How to create a decomposer
You can extend ChupaText by Ruby. You can add supported input type by writing a decomposer module.
Overview
Decomposer is a Ruby class. It needs the following two API:
target?decompose
Both of them accept only one argument data. data is an input
data.
First, ChupaText calls target? method of your decomposer. If your
decomposer can decompose the input data, your target? method should
return true.
If your decomposer’s target? method returns true, ChupaText calls
decomposer method of your decomposer. Your decomposer needs to
decomposer the input data and yield extracted text data or other
format data that will be decomposed by other decomposers. Your
decomposer can yield multiple times.
If your decomposer decomposes an archive file such as tar and zip
archives, your decompose method will yield other format data. If
your decomposer extracts text and meta-data from an input such as
HTML, your decompose method will yield text data.
Example
Let’s create a simple XML decomposer as an example. It extracts text data from input XML.
For example, here is an input XML:
```xml
```
The XML decomposer extracts the following text:
text
Hello & World!
ChupaText provides chupa-text-genearte-decomposer command. It
generates skeleton code for a new decomposer. Let’s use it.
chupa-text-genearte-decomposer accepts required information by
command line options or reading from standard input. You can confirm
the required information by --help option:
text
% chupa-text-generate-decomposer --help
Usage: chupa-text-generate-decomposer [options]
--name=NAME Decomposer name
(e.g.: html)
--extensions=EXTENSION1,EXTENSION2,...
Target file extensions
(e.g.: htm,html,xhtml)
--mime-types=TYPE1,TYPE2,... Target MIME types
(e.g.: text/html,application/xhtml+xml)
--author=AUTHOR Author
(e.g.: 'Your Name')
(default: Kouhei Sutou)
--email=EMAIL Author E-mail
(e.g.: your@email.address)
(default: kou@clear-code.com)
--license=LICENSE License
(e.g.: MIT)
(default: LGPLv2.1 or later)
Some pieces of information have the default values. In the above case,
--author, --email and -license have the default values.
XML decomposer uses the following information:
--name:xml--extensions:xml--mime-types:text/xml
Run with the above information:
text
% chupa-text-generate-decomposer --name xml --extensions xml --mime-types text/xml
Creating directory: chupa-text-decomposer-xml
Creating file: chupa-text-decomposer-xml/chupa-text-decomposer-xml.gemspec
Creating file: chupa-text-decomposer-xml/Gemfile
Creating file: chupa-text-decomposer-xml/Rakefile
Creating file: chupa-text-decomposer-xml/LICENSE.txt
Creating directory: chupa-text-decomposer-xml/lib/chupa-text/decomposers
Creating file: chupa-text-decomposer-xml/lib/chupa-text/decomposers/xml.rb
Creating directory: chupa-text-decomposer-xml/test
Creating file: chupa-text-decomposer-xml/test/test-xml.rb
Creating file: chupa-text-decomposer-xml/test/helper.rb
Creating file: chupa-text-decomposer-xml/test/run-test.rb
chupa-text-generate-decomposer generates a directory that is named
as chupa-text-decomposer-#{name}/.
Look lib/chupa-text/decomposers/xml.rb:
``` module ChupaText module Decomposers class Xml < Decomposer def target?(data) [“xml”].include?(data.extension) or [“text/xml”].include?(data.mime_type) end
def decompose(data)
raise NotImplementedError, "#{self.class}##{__method__} isn't implemented yet."
text = "IMPLEMENTED ME"
text_data = TextData.new(text)
yield(text_data)
end
end end end ```
The generated code implements target? method but doesn’t implemented
decompose method completely. Let’s implement decompose method:
``` require “cgi”
…
def decompose(data)
text = CGI.unescapeHTML(untag(data.body).strip)
text_data = TextData.new(text)
yield(text_data)
end
private
def untag(xml)
xml.gsub(/<.+?>/m, "")
end # ... ```
chupa-text-generate-decomposer also generates a test. Run the test:
``` % bundle install % rake /usr/bin/ruby2.0 test/run-test.rb Loaded suite . Started F =============================================================================== Failure: test_body(decompose) /tmp/chupa-text-decomposer-xml/test/test-xml.rb:24:in `test_body’ 21: def test_body 22: input_body = “TODO (input)” 23: expected_text = “TODO (extracted)” => 24: assert_equal([expected_text], 25: decompose(input_body).collect(&:body)) 26: end 27: end <[“TODO (extracted)”]> expected but was <[“TODO (input)”]>
diff:
? [“TODO (ex tracted)”]
? inpu
===============================================================================
Finished in 0.013355116 seconds.
1 tests, 1 assertions, 1 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications 0% passed
74.88 tests/s, 74.88 assertions/s
rake aborted!
Command failed with status (1): [/usr/bin/ruby2.0 test/run-test.rb…]
/tmp/chupa-text-decomposer-xml/Rakefile:9:in block in <top (required)>'
``
The generated test fails because the test has place holders. Look the generated test:
``` class TestXml < Test::Unit::TestCase include Helper
def setup @decomposer = ChupaText::Decomposers::Xml.new({}) end
sub_test_case(“decompose”) do def decompose(input_body) data = ChupaText::Data.new data.mime_type = “text/xml” data.body = input_body
decomposed = []
@decomposer.decompose(data) do |decomposed_data|
decomposed << decomposed_data
end
decomposed
end
def test_body
input_body = "TODO (input)"
expected_text = "TODO (extracted)"
assert_equal([expected_text],
decompose(input_body).collect(&:body))
end end end ```
test_body has TODO codes as place holder:
# ...
def test_body
input_body = "TODO (input)"
expected_text = "TODO (extracted)"
assert_equal([expected_text],
decompose(input_body).collect(&:body))
end
# ...
Fill the TODO by test XML and expected result:
``` # … def test_body input_body = «-XML
XML
expected_text = "Hello & World!"
assert_equal([expected_text],
decompose(input_body).collect(&:body))
end # ... ```
Run test again:
``` % rake /usr/bin/ruby2.0 test/run-test.rb Loaded suite . Started .
Finished in 0.000915172 seconds.
1 tests, 1 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications 100% passed
1092.69 tests/s, 1092.69 assertions/s ```
The test is passed!
You can release the generator by the following command. It requires an account on https://rubygems.org/.
% rake release
Can you understand how to create a new decomposer?
API reference
data
Both of target? and decompose receives an argument data. It is a
ChupaText::Data instance or an instance of its sub class. You need
to see the API reference manual just for ChupaText::Data. You don’t
use sub class specific API. It is not portable.
target?
target? should return true or false. The decomposer should
return true if the decomposer can decompose received data, false
otherwise.
decompose
decompose decomposes input data and yield extracted text data or
decomposed other type data. decompose can yield zero or more
times.
Here is a template code to yield extracted text data:
def decompose(data)
text = extract_text(data)
text_data = ChupaText::TextData.new(text)
# text_data["meta-data1"] = meta_data_value1
# text_data["meta-data2"] = meta_data_value2
# ...
yield(text_data)
end
See lib/chupa-text/decomposers/csv.rb as an example of extracting text data.
Here is a template code to yield other type data:
def decompose(data)
entries = decompose_archive(data)
entries.each do |entry|
path = entry.path
if entry.respond_to?(:read)
# The input must have "read" method.
input = entry
else
# If the entry doesn't have "read" method, wrap String data
# by StringIO.
input = StringIO.new(entry.data)
end
decomposed_data = ChupaText::VirtualFileData.new(path, input)
decomposed_data.source = data
yield(decomposed_data)
end
end
See lib/chupa-text/decomposers/tar.rb as an example of decomposing to other type data.