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Minify, Compress, Cache-control and Serve static files in Plack applications

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README
NAME
    Plack::App::MCCS - Minify, Compress, Cache-control and Serve static
    files from Plack applications

EXTENDS
    Plack::Component

SYNOPSIS
            # in your app.psgi:
            use Plack::Builder;
            use Plack::App::MCCS;

            my $app = sub { ... };

            # be happy with the defaults:
            builder {
                    mount '/static' => Plack::App::MCCS->new(root => '/path/to/static_files')->to_app;
                    mount '/' => $app;
            };

            # or tweak the app to suit your needs:
            builder {
                    mount '/static' => Plack::App::MCCS->new(
                            root => '/path/to/static_files',
                            defaults => {
                                    valid_for => 86400,
                                    cache_control => ['private'],
                            },
                            types => {
                                    '.htc' => {
                                            content_type => 'text/x-component',
                                            valid_for => 360,
                                            cache_control => ['no-cache', 'must-revalidate'],
                                    },
                            },
                    )->to_app;
                    mount '/' => $app;
            };

            # or use the supplied middleware
            builder {
                    enable 'Plack::Middleware::MCCS',
                            path => qr{^/static/},
                            root => '/path/to/static_files'; # all other options are supported
                    $app;
            };

DESCRIPTION
    "Plack::App::MCCS" is a Plack application that serves static files from
    a directory. It will prefer serving precompressed versions of files if
    they exist and the client supports it, and also prefer minified versions
    of CSS/JS files if they exist.

    If IO::Compress::Gzip is installed, "MCCS" will also automatically
    compress files that do not have a precompressed version and save the
    compressed versions to disk (so it only happens once and not on every
    request to the same file).

    If CSS::Minifier::XS and/or JavaScript::Minifier::XS are installed, it
    will also automatically minify CSS/JS files that do not have a
    preminified version and save them to disk (once again, will only happen
    once per file).

    This means "MCCS" needs to have write privileges to the static files
    directory. It would be better if files are preminified and
    precompressed, say automatically in your build process (if such a
    process exists). However, at some projects where you don't have an
    automatic build process, it is not uncommon to forget to
    minify/precompress. That's where automatic minification/compression is
    useful.

    Most importantly, "MCCS" will generate proper Cache Control headers for
    every file served, including "Last-Modified", "Expires", "Cache-Control"
    and even "ETag" (ETags are created automatically, once per file, and
    saved to disk for future requests). It will appropriately respond with
    "304 Not Modified" for requests with headers "If-Modified-Since" or
    "If-None-Match" when these cache validations are fulfilled, without
    actually having to read the files' contents again.

    "MCCS" is active by default, which means that if there are some things
    you *don't* want it to do, you have to *tell* it not to. This is on
    purpose, because doing these actions is the whole point of "MCCS".

  WAIT, AREN'T THERE EXISTING PLACK MIDDLEWARES FOR THAT?
    Yes and no. A similar functionality can be added to an application by
    using the following Plack middlewares:

    *   Plack::Middleware::Static or Plack::App::File - will serve static
        files

    *   Plack::Middleware::Static::Minifier - will minify CSS/JS

    *   Plack::Middleware::Precompressed - will serve precompressed .gz
        files

    *   Plack::Middleware::Deflater - will compress representations with
        gzip/deflate algorithms

    *   Plack::Middleware::ETag - will create ETags for files

    *   Plack::Middleware::ConditionalGET - will handle "If-None-Match" and
        "If-Modified-Since"

    *   Plack::Middleware::Header - will allow you to add cache control
        headers manually

    So why wouldn't I just use these middlewares? Here are my reasons:

    *   "Static::Minifier" will not minify to disk, but will minify on every
        request, even to the same file (unless you provide it with a cache,
        which is not that better). This pointlessly increases the load on
        the server.

    *   "Precompressed" is nice, but it relies on appending ".gz" to every
        request and sending it to the app. If the app returns "404 Not
        Found", it sends the request again without the ".gz" part. This
        might pollute your logs and I guess two requests to get one file is
        not better than one request. You can circumvent that with regex
        matching, but that isn't very comfortable.

    *   "Deflater" will not compress to disk, but do that on every request.
        So once again, this is a big load on the server for no real reason.
        It also has a long standing bug where deflate responses fail on
        Firefox, which is annoying.

    *   "ETag" will calculate the ETag again on every request.

    *   "ConditionalGET" does not prevent the requested file to be opened
        for reading even if "304 Not Modified" is to be returned (since that
        check is performed later). I'm not sure if it affects performance in
        anyway, probably not.

    *   No possible combination of any of the aformentioned middlewares
        seems to return proper (and configurable) Cache Control headers, so
        you need to do that manually, possibly with
        Plack::Middleware::Header, which is not just annoying if different
        file types have different cache settings, but doesn't even seem to
        work.

    *   I don't really wanna use so many middlewares just for this
        functionality.

    "Plack::App::MCCS" attempts to perform all of this faster and better.
    Read the next section for more info.

  HOW DOES MCCS HANDLE REQUESTS?
    When a request is handed to "Plack::App::MCCS", the following process is
    performed:

    1. Discovery:
        "MCCS" will try to find the requested path in the root directory. If
        the path is not found, "404 Not Found" is returned. If the path
        exists but is a directory, "403 Forbidden" is returned (directory
        listings might be supported in the future).

    2. Examination:
        "MCCS" will try to find the content type of the file, either by its
        extension (relying on Plack::MIME for that), or by a specific
        setting provided to the app by the user (will take precedence). If
        not found (or file has no extension), "text/plain" is assumed (which
        means you should give your files proper extensions if possible).

        "MCCS" will also determine for how long to allow browsers/proxy
        caches/whatever caches to cache the file. By default, it will set a
        representation as valid for 86400 seconds (i.e. one day). However,
        this can be changed in two ways: either by setting a different
        default when creating an instance of the application (see more info
        at the "new()" method's documentation below), or by setting a
        specific value for certain file types. Also, "MCCS" by default sets
        the "public" option for the "Cache-Control" header, meaning caches
        are allowed to save responses even when authentication is performed.
        You can change that the same way.

    3. Minification
        If the content type is "text/css" or "application/javascript",
        "MCCS" will try to find a preminified version of it on disk
        (directly, not with a second request). If found, this version will
        be marked for serving. If not found, and CSS::Minifier::XS or
        JavaScript::Minifier:XS are installed, "MCCS" will minify the file,
        save the minified version to disk, and mark it as the version to
        serve. Future requests to the same file will see the minified
        version and not minify again.

        "MCCS" searches for files that end with ".min.css" and ".min.js",
        and that's how it creates them too. So if a request comes to
        "style.css", "MCCS" will look for "style.min.css", possibly creating
        it if not found. The request path remains the same ("style.css")
        though, even internally. If a request comes to "style.min.css"
        (which you don't really want when using "MCCS"), the app will not
        attempt to minify it again (so you won't get things like
        "style.min.min.css").

    4. Compression
        If the client supports gzip encoding (deflate to be added in the
        future, probably), as noted with the "Accept-Encoding" header,
        "MCCS" will try to find a precompressed version of the file on disk.
        If found, this version is marked for serving. If not found, and
        IO::Compress::Gzip is installed, "MCCS" will compress the file, save
        the gzipped version to disk, and mark it as the version to serve.
        Future requests to the same file will see the compressed version and
        not compress again.

        "MCCS" searches for files that end with ".gz", and that's how it
        creates them too. So if a request comes to "style.css" (and it was
        minified in the previous step), "MCCS" will look for
        "style.min.css.gz", possibly creating it if not found. The request
        path remains the same ("style.css") though, even internally.

    5. Cache Validation
        If the client provided the "If-Modified-Since" header, "MCCS" will
        determine if the file we're serving has been modified after the
        supplied date, and return "304 Not Modified" immediately if not.

        Unless the file has the 'no-store' cache control option, and if the
        client provided the "If-None-Match" header, "MCCS" will look for a
        file that has the same name as the file we're going to serve, plus
        an ".etag" suffix, such as "style.min.css.gz.etag" for example. If
        found, the contents of this file is read and compared with the
        provided ETag. If the two values are equal, "MCCS" will immediately
        return "304 Not Modified".

    6. ETagging
        If an ".etag" file wasn't found in the previous step (and the file
        we're serving doesn't have the 'no-store' cache control option),
        "MCCS" will create one from the file's inode, last modification date
        and size. Future requests to the same file will see this ETag file,
        so it is not created again.

    7. Headers and Cache-Control
        "MCCS" now sets headers, especially cache control headers, as
        appropriate:

        "Content-Encoding" is set to "gzip" if a compressed version is
        returned.

        "Content-Length" is set with the size of the file in bytes.

        "Content-Type" is set with the type of the file (if a text file,
        charset string is appended, e.g. "text/css; charset=UTF-8").

        "Last-Modified" is set with the last modification date of the file
        in HTTP date format.

        "Expires" is set with the date in which the file will expire
        (determined in stage 2), in HTTP date format.

        "Cache-Control" is set with the number of seconds the representation
        is valid for (unless caching of the file is not allowed) and other
        options (determined in stage 2).

        "Etag" is set with the ETag value (if exists).

        "Vary" is set with "Accept-Encoding".

    8. Serving
        The file handle is returned to the Plack handler/server for serving.

  HOW DO WEB CACHES WORK ANYWAY?
    If you need more information on how caches work and cache control
    headers, read this great article <http://www.mnot.net/cache_docs/>.

CLASS METHODS
  new( %opts )
    Creates a new instance of this module. %opts *must* have the following
    keys:

    root - the path to the root directory where static files reside.

    %opts *may* have the following keys:

    encoding - the character set to append to content-type headers when text
    files are returned. Defaults to UTF-8.

    defaults - a hash-ref with some global defaults, the following options
    are supported:

    *   valid_for: the default number of seconds caches are allowed to save
        a response.

    *   cache_control: takes an array-ref of options for the "Cache-Control"
        header (all except for "max-age", which is automatically calculated
        from the resource's "valid_for" setting).

    *   minify: give this option a false value (0, empty string, "undef") if
        you don't want "MCCS" to automatically minify CSS/JS files (it will
        still look for preminified versions though).

    *   compress: like "minify", give this option a false value if you don't
        want "MCCS" to automatically compress files (it will still look for
        precompressed versions).

    *   etag: as above, give this option a false value if you don't want
        "MCCS" to automatically create and save ETags. Note that this will
        mean "MCCS" will NOT handle ETags at all (so if the client sends the
        "If-None-Match" header, "MCCS" will ignore it).

    Giving "minify", "compress" and "etag" false values is useful during
    development, when you don't want your project to be "polluted" with all
    those .gz, .min and .etag files.

    types - a hash-ref with file extensions that may be served (keys must
    begin with a dot, so give '.css' and not 'css'). Every extension takes a
    hash-ref that might have valid_for and cache_control as with the
    "defaults" option, but also content_type with the content type to return
    for files with this extension (useful when Plack::MIME doesn't know the
    content type of a file).

    If you don't want something to be cached, you need to give the valid_for
    option (either in "defaults" or for a specific file type) a value of
    either zero, or preferably any number lower than zero, which will cause
    "MCCS" to set an "Expires" header way in the past. You should also pass
    the cache_control option "no_store" and probably "no_cache". When "MCCS"
    encounteres the "no_store" option, it does not automatically add the
    "max-age" option to the "Cache-Control" header.

OBJECT METHODS
  call( \%env )
    Plack automatically calls this method to handle a request. This is where
    the magic (or disaster) happens.

CAVEATS AND THINGS TO CONSIDER
    *   You can't tell "MCCS" to not minify/compress a specific file type
        yet but only disable minification/compression altogether (in the
        "defaults" setting for the "new()" method).

    *   Directory listings are not supported yet (not sure if they will be).

    *   Deflate compression is not supported yet (just gzip).

    *   Caching middlewares such as Plack::Middleware::Cache and
        Plack::Middleware::Cached don't rely on Cache-Control headers (or so
        I understand) for their expiration values, which makes them less
        useful for applications that rely on "MCCS". You'll probably be
        better off with an external cache like Varnish
        <https://www.varnish-cache.org/> if you want a cache on your
        application server. Even without a server cache, your application
        should still appear faster for users due to browser caching (and
        also server load should be decreased).

    *   "Range" requests are not supported. See Plack::App::File::Range if
        you need that.

    *   The app is mounted on a directory and can't be set to only serve
        requests that match a certain regex. Use the middleware for that.

DIAGNOSTICS
    This module doesn't throw any exceptions, instead returning HTTP errors
    for the client and possibly issuing some "warn"s. The following list
    should help you to determine some potential problems with "MCCS":

    "failed gzipping %s: %s"
        This warning is issued when IO::Compress::Gzip fails to gzip a file.
        When it happens, "MCCS" will simply not return a gzipped
        representation.

    "Can't open ETag file %s.etag for reading"
        This warning is issued when "MCCS" can't read an ETag file, probably
        because it does not have enough permissions. The request will still
        be fulfilled, but it won't have the "ETag" header.

    "Can't open ETag file %s.etag for writing"
        Same as before, but when "MCCS" can't write an ETag file.

    "403 Forbidden" is returned for files that exist
        If a request for a certain file results in a "403 Forbidden" error,
        it probably means "MCCS" has no read permissions for that file.

CONFIGURATION AND ENVIRONMENT
    "Plack::App::MCCS" requires no configuration files or environment
    variables.

DEPENDENCIES
    "Plack::App::MCCS" depends on the following CPAN modules:

    *   parent

    *   Cwd

    *   Fcntl

    *   File::Spec::Unix

    *   HTTP::Date

    *   Module::Load::Conditional

    *   Plack (obviously)

    "Plack::App::MCCS" will use the following modules if they exist, in
    order to minify/compress files (if they are not installed, "MCCS" will
    not be able to minify/compress on its own):

    *   CSS::Minifier::XS

    *   JavaScript::Minifier::XS

    *   IO::Compress::Gzip

INCOMPATIBILITIES WITH OTHER MODULES
    None reported.

BUGS AND LIMITATIONS
    No bugs have been reported.

    Please report any bugs or feature requests to
    "bug-Plack-App-MCCS@rt.cpan.org", or through the web interface at
    <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Plack-App-MCCS>.

SEE ALSO
    Plack::Middleware::MCCS, Plack::Middleware::Static, Plack::App::File,
    Plack::Builder.

ACKNOWLEDGMENTS
    Some of this module's code is based on Plack::App::File by Tatsuhiko
    Miyagawa and Plack::Middleware::ETag by Franck Cuny.

AUTHOR
    Ido Perlmuter <ido@ido50.net>

LICENSE AND COPYRIGHT
    Copyright (c) 2011-2014, Ido Perlmuter "ido@ido50.net".

    This module is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself, either version 5.8.1 or any later
    version. See perlartistic and perlgpl.

    The full text of the license can be found in the LICENSE file included
    with this module.

DISCLAIMER OF WARRANTY
    BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
    FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
    OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
    PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER
    EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
    WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
    ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH
    YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
    NECESSARY SERVICING, REPAIR, OR CORRECTION.

    IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
    WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
    REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE
    TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR
    CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
    SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING
    RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A
    FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF
    SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
    DAMAGES.

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