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Latexjs (BETA)

Latexjs is a complete, cross-platform, self-contained, LaTeX compile toolchain, whose only external dependency is a node interpreter.

There is no large monolithic latex distribution to install - Latexjs dynamically downloads only the files files required for compilation and stores them in a local cache.

Here's the steps for getting going on any machine (Mac, Windows, or Linux) with node available:

1. Download latex.js and run

node latex.js install

to setup a minimal LaTeX toolchain at ~/.latexjs.

2. Run

node ~/.latexjs/apps/latex.js compile ./main.tex

to trigger a compilation of the main.tex file with latexmk/pdflatex/bibtex with support for synctex. Note that the file to be compiled must be a relative path that is within the current working directory. This is about the only restriction of Latexjs vs directly using a native LaTeX installation.

3. The exact files required from a complete up-to-date TeX Live install will be downloaded to a ~/.latexjs cache from the Latexjs server. For my thesis, that's about 35MB.
4. That's it. Latexjs will only download new files if they are required (i.e. you compile a different document which uses a new package).

FAQ

How does this work?

Latexjs uses Emscripten to compile TeX Live tools like pdflatex and bibtex to asm.js, a subset of javascript that modern interpreters can run at close to native speeds.

Emscripten also provides a virtual file system for the compiled binary to run in, which can be controlled. Latexjs uses a custom Emscripten file system called THINFS, which handles all file system requests that the TeX Live binaries try to make to the TeX Live installation folder. THINFS dynamically downloads new files as required when a fs.open command is intercepted.

Surely this can't work for everything a full proper TeX Live install would work for?

The running binary is oblivious to the THINFS caching filesystem layer, so we can guarantee full compatibility with a complete TeX Live install. If something doesn't work with pdflatex.js that does work with pdflatex from TeX Live, please raise an issue, because it is a bug.

OK, but there must be some limitations?

Here's everything I am aware of where behavior would differ from native equivalents:

1. All files to be processed (that aren't part of TeX Live) need to be under the current working directory. We mount the current working directory inside the Emscripten virtual file system - trying to access above that (../) won't work.

2. The -shell-escape flag for pdflatex does not work. See #22 for details.

That's it for now.

How's the performance?

Currently performance is anywhere for 2x-6x slower than native alternatives. We haven't focused on optimization yet, and are confident that we can lower that somewhat.

Why make this?

LaTeX can be a bit of a pain to get going with on a machine. Generally speaking it involves downloading a Latex distribution, of which there are a few, although the big three tend to be:

• MikTeX (Windows)
• MacTeX (macOS)
• TeX Live (Linux)

These distributions have installers, and the way they need to be installed is platform specific. In general they are large monolithic downloads, and are a bit of a pain to keep up to date. Latexjs provides a simpler solution that works the same on any platform.

A particularly compelling use case is using Latexjs within an Electron app, where an up to date version of node is guaranteed to be available.

How are updates handled?

Latexjs is designed to be kept up to date continuously. There are three levels of versioning that are enforced in Latexjs:

1. latexjs.version - a version number tracking the overall design of the system. We expect this version number to change very infrequently (ideally, never!). Upgrades between these version numbers will be more involved. The present version number is "1".
2. texlive.version - a version number tracking the version of TeX Live that Latexjs currently uses. The current version is "2016", and represents an up to date snapshot of TeX Live 2016 taken around the time Latexjs was devised (April 2017). Migration to newer texlive.version numbers is not presently supported but will be easy given the design of the system. The version number can increase in-between annual releases if new updates are deemed important for Latexjs users (e.g. "2016.1")
3. Invididual app checksums - each app has a checksum - newer versions of each app can be downloaded at a rate independent from texlive.version (say for instance we improve the performance by tweaking Emscripten settings - this doesn't require a new TeX Live version, but we can still push out new apps).

Running

node ~/.latexjs/apps/latex.js install

Will perform an in-place upgrade. Before we need to use the texlive.version and latexjs.version options, upgrades will be made to Latexjs to be able to handle these types of updates (for now only apps are updated).

Where is this stuff hosted?

For now I'm running three instances of the Latexjs servers in London, San Fransisco, and Singapore. Before a download starts the client determines the optimal server to talk to based on response time. The servers are simple deployments of the open Docker images that are outlined below, and all files are checksumed. Everything is served over SSL.

Isn't that going to be really slow if you are always going to the server for files?

No. This only happens the first time a new file is required, i.e. when a new package is processed by Latexjs for the first time. Subsequent runs are close to native speeds as the locally cached file is used.

Building

Latexjs is built in a series of Docker containers.

Our first image, latexjs/texlive, installs the latest texlive install, gzips every file, takes it's SHA1 checksum, and builds a THINFS DB file that can be used be the client to emulate all filesystem calls up until open().

Our second image, latexjs/latexjs, builds on this by installing Emscripten, downloading the latest texlive source, and compiles nessessary JS binaries.

Our final image latexjs/server, builds on this to install nginx to serve this content.

The latexjs/server image can be bumped frequently to get security patches, latexjs/latexjs bumped for changes in our toolchain, and latexjs/texlive less frequently only when we discover any issues that need resolving in texlive for users. We use the experimental --squash flag to keep images small (the Emscripten install from source is 30GB!)

Buiding latexmk Windows binary

To be a complete LaTeX toolchain we need something like latexmk to be able to perform the correct number of executions of pdflatex and bibtex, and unfortunately there isn't a good native (and hence Emscripten-able) or Javascript solution for this. As a stopgap, we currently use latexmk and rely on a system Perl interpreter for macOS/Linux (a reasonably safe bet) and use pp to compile a standalone Windows binary of latexmk for Windows (where we can't guarantee at all that a perl interpreter will be kicking around).

See latexjs/latexmk for details.

Deployment

LatexJS is built in a series of Docker images that can be found on our Docker Hub repo. The final image to run the server is latexjs/server. Deployment (and update) is handled with docker-compose:

docker-compose pull && docker compose down || docker-compose up -d

But first a little setup is needed (using DO one-click Docker 16.04)

1. Setting up SSL

We use Docker + Let's Encrypt to initially get hold of a cert:

docker run -it --rm -p 443:443 -p 80:80 --name certbot -v "/etc/letsencrypt:/etc/letsencrypt" -v "/var/lib/letsencrypt:/var/lib/letsencrypt" certbot/certbot certonly

To renew:

docker run -it --rm -p 443:443 -p 80:80 --name certbot -v "/etc/letsencrypt:/etc/letsencrypt" -v "/var/lib/letsencrypt:/var/lib/letsencrypt" certbot/certbot renew && docker restart latexjs

2. Setting up docker-compose

vim /usr/local/bin/docker-compose

Change version to 1.12

And download the latest docker-compose.yml

wget https://github.com/latexjs/latexjs/raw/master/docker-compose.yml

Finally, edit ./.env to contain the server prefix:

SERVER_LOCATION=london

Acknowledgments

A huge thank you to texlive.js who were the first to figure out how to Emscripten TeX Live binaries.

Licensing

The code in this repository is BSD-licensed, see LICENSE. This code includes:

1. A collection of scripts for downloading and building TeX Live though Emscripten.
2. A custom Emscripten File System (THINFS), which is completely general purpose.

It does not include anything from TeX Live.

This code produces a TeX Live instance and a collection of Javascript files which are transpiled from TeX Live sources. These produced artifacts are licensed under the TeX Live licencing. For details of this licensing, please see the LICENSE.TL and LICENSE.CTAN text files.

TL;DR (IANAL) - you can use my code (THINFS, these build scripts) under a BSD-license, but the produced files (e.g. pdflatex.js) are licensed under the TeX Live licencing.