我想做一些大致相当于下面代码示例的事情。我想生成并提供数据流，而不必在任何时候将整个数据集都放在内存中。
看起来我需要一些在其构造函数中接受IEnumerable<string>（或IEnumerable<byte>）的Stream实现。在内部，此Stream只会在读取Stream或根据需要时移动IEnumerable。但我不知道这样的任何Stream实现。
我是在正确的轨道上吗？你知道怎么办这样的事吗？
public FileStreamResult GetResult()
{
IEnumerable<string> data = GetDataForStream();
Stream dataStream = ToStringStream(Encoding.UTF8, data);
return File(dataStream, "text/plain", "Result");
}
private IEnumerable<string> GetDataForStream()
{
StringBuilder sb;
for (int i = 0; i < 10000; i++)
{
yield return i.ToString();
yield return "\r\n";
}
}
private Stream ToStringStream(Encoding encoding, IEnumerable<string> data)
{
// I have to write my own implementation of stream?
throw new NotImplementedException();
}
我创建了一个名为ProducerConsumerStream的类来执行此操作。生产者将数据写入流并且消费者读取。中间有一个缓冲区，以便生产者可以“先写”一点。您可以定义缓冲区的大小。
无论如何，如果它不是你正在寻找的，我怀疑它会让你很好地了解它是如何完成的。见Building a new type of stream。
链接过时了，所以我在这里复制了我的代码。原始文章仍然可以在https://web.archive.org/web/20151210235510/http://www.informit.com/guides/content.aspx?g=dotnet&seqNum=852的Wayback机器上找到
首先，ProducerConsumerStream类：
using System;
using System.IO;
using System.Threading;
using System.Diagnostics;
namespace Mischel.IO
{
// This class is safe for 1 producer and 1 consumer.
public class ProducerConsumerStream : Stream
{
private byte[] CircleBuff;
private int Head;
private int Tail;
public bool IsAddingCompleted { get; private set; }
public bool IsCompleted { get; private set; }
// For debugging
private long TotalBytesRead = 0;
private long TotalBytesWritten = 0;
public ProducerConsumerStream(int size)
{
CircleBuff = new byte[size];
Head = 1;
Tail = 0;
}
[Conditional("JIM_DEBUG")]
private void DebugOut(string msg)
{
Console.WriteLine(msg);
}
[Conditional("JIM_DEBUG")]
private void DebugOut(string fmt, params object[] parms)
{
DebugOut(string.Format(fmt, parms));
}
private int ReadBytesAvailable
{
get
{
if (Head > Tail)
return Head - Tail - 1;
else
return CircleBuff.Length - Tail + Head - 1;
}
}
private int WriteBytesAvailable { get { return CircleBuff.Length - ReadBytesAvailable - 1; } }
private void IncrementTail()
{
Tail = (Tail + 1) % CircleBuff.Length;
}
public override int Read(byte[] buffer, int offset, int count)
{
if (disposed)
{
throw new ObjectDisposedException("The stream has been disposed.");
}
if (IsCompleted)
{
throw new EndOfStreamException("The stream is empty and has been marked complete for adding.");
}
if (count == 0)
{
return 0;
}
lock (CircleBuff)
{
DebugOut("Read: requested {0:N0} bytes. Available = {1:N0}.", count, ReadBytesAvailable);
while (ReadBytesAvailable == 0)
{
if (IsAddingCompleted)
{
IsCompleted = true;
return 0;
}
Monitor.Wait(CircleBuff);
}
// If Head < Tail, then there are bytes available at the end of the buffer
// and also at the front of the buffer.
// If reading from Tail to the end doesn't fulfill the request,
// and there are still bytes available,
// then read from the start of the buffer.
DebugOut("Read: Head={0}, Tail={1}, Avail={2}", Head, Tail, ReadBytesAvailable);
IncrementTail();
int bytesToRead;
if (Tail > Head)
{
// When Tail > Head, we know that there are at least
// (CircleBuff.Length - Tail) bytes available in the buffer.
bytesToRead = CircleBuff.Length - Tail;
}
else
{
bytesToRead = Head - Tail;
}
// Don't read more than count bytes!
bytesToRead = Math.Min(bytesToRead, count);
Buffer.BlockCopy(CircleBuff, Tail, buffer, offset, bytesToRead);
Tail += (bytesToRead - 1);
int bytesRead = bytesToRead;
// At this point, either we've exhausted the buffer,
// or Tail is at the end of the buffer and has to wrap around.
if (bytesRead < count && ReadBytesAvailable > 0)
{
// We haven't fulfilled the read.
IncrementTail();
// Tail is always equal to 0 here.
bytesToRead = Math.Min((count - bytesRead), (Head - Tail));
Buffer.BlockCopy(CircleBuff, Tail, buffer, offset + bytesRead, bytesToRead);
bytesRead += bytesToRead;
Tail += (bytesToRead - 1);
}
TotalBytesRead += bytesRead;
DebugOut("Read: returning {0:N0} bytes. TotalRead={1:N0}", bytesRead, TotalBytesRead);
DebugOut("Read: Head={0}, Tail={1}, Avail={2}", Head, Tail, ReadBytesAvailable);
Monitor.Pulse(CircleBuff);
return bytesRead;
}
}
public override void Write(byte[] buffer, int offset, int count)
{
if (disposed)
{
throw new ObjectDisposedException("The stream has been disposed.");
}
if (IsAddingCompleted)
{
throw new InvalidOperationException("The stream has been marked as complete for adding.");
}
lock (CircleBuff)
{
DebugOut("Write: requested {0:N0} bytes. Available = {1:N0}", count, WriteBytesAvailable);
int bytesWritten = 0;
while (bytesWritten < count)
{
while (WriteBytesAvailable == 0)
{
Monitor.Wait(CircleBuff);
}
DebugOut("Write: Head={0}, Tail={1}, Avail={2}", Head, Tail, WriteBytesAvailable);
int bytesToCopy = Math.Min((count - bytesWritten), WriteBytesAvailable);
CopyBytes(buffer, offset + bytesWritten, bytesToCopy);
TotalBytesWritten += bytesToCopy;
DebugOut("Write: {0} bytes written. TotalWritten={1:N0}", bytesToCopy, TotalBytesWritten);
DebugOut("Write: Head={0}, Tail={1}, Avail={2}", Head, Tail, WriteBytesAvailable);
bytesWritten += bytesToCopy;
Monitor.Pulse(CircleBuff);
}
}
}
private void CopyBytes(byte[] buffer, int srcOffset, int count)
{
// Insert at head
// The copy might require two separate operations.
// copy as much as can fit between Head and end of the circular buffer
int offset = srcOffset;
int bytesCopied = 0;
int bytesToCopy = Math.Min(CircleBuff.Length - Head, count);
if (bytesToCopy > 0)
{
Buffer.BlockCopy(buffer, offset, CircleBuff, Head, bytesToCopy);
bytesCopied = bytesToCopy;
Head = (Head + bytesToCopy) % CircleBuff.Length;
offset += bytesCopied;
}
// Copy the remainder, which will go from the beginning of the buffer.
if (bytesCopied < count)
{
bytesToCopy = count - bytesCopied;
Buffer.BlockCopy(buffer, offset, CircleBuff, Head, bytesToCopy);
Head = (Head + bytesToCopy) % CircleBuff.Length;
}
}
public void CompleteAdding()
{
if (disposed)
{
throw new ObjectDisposedException("The stream has been disposed.");
}
lock (CircleBuff)
{
DebugOut("CompleteAdding: {0:N0} bytes written.", TotalBytesWritten);
IsAddingCompleted = true;
Monitor.Pulse(CircleBuff);
}
}
public override bool CanRead { get { return true; } }
public override bool CanSeek { get { return false; } }
public override bool CanWrite { get { return true; } }
public override void Flush() { /* does nothing */ }
public override long Length { get { throw new NotImplementedException(); } }
public override long Position
{
get { throw new NotImplementedException(); }
set { throw new NotImplementedException(); }
}
public override long Seek(long offset, SeekOrigin origin)
{
throw new NotImplementedException();
}
public override void SetLength(long value)
{
throw new NotImplementedException();
}
private bool disposed = false;
protected override void Dispose(bool disposing)
{
if (!disposed)
{
base.Dispose(disposing);
disposed = true;
}
}
}
}
以及如何使用它的示例：
class Program
{
static readonly string TestText = "This is a test of the emergency broadcast system.";
static readonly byte[] TextBytes = Encoding.UTF8.GetBytes(TestText);
const int Megabyte = 1024 * 1024;
const int TestBufferSize = 12;
const int ProducerBufferSize = 4;
const int ConsumerBufferSize = 5;
static void Main(string[] args)
{
Console.WriteLine("TextBytes contains {0:N0} bytes.", TextBytes.Length);
using (var pcStream = new ProducerConsumerStream(TestBufferSize))
{
Thread ProducerThread = new Thread(ProducerThreadProc);
Thread ConsumerThread = new Thread(ConsumerThreadProc);
ProducerThread.Start(pcStream);
Thread.Sleep(2000);
ConsumerThread.Start(pcStream);
ProducerThread.Join();
ConsumerThread.Join();
}
Console.Write("Done. Press Enter.");
Console.ReadLine();
}
static void ProducerThreadProc(object state)
{
Console.WriteLine("Producer: started.");
var pcStream = (ProducerConsumerStream)state;
int offset = 0;
while (offset < TestText.Length)
{
int bytesToWrite = Math.Min(ProducerBufferSize, TestText.Length - offset);
pcStream.Write(TextBytes, offset, bytesToWrite);
offset += bytesToWrite;
}
pcStream.CompleteAdding();
Console.WriteLine("Producer: {0:N0} total bytes written.", offset);
Console.WriteLine("Producer: exit.");
}
static void ConsumerThreadProc(object state)
{
Console.WriteLine("Consumer: started.");
var instream = (ProducerConsumerStream)state;
int testOffset = 0;
var inputBuffer = new byte[TextBytes.Length];
int bytesRead;
do
{
int bytesToRead = Math.Min(ConsumerBufferSize, inputBuffer.Length - testOffset);
bytesRead = instream.Read(inputBuffer, testOffset, bytesToRead);
//Console.WriteLine("Consumer: {0:N0} bytes read.", bytesRead);
testOffset += bytesRead;
} while (bytesRead != 0);
Console.WriteLine("Consumer: {0:N0} total bytes read.", testOffset);
// Compare bytes read with TextBytes
for (int i = 0; i < TextBytes.Length; ++i)
{
if (inputBuffer[i] != TextBytes[i])
{
Console.WriteLine("Read error at position {0}", i);
break;
}
}
Console.WriteLine("Consumer: exit.");
}
}
这是一个使用Stream作为输入的只读IEnumerable<byte>实现：
public class ByteStream : Stream, IDisposable
{
private readonly IEnumerator<byte> _input;
private bool _disposed;
public ByteStream(IEnumerable<byte> input)
{
_input = input.GetEnumerator();
}
public override bool CanRead => true;
public override bool CanSeek => false;
public override bool CanWrite => false;
public override long Length => 0;
public override long Position { get; set; } = 0;
public override int Read(byte[] buffer, int offset, int count)
{
int i = 0;
for (; i < count && _input.MoveNext(); i++)
buffer[i + offset] = _input.Current;
return i;
}
public override long Seek(long offset, SeekOrigin origin) => throw new InvalidOperationException();
public override void SetLength(long value) => throw new InvalidOperationException();
public override void Write(byte[] buffer, int offset, int count) => throw new InvalidOperationException();
public override void Flush() => throw new InvalidOperationException();
void IDisposable.Dispose()
{
if (_disposed)
return;
_input.Dispose();
_disposed= true;
}
}
你还需要的是一个将IEnumerable<string>转换为IEnumerable<byte>的函数：
public static IEnumerable<byte> Encode(IEnumerable<string> input, Encoding encoding)
{
byte[] newLine = encoding.GetBytes(Environment.NewLine);
foreach (string line in input)
{
byte[] bytes = encoding.GetBytes(line);
foreach (byte b in bytes)
yield return b;
foreach (byte b in newLine)
yield return b;
}
}
最后，这是如何在您的控制器中使用它：
public FileResult GetResult()
{
IEnumerable<string> data = GetDataForStream();
var stream = new ByteStream(Encode(data, Encoding.UTF8));
return File(stream, "text/plain", "Result.txt");
}
我有同样的问题。在我的情况下，第三方包只接受流，但我有一个IEnumerable，并且无法在线找到答案，所以我写了自己的，我将分享：
public class IEnumerableStringReader : TextReader
{
private readonly IEnumerator<string> _enumerator;
private bool eof = false; // is set to true when .MoveNext tells us there is no more data.
private char[] curLine = null;
private int curLinePos = 0;
private bool disposed = false;
public IEnumerableStringReader(IEnumerable<string> input)
{
_enumerator = input.GetEnumerator();
}
private void GetNextLine()
{
if (eof) return;
eof = !_enumerator.MoveNext();
if (eof) return;
curLine = $"{_enumerator.Current}\r\n" // IEnumerable<string> input implies newlines exist betweent he lines.
.ToCharArray();
curLinePos = 0;
}
public override int Peek()
{
if (disposed) throw new ObjectDisposedException("The stream has been disposed.");
if (curLine == null || curLinePos == curLine.Length) GetNextLine();
if (eof) return -1;
return curLine[curLinePos];
}
public override int Read()
{
if (disposed) throw new ObjectDisposedException("The stream has been disposed.");
if (curLine == null || curLinePos == curLine.Length) GetNextLine();
if (eof) return -1;
return curLine[curLinePos++];
}
public override int Read(char[] buffer, int index, int count)
{
if (disposed) throw new ObjectDisposedException("The stream has been disposed.");
if (count == 0) return 0;
int charsReturned = 0;
int maxChars = Math.Min(count, buffer.Length - index); // Assuming we dont run out of input chars, we return count characters if we can. If the space left in the buffer is not big enough we return as many as will fit in the buffer.
while (charsReturned < maxChars)
{
if (curLine == null || curLinePos == curLine.Length) GetNextLine();
if (eof) return charsReturned;
int maxCurrentCopy = maxChars - charsReturned;
int charsAtTheReady = curLine.Length - curLinePos; // chars available in current line
int copySize = Math.Min(maxCurrentCopy, charsAtTheReady); // stop at end of buffer.
// cant use Buffer.BlockCopy because it's byte based and we're dealing with chars.
Array.ConstrainedCopy(curLine, curLinePos, buffer, index, copySize);
index += copySize;
curLinePos += copySize;
charsReturned += copySize;
}
return charsReturned;
}
public override string ReadLine()
{
if (curLine == null || curLinePos == curLine.Length) GetNextLine();
if (eof) return null;
if (curLinePos > 0) // this is necessary in case the client uses both Read() and ReadLine() calls
{
var tmp = new string(curLine, curLinePos, (curLine.Length - curLinePos) - 2); // create a new string from the remainder of the char array. The -2 is because GetNextLine appends a crlf.
curLinePos = curLine.Length; // so next call will re-read
return tmp;
}
// read full line.
curLinePos = curLine.Length; // so next call will re-read
return _enumerator.Current; // if all the client does is call ReadLine this (faster) code path will be taken.
}
protected override void Dispose(bool disposing)
{
if (!disposed)
{
_enumerator.Dispose();
base.Dispose(disposing);
disposed = true;
}
}
}
就我而言，我想将它用作Datastreams.Csv的输入：
using (var tr = new IEnumerableStringReader(input))
using (var reader = new CsvReader(tr))
{
while (reader.ReadRecord())
{
// do whatever
}
}
史蒂夫萨德勒写了一个完美的答案。然而，他使得比需要更困难
根据reference source of TextReader你只需要覆盖Peek和Read：
子类必须最低限度地实现Peek（）和Read（）方法。
所以首先我编写一个将IEnumerable<string>转换为IEnumerable<char>的函数，其中在每个字符串的末尾添加一个新行：
private static IEnumerable<char> ReadCharacters(IEnumerable<string> lines)
{
foreach (string line in lines)
{
foreach (char c in line + Environment.NewLine)
{
yield return c;
}
}
}
Environment.NewLine是在每个字符串末尾添加新行的部分。
现在课程相当简单：
class EnumStringReader : TextReader
{
public EnumStringReader(IEnumerable<string> lines)
{
this.enumerator = ReadCharacters(lines).GetEnumerator();
this.dataAvailable = this.enumerator.MoveNext();
}
private bool disposed = false;
private bool dataAvailable;
private readonly IEnumerator<char> enumerator;
构造函数需要读取一系列行。它使用此序列和较早编写的函数将序列转换为添加了Environment.NewLine的字符序列。
它获取转换序列的枚举器，并移动到第一个字符。它记得DataAvailable中是否有第一个角色
现在我们准备Peek：如果没有可用数据：return -1，否则返回当前字符为int。不要前进：
public override int Peek()
{
this.ThrowIfDisposed();
return this.dataAvailable ? this.enumerator.Current : -1;
}
读取：如果没有可用数据，则返回-1，否则返回当前字符为int。前进到下一个字符并记住是否有可用的数据：
public override int Read()
{
this.ThrowIfDisposed();
if (this.dataAvailable)
{
char nextChar = this.enumerator.Current;
this.dataAvailable = this.enumerator.MoveNext();
return (int)nextChar;
}
else
{
return -1;
}
}
不要忘记覆盖处理枚举器的Dispose（bool）。
这就是所需要的一切。所有其他功能都将使用这两个。
现在用以下行填充您的流：
IEnumerable<string> lines = ...
using (TextWriter writer = System.IO.File.CreateText(...))
{
using (TextReader reader = new EnumStringReader(lines);
{
// either write per char:
while (reader.Peek() != -1)
{
char c = (char)reader.Read();
writer.Write(c);
}
// or write per line:
string line = reader.ReadLine();
// line is without newLine!
while (line != null)
{
writer.WriteLine(line);
line = reader.ReadLine();
}
// or write per block
buffer buf = new char[4096];
int nrRead = reader.ReadBlock(buf, 0, buf.Length)
while (nrRead > 0)
{
writer.Write(buf, 0, nrRead);
nrRead = reader.ReadBlock(buf, 0, buf.Length);
}
}
}