streaming-psgi.pl

# StreamingPSGI - Everything is streaming, no special cases
my $env = {
  SERVER_NAME         => 'localhost',
  SERVER_PORT         => 80,
  SCRIPT_NAME         => '',
  REQUEST_METHOD      => 'GET',
  HTTP_CONTENT_LENGTH => 12,
  version             => 3,
  url_scheme          => 'http',
  read                => sub {...},
  status              => sub {...},
  write               => sub {...}
};

# Streaming application
my $app = sub {
  my $env = shift;

  # Request body
  my $input = '';
  $env->{read} = sub {
    my $chunk = shift;
    return $input .= $chunk if defined $chunk;

    # Response
    my $output = "echo: $input";
    $env->{status}->(200, 'OK', ['Content-Length' => length($output)]);
    $env->{write}->($output);
  };
};

# Streaming middleware
my $middleware = sub {
  my ($env, $next) = @_;

  # Response body
  my $write = $env->{write};
  $env->{write} = sub {
    my $chunk = shift;
    say "OUTPUT CHUNK: $chunk";
    return $write->($chunk);
  };

  # Forward to next middleware
  $next->();

  # Request body
  my $read = $env->{read};
  $env->{read} = sub {
    my $chunk = shift;
    say "INPUT CHUNK: $chunk";
    return $read->($chunk);
  };
};

Ruby version:

env = {
  :read => proc { },
  :write => proc { },
  :status => proc { }
}

app = proc do |env|
  input = ""
  read = env[:read]
  env[:read] = proc do
    # Chunking
    chunk = read.call
    return input << chunk if chunk

    # Response
    body = "Hello World!"
    env[:status].call([200, {'Content-Length' => body.size}])
    env[:write].call(body)
  end
end

class Middleware
  def initialize(app)
    @app = app
  end

  def call(env)
    # Request body
    read = env[:read]
    env[:read] = proc do
      read.call.tap do |chunk|
        puts "INPUT CHUNK: %p" % chunk
      end
    end

    # Response body
    write = env[:write]
    env[:write] = proc do
      write.call.tap do |chunk|
        puts "OUTPUT CHUNK: %p" % chunk
      end
    end

    @app.call(env)
  end
end