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我有一些包含非法字符(0x1 等)的大型 XML 提要文件。这些文件是第三方的,我无法更改编写它们的过程。
我想使用 XmlReader
处理这些文件,但它会在这些非法字符上爆炸。
我可以读取文件,过滤掉坏字符,保存它们,然后处理它们......但这是很多 I/O,而且看起来应该是不必要的。
我想做的是这样的:
using(var origStream = File.OpenRead(fileName))
using(var cleanStream = new CleansedXmlStream(origStream))
using(var streamReader = new StreamReader(cleanStream))
using(var xmlReader = XmlReader.Create(streamReader))
{
//do stuff with reader
}
我尝试从 Stream
继承,但是当我开始实现 Read(byte[] buffer, int offset, int count)
时,我失去了一些信心。毕竟,我正计划删除字符,所以看起来计数会关闭,而且我必须将每个字节转换为 char
这看起来很昂贵(尤其是在大文件上)而且我是不清楚这如何与 Unicode 编码一起工作,但我的问题的答案并不直观。
在谷歌搜索“c# stream wrapper”或“c# filter stream”时,我没有得到满意的结果。有可能我使用了错误的词语或描述了错误的概念,所以我希望 SO 社区能够纠正我。
使用上面的示例,CleansedXmlStream
会是什么样子?
这是我第一次尝试的样子:
public class CleansedXmlStream : Stream
{
private readonly Stream _baseStream;
public CleansedXmlStream(Stream stream)
{
this._baseStream = stream;
}
public new void Dispose()
{
if (this._baseStream != null)
{
this._baseStream.Dispose();
}
base.Dispose();
}
public override bool CanRead
{
get { return this._baseStream.CanRead; }
}
public override bool CanSeek
{
get { return this._baseStream.CanSeek; }
}
public override bool CanWrite
{
get { return this._baseStream.CanWrite; }
}
public override long Length
{
get { return this._baseStream.Length; }
}
public override long Position
{
get { return this._baseStream.Position; }
set { this._baseStream.Position = value; }
}
public override void Flush()
{
this._baseStream.Flush();
}
public override int Read(byte[] buffer, int offset, int count)
{
//what does this look like?
throw new NotImplementedException();
}
public override long Seek(long offset, SeekOrigin origin)
{
return this._baseStream.Seek(offset, origin);
}
public override void SetLength(long value)
{
this._baseStream.SetLength(value);
}
public override void Write(byte[] buffer, int offset, int count)
{
throw new NotSupportedException();
}
}
最佳答案
受@CharlesMager 评论的启发,我最终没有制作Stream
,而是制作了一个StreamReader
,如下所示:
public class CleanTextReader : StreamReader
{
private readonly ILog _logger;
public CleanTextReader(Stream stream, ILog logger) : base(stream)
{
this._logger = logger;
}
public CleanTextReader(Stream stream) : this(stream, LogManager.GetLogger<CleanTextReader>())
{
//nothing to do here.
}
/// <summary>
/// Reads a specified maximum of characters from the current stream into a buffer, beginning at the specified index.
/// </summary>
/// <returns>
/// The number of characters that have been read, or 0 if at the end of the stream and no data was read. The number
/// will be less than or equal to the <paramref name="count" /> parameter, depending on whether the data is available
/// within the stream.
/// </returns>
/// <param name="buffer">
/// When this method returns, contains the specified character array with the values between
/// <paramref name="index" /> and (<paramref name="index + count - 1" />) replaced by the characters read from the
/// current source.
/// </param>
/// <param name="index">The index of <paramref name="buffer" /> at which to begin writing. </param>
/// <param name="count">The maximum number of characters to read. </param>
/// <exception cref="T:System.ArgumentException">
/// The buffer length minus <paramref name="index" /> is less than
/// <paramref name="count" />.
/// </exception>
/// <exception cref="T:System.ArgumentNullException"><paramref name="buffer" /> is null. </exception>
/// <exception cref="T:System.ArgumentOutOfRangeException">
/// <paramref name="index" /> or <paramref name="count" /> is
/// negative.
/// </exception>
/// <exception cref="T:System.IO.IOException">An I/O error occurs, such as the stream is closed. </exception>
public override int Read(char[] buffer, int index, int count)
{
try
{
var rVal = base.Read(buffer, index, count);
var filteredBuffer = buffer.Select(x => XmlConvert.IsXmlChar(x) ? x : ' ').ToArray();
Buffer.BlockCopy(filteredBuffer, 0, buffer, 0, count);
return rVal;
}
catch (Exception ex)
{
this._logger.Error("Read(char[], int, int)", ex);
throw;
}
}
/// <summary>
/// Reads a maximum of <paramref name="count" /> characters from the current stream, and writes the data to
/// <paramref name="buffer" />, beginning at <paramref name="index" />.
/// </summary>
/// <returns>
/// The position of the underlying stream is advanced by the number of characters that were read into
/// <paramref name="buffer" />.The number of characters that have been read. The number will be less than or equal to
/// <paramref name="count" />, depending on whether all input characters have been read.
/// </returns>
/// <param name="buffer">
/// When this method returns, this parameter contains the specified character array with the values
/// between <paramref name="index" /> and (<paramref name="index" /> + <paramref name="count" /> -1) replaced by the
/// characters read from the current source.
/// </param>
/// <param name="index">The position in <paramref name="buffer" /> at which to begin writing.</param>
/// <param name="count">The maximum number of characters to read. </param>
/// <exception cref="T:System.ArgumentNullException"><paramref name="buffer" /> is null. </exception>
/// <exception cref="T:System.ArgumentException">
/// The buffer length minus <paramref name="index" /> is less than
/// <paramref name="count" />.
/// </exception>
/// <exception cref="T:System.ArgumentOutOfRangeException">
/// <paramref name="index" /> or <paramref name="count" /> is
/// negative.
/// </exception>
/// <exception cref="T:System.ObjectDisposedException">The <see cref="T:System.IO.TextReader" /> is closed. </exception>
/// <exception cref="T:System.IO.IOException">An I/O error occurs. </exception>
public override int ReadBlock(char[] buffer, int index, int count)
{
try
{
var rVal = base.ReadBlock(buffer, index, count);
var filteredBuffer = buffer.Select(x => XmlConvert.IsXmlChar(x) ? x : ' ').ToArray();
Buffer.BlockCopy(filteredBuffer, 0, buffer, 0, count);
return rVal;
}
catch (Exception ex)
{
this._logger.Error("ReadBlock(char[], in, int)", ex);
throw;
}
}
/// <summary>
/// Reads the stream from the current position to the end of the stream.
/// </summary>
/// <returns>
/// The rest of the stream as a string, from the current position to the end. If the current position is at the end of
/// the stream, returns an empty string ("").
/// </returns>
/// <exception cref="T:System.OutOfMemoryException">
/// There is insufficient memory to allocate a buffer for the returned
/// string.
/// </exception>
/// <exception cref="T:System.IO.IOException">An I/O error occurs. </exception>
public override string ReadToEnd()
{
var chars = new char[4096];
int len;
var sb = new StringBuilder(4096);
while ((len = Read(chars, 0, chars.Length)) != 0)
{
sb.Append(chars, 0, len);
}
return sb.ToString();
}
}
我的单元测试是这样的:
[TestMethod]
public void CleanTextReaderCleans()
{
//arrange
var originalString = "The quick brown fox jumped over the lazy dog.";
var badChars = new string(new[] {(char) 0x1});
var concatenated = string.Concat(badChars, originalString);
//act
using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(concatenated)))
{
using (var reader = new CleanTextReader(stream))
{
var newString = reader.ReadToEnd().Trim();
//assert
Assert.IsTrue(originalString.Equals(newString));
}
}
}
... 用法如下所示:
using(var origStream = File.OpenRead(fileName))
using(var streamReader = new CleanTextReader(origStream))
using(var xmlReader = XmlReader.Create(streamReader))
{
//do stuff with reader
}
如果有人有改进建议,我很乐意听取。
关于c# - 如何为 XML 编写 "filter"流包装器?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31796689/
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