File size: 3,088 Bytes
fab29d7 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 | using System;
using System.Collections.Generic;
using System.IO;
using System.Threading.Tasks;
using System.Xml;
using System.Xml.Linq;
using VersOne.Epub.Options;
namespace VersOne.Epub.Internal
{
internal static class XmlUtils
{
private const string XML_DECLARATION_FIRST_CHARS = "<?xml";
public static async Task<XDocument> LoadDocumentAsync(Stream stream, XmlReaderOptions? xmlReaderOptions = null)
{
using MemoryStream memoryStream = new();
await stream.CopyToAsync(memoryStream).ConfigureAwait(false);
memoryStream.Position = 0;
if (xmlReaderOptions != null && xmlReaderOptions.SkipXmlHeaders)
{
SkipXmlHeader(memoryStream);
}
XmlReaderSettings xmlReaderSettings = new()
{
DtdProcessing = DtdProcessing.Ignore,
Async = true
};
using XmlReader xmlReader = XmlReader.Create(memoryStream, xmlReaderSettings);
return await Task.Run(() => XDocument.Load(xmlReader)).ConfigureAwait(false);
}
// This is a workaround for an issue that XML 1.1 files are not supported in .NET.
// See https://github.com/vers-one/EpubReader/issues/34 for more details.
// This method checks if the stream content starts with an XML declaration (<?xml ...)
// in which case it moves the stream position to the next '<' character
// (i.e. to the first XML content node, effectively skipping the XML header).
// Files with no XML declaration are treated as XML 1.0 files by .NET.
// If the stream content doesn't contain XML declaration, this method does not change its position.
private static void SkipXmlHeader(MemoryStream memoryStream)
{
bool IsMatch(IList<byte> buffer, string pattern, int startPosition)
{
for (int i = 0; i < pattern.Length; i++)
{
if (buffer[startPosition + i] != pattern[i])
{
return false;
}
}
return true;
}
int IndexOf(IList<byte> buffer, string pattern, int startPosition)
{
for (int i = startPosition; i < buffer.Count - pattern.Length; i++)
{
if (IsMatch(buffer, pattern, i))
{
return i;
}
}
return -1;
}
memoryStream.TryGetBuffer(out ArraySegment<byte> memoryStreamBuffer);
int position = IndexOf(memoryStreamBuffer, XML_DECLARATION_FIRST_CHARS, 0);
if (position == -1)
{
return;
}
position = IndexOf(memoryStreamBuffer, "<", position + XML_DECLARATION_FIRST_CHARS.Length);
if (position == -1)
{
return;
}
memoryStream.Position = position;
}
}
}
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