Render plantuml text files into binary images

[yaloki]

I need to implement a Filter that takes plain text PlantUML and renders into a PNG.

Simple naive implementation (1) (can't be bothered with popen3 magic at this time):

class Plantuml < Nanoc::Filter
  identifier :plantuml
  type :binary
  def run(content, params={})
    system("java -Xmx128m -jar lib/plantuml.jar -pipe < #{filename} > #{output_filename}")
  end
end

Problem is... the input is text and the output is binary and Nanoc assumes that the output "type" is the same as the input "type".

The options I see:


• use a binary filter as above: problem is, I'd also like to use ERB filtering on the source file before compiling it into a PNG
• mark PlantUML source files as text instead of binary: that would make the Filter more annoying to implement as the output (PNG binary data) needs to be buffered into memory by Nanoc instead of being written to a temporary file as with binary filters (e.g. code above (1))
  
• create Nanoc Item objects programatically at the preprocess stage (2) and route the original PlantUML source text files into oblivion (3)

Anything I'm missing here ? Does someone have a better idea ?

(2) Create items programatically (untested):

preprocess do
  @items.select{|item| item[:extension] == 'pu'}.each do |pu|
    file = ... # similar to above + create a temp file myself
    png = Nanoc::Item.new(file, {}, "/plantuml#{item.identifier}", { :mtime => item.mtime, :binary => true })
    @items << png
  end
end

(3) Route original PlantUML sources into void:

route '*' do
  if item[:extension] != 'pu'
    # ...
  else
    # do nothing, don't output anywhere, might have to return nil here, idk.
  end    
end

[yaloki]

And another option which is a bit annoying as it duplicates code from Nanoc::Filters::ERB:

class ERB_binary < Nanoc::Filter

  requires 'erb'

  identifier :erbbinary

  type :binary

  def run(f, params={})

    assigns.merge!(params[:locals] || {})

    context = ::Nanoc::Context.new(assigns)

    proc = assigns[:content] ? -> { assigns[:content] } : nil

    assigns_binding = context.get_binding(&proc)

    content = IO.read(f)

    # Get result

    safe_level = params[:safe_level]

    trim_mode = params[:trim_mode]

    erb = ::ERB.new(content, safe_level, trim_mode)

    erb.filename = filename

    result = erb.result(assigns_binding)

    File.open(output_filename, "w") {|o| o.write(result)}

  end

end

[Eric Sunshine]

On Tue, Sep 8, 2015 at 8:23 AM, yaloki <pascal...@gmail.com> wrote:
> I need to implement a Filter that takes plain text PlantUML and renders into
> a PNG.
>
> Simple naive implementation (1) (can't be bothered with popen3 magic at this
> time):
>
> class Plantuml < Nanoc::Filter
> identifier :plantuml
> type :binary
> def run(content, params={})
> system("java -Xmx128m -jar lib/plantuml.jar -pipe < #{filename} >
> #{output_filename}")
> end
> end
>
> Problem is... the input is text and the output is binary and Nanoc assumes
> that the output "type" is the same as the input "type".

Declare the filter as text-to-binary:

type :text => :binary

[yaloki]

> Problem is... the input is text and the output is binary and Nanoc assumes
> that the output "type" is the same as the input "type".

Declare the filter as text-to-binary:

   type :text => :binary

Perfect, that does the trick :)

For reference (would require a nicer version with popen3):

 

class Plantuml < Nanoc::Filter

  identifier :plantuml

  type :text => :binary

[yaloki]

And an even better version below. It works great, except that Nanoc doesn't recompile when the PlantUML source file is modified.

Here is the filter:

class Plantuml < Nanoc::Filter

  identifier :plantuml

  type :text => :binary

  requires 'open3'

  def run(content, params={})

    content = "@startuml\n" + content unless content =~ %r{^\s*@startuml\b}x

    content += "\n@enduml" unless content =~ %r{\b@enduml$}x

    o, e, s = Open3.capture3(

      'java', '-Djava.awt.headless=true', '-Xmx128m', '-jar', 'lib/plantuml.jar', '-pipe',

      :stdin_data => content,

      :binmode => true

    )

    unless s.success?

      fail "error running plantuml: #{e}\n#{o}"

    end

    File.open(output_filename, "w") do |out|

      out.write(o)

    end

  end

end

And here the Rules:

compile '*' do

  unless item.binary?

    filter :erb

    case item[:extension]

    when 'markdown'

      filter :kramdown

      layout 'default'

      filter :relativize_paths, :type => :html

    when 'html'

      layout 'default'

      filter :relativize_paths, :type => :html

    when 'pu'

      filter :plantuml

    end

  end

end

route '*' do

  if item.binary?

    item.identifier.chop + (item[:extension] ? '.' + item[:extension] : '')

  elsif item.identifier == '/'

    '/index.html'

  else

    case item[:extension]

    when 'markdown', 'html'

      item.identifier.chop + '.html'

    when 'pu'

      item.identifier.chop + '.png'

    else

      item.identifier.chop + '.' + item[:extension]

    end

  end

end

layout '*', :erb

An idea what might be causing this (modifications to .pu files don't cause nanoc to run the filter on them) ?