Future::Buffer - a string buffer that uses Futures


       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";


    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.



       $buffer = Future::Buffer->new( %args )

    Returns a new Future::Buffer instance.

    Takes the following named arguments:

    fill => CODE

         $f = $fill->()
            $data = $f->get

      Optional callback which the buffer will invoke when it needs more

      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.



       $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.


       $empty = $buffer->is_empty

    Returns true if the stored length is zero.


       $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.


       $f = $buffer->read_atmost( $len )
          $data = $f->get

    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.


       $f = $buffer->read_exactly( $len )
          $data = $f->get

    Returns a future which will complete when there is enough data
    available in the buffer to yield exactly the length given.


       $f = $buffer->read_until( $pattern )
          $data = $f->get

    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.

    For example, a readline-like operation can be performed by

       $f = $buffer->read_until( "\x0d\x0a" );


      * An "on-read" event, taking maybe inspiration from
      IO::Async::Stream. This would allow both pull- and push-based

      * 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 some read + unpack assistance, to allow nice handling of
      binary protocols by unpacking out of the buffer directly.

      * Consider what happens at EOF. Add a close method for producers to
      call. Understand what fill would do there. Have all the pending read
      futures yield an empty list maybe?


    Paul Evans <>

    Inspired by Ryu::Buffer by Tom Molesworth <>