Convert to ePUB using tex4ebook

Question

I am trying to convert my document into ePUB using tex4ebook. In this bilingual writing, the free font Kalpurush is used.

Here's the MWE file.tex:

% !TEX program = xelatex
% !BIB program = biblatex
\documentclass[12pt, twoside]{book}
% For a bilingual document    
\usepackage[banglamainfont=Kalpurush, banglattfont=Kalpurush]{latexbangla}                               
%activate polyglossia
\setdefaultlanguage[numerals=Bengali, changecounternumbering=true]{bengali}
%number all levels
\setcounter{secnumdepth}{5}
  \setotherlanguage{english}
\usepackage[autostyle]{csquotes}
% \usepackage[backend=biber, sorting=none, language=english, autolang=other, block=ragged]{biblatex}
% \addbibresource{bookbib.bib}
\usepackage{lipsum}
\usepackage{enumitem}
\setlist[itemize]{label*={\fontfamily{lmr}\selectfont\textbullet}}
\begin{document}
\tableofcontents
\chapter{First Chapter}
\section*{First Section}
পিথাগোরাস (Pythagoras)-এর উপপাদ্যটি হল,\
``সমকোণী ত্রিভুজের অতিভুজের উপর অঙ্কিত বর্গক্ষেত্রের ক্ষেত্রফল অপর দুই বাহুর উপর অঙ্কিত বর্গক্ষেত্রের ক্ষেত্রফলের সমষ্টির সমান।" \
অর্থাৎ কোন সমকোণী ত্রিভুজের অতিভুজ $c$ এবং অপর দুই বাহু $a$ এবং $b$ হলে,
[c^2=a^2+b^2]
\begin{itemize}
  \item The individual entries are indicated with a black dot, a so-called bullet.
  \item The text in the entries may be of any length.
\end{itemize}
% \nocite{*} % adds all entries in the bib file to the bibliography  % https://tex.stackexchange.com/a/13513/114006
% \printbibliography
\end{document}

By using the command:

tex4ebook -x -f epub3 file.tex mathml

I am getting the following the errors:

[STATUS]  tex4ebook: Conversion started                                                                 
[STATUS]  tex4ebook: Input file: testing_bangla.tex                                                     
[WARNING] tocid: char-def module not found                                                              
[WARNING] tocid: cannot fix section id's                                                                
This is XeTeX, Version 3.141592653-2.6-0.999994 (MiKTeX 22.3) (preloaded format=xelatex.fmt)            
 restricted \write18 enabled.                                                                           
entering extended mode     

But no ePUB file is generated. How can I solve it? If a config file is needed, what should be included there?

Answer 1

The problem is that Bengali numbers are written to the auxilary file that TeX4ht uses for storing cross references. When the cross-references are loaded, these numbers cause compilation error, as they are active characters.

As a workaround, turn off Bengali numbering with TeX4ebook:

% !TEX program = xelatex
% !BIB program = biblatex
\documentclass[12pt, twoside]{book}
% For a bilingual document    
\usepackage[banglamainfont=Kalpurush, banglattfont=Kalpurush]{latexbangla}                               
%activate polyglossia
\ifdefined\HCode
\setdefaultlanguage[numerals=Bengali, changecounternumbering=false]{bengali}
\else
\setdefaultlanguage[numerals=Bengali, changecounternumbering=true]{bengali}
\fi
%number all levels
\setcounter{secnumdepth}{5}
  \setotherlanguage{english}
\usepackage[autostyle]{csquotes}
% \usepackage[backend=biber, sorting=none, language=english, autolang=other, block=ragged]{biblatex}
% \addbibresource{bookbib.bib}
\usepackage{lipsum}
\usepackage{enumitem}
\setlist[itemize]{label*={\fontfamily{lmr}\selectfont\textbullet}}
\begin{document}
\tableofcontents
\chapter{First Chapter}
\section*{First Section}
পিথাগোরাস (Pythagoras)-এর উপপাদ্যটি হল,\
``সমকোণী ত্রিভুজের অতিভুজের উপর অঙ্কিত বর্গক্ষেত্রের ক্ষেত্রফল অপর দুই বাহুর উপর অঙ্কিত বর্গক্ষেত্রের ক্ষেত্রফলের সমষ্টির সমান।" \
অর্থাৎ কোন সমকোণী ত্রিভুজের অতিভুজ $c$ এবং অপর দুই বাহু $a$ এবং $b$ হলে,
[c^2=a^2+b^2]
\begin{itemize}
  \item The individual entries are indicated with a black dot, a so-called bullet.
  \item The text in the entries may be of any length.
\end{itemize}
% \nocite{*} % adds all entries in the bib file to the bibliography  % https://tex.stackexchange.com/a/13513/114006
% \printbibliography
\end{document}

Note this code that checks for TeX4ht:

\ifdefined\HCode
\setdefaultlanguage[numerals=Bengali, changecounternumbering=false]{bengali}
\else
\setdefaultlanguage[numerals=Bengali, changecounternumbering=true]{bengali}
\fi

Sometimes it is easiest to include packages or their options conditionally.

You can still can get the numbers in chapters and in TOC, thanks to a build file (build.lua):

local domfilter = require "make4ht-domfilter"
local filter    = require "make4ht-filter"
local domobject = require "luaxml-domobject"
-- we will calculate unicode character from this
local bengali_zero = 0x09E6 - 48
local uchar = utf8.char
local ubyte = utf8.codepoint
-- convert arabic number to bengali
local function arabic_to_bengali(text)
  return text:gsub("([0-9])", function(a)
    return uchar(ubyte(a) + bengali_zero)
  end)
end
local function process_children(head)
  for _, child in ipairs(head._children) do
    if child:is_text() then
      child._text = arabic_to_bengali(child._text)
    end
  end
end
local process = domfilter {
  function(dom)
    -- process section numbers
    for _, head in ipairs(dom:query_selector(".titlemark")) do
      process_children(head)
    end
    -- process TOC
    for _, toc in ipairs(dom:query_selector(".tableofcontents span,nav#toc li")) do
      process_children(toc)
    end
    return dom
  end
}
-- we must fix also the ncx file, which is used for Epub TOC
-- we must clean it first, in order to be able to process it using LuaXML
local ncx_process = filter {
  function(text)
    local text = text:gsub("^%s*", "") -- remove whitespace at the beginning
    local dom  = domobject.parse(text) -- convert text to DOM
    for _, mark in ipairs(dom:query_selector("navmark")) do -- process elements that can contain numbers
      process_children(mark)
    end
    return dom:serialize()
  end
}
Make:match("html$", process)
Make:match("ncx", ncx_process)

It uses LuaXML to process the generated HTML files, and to replace Arabic to Bengali numbers in sections and in TOC.

You can execute it in this way:

tex4ebook -f epub3 -x -e build.lua file.tex "mathml"

This is the result: