Class: Amazon::AWS::Cache

Inherits:
Object
  • Object
show all
Defined in:
lib/ruby-paa/aws/cache.rb

Overview

This class provides a simple results caching system for operations performed by AWS.

To use it, set cache to true in either /etc/amazonrc or ~/.amazonrc.

By default, the cache directory used is /tmp/amazon, but this can be changed by defining cache_dir in either /etc/amazonrc or ~/.amazonrc.

When a cache is used, Ruby/AWS will check the cache directory for a recent copy of a response to the exact operation that you are performing. If found, the cached response will be returned instead of the request being forwarded to the AWS servers for processing. If no (recent) copy is found, the request will be forwarded to the AWS servers as usual. Recency is defined here as less than 24 hours old.

Defined Under Namespace

Classes: PathError

Constant Summary collapse

ONE_DAY =

Length of one day in seconds

86400
MAX_AGE =

Age in days below which to consider cache files valid.

1.0
DEFAULT_CACHE_DIR =

Default cache location.

'/tmp/amazon'

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(path = DEFAULT_CACHE_DIR) ⇒ Cache

Returns a new instance of Cache.



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# File 'lib/ruby-paa/aws/cache.rb', line 55

def initialize(path=DEFAULT_CACHE_DIR)
	path ||= DEFAULT_CACHE_DIR

	::FileUtils::mkdir_p( path ) unless File.exists? path

	unless File.directory? path 
	  raise PathError, "cache path #{path} is not a directory"
	end

	unless File.readable? path 
	  raise PathError, "cache path #{path} is not readable"
	end

	unless File.writable? path
	  raise PathError, "cache path #{path} is not writable"
	end

	@path = path
end

Instance Attribute Details

#path ⇒ Object (readonly)

Returns the value of attribute path.



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# File 'lib/ruby-paa/aws/cache.rb', line 53

def path
  @path
end

Instance Method Details

#cached?(url) ⇒ Boolean

Determine whether or not the the response to a given URL is cached. Returns true or false.

Returns:

  • (Boolean) 


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# File 'lib/ruby-paa/aws/cache.rb', line 79

def cached?(url)
	digest = Digest::MD5.hexdigest( url )

	cache_files = Dir.glob( File.join( @path, '*' ) ).map do |d|
	  File.basename( d )
	end

	return cache_files.include?( digest ) &&
	  ( Time.now - File.mtime( File.join( @path, digest ) ) ) /
	  ONE_DAY <= MAX_AGE
end

#fetch(url) ⇒ Object

Retrieve the cached response associated with url.



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# File 'lib/ruby-paa/aws/cache.rb', line 94

def fetch(url)
	digest = Digest::MD5.hexdigest( url )
	cache_file = File.join( @path, digest )

	return nil unless File.exist? cache_file

	Amazon.dprintf( 'Fetching %s from cache...', digest )
	File.open( File.join( cache_file ) ).readlines.to_s
end

#flush_all ⇒ Object

This method flushes all files from the cache directory specified in the object’s @path variable.



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# File 'lib/ruby-paa/aws/cache.rb', line 119

def flush_all
 FileUtils.rm Dir.glob( File.join( @path, '*' ) )
end

#flush_expired ⇒ Object

This method flushes expired files from the cache directory specified in the object’s @path variable.



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# File 'lib/ruby-paa/aws/cache.rb', line 127

def flush_expired
	now = Time.now

	expired_files = Dir.glob( File.join( @path, '*' ) ).find_all do |f|
	  ( now - File.mtime( f ) ) / ONE_DAY > MAX_AGE
	end

	FileUtils.rm expired_files
end

#store(url, contents) ⇒ Object

Cache the data from contents and associate it with url.



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# File 'lib/ruby-paa/aws/cache.rb', line 107

def store(url, contents)
	digest = Digest::MD5.hexdigest( url )
	cache_file = File.join( @path, digest )

	Amazon.dprintf( 'Caching %s...', digest )
	File.open( cache_file, 'w' ) { |f| f.puts contents }
end