我有一个以自定义文件格式存储的大型数据集(~1 1GB),其中最后16个字节是文件所有先前字节的MD5散列。
我想使用HashAlgorithm.ComputeHash(流)根据嵌入的MD5来验证这个文件的MD5,但是这会计算整个文件的哈希值,包括最后16个字节的哈希值,这显然不会起作用。
如何计算部分流的MD5哈希值?我知道我可以将流读入一个数组并将其传递给HashAlgorithm.ComputeHash(字节),但是在内存中复制这1 1GB数据的开销是很高的。
发布于 2011-05-18 15:20:59
取自here,在那里您还可以获得其他方法。
创建一个部分文件流类,读取你想要的大小,并对其进行散列。
class PartialFileStream : FileStream
{
public PartialFileStream(string path, FileMode mode, long startPosition, long endPosition): base(path, mode)
{
base.Seek(startPosition, SeekOrigin.Begin);
ReadTillPosition = endPosition;
}
public long ReadTillPosition { get; set; }
public override int Read(byte[] array, int offset, int count)
{
if (base.Position >= this.ReadTillPosition)
return 0;
if (base.Position + count > this.ReadTillPosition)
count = (int)(this.ReadTillPosition - base.Position);
return base.Read(array, offset, count);
}
}
发布于 2011-05-18 15:22:28
您可以使用FileStream.Seek选项查找到流的特定位置并从中读取。
发布于 2019-06-13 07:30:33
我发现自己在6个月内第二次需要这个,所以发布了我的部分输入流的解决方案。
class PartialStream: Stream {
public Stream Source { get; }
public long Offset { get; }
public override long Length { get; }
private long End => Offset + Length;
public override bool CanRead => true;
public override bool CanSeek => false;
public override bool CanWrite => false;
public override long Position {
get => Source.Position - Offset;
set => throw new NotSupportedException();
}
public PartialStream(Stream source, long length) {
Offset = source.Position;
Length = length;
}
public PartialStream(Stream source, long offset, long length, bool seekToOffset = true) {
if (seekToOffset) source.Seek(offset, SeekOrigin.Begin);
Offset = offset;
Length = length;
}
public override int Read(byte[] array, int offset, int count) {
if (Source.Position >= End) return 0;
if (Source.Position + count > End)
count = (int)(End - Source.Position);
return Source.Read(array, offset, count);
}
public override void Flush() => throw new NotSupportedException();
public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
public override void SetLength(long value) => throw new NotSupportedException();
public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
}
https://stackoverflow.com/questions/6041117
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