我遇到了从 HttpResponseStream 读取失败的问题，因为我包裹的 StreamReader 读取速度比响应流获得实际响应的速度更快。我正在检索一个相当小的文件（大约 60k），但是将响应处理为实际对象的解析器失败了，因为它遇到了一个意外字符（代码 65535），根据经验，我知道这是您从StreamReader 并且没有更多可用的字符。
作为记录，我知道返回的内容是有效的并且会正确解析，因为每次运行代码时都会在文件中的不同点发生故障。失败的地方是下面的 parser.Load() 行。
有没有办法确保我在尝试解析它之前已经阅读了所有内容，而不是将响应流复制到 MemoryStream 或字符串中然后处理它？
/// <summary>
/// Makes a Query where the expected Result is an RDF Graph ie. CONSTRUCT and DESCRIBE Queries
/// </summary>
/// <param name="sparqlQuery">SPARQL Query String</param>
/// <returns>RDF Graph</returns>
public Graph QueryWithResultGraph(String sparqlQuery)
{
try
{
//Build the Query URI
StringBuilder queryUri = new StringBuilder();
queryUri.Append(this._endpoint.ToString());
queryUri.Append("?query=");
queryUri.Append(Uri.EscapeDataString(sparqlQuery));
if (!this._defaultGraphUri.Equals(String.Empty))
{
queryUri.Append("&default-graph-uri=");
queryUri.Append(Uri.EscapeUriString(this._defaultGraphUri));
}
//Make the Query via HTTP
HttpWebResponse httpResponse = this.DoQuery(new Uri(queryUri.ToString()),false);
//Set up an Empty Graph ready
Graph g = new Graph();
g.BaseURI = this._endpoint;
//Parse into a Graph based on Content Type
String ctype = httpResponse.ContentType;
IRDFReader parser = MIMETypesHelper.GetParser(ctype);
parser.Load(g, new StreamReader(httpResponse.GetResponseStream()));
return g;
}
catch (UriFormatException uriEx)
{
//URI Format Invalid
throw new Exception("The format of the URI was invalid", uriEx);
}
catch (WebException webEx)
{
//Some sort of HTTP Error occurred
throw new Exception("A HTTP Error occurred", webEx);
}
catch (RDFException)
{
//Some problem with the RDF or Parsing thereof
throw;
}
catch (Exception)
{
//Other Exception
throw;
}
}
/// <summary>
/// Internal Helper Method which executes the HTTP Requests against the SPARQL Endpoint
/// </summary>
/// <param name="target">URI to make Request to</param>
/// <param name="sparqlOnly">Indicates if only SPARQL Result Sets should be accepted</param>
/// <returns>HTTP Response</returns>
private HttpWebResponse DoQuery(Uri target, bool sparqlOnly)
{
//Expect errors in this function to be handled by the calling function
//Set-up the Request
HttpWebRequest httpRequest;
HttpWebResponse httpResponse;
httpRequest = (HttpWebRequest)WebRequest.Create(target);
//Use HTTP GET/POST according to user set preference
if (!sparqlOnly)
{
httpRequest.Accept = MIMETypesHelper.HTTPAcceptHeader();
//For the time being drop the application/json as this doesn't play nice with Virtuoso
httpRequest.Accept = httpRequest.Accept.Replace("," + MIMETypesHelper.JSON[0], String.Empty);
}
else
{
httpRequest.Accept = MIMETypesHelper.HTTPSPARQLAcceptHeader();
}
httpRequest.Method = this._httpMode;
httpRequest.Timeout = this._timeout;
//HTTP Debugging
if (Options.HTTPDebugging)
{
Tools.HTTPDebugRequest(httpRequest);
}
httpResponse = (HttpWebResponse)httpRequest.GetResponse();
//HTTP Debugging
if (Options.HTTPDebugging)
{
Tools.HTTPDebugResponse(httpResponse);
}
return httpResponse;
}
编辑
为了澄清我已经说过这不是Parser 中的错误，这是 StreamReader 读取速度快于响应流提供数据的问题。我可以通过执行以下操作来解决这个问题，但希望得到更好或更优雅的解决方案的建议：
//Parse into a Graph based on Content Type
String ctype = httpResponse.ContentType;
IRDFReader parser = MIMETypesHelper.GetParser(ctype);
Stream response = httpResponse.GetResponseStream();
MemoryStream temp = new MemoryStream();
Tools.StreamCopy(response, temp);
response.Close();
temp.Seek(0, SeekOrigin.Begin);
parser.Load(g, new StreamReader(temp));
编辑 2
根据 Eamon 的建议，BlockingStreamReader 类：
/// <summary>
/// A wrapper to a Stream which does all its Read() and Peek() calls using ReadBlock() to handle slow underlying streams (eg Network Streams)
/// </summary>
public sealed class BlockingStreamReader : StreamReader
{
private bool _peeked = false;
private int _peekChar = -1;
public BlockingStreamReader(StreamReader reader) : base(reader.BaseStream) { }
public BlockingStreamReader(Stream stream) : base(stream) { }
public override int Read()
{
if (this._peeked)
{
this._peeked = false;
return this._peekChar;
}
else
{
if (this.EndOfStream) return -1;
char[] cs = new char[1];
base.ReadBlock(cs, 0, 1);
return cs[0];
}
}
public override int Peek()
{
if (this._peeked)
{
return this._peekChar;
}
else
{
if (this.EndOfStream) return -1;
this._peeked = true;
char[] cs = new char[1];
base.ReadBlock(cs, 0, 1);
this._peekChar = cs[0];
return this._peekChar;
}
}
public new bool EndOfStream
{
get
{
return (base.EndOfStream && !this._peeked);
}
}
}
编辑 3
这是一个大大改进的解决方案，可以包装任何内容TextReader并提供EndOfStream属性。它使用一个内部缓冲区，该缓冲区通过使用ReadBlock()包装的TextReader. 阅读器的所有 Read() 方法都可以使用这个缓冲区来定义，缓冲区大小是可配置的：
/// <summary>
/// The BlockingTextReader is an implementation of a <see cref="TextReader">TextReader</see> designed to wrap other readers which may or may not have high latency.
/// </summary>
/// <remarks>
/// <para>
/// This is designed to avoid premature detection of end of input when the input has high latency and the consumer tries to read from the input faster than it can return data. All methods are defined by using an internal buffer which is filled using the <see cref="TextReader.ReadBlock">ReadBlock()</see> method of the underlying <see cref="TextReader">TextReader</see>
/// </para>
/// </remarks>
public sealed class BlockingTextReader : TextReader
{
private char[] _buffer;
private int _pos = -1;
private int _bufferAmount = -1;
private bool _finished = false;
private TextReader _reader;
public const int DefaultBufferSize = 1024;
public BlockingTextReader(TextReader reader, int bufferSize)
{
if (reader == null) throw new ArgumentNullException("reader", "Cannot read from a null TextReader");
if (bufferSize < 1) throw new ArgumentException("bufferSize must be >= 1", "bufferSize");
this._reader = reader;
this._buffer = new char[bufferSize];
}
public BlockingTextReader(TextReader reader)
: this(reader, DefaultBufferSize) { }
public BlockingTextReader(Stream input, int bufferSize)
: this(new StreamReader(input), bufferSize) { }
public BlockingTextReader(Stream input)
: this(new StreamReader(input)) { }
private void FillBuffer()
{
this._pos = -1;
if (this._finished)
{
this._bufferAmount = 0;
}
else
{
this._bufferAmount = this._reader.ReadBlock(this._buffer, 0, this._buffer.Length);
if (this._bufferAmount == 0 || this._bufferAmount < this._buffer.Length) this._finished = true;
}
}
public override int ReadBlock(char[] buffer, int index, int count)
{
if (count == 0) return 0;
if (buffer == null) throw new ArgumentNullException("buffer");
if (index < 0) throw new ArgumentException("index", "Index must be >= 0");
if (count < 0) throw new ArgumentException("count", "Count must be >= 0");
if ((buffer.Length - index) < count) throw new ArgumentException("Buffer too small");
if (this._bufferAmount == -1 || this._pos >= this._bufferAmount)
{
if (!this._finished)
{
this.FillBuffer();
if (this.EndOfStream) return 0;
}
else
{
return 0;
}
}
this._pos = Math.Max(0, this._pos);
if (count <= this._bufferAmount - this._pos)
{
//If we have sufficient things buffered to fufill the request just copy the relevant stuff across
Array.Copy(this._buffer, this._pos, buffer, index, count);
this._pos += count;
return count;
}
else
{
int copied = 0;
while (copied < count)
{
int available = this._bufferAmount - this._pos;
if (count < copied + available)
{
//We can finish fufilling this request this round
int toCopy = Math.Min(available, count - copied);
Array.Copy(this._buffer, this._pos, buffer, index + copied, toCopy);
copied += toCopy;
this._pos += toCopy;
return copied;
}
else
{
//Copy everything we currently have available
Array.Copy(this._buffer, this._pos, buffer, index + copied, available);
copied += available;
this._pos = this._bufferAmount;
if (!this._finished)
{
//If we haven't reached the end of the input refill our buffer and continue
this.FillBuffer();
if (this.EndOfStream) return copied;
this._pos = 0;
}
else
{
//Otherwise we have reached the end of the input so just return what we've managed to copy
return copied;
}
}
}
return copied;
}
}
public override int Read(char[] buffer, int index, int count)
{
return this.ReadBlock(buffer, index, count);
}
public override int Read()
{
if (this._bufferAmount == -1 || this._pos >= this._bufferAmount - 1)
{
if (!this._finished)
{
this.FillBuffer();
if (this.EndOfStream) return -1;
}
else
{
return -1;
}
}
this._pos++;
return (int)this._buffer[this._pos];
}
public override int Peek()
{
if (this._bufferAmount == -1 || this._pos >= this._bufferAmount - 1)
{
if (!this._finished)
{
this.FillBuffer();
if (this.EndOfStream) return -1;
}
else
{
return -1;
}
}
return (int)this._buffer[this._pos + 1];
}
public bool EndOfStream
{
get
{
return this._finished && (this._pos >= this._bufferAmount - 1);
}
}
public override void Close()
{
this._reader.Close();
}
protected override void Dispose(bool disposing)
{
this.Close();
this._reader.Dispose();
base.Dispose(disposing);
}
}