/ 
Plack-App-MCCS-2.000000
River stage one • 2 direct dependents • 2 total dependents
/ Plack::App::MCCS

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',
		min_cache_dir => 'min_cache',
		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.

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).

If min_cache_dir is specified, it will do all its searching and storing of generated minified files within root/$min_cache_dir and ignore minified files outside that directory.

4. Compression

If the client supports compressed responses (via either the gzip, deflate or zstd encodings), as noted by 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 the appropriate compression module is installed, MCCS will compress the file, save the compressed 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 (or the appropriate extension for the algorithm), 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.

COMPARISON WITH OTHER MODULES

NOTE: this section is probably out of date.

Similar functionalities can be added to an application by using one or more of the following Plack middlewares (among others):

Plack::Middleware::Static or Plack::App::File will serve static files, but lack all the features of this module.

Plack::Middleware::Static::Minifier will minify CSS and JS on every request, even to the same file.

Plack::Middleware::Precompressed will serve precompressed .gz files, 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

Plack::Middleware::Deflater will compress representations with gzip/deflate algorithms on every request, even to the same file.

Plack::Middleware::ETag - will create ETags for files, but will calculate them again on every request.

Plack::Middleware::ConditionalGET will handle If-None-Match and If-Modified-Since, but it does not prevent the requested file from being opened for reading even if 304 Not Modified is to be returned, wasting system calls.

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

In any case, 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.

Plack::App::MCCS attempts to perform all of this faster and better.

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).

min_cache_dir - For unminified files, by default minified files are generated in the same directory as the original file. If this attribute is specified they are instead generated within root/$min_cache_dir, and minified files outside that directory are ignored, unless requested directly. This can make it easier to filter out generated files when validating a deployment.

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 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 warns. 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:

Plack::App::MCCS will use the following modules if they exist, in order to minify files or compress with specific algorithms.

INCOMPATIBILITIES WITH OTHER MODULES

None reported.

BUGS AND LIMITATIONS

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.

AUTHOR

Ido Perlmuter <ido@ido50.net>

ACKNOWLEDGMENTS

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

Christian Walde contributed new features and fixes for the 1.0.0 release.

LICENSE AND COPYRIGHT

Copyright (c) 2011-2023, Ido Perlmuter ido@ido50.net.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.