NAME
Future::Buffer - a string buffer that uses Futures
SYNOPSIS
use Future::Buffer;
use Future::AsyncAwait;
use Future::IO;
my $buffer = Future::Buffer->new(
fill => sub { Future::IO->sysread( $socket, 8192 ) }
);
async sub print_lines
{
while(1) {
my $line = await $buffer->read_until( "\n" );
chomp $line;
say "Got a line: $line";
}
}
await print_lines();
DESCRIPTION
Objects in this class provide a string buffer, on which operations
return Future instances which will complete when data is available.
Data can be inserted into the buffer either in a push-based manner by
calling the write method, or in a pull-based manner by providing it
with a fill callback by which it can request data itself. This
flexibility allows the buffer to act as an adapter between push- and
pull-based providers and consumers.
Each read-like method returns a Future which will complete once there
are enough bytes in the buffer to satisfy the required condition. The
buffer behaves somewhat like a pipe, where bytes provided at the
writing end (either by the write method or the fill callback) are
eventually consumed at the reading end by one of the read futures.
Multiple read futures can remain pending at once, and will be completed
in the order they were created when more data is eventually available.
Thus, any call to the write method to provide more data can potentially
result in multiple futures becoming ready.
Since version 0.04 the buffer supports an end-of-file condition. The
"close" method or a fill callback future yielding an empty result will
mark that the buffer is now closed. Once it has exhausted the remaining
stored data any further read futures will yield empty.
CONSTRUCTOR
new
$buffer = Future::Buffer->new( %args );
Returns a new Future::Buffer instance.
Takes the following named arguments:
fill => CODE
$data = await $fill->();
Optional callback which the buffer will invoke when it needs more
data.
Any read futures which are waiting on the fill future are constructed
by using the fill future as a prototype, ensuring they have the
correct type.
If the result is an empty list this will be treated as an end-of-file
notification and the buffer is closed.
METHODS
length
$len = $buffer->length;
Returns the length of the currently-stored data; that is, data that has
been provided by write calls or the fill callback but not yet consumed
by a read future.
is_empty
$empty = $buffer->is_empty;
Returns true if the stored length is zero.
write
$f = $buffer->write( $data );
Appends to the stored data, invoking any pending read futures that are
outstanding and can now complete.
Currently this method returns an already-completed Future. Some later
version may implement a buffer maximum size, and choose not to complete
this future until there is enough space to accept the new data. For now
it is safe for the caller to ignore the return value, but it may become
not so.
close
$buffer->close;
Marks that the buffer is now at EOF condition. Once any remaining
buffered content is consumed, any further read futures will all yield
EOF condition.
read_atmost
$data = await $buffer->read_atmost( $len );
Returns a future which will complete when there is some data available
in the buffer and will yield up too the given length. Note that,
analogous to calling the read IO method on a filehandle, this can still
complete and yield a shorter length if less is currently available.
If the stream is closed and there is no remaining data, the returned
future will yield empty.
read_exactly
$data = await $buffer->read_exactly( $len );
Returns a future which will complete when there is enough data
available in the buffer to yield exactly the length given.
If the stream is closed and there is no remaining data, the returned
future will yield empty.
read_until
$data = await $buffer->read_until( $pattern );
Returns a future which will complete when the buffer contains a match
for the given pattern (which may either be a plain string or a compiled
Regexp). The future will yield the contents of the buffer up to and
including this match.
If the stream is closed and there is no remaining data, the returned
future will yield empty.
For example, a readline-like operation can be performed by
$f = $buffer->read_until( "\x0d\x0a" );
read_unpacked
$data = await $buffer->read_unpacked( $pack_format );
Since version 0.03.
Returns a future which will complete when the buffer contains enough
data to unpack all of the requested fields using the given pack()
format. The future will yield a list of all the fields extracted by the
format.
If the stream is closed and there is no remaining data, the returned
future will yield empty.
Note that because the implementation is shamelessly stolen from
IO::Handle::Packable the same limitations on what pack formats are
recognized will apply.
unread
$buffer->unread( $data );
Since version 0.03.
Prepends more data back into the buffer,
It is uncommon to need this method, but it may be useful in certain
situations such as when it is hard to determine upfront how much data
needs to be read for a single operation, and it turns out too much was
read. The trailing content past what is needed can be put back for a
later operation.
Note that use of this method causes an inherent race condition between
outstanding read futures and existing data in the buffer. If there are
no pending futures then this is safe. If there is no existing data
already in the buffer this is also safe. If neither of these is true
then a warning is printed indicating that the logic of the caller is
not well-defined.
TODO
* An "on-read" event, taking maybe inspiration from
IO::Async::Stream. This would allow both pull- and push-based
consumers.
* Size limitation. Allow an upper bound of stored data, make write
calls return pending futures until buffer can accept it. Needs
consideration of unbounded read_until though.
* Consider extensions of the "read_unpacked" method to handle more
situations. This may require building a shared CPAN module for doing
streaming-unpack along with IO::Handle::Packable and other
situations.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
Inspired by Ryu::Buffer by Tom Molesworth <TEAM@cpan.org>