您应该传入以下之一:
- 包含要计算哈希值的数据块的字节数组
- 限制访问要计算哈希值的数据块的流
第二个选项并不那么难,这里是我做的一个快速LINQPad程序。请注意,它缺少相当多的错误处理,例如检查块是否实际可用(即,您正在传递流的位置和长度实际存在且没有超出基础流的末尾)。
不用说,如果这将成为生产代码,我会添加大量的错误处理,并编写大量单元测试以确保正确处理所有边缘情况。
您可以像这样构造文件的PartialStream
实例:
const long gb = 1024 * 1024 * 1024;
using (var fileStream = new FileStream(@"d:\temp\too_long_file.bin", FileMode.Open))
using (var chunk = new PartialStream(fileStream, 2 * gb, 1 * gb))
{
var hash = hashAlgorithm.ComputeHash(chunk);
}
这是 LINQPad 的测试程序:
void Main()
{
var buffer = Enumerable.Range(0, 256).Select(i => (byte)i).ToArray();
using (var underlying = new MemoryStream(buffer))
using (var partialStream = new PartialStream(underlying, 64, 32))
{
var temp = new byte[1024];
partialStream.Read(temp, 0, temp.Length);
temp.Dump();
}
}
public class PartialStream : Stream
{
private readonly Stream _UnderlyingStream;
private readonly long _Position;
private readonly long _Length;
public PartialStream(Stream underlyingStream, long position, long length)
{
if (!underlyingStream.CanRead || !underlyingStream.CanSeek)
throw new ArgumentException("underlyingStream");
_UnderlyingStream = underlyingStream;
_Position = position;
_Length = length;
_UnderlyingStream.Position = position;
}
public override bool CanRead
{
get
{
return _UnderlyingStream.CanRead;
}
}
public override bool CanWrite
{
get
{
return false;
}
}
public override bool CanSeek
{
get
{
return true;
}
}
public override long Length
{
get
{
return _Length;
}
}
public override long Position
{
get
{
return _UnderlyingStream.Position - _Position;
}
set
{
_UnderlyingStream.Position = value + _Position;
}
}
public override void Flush()
{
throw new NotSupportedException();
}
public override long Seek(long offset, SeekOrigin origin)
{
switch (origin)
{
case SeekOrigin.Begin:
return _UnderlyingStream.Seek(_Position + offset, SeekOrigin.Begin) - _Position;
case SeekOrigin.End:
return _UnderlyingStream.Seek(_Length + offset, SeekOrigin.Begin) - _Position;
case SeekOrigin.Current:
return _UnderlyingStream.Seek(offset, SeekOrigin.Current) - _Position;
default:
throw new ArgumentException("origin");
}
}
public override void SetLength(long length)
{
throw new NotSupportedException();
}
public override int Read(byte[] buffer, int offset, int count)
{
long left = _Length - Position;
if (left < count)
count = (int)left;
return _UnderlyingStream.Read(buffer, offset, count);
}
public override void Write(byte[] buffer, int offset, int count)
{
throw new NotSupportedException();
}
}
TransformBlock
和TransformFinalBlock
。 - CodesInChaosComputeHash(stream)
会分块读取流,对每个块调用TransformBlock
方法,并在最后调用TransformFinalBlock
方法。你不需要使用 1GB 的数组来计算 1GB 块的哈希值。 - CodesInChaos