307 lines
10 KiB
C#
307 lines
10 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 Microsoft.AspNetCore.Server.Kestrel.Infrastructure;
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namespace Microsoft.AspNetCore.Server.Kestrel.Http
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{
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public class UrlPathDecoder
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{
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/// <summary>
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/// Unescapes the string between given memory iterators in place.
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/// </summary>
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/// <param name="start">The iterator points to the beginning of the sequence.</param>
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/// <param name="end">The iterator points to the byte behind the end of the sequence.</param>
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/// <returns>The iterator points to the byte behind the end of the processed sequence.</returns>
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public static MemoryPoolIterator2 Unescape(MemoryPoolIterator2 start, MemoryPoolIterator2 end)
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{
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// the slot to read the input
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var reader = start;
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// the slot to write the unescaped byte
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var writer = reader;
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while (true)
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{
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if (CompareIterators(ref reader, ref end))
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{
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return writer;
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}
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if (reader.Peek() == '%')
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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))
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{
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Copy(reader, decodeReader, ref writer);
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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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writer.Put((byte)reader.Take());
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}
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}
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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 sequence</param>
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private static bool DecodeCore(ref MemoryPoolIterator2 reader, ref MemoryPoolIterator2 writer, MemoryPoolIterator2 end)
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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);
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if (byte1 == -1)
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{
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return false;
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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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writer.Put((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 & 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 & 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 & 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 (CompareIterators(ref reader, ref end))
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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);
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if (nextByte == -1)
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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 & 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;
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}
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else if (byteCount - remainingBytes == 3)
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{
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byte3 = nextByte;
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}
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else if (byteCount - remainingBytes == 4)
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{
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byte4 = nextByte;
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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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writer.Put((byte)byte1);
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}
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if (byteCount > 1)
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{
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writer.Put((byte)byte2);
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}
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if (byteCount > 2)
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{
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writer.Put((byte)byte3);
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}
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if (byteCount > 3)
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{
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writer.Put((byte)byte4);
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}
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return true;
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}
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private static void Copy(MemoryPoolIterator2 head, MemoryPoolIterator2 tail, ref MemoryPoolIterator2 writer)
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{
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while (!CompareIterators(ref head, ref tail))
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{
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writer.Put((byte)head.Take());
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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 sequence</param>
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/// <returns>The unescaped byte if success. Otherwise return -1.</returns>
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private static int UnescapePercentEncoding(ref MemoryPoolIterator2 scan, MemoryPoolIterator2 end)
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{
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if (scan.Take() != '%')
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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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int value1 = ReadHex(ref probe, end);
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if (value1 == -1)
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{
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return -1;
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}
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int value2 = ReadHex(ref probe, end);
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if (value2 == -1)
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{
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return -1;
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}
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if (SkipUnescape(value1, value2))
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{
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return -1;
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}
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scan = probe;
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return (value1 << 4) + value2;
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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 sequence</param>
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/// <returns>The hexadecimal value if successes, otherwise -1.</returns>
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private static int ReadHex(ref MemoryPoolIterator2 scan, MemoryPoolIterator2 end)
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{
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if (CompareIterators(ref scan, ref end))
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{
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return -1;
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}
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var value = scan.Take();
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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 -1;
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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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private static bool CompareIterators(ref MemoryPoolIterator2 lhs, ref MemoryPoolIterator2 rhs)
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{
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// uses ref parameter to save cost of copying
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return (lhs.Block == rhs.Block) && (lhs.Index == rhs.Index);
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}
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}
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}
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