Musings

Both considerations pointed towards creating a separate, standalone piece of software to handle the conversion, which communicates with Instiki over a (local or remote) port. tex2svg 1.0.1 requires a working TeX installation and the pdf2svg commandline utility. The latter, in turn, requires the poppler-glib library, which is easily obtained from your favourite package manager. E.g., under Fink, on MacOS, you do a

fink install poppler8-glib

before install pdf2svg.

But portability is not enough. If you’re going to expose Instiki over the internet, you also need to make it secure. TeX is a Turing-complete language with (limited) access to the file system. It is trivial to compose some simple LaTeX input which, when compiled, will

• exfiltrate sensitive information from the machine or
• DoS the machine by using up 100% of the CPU time or filling up 100% of the available disk space.

You should never, ever compile a TeX file from an untrusted source.

tex2svg rigorously filters its input, allowing only a known-safe subset of LaTeX commands through. And it limits the size of the input. So it should be safe to use, even on the internet.

After starting up the tex2svg server, you just uncomment the last line of config/environments/production.rb and restart Instiki. Now you can write something like

\begin{tikzpicture}[decoration={markings,
mark=at position .5 with {\arrow{>}}}]
\usetikzlibrary{arrows,shapes,decorations.markings}
\begin{scope}[scale=2.0]
\node[Bl,scale=.75] (or1) at (8,3) {};
\node[scale=1] at (8.7,2.9) {$D3$ brane};
\node[draw,diamond,fill=yellow,scale=.3] (A1) at (7,0) {}; 
\draw[dashed] (A1) -- (7,-.7);
\node[draw,diamond,fill=yellow,scale=.3] (A2) at (7.5,0) {}; 
\draw[dashed] (A2) -- (7.5,-.7);
\node[draw,diamond,fill=yellow,scale=.3] (A3) at (8,0) {}; 
\draw[dashed] (A3) -- (8,-.7);
\node[draw,diamond,fill=yellow,scale=.3] (A4) at (8.5,0) {}; 
\draw[dashed] (A4) -- (8.5,-.7);
\node[draw,diamond,fill=yellow,scale=.3] (A5) at (9,0) {};
\draw[dashed] (A5) -- (9,-.7);
\node[draw,circle,fill=aqua,scale=.3] (B) at (9.5,0) {};
\draw[dashed] (B) -- (9.5,-.7);
\node[draw,regular polygon,regular polygon sides=5,fill=purple,scale=.3] (C1) at (10,0) {}; 
\draw[dashed] (C1) -- (10,-.7);
\node[draw,regular polygon,regular polygon sides=5,fill=purple,scale=.3] (C2) at (10.5,0) {};
\draw[dashed] (C2) -- (10.5,-.7);
\draw (6.8,-.7) -- (6.8,-.9) to (9.2,-.9) to (9.2,-.7);
\draw (9.8,-.7) -- (9.8,-.9) to (10.7,-.9) to (10.7,-.7);
\draw[->-=.75] (C2) to (10.2,.35);
\draw[->-=.75] (C1) to (10.2,.35);
\node[scale=.6] at (9.9,.35) {$(2,2)$};
\draw[->-=.7] (B) to (9.6,.7);
\draw (10.2,.35) to (9.6,.7);
\node[scale=.6] at (9.35,.9) {$(4,0)$};
\draw[->-=.5] (9.1,.8) to (A5);
\draw (9.6,.7) to (9.1,.8) to (A5);
\draw (9.1,.8) to [out=170,in=280] (8.3,1.45);
\draw[dashed] (8.3,1.45) to (8.1,2.5);
\draw[->-=.5] (8.1,2.5) to (or1);
\node[scale=.75] at (7.7,2.7) {$(3,0)$};
%\draw (11.4,2.4) to [out=180,in=90] (6.2,-.5) to [out=90,in=0] (or1) -- cycle;
\node[scale=.75] at (8,-1.1) {A-type};
\node[scale=.75] at (9.5,-1.1) {B-type};
\node[scale=.75] at (10.25,-1.1) {C-type};
\draw[dashed] (8.7,.6) to [out=180,in=90] (6.2,-.55) to [out=270,in=180] (8.7,-1.6) to [out=0,in=270] (11.2,-.55) to [out=90,in=0] (8.7,.6) -- cycle;
\node[scale=1] at (12,.6) {$E_6$ singularity};
\end{scope}
\end{tikzpicture}

in Instiki and have it produce

Instiki 0.30.0 incorporates these changes, is compatible with Ruby 2.6, and greatly accelerates the process of saving pages (over previous versions).