blocks|key|896872|text|取自here，在那里您还可以获得其他方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|896873|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。|896874|+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+%2B+count+>+this.ReadTillPosition)
+++count+=+(int)(this.ReadTillPosition+-+base.Position);

+return+base.Read(array,+offset,+count);
++}
}|code-block|syntax|javascript|896875|entityMap|0|LINK|mutability|MUTABLE|url|http://www.pcreview.co.uk/forums/partial-file-hashing-t3692182.html^0|2|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

Taken from <a href="http://www.pcreview.co.uk/forums/partial-file-hashing-t3692182.html" rel="noreferrer">here</a> where you can also get other ways of doing so.

Make a partial file stream class, read the size you want and make hash of it.

<pre><code> 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 &gt;= this.ReadTillPosition)
 return 0;

 if (base.Position + count &gt; this.ReadTillPosition)
 count = (int)(this.ReadTillPosition - base.Position);

 return base.Read(array, offset, count);
 }
}
</code></pre>

blocks|key|680181|text|您可以使用FileStream.Seek选项查找到流的特定位置并从中读取。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|680182|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.io.filestream.seek.aspx^0|5|F|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You can use the <a href="http://msdn.microsoft.com/en-us/library/system.io.filestream.seek.aspx" rel="nofollow">FileStream.Seek</a> option to seek to a particular position of the stream and read from there.

blocks|key|680252|text|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。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|680253|class+PartialStream:+Stream+{
++++public+Stream+Source+{+get;+}
++++public+long+Offset+{+get;+}
++++public+override+long+Length+{+get;+}

++++private+long+End+=>+Offset+%2B+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+%2B+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();
}|code-block|syntax|javascript|680254|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I've found myself needing this for a second time within 6 months, so posting my solution for a partial input stream.

<pre><code>class PartialStream: Stream {
 public Stream Source { get; }
 public long Offset { get; }
 public override long Length { get; }

 private long End =&gt; Offset + Length;

 public override bool CanRead =&gt; true;

 public override bool CanSeek =&gt; false;

 public override bool CanWrite =&gt; false;

 public override long Position {
 get =&gt; Source.Position - Offset;
 set =&gt; 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 &gt;= End) return 0;

 if (Source.Position + count &gt; End)
 count = (int)(End - Source.Position);

 return Source.Read(array, offset, count);
 }

 public override void Flush() =&gt; throw new NotSupportedException();
 public override long Seek(long offset, SeekOrigin origin) =&gt; throw new NotSupportedException();
 public override void SetLength(long value) =&gt; throw new NotSupportedException();
 public override void Write(byte[] buffer, int offset, int count) =&gt; throw new NotSupportedException();
}
</code></pre>

I have a large dataset (~1GB) stored in a custom file format, the last 16 bytes of which is an MD5 hash of all previous bytes of the file.

I want to verify the MD5 of this file against the embedded MD5 using HashAlgorithm.ComputeHash(Stream), however this will calculate the hash of the entire file INCLUDING the hash in the last 16bytes, which obviously wont work.

How do I compute the MD5 hash of PART of a stream? I know I can read the stream into an array and pass this to HashAlgorithm.ComputeHash(Bytes), however the overhead of duplicating this 1GB of data in memory is prohibitive.

Calculating MD5 hash of a partial stream

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...

问计算部分流的MD5散列
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