LaTeX multi-page table with inter-row page breaks

tblbrk.tex

% First version published on https://groups.google.com/d/msg/comp.text.tex/gE80AAOQ83U/woX-CFfUQYEJ
% Several changes are applied

\documentclass{article}
\usepackage{lipsum}
\usepackage{cals}
\usepackage[latin]{babel}
\showboxbreadth=100
\showboxdepth=100

\makeatletter
\let\oldDispatch=\cals@row@dispatch
\newbox\rowBefore
\newbox\rowAfter
\newbox\decorationCopy
\newdimen\splitHeight

\def\cals@row@dispatch{%
  \cals@ifbreak\iftrue % detect that a break is required
  \splitHeight=\pagegoal \advance\splitHeight -\pagetotal
  \ifdim \splitHeight>50pt % break inrow only if at least 100pt left
  \advance\splitHeight -5pt % avoid pagebreak due to overflows
  %
  % Split the current row on two: before and after the break
  %
  \setbox\rowBefore=\hbox{}
  \setbox\rowAfter=\hbox{}
  \def\next{%
    \setbox0=\lastbox
    \ifvoid0
    \def\next{\global\setbox\rowBefore=\box\rowBefore
      \global\setbox\rowAfter=\box\rowAfter }%
    \else
    \setbox2=\vsplit0 to\splitHeight
    \ifvoid0
      \setbox0=\vbox{\hbox to \wd2{}}%
    \fi
    \setbox\rowBefore=\hbox{\box2 \unhbox\rowBefore
      \hbox to 0pt{\hss\vbox{\hrule width\wd\cals@current@cs}}}%
    \setbox\rowAfter=\hbox{\box0 \unhbox\rowAfter}%
    \fi
    \next}
  \setbox0=\hbox{\unhbox\cals@current@row \next}
  %
  % Decoration backup, typeset the first row,
  % restore context, typeset the second at the end of macro
  %
  \setbox\decorationCopy=\copy\cals@current@cs
  \setbox\cals@current@row=\box\rowBefore
  \ht\cals@current@cs=\ht\cals@current@row
  \oldDispatch
  \cals@issue@break
  \cals@thead@tokens
  \setbox\cals@current@row=\box\rowAfter
  \cals@reheight@cells\cals@current@row
  \setbox\cals@current@cs=\box\decorationCopy
  \ht\cals@current@cs=\ht\cals@current@row
  \let\cals@current@context=b
  \fi
  \fi
  \oldDispatch}

\begin{document}
\begin{calstable}
\colwidths{{150pt}{150pt}{150pt}}
\thead{\brow \bfseries \cell{header1}\cell{header2}\cell{header3}
  \mdseries \erow}
\brow \cell{\lipsum[ 1]}\cell{\lipsum[ 2]}\cell{\lipsum[ 3]} \erow
\brow \cell{\lipsum[ 4]}\cell{\lipsum[ 5]}\cell{\lipsum[ 6]} \erow
\brow \cell{\lipsum[ 7]}\cell{\lipsum[ 8]}\cell{\lipsum[ 9]} \erow
\brow \cell{\lipsum[10]}\cell{\lipsum[11]}\cell{\lipsum[12]} \erow
\brow \cell{\lipsum[13]}\cell{\lipsum[14]}\cell{\lipsum[15]} \erow
\brow \cell{\lipsum[16]}\cell{\lipsum[17]}\cell{\lipsum[18]} \erow
\end{calstable}
\end{document}