Module: MaquinaStream::TextDirection

Defined in:
lib/maquina_stream/text_direction.rb

Overview

Which way a piece of text reads.

A message is one document but not necessarily one direction: an assistant answering in Arabic quotes an English identifier, a Hebrew paragraph sits next to a Ruby fence. Direction is therefore decided per block, the way the bidi algorithm decides it — by the FIRST STRONG character — and not by the document, the locale or the host.

dir="auto" on every block would let the browser do exactly this, at the cost of eleven bytes on every block of every frame for the majority of documents that are left-to-right and need nothing. So the strong character is found here and the attribute is emitted only when it changes something.

The render pipeline calls this per block. A host calls it when it renders text of its own — a message header, an attachment filename — that came from the same place the buffer did.

Constant Summary collapse

RTL =

The scripts written right to left, as Ruby knows them.

/[\p{Hebrew}\p{Arabic}\p{Syriac}\p{Thaana}\p{Nko}\p{Samaritan}\p{Mandaic}\p{Adlam}]/
STRONG =

Only a letter is strong. Digits, punctuation and whitespace take their direction from what surrounds them, which is why "١٢٣ Ruby" reads left-to-right and "مرحبا 123" does not.

/[\p{L}\p{Nl}]/
CONTROLS =

Explicit bidi controls. They are what a Trojan Source attack is made of: an override inside a comment reorders the rendering of code that the parser reads in a different order entirely.

/[\u061C\u200E\u200F\u202A-\u202E\u2066-\u2069]/

Class Method Summary collapse

Class Method Details

.controls?(text) ⇒ Boolean

Whether text contains an explicit bidi control character.

True is a reason to be suspicious, not to render differently: see CONTROLS. Code that displays a filename or a link target unescaped should check this first.

Returns:

  • (Boolean) 


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# File 'lib/maquina_stream/text_direction.rb', line 52

def self.controls?(text)
  text.to_s.match?(CONTROLS)
end

.of(text) ⇒ Object

The direction text reads in: :rtl, :ltr, or nil when nothing in it is strong either way.

Nil is a real answer, not a failure — a block of digits or punctuation has no direction of its own, and stamping one on it would be a guess. The caller emits no dir attribute for it.



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# File 'lib/maquina_stream/text_direction.rb', line 40

def self.of(text)
  strong = text.to_s[STRONG]
  return nil unless strong

  strong.match?(RTL) ? :rtl : :ltr
end