Dancer::Plugin::StreamData - stream responses that are of indeterminate
    (but potentially long) length

        package MyWebApp;
        use Dancer;
        use Dancer::Plugin::StreamData;
        get '/some_route' => sub {

            # ...
            return stream_data($data_obj, \&stream_my_data);
        sub stream_my_data {
            my ($data_obj, $writer) = @_;
            while ( $output = $data_obj->get_some_data() )

    This plugin is useful for situations in which a Dancer application wants
    to return a large set of data, of indeterminate length, such as the
    results from a database query. This is especially important where the
    result set might total tens or hundreds of megabytes, which would be
    awkward to marshall within the memory of a single server process and
    could lead to a long delay before the start of data delivery.

    The "stream_data" function allows the application to stream a response
    one chunk at a time. For example, the data could be fetched row by row
    from a database server, with each row processed and then dispatched to
    the client via the write() method.

    This module can be used with any PSGI compatible web server that
    supports streaming.

    This function takes two parameters: a data object, and a stream
    callback. The data object need not contain the data itself; it may be a
    database handle or other reference by means of which the data will be
    obtained. The callback can be specified either as a code reference, or
    as a string. In the latter case, it will be invoked as a method call on
    the data object.

    Before calling "stream_data", the HTTP status and response headers may
    be set by the usual mechanisms of Dancer. A call to "stream_data" will
    terminate route processing, analagous to "send_file". Any further code
    in the route will be ignored. If an 'after' hook is defined in this app,
    it will be called as usual after route processing and may modify the
    response status and/or headers.

    The callback is invoked after the response headers have been sent. Its
    job is to stream the body of the response. The callback is passed two
    parameters: the data object, and a 'writer' object.

    The writer object, as specified by PSGI, implements two methods:

    Sends its argument immediately to the client as part of the response
    body. You can call this method as many times as necessary to send all of
    the data.

    Closes the connection to the client, terminating the response. It is
    important to call "close" at the end of processing, otherwise the client
    will erroneously report that the connection was closed prematurely
    before all of the data was sent.

    This function returns true if the server you are working with supports
    PSGI-style streaming, false otherwise.

        if ( server_supports_streaming ) {
            stream_data($query, 'streamResult');
        } else {
            return $query->generateResult();

    Michael McClennen, <>



    Copyright (C) 2012 by Michael McClennen

    This program is free software; you can redistribute it and/or modify it
    under the terms of either: the GNU General Public License as published
    by the Free Software Foundation; or the Artistic License.

    See for more information.