Vector cleared after use so it can be shrunk.

[simpsonst]

Sorry, I missed something in 5ea2004. The vector::shrink_to_fit call at XrdTpcStream.hh line 133 relies upon the vector size (which used to be always 0) being less than its capacity. (It seems it's only invoked when 'low buffer occupancy' is detected.) Now the (size, capacity) will only ever be either (0, 0) or (m_capacity, >=m_capacity), instead of (0, 0) or (0, m_capacity), so shrink_to_fit won't be able to fully de-allocate. I don't think it's a functional failure, but it could mean the allocation is retained for longer than expected.
By clearing the vector just after its contents are transmitted (and when m_size and m_offset are reset, marking the buffer as empty and available), shrink_to_fit should become effective again.