How to run binary on Heroku

Question

I have a simple node.js app that runs great on my OSX dev environment. But when I push the same code to Heroku, I get undefined returned in unexpected places.

The library that is behaving unpredictably is called pandoc. It converts document formats. I integrating it into my node app using the wrapper package node-pdc. Pdc requires pandoc to be installed, but it accepts a path to specify the location of pandoc, which I'm doing locally and it works great. I uninstalled pandoc globally on my local machine to make sure I was pointing to the correct location of the executable file.

This works exactly as expected locally:

var pdc = require('pdc');
var path = require('path');
var fs = require('fs');
var Q = require('q');

// optional, if pandoc is not in PATH
pdc.path = path.resolve(__dirname +'/pandoc/1.15.0.6/bin/pandoc');

module.exports.mdToHtml = function (input, callback) {

    //TEST
    pdc('## Emerson', 'markdown', 'html', ['--template=smashingtemplate'], function(err, result){
        console.log(result); // <h2>Emerson</h2>
    });
    ...

But on Heroku, I see undefined in the logs. It does not throw any errors. Why does it work on my laptop but not on Heroku?

Both environments are running node v4.0.0

Update 1: I tested to see if pandoc was available on Heroku...

$ heroku run bash 

~ $ ls /app/pandoc/1.15.0.6/bin/      
pandoc
~ $ /app/pandoc/1.15.0.6/bin/pandoc --version
bash: /app/pandoc/1.15.0.6/bin/pandoc: cannot execute binary file: Exec format error
~ $ ls /app/pandoc/1.15.0.6/bin/ -lah 
total 73M
drwx------ 2 u35911 dyno 4.0K Jun  5 04:48 .
drwx------ 4 u35911 dyno 4.0K Jun  5 04:48 ..
-rwx------ 1 u35911 dyno  73M Jun  5 04:48 pandoc

The binary files are there. But I can't run them...

Update 2

~ $ objdump -i /app/pandoc/1.15.0.6/bin/pandoc
BFD header file version (GNU Binutils for Ubuntu) 2.24
elf64-x86-64
 (header little endian, data little endian)
  i386
elf32-i386
 (header little endian, data little endian)
  i386
elf32-x86-64
 (header little endian, data little endian)
  i386
a.out-i386-linux
 (header little endian, data little endian)
  i386
pei-i386
 (header little endian, data little endian)
  i386
pei-x86-64
 (header little endian, data little endian)
  i386
elf64-l1om
 (header little endian, data little endian)
  l1om
elf64-k1om
 (header little endian, data little endian)
  k1om
elf64-little
 (header little endian, data little endian)
  i386
  l1om
  k1om
  plugin
elf64-big
 (header big endian, data big endian)
  i386
  l1om
  k1om
  plugin
elf32-little
 (header little endian, data little endian)
  i386
  l1om
  k1om
  plugin
elf32-big
 (header big endian, data big endian)
  i386
  l1om
  k1om
  plugin
pe-x86-64
 (header little endian, data little endian)
  i386
pe-i386
 (header little endian, data little endian)
  i386
plugin
 (header little endian, data little endian)
srec
 (header endianness unknown, data endianness unknown)
  i386
  l1om
  k1om
  plugin
symbolsrec
 (header endianness unknown, data endianness unknown)
  i386
  l1om
  k1om
  plugin
verilog
 (header endianness unknown, data endianness unknown)
  i386
  l1om
  k1om
  plugin
tekhex
 (header endianness unknown, data endianness unknown)
  i386
  l1om
  k1om
  plugin
binary
 (header endianness unknown, data endianness unknown)
  i386
  l1om
  k1om
  plugin
ihex
 (header endianness unknown, data endianness unknown)
  i386
  l1om
  k1om
  plugin

               elf64-x86-64 elf32-i386 elf32-x86-64 a.out-i386-linux pei-i386 pei-x86-64 elf64-l1om elf64-k1om elf64-little 
          i386 elf64-x86-64 elf32-i386 elf32-x86-64 a.out-i386-linux pei-i386 pei-x86-64 ---------- ---------- elf64-little 
          l1om ------------ ---------- ------------ ---------------- -------- ---------- elf64-l1om ---------- elf64-little 
          k1om ------------ ---------- ------------ ---------------- -------- ---------- ---------- elf64-k1om elf64-little 
        plugin ------------ ---------- ------------ ---------------- -------- ---------- ---------- ---------- elf64-little 

               elf64-big elf32-little elf32-big pe-x86-64 pe-i386 plugin srec symbolsrec verilog tekhex binary ihex 
          i386 elf64-big elf32-little elf32-big pe-x86-64 pe-i386 ------ srec symbolsrec verilog tekhex binary ihex 
          l1om elf64-big elf32-little elf32-big --------- ------- ------ srec symbolsrec verilog tekhex binary ihex 
          k1om elf64-big elf32-little elf32-big --------- ------- ------ srec symbolsrec verilog tekhex binary ihex 
        plugin elf64-big elf32-little elf32-big --------- ------- ------ srec symbolsrec verilog tekhex binary ihex 

And...

~ $ uname -a    
Linux 7f4e1d74-8fc2-47d2-89b7-97bfc9db30dd 3.13.0-85-generic #129-Ubuntu SMP Thu Mar 17 20:50:15 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

I might not be understanding it correctly, but it looks like they're both for 64 architecture.

~ $ file  /app/pandoc/1.15.0.6/bin/pandoc
/app/pandoc/1.15.0.6/bin/pandoc: Mach-O 64-bit x86_64 executable

Update 3

Following @mbs1's suggestions...

Creating a relocatable binary
-----------------------------

It is possible to compile pandoc such that the data files
pandoc uses are embedded in the binary.  The resulting binary
can be run from any directory and is completely self-contained.

    cabal install hsb2hs  # a required build tool
    cabal install --flags="embed_data_files" citeproc-hs
    cabal configure --flags="embed_data_files"
    cabal build

You can find the pandoc executable in `dist/build/pandoc`.  Copy this wherever
you please.

When I do cabal build it says:

cabal: No cabal file found.
Please create a package description file <pkgname>.cabal 

Solution

I couldn't get it to work with any of the solutions requiring cabal. I did finally get it to work using stack (once I figured out how to get it installed).

$ stack install pandoc --flag pandoc:embed-data_files

Then I copied the generated exec file out of the vm and pushed it to Heroku.

Answer 1

You need to build a relocatable-binary of pandoc on the exact same OS as Heroku uses, so an Ubuntu Linux system (install it in a virtual machine if you're on Mac OS X) and then follow this or this. Basically the following should create a re-locatable binary:

stack install pandoc --flag pandoc:embed_data_files

Alternatively, you could also use Docverter, which is kind of pandoc as a service.

Answer 2

You're running OSX locally. Heroku runs on Ubuntu Linux. These architectures are not binary compatible.