Unify BufferedFileStreamStrategy seeking

[adamsitnik]

Today while trying to find an answer to #78390 I've realized that BufferedFileStreamStrategy has two different approaches to seeking.

Seek provides a smart way of seeking that tries to avoid losing the buffered data if possible:

runtime/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/BufferedFileStreamStrategy.cs

Lines 936 to 946 in 031a16a

	// If the offset of the updated seek pointer in the buffer is still legal, then we can keep using the buffer:
	if (0 <= readPos && readPos < _readLen)
	{
	_readPos = (int)readPos;
	// Adjust the seek pointer of the underlying stream to reflect the amount of useful bytes in the read buffer:
	_strategy.Seek(_readLen - _readPos, SeekOrigin.Current);
	}
	else
	{ // The offset of the updated seek pointer is not a legal offset. Loose the buffer.
	_readPos = _readLen = 0;
	}

While Position setter is plain simple and always loses the buffered data:

runtime/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/BufferedFileStreamStrategy.cs

Lines 66 to 77 in 031a16a

	set
	{
	if (_writePos > 0)
	{
	FlushWrite();
	}
	_readPos = 0;
	_readLen = 0;
	_strategy.Position = value;
	}

Position should be "smart" too and most likely just delegate the work to Seek

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Issue Details

---

Today while trying to find an answer to #78390 I've realized that BufferedFileStreamStrategy has two different approaches to seeking.

Seek provides a smart way of seeking that tries to avoid losing the buffered data if possible:

runtime/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/BufferedFileStreamStrategy.cs

Lines 936 to 946 in 031a16a

	// If the offset of the updated seek pointer in the buffer is still legal, then we can keep using the buffer:
	if (0 <= readPos && readPos < _readLen)
	{
	_readPos = (int)readPos;
	// Adjust the seek pointer of the underlying stream to reflect the amount of useful bytes in the read buffer:
	_strategy.Seek(_readLen - _readPos, SeekOrigin.Current);
	}
	else
	{ // The offset of the updated seek pointer is not a legal offset. Loose the buffer.
	_readPos = _readLen = 0;
	}

While Position setter is plain simple and always loses the buffered data:

runtime/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/BufferedFileStreamStrategy.cs

Lines 66 to 77 in 031a16a

	set
	{
	if (_writePos > 0)
	{
	FlushWrite();
	}
	_readPos = 0;
	_readLen = 0;
	_strategy.Position = value;
	}

Position should be "smart" too and most likely just delegate the work to Seek

Author:	adamsitnik
Assignees:	-
Labels:	area-System.IO, good first issue, help wanted
Milestone:	8.0.0