Problem $1.$ A certain file foo contains the ASCII text string "This file contains $28$ bytes.". That is$,$ the bytes of the file, viewed as $8-$bit integers, contain the values $0$x$54,0$x$65,0$x$73,0$x$74,$ and $0$x$20,$ etc.

a$.$ Suppose a program opens foo for reading and writing $($file descriptor fd is returned$),$ and it contains a declaration char buf$[30]$;

The program then does the following.

if $(($rv $=$ read$($fd$,$buf,$10))<0)\{...$handle error... $\}$ if $(($rv $=$ write$($fd$,$buf,$10))<0)\{...$ handle error... $\}$

Assuming both calls return $10,$ what does the file contain after this code runs?

b$.$ Suppose the same program next calls lseek$($fd$,0,$SEEK$\_$SET$)$ to $$rewind$$ the file offset to the beginning, and then does the following:

if $(($rv $=$ read$($fd$,$buf,$30))<0)\{...$handle error... $\}$ strcpy$($buf$,$"That"$)$; if $(($rv $=$ write$($fd$,$buf,rv$))<0)\{...$ handle error... $\}$

What does the file now contain?