Read input pending in the input buffer of StreamIn and return
it in the difference list Codes-Tail. That is, the
available characters codes are used to create the list Codes
ending in the tail Tail. On encountering end-of-file, both
Codes and Tail are unified with the empty list ([]).
This predicate is intended for efficient unbuffered copying and
filtering of input coming from network connections or devices. It also
enables the library library(pure_input), which processes
input from files and streams using a DCG.
The following code fragment realises efficient non-blocking copying
of data from an input to an output stream. The at_end_of_stream/1
call checks for end-of-stream and fills the input buffer. Note that the
use of a get_code/2
and put_code/2
based loop requires a flush_output/1
call after each put_code/2.
The copy_stream_data/2
does not allow for inspection of the copied data and suffers from the
same buffering issues.
copy(In, Out) :-
repeat,
fill_buffer(In),
read_pending_codes(In, Chars, Tail),
\+ \+ ( Tail = [],
format(Out, '~s', [Chars]),
flush_output(Out)
),
( Tail == []
-> !
; fail
).
