end of the buffer</param>
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/// <param name="buffer">The byte array</param>
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private static bool DecodeCore(ref int reader, ref int writer, int end, Span<byte> buffer)
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{
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// preserves the original head. if the percent-encodings cannot be interpreted as sequence of UTF-8 octets,
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// bytes from this till the last scanned one will be copied to the memory pointed by writer.
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var byte1 = UnescapePercentEncoding(ref reader, end, buffer);
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if (!byte1.HasValue)
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{
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return false;
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}
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if (byte1 == 0)
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{
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throw new InvalidOperationException("The path contains null characters.");
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}
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if (byte1 <= 0x7F)
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{
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// first byte < U+007f, it is a single byte ASCII
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buffer[writer++] = (byte)byte1;
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return true;
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}
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int byte2 = 0, byte3 = 0, byte4 = 0;
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// anticipate more bytes
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var currentDecodeBits = 0;
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var byteCount = 1;
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var expectValueMin = 0;
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if ((byte1 & 0xE0) == 0xC0)
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{
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// 110x xxxx, expect one more byte
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currentDecodeBits = byte1.Value & 0x1F;
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byteCount = 2;
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expectValueMin = 0x80;
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}
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else if ((byte1 & 0xF0) == 0xE0)
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{
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// 1110 xxxx, expect two more bytes
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currentDecodeBits = byte1.Value & 0x0F;
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byteCount = 3;
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expectValueMin = 0x800;
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}
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else if ((byte1 & 0xF8) == 0xF0)
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{
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// 1111 0xxx, expect three more bytes
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currentDecodeBits = byte1.Value & 0x07;
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byteCount = 4;
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expectValueMin = 0x10000;
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}
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else
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{
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// invalid first byte
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return false;
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}
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var remainingBytes = byteCount - 1;
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while (remainingBytes > 0)
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{
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// read following three chars
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if (reader == buffer.Length)
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{
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return false;
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}
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var nextItr = reader;
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var nextByte = UnescapePercentEncoding(ref nextItr, end, buffer);
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if (!nextByte.HasValue)
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{
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return false;
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}
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if ((nextByte & 0xC0) != 0x80)
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{
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// the follow up byte is not in form of 10xx xxxx
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return false;
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}
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currentDecodeBits = (currentDecodeBits << 6) | (nextByte.Value & 0x3F);
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remainingBytes--;
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if (remainingBytes == 1 && currentDecodeBits >= 0x360 && currentDecodeBits <= 0x37F)
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{
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// this is going to end up in the range of 0xD800-0xDFFF UTF-16 surrogates that
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// are not allowed in UTF-8;
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return false;
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}
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if (remainingBytes == 2 && currentDecodeBits >= 0x110)
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{
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// this is going to be out of the upper Unicode bound 0x10FFFF.
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return false;
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}
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reader = nextItr;
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if (byteCount - remainingBytes == 2)
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{
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byte2 = nextByte.Value;
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}
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else if (byteCount - remainingBytes == 3)
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{
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byte3 = nextByte.Value;
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}
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else if (byteCount - remainingBytes == 4)
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{
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byte4 = nextByte.Value;
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}
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}
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if (currentDecodeBits < expectValueMin)
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{
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// overlong encoding (e.g. using 2 bytes to encode something that only needed 1).
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return false;
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}
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// all bytes are verified, write to the output
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if (byteCount > 0)
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{
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buffer[writer++] = (byte)byte1;
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}
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if (byteCount > 1)
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{
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buffer[writer++] = (byte)byte2;
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}
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if (byteCount > 2)
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{
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buffer[writer++] = (byte)byte3;
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}
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if (byteCount > 3)
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{
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buffer[writer++] = (byte)byte4;
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}
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return true;
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}
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private static void Copy(int begin, int end, ref int writer, Span<byte> buffer)
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{
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while (begin != end)
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{
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buffer[writer++] = buffer[begin++];
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}
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}
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/// <summary>
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/// Read the percent-encoding and try unescape it.
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///
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/// The operation first peek at the character the <paramref name="scan"/>
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/// iterator points at. If it is % the <paramref name="scan"/> is then
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/// moved on to scan the following to characters. If the two following
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/// characters are hexadecimal literals they will be unescaped and the
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/// value will be returned.
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///
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/// If the first character is not % the <paramref name="scan"/> iterator
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/// will be removed beyond the location of % and -1 will be returned.
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///
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/// If the following two characters can't be successfully unescaped the
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/// <paramref name="scan"/> iterator will be move behind the % and -1
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/// will be returned.
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/// </summary>
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/// <param name="scan">The value to read</param>
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/// <param name="end">The end of the buffer</param>
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/// <param name="buffer">The byte array</param>
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/// <returns>The unescaped byte if success. Otherwise return -1.</returns>
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private static int? UnescapePercentEncoding(ref int scan, int end, ReadOnlySpan<byte> buffer)
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{
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if (buffer[scan++] != '%')
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{
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return -1;
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}
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var probe = scan;
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var value1 = ReadHex(ref probe, end, buffer);
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if (!value1.HasValue)
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{
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return null;
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}
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var value2 = ReadHex(ref probe, end, buffer);
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if (!value2.HasValue)
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{
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return null;
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}
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if (SkipUnescape(value1.Value, value2.Value))
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{
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return null;
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}
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scan = probe;
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return (value1.Value << 4) + value2.Value;
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}
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/// <summary>
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/// Read the next char and convert it into hexadecimal value.
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///
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/// The <paramref name="scan"/> iterator will be moved to the next
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/// byte no matter no matter whether the operation successes.
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/// </summary>
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/// <param name="scan">The value to read</param>
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/// <param name="end">The end of the buffer</param>
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/// <param name="buffer">The byte array</param>
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/// <returns>The hexadecimal value if successes, otherwise -1.</returns>
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private static int? ReadHex(ref int scan, int end, ReadOnlySpan<byte> buffer)
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{
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if (scan == end)
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{
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return null;
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}
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var value = buffer[scan++];
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var isHead = (((value >= '0') && (value <= '9')) ||
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((value >= 'A') && (value <= 'F')) ||
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((value >= 'a') && (value <= 'f')));
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if (!isHead)
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{
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return null;
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}
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if (value <= '9')
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{
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return value - '0';
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}
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else if (value <= 'F')
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{
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return (value - 'A') + 10;
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}
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else // a - f
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{
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return (value - 'a') + 10;
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}
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}
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private static bool SkipUnescape(int value1, int value2)
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{
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// skip %2F - '/'
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if (value1 == 2 && value2 == 15)
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{
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return true;
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}
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return false;
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}
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}
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}
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