Lots more documentation, including events and processors

README.rdoc

 =Paperclip
 
-Paperclip is intended as an easy file attachment library for ActiveRecord. The intent behind it was to keep setup as easy as possible and to treat files as much like other attributes as possible. This means they aren't saved to their final locations on disk, nor are they deleted if set to nil, until ActiveRecord::Base#save is called. It manages validations based on size and presence, if required. It can transform its assigned image into thumbnails if needed, and the prerequisites are as simple as installing ImageMagick (which, for most modern Unix-based systems, is as easy as installing the right packages). Attached files are saved to the filesystem and referenced in the browser by an easily understandable specification, which has sensible and useful defaults.
-
-See the documentation for the +has_attached_file+ method for options.
-
-==Usage
+Paperclip is intended as an easy file attachment library for ActiveRecord. The
+intent behind it was to keep setup as easy as possible and to treat files as
+much like other attributes as possible. This means they aren't saved to their
+final locations on disk, nor are they deleted if set to nil, until
+ActiveRecord::Base#save is called. It manages validations based on size and
+presence, if required. It can transform its assigned image into thumbnails if
+needed, and the prerequisites are as simple as installing ImageMagick (which,
+for most modern Unix-based systems, is as easy as installing the right
+packages). Attached files are saved to the filesystem and referenced in the
+browser by an easily understandable specification, which has sensible and
+useful defaults.
+
+See the documentation for +has_attached_file+ in Paperclip::ClassMethods for
+more detailed options.
+
+==Quick Start
 
 In your model:
 
@@ -48,12 +59,114 @@ In your show view:
   <%= image_tag @user.avatar.url(:medium) %>
   <%= image_tag @user.avatar.url(:thumb) %>
 
+==Usage
+
+The basics of paperclip are quite simple: Declare that your model has an
+attachment with the has_attached_file method, and give it a name. Paperclip
+will wrap up up to four attributes (all prefixed with that attachment's name,
+so you can have multiple attachments per model if you wish) and give the a
+friendly front end. The attributes are <attachment>_file_name,
+<attachment>_file_size, <attachment>_content_type, and <attachment>_updated_at.
+Only <attachment>_file_name is required for paperclip to operate. More
+information about the options to has_attached_file is available in the
+documentation of Paperclip::ClassMethods.
+
+Attachments can be validated with Paperclip's validation methods,
+validates_attachment_presence, validates_attachment_content_type, and
+validates_attachment_size.
+
+==Storage
+
+The files that are assigned as attachments are, by default, placed in the
+directory specified by the :path option to has_attached_file. By default, this
+location is
+":rails_root/public/system/:attachment/:id/:style/:basename.:extension". This
+location was chosen because on standard Capistrano deployments, the
+public/system directory is symlinked to the app's shared directory, meaning it
+will survive between deployments. For example, using that :path, you may have a
+file at
+
+  /data/myapp/releases/20081229172410/public/system/avatars/13/small/my_pic.png
+
+NOTE: This is a change from previous versions of Paperclip, but is overall a
+safer choice for the defaul file store.
+
+You may also choose to store your files using Amazon's S3 service. You can find
+more information about S3 storage at the description for
+Paperclip::Storage::S3.
+
+Files on the local filesystem (and in the Rails app's public directory) will be
+available to the internet at large. If you require access control, it's
+possible to place your files in a different location. You will need to change
+both the :path and :url options in order to make sure the files are unavailable
+to the public. Both :path and :url allow the same set of interpolated
+variables.
+
+==Post Processing
+
+Paperclip supports an extendible selection of post-processors. When you define
+a set of styles for an attachment, by default it is expected that those
+"styles" are actually "thumbnails". However, you can do more than just
+thumbnail images. By defining a subclass of Paperclip::Processor, you can
+perform any processing you want on the files that are attached. Any file in
+your Rails app's lib/paperclip_processor directory is automatically loaded by
+paperclip, allowing you to easily define custom processors. You can specify a
+processor with the :processors option to has_attached_file:
+
+  has_attached_file :scan, :styles => { :text => { :quality => :better } },
+                           :processors => [:ocr]
+
+This would load the hypothetical class Paperclip::Ocr, which would have the
+hash "{ :quality => :better }" passed to it along with the uploaded file. For
+more information about defining processors, see Paperclip::Processor.
+
+The default processor is Paperclip::Thumbnail. For backwards compatability
+reasons, you can pass a single geometry string or an array containing a
+geometry and a format, which the file will be converted to, like so:
+
+  has_attached_file :avatar, :styles => { :thumb => ["32x32#", :png] }
+
+This will convert the "thumb" style to a 32x32 square in png format, regardless
+of what was uploaded. If the format is not specified, it is kept the same (i.e.
+jpgs will remain jpgs).
+
+Multiple processors can be specified, and they will be invoked in the order
+they are defined in the :processors array. Each successive processor will
+be given the result of the previous processor's execution. All processors will
+receive the same parameters, which are what you define in the :styles hash.
+For example, assuming we had this definition:
+
+  has_attached_file :scan, :styles => { :text => { :quality => :better } },
+                           :processors => [:rotator, :ocr]
+
+then both the :rotator processor and the :ocr processor would receive the 
+options "{ :quality => :better }". This parameter may not mean anything to one
+or more or the processors, and they are free to ignore it.
+
+==Events
+
+Before and after the Post Processing step, Paperclip calls back to the model
+with a few callbacks, allowing the model to change or cancel the processing
+step. The callbacks are "before_post_process" and "after_post_process" (which
+are called before and after the processing of each attachment), and the
+attachment-specific "before_<attachment>_post_process" and
+"after_<attachment>_post_process". The callbacks are intended to be as close to
+normal ActiveRecord callbacks as possible, so if you return false (specifically
+-- returning nil is not the same) in a before_ filter, the post processing step
+will halt. Returning false in an after_ filter will not halt anything, but you
+can access the model and the attachment if necessary.
+
+NOTE: Post processing will not even *start* if the attachment is not valid
+according to the validations. Your callbacks (and processors) will only be
+called with valid attachments.
+
 ==Contributing
 
-If you'd like to contribute a feature or bugfix, thanks! To make sure your fix/feature
-has a high chance of being added, please read the following guidelines:
+If you'd like to contribute a feature or bugfix: Thanks! To make sure your
+fix/feature has a high chance of being included, please read the following
+guidelines:
 
 1. Ask on the mailing list, or post a ticket in Lighthouse.
-2. Make sure there are tests! I will not accept any patch that is not tested.
-   It's a rare time when explicit tests aren't needed. If you have questions about
-   writing tests for paperclip, please ask the mailing list.
+2. Make sure there are tests! We will not accept any patch that is not tested.
+   It's a rare time when explicit tests aren't needed. If you have questions 
+   about writing tests for paperclip, please ask the mailing list.

lib/paperclip.rb

@@ -71,7 +71,16 @@ module Paperclip
       File.join(*path)
     end
 
-    def run cmd, params = "", expected_outcodes = 0 #:nodoc:
+    # The run method takes a command to execute and a string of parameters
+    # that get passed to it. The command is prefixed with the :command_path
+    # option from Paperclip.options. If you have many commands to run and
+    # they are in different paths, the suggested course of action is to
+    # symlink them so they are all in the same directory.
+    #
+    # If the command returns with a result code that is not one of the
+    # expected_outcodes, a PaperclipCommandLineError will be raised. Generally
+    # a code of 0 is expected, but a list of codes may be passed if necessary.
+    def run cmd, params = "", expected_outcodes = 0
       output = `#{%Q[#{path_for_command(cmd)} #{params} 2>#{bit_bucket}].gsub(/\s+/, " ")}`
       unless [expected_outcodes].flatten.include?($?.exitstatus)
         raise PaperclipCommandLineError, "Error while running #{cmd}"

lib/paperclip/processor.rb

 module Paperclip
+  # Paperclip processors allow you to modify attached files when they are
+  # attached in any way you are able. Paperclip itself uses command-line
+  # programs for its included Thumbnail processor, but custom processors
+  # are not required to follow suit.
+  #
+  # Processors are required to be defined inside the Paperclip module and
+  # are also required to be a subclass of Paperclip::Processor. There are
+  # only two methods you must implement to properly be a subclass: 
+  # #initialize and #make. Initialize's arguments are the file that will
+  # be operated on (which is an instance of File), and a hash of options
+  # that were defined in has_attached_file's style hash.
+  #
+  # All #make needs to do is return an instance of File (Tempfile is
+  # acceptable) which contains the results of the processing.
+  #
+  # See Paperclip.run for more information about using command-line
+  # utilities from within Processors.
   class Processor
     attr_accessor :file, :options
 
@@ -14,4 +31,17 @@ module Paperclip
       new(file, options).make
     end
   end
+  
+  # Due to how ImageMagick handles its image format conversion and how Tempfile
+  # handles its naming scheme, it is necessary to override how Tempfile makes
+  # its names so as to allow for file extensions. Idea taken from the comments
+  # on this blog post:
+  # http://marsorange.com/archives/of-mogrify-ruby-tempfile-dynamic-class-definitions
+  class Tempfile < ::Tempfile
+    # Replaces Tempfile's +make_tmpname+ with one that honors file extensions.
+    def make_tmpname(basename, n)
+      extension = File.extname(basename)
+      sprintf("%s,%d,%d%s", File.basename(basename, extension), $$, n, extension)
+    end
+  end
 end

lib/paperclip/thumbnail.rb

@@ -67,17 +67,4 @@ module Paperclip
       trans
     end
   end
-
-  # Due to how ImageMagick handles its image format conversion and how Tempfile
-  # handles its naming scheme, it is necessary to override how Tempfile makes
-  # its names so as to allow for file extensions. Idea taken from the comments
-  # on this blog post:
-  # http://marsorange.com/archives/of-mogrify-ruby-tempfile-dynamic-class-definitions
-  class Tempfile < ::Tempfile
-    # Replaces Tempfile's +make_tmpname+ with one that honors file extensions.
-    def make_tmpname(basename, n)
-      extension = File.extname(basename)
-      sprintf("%s,%d,%d%s", File.basename(basename, extension), $$, n, extension)
-    end
-  end
 end