middleman/lib/middleman/fastimage.rb
2009-11-13 12:25:16 -08:00

282 lines
8.9 KiB
Ruby
Executable file

# FastImage finds the size or type of an image given its uri.
# It is careful to only fetch and parse as much of the image as is needed to determine the result.
# It does this by using a feature of Net::HTTP that yields strings from the resource being fetched
# as soon as the packets arrive.
#
# No external libraries such as ImageMagick are used here, this is a very lightweight solution to
# finding image information.
#
# FastImage knows about GIF, JPEG, BMP and PNG files.
#
# FastImage can also read files from the local filesystem by supplying the path instead of a uri.
# In this case FastImage uses the open-uri library to read the file in chunks of 256 bytes until
# it has enough. This is possibly a useful bandwidth-saving feature if the file is on a network
# attached disk rather than truly local.
#
# === Examples
# require 'fastimage'
#
# FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
# => [266, 56]
# FastImage.type("http://stephensykes.com/images/pngimage")
# => :png
# FastImage.type("/some/local/file.gif")
# => :gif
#
# === References
# * http://snippets.dzone.com/posts/show/805
# * http://www.anttikupila.com/flash/getting-jpg-dimensions-with-as3-without-loading-the-entire-file/
# * http://pennysmalls.com/2008/08/19/find-jpeg-dimensions-fast-in-ruby/
# * http://imagesize.rubyforge.org/
#
require 'net/https'
require 'open-uri'
module Middleman
class FastImage
attr_reader :size, :type
class FastImageException < StandardError # :nodoc:
end
class MoreCharsNeeded < FastImageException # :nodoc:
end
class UnknownImageType < FastImageException # :nodoc:
end
class ImageFetchFailure < FastImageException # :nodoc:
end
class SizeNotFound < FastImageException # :nodoc:
end
DefaultTimeout = 2
LocalFileChunkSize = 256
# Returns an array containing the width and height of the image.
# It will return nil if the image could not be fetched, or if the image type was not recognised.
#
# By default there is a timeout of 2 seconds for opening and reading from a remote server.
# This can be changed by passing a :timeout => number_of_seconds in the options.
#
# If you wish FastImage to raise if it cannot size the image for any reason, then pass
# :raise_on_failure => true in the options.
#
# FastImage knows about GIF, JPEG, BMP and PNG files.
#
# === Example
#
# require 'fastimage'
#
# FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
# => [266, 56]
# FastImage.size("http://stephensykes.com/images/pngimage")
# => [16, 16]
# FastImage.size("http://farm4.static.flickr.com/3023/3047236863_9dce98b836.jpg")
# => [500, 375]
# FastImage.size("http://www-ece.rice.edu/~wakin/images/lena512.bmp")
# => [512, 512]
# FastImage.size("test/fixtures/test.jpg")
# => [882, 470]
# FastImage.size("http://pennysmalls.com/does_not_exist")
# => nil
# FastImage.size("http://pennysmalls.com/does_not_exist", :raise_on_failure=>true)
# => raises FastImage::ImageFetchFailure
# FastImage.size("http://stephensykes.com/favicon.ico", :raise_on_failure=>true)
# => raises FastImage::UnknownImageType
# FastImage.size("http://stephensykes.com/favicon.ico", :raise_on_failure=>true, :timeout=>0.01)
# => raises FastImage::ImageFetchFailure
# FastImage.size("http://stephensykes.com/images/faulty.jpg", :raise_on_failure=>true)
# => raises FastImage::SizeNotFound
#
# === Supported options
# [:timeout]
# Overrides the default timeout of 2 seconds. Applies both to reading from and opening the http connection.
# [:raise_on_failure]
# If set to true causes an exception to be raised if the image size cannot be found for any reason.
#
def self.size(uri, options={})
new(uri, options).size
end
# Returns an symbol indicating the image type fetched from a uri.
# It will return nil if the image could not be fetched, or if the image type was not recognised.
#
# By default there is a timeout of 2 seconds for opening and reading from a remote server.
# This can be changed by passing a :timeout => number_of_seconds in the options.
#
# If you wish FastImage to raise if it cannot find the type of the image for any reason, then pass
# :raise_on_failure => true in the options.
#
# === Example
#
# require 'fastimage'
#
# FastImage.type("http://stephensykes.com/images/ss.com_x.gif")
# => :gif
# FastImage.type("http://stephensykes.com/images/pngimage")
# => :png
# FastImage.type("http://farm4.static.flickr.com/3023/3047236863_9dce98b836.jpg")
# => :jpeg
# FastImage.type("http://www-ece.rice.edu/~wakin/images/lena512.bmp")
# => :bmp
# FastImage.type("test/fixtures/test.jpg")
# => :jpeg
# FastImage.type("http://pennysmalls.com/does_not_exist")
# => nil
#
# === Supported options
# [:timeout]
# Overrides the default timeout of 2 seconds. Applies both to reading from and opening the http connection.
# [:raise_on_failure]
# If set to true causes an exception to be raised if the image type cannot be found for any reason.
#
def self.type(uri, options={})
new(uri, options.merge(:type_only=>true)).type
end
def initialize(uri, options={})
@property = options[:type_only] ? :type : :size
@timeout = options[:timeout] || DefaultTimeout
@uri = uri
@parsed_uri = URI.parse(uri.gsub(/\s/, "%20"))
if @parsed_uri.scheme == "http" || @parsed_uri.scheme == "https"
fetch_using_http
else
fetch_using_open_uri
end
raise SizeNotFound if options[:raise_on_failure] && @property == :size && !@size
rescue Timeout::Error, SocketError, Errno::ECONNREFUSED, Errno::EHOSTUNREACH, Errno::ECONNRESET, ImageFetchFailure
raise ImageFetchFailure if options[:raise_on_failure]
rescue Errno::ENOENT
raise ImageFetchFailure if options[:raise_on_failure]
rescue UnknownImageType
raise UnknownImageType if options[:raise_on_failure]
end
private
def fetch_using_http
setup_http
@http.request_get(@parsed_uri.request_uri) do |res|
raise ImageFetchFailure unless res.is_a?(Net::HTTPSuccess)
res.read_body do |str|
break if parse_packet(str)
end
end
end
def setup_http
@http = Net::HTTP.new(@parsed_uri.host, @parsed_uri.port)
@http.use_ssl = (@parsed_uri.scheme == "https")
@http.verify_mode = OpenSSL::SSL::VERIFY_NONE
@http.open_timeout = @timeout
@http.read_timeout = @timeout
end
def fetch_using_open_uri
open(@uri) do |s|
while str = s.read(LocalFileChunkSize)
break if parse_packet(str)
end
end
end
# returns true once result is achieved
#
def parse_packet(str)
@str = (@unused_str || "") + str
@strpos = 0
begin
result = send("parse_#{@property}")
if result
instance_variable_set("@#{@property}", result)
true
end
rescue MoreCharsNeeded
false
end
end
def parse_size
@type = parse_type unless @type
send("parse_size_for_#{@type}")
end
def get_chars(n)
if @strpos + n - 1 >= @str.size
@unused_str = @str[@strpos..-1]
raise MoreCharsNeeded
else
result = @str[@strpos..(@strpos + n - 1)]
@strpos += n
result
end
end
def get_byte
get_chars(1).unpack("C")[0]
end
def read_int(str)
size_bytes = str.unpack("CC")
(size_bytes[0] << 8) + size_bytes[1]
end
def parse_type
case get_chars(2)
when "BM"
:bmp
when "GI"
:gif
when 0xff.chr + 0xd8.chr
:jpeg
when 0x89.chr + "P"
:png
else
raise UnknownImageType
end
end
def parse_size_for_gif
get_chars(9)[4..8].unpack('SS')
end
def parse_size_for_png
get_chars(23)[14..22].unpack('NN')
end
def parse_size_for_jpeg
loop do
@state = case @state
when nil
get_chars(2)
:started
when :started
get_byte == 0xFF ? :sof : :started
when :sof
c = get_byte
if (0xe0..0xef).include?(c)
:skipframe
elsif [0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF].detect {|r| r.include? c}
:readsize
else
:skipframe
end
when :skipframe
@skip_chars = read_int(get_chars(2)) - 2
:do_skip
when :do_skip
get_chars(@skip_chars)
:started
when :readsize
s = get_chars(7)
return [read_int(s[5..6]), read_int(s[3..4])]
end
end
end
def parse_size_for_bmp
d = get_chars(27)[12..26]
d[0] == 40 ? d[4..-1].unpack('LL') : d[4..8].unpack('SS')
end
end
end