Setting up rApache on Mac OS X

Someone asked me to set up rApache on Mac OS X 10.9 (Mavericks). All these instructions worked on 10.11 (El Capitan) though.

Why rApache? It was the easiest way for this application to embed R code in some HTML files without having to set up a virtual machine for an OpenCPU server. OpenCPU would be the best way to do it if you know Javascript and are capable of setting up an Ubuntu or Debian server. Plus, there are some good OpenCPU web app examples that have high-resolution icons.

Unfortunately, there is no rApache package for OS X in brew or macports, so you’ll have to build it from source.

The three pre-requisites for building from source are listed on rApache’s website:

R installed as a shared library
Apache 2.2 or greater
libapreq2 2.05 or higher (there is a version bundled with rApache, so it’s not necessary to build this separately)

Installing Apache

Using brew, Apache 2.2 or 2.4 is easy enough to install with brew install homebrew/apache/httpd22 (or httpd24). You can also brew tap homebrew/apache and then brew install httpd22 or httpd24.

Brew’s version of Apache will install by default into /usr/local/. The configuration will be in /usr/local/etc/apache2/2.2/httpd.conf (for httpd22) and the default web server root will be at /usr/local/var/www/htdocs.

XAMPP and rApache — I wasn’t able to install rApache when using the latest version of XAMPP (5.6.19). The problem appeared to be an inconsistent version of libiconv.2.dylib between XAMPP’s build and the one that I built mod_R.so. I was seeing an error with an undefined symbol _iconv in /Applications/XAMPP/xamppfiles/lib.

It seems like this problem happens with a lot of software, but I couldn’t find a good solution. I tried to get around this problem by installing libiconv with brew, but it didn’t solve the problem. Installing Apache with brew gets around this problem, but you’ll have to install PHP, MySQL, and everything else that XAMPP supplies on your own.

A quick check of rApache’s Google Group was not enlightening, except to see that other people had the same issue.

Installing R

I installed R with brew which by default installs R as a shared library. It installs into /usr/local/bin/r.

Building R from source works, too, as long as you run ./configure --enable-R-shlib. More details for downloading and installing R from source are available at R’s website.

You probably will also want to install the brew package for R by running install.packages("brew") at the R console. This allows the really convenient addition of R code into HTML like you would do with PHP using the <% and %> tags.

Installing libapreq2

There is a version of libapreq2 that comes with rApache and will build and install by default if you don’t specify your own apreq2 when you configure rApache. I recommend this route for ease. Also, I quickly scanned the changelog for libapreq2 and it didn’t seem like any major bugs were fixed between the bundled version 2.05 and the current version 2.13. But I compiled it anyway for completeness and to avoid the kind of bugs that I saw installing with XAMPP.

To install libapreq2 on OS X, I used Subversion to download the latest build using svn checkout httpvn.apache.org/repos/asf/httpd/apreq/trunk/ httpd-apreq-2. If you go this route, you’ll have to brew install libtool (this is really glibtool if you’re using brew), brew install automake autoconf, and run cpan then install ExtUtils::XSBuilder. You’ll also have to change libtool to glibtool in the configure file so that you use the GNU-compatible glibtool you installed with brew instead of OS X’s older libtool.

Then you can ./configure --with-apache2-apxs=/usr/local/bin/apxs before running make and make install.

Installing rApache

Finally, you should be able to install rApache. I used git clone https://github.com/jeffreyhorner/rapache.git. After you change directory into the rapache folder, you can run the configure script and specify ./configure --with-R=/usr/local/bin/r --with-apxs=/usr/local/bin/apxs

If you built libapreq2 from source, you’ll have to add the --with-apreq2-config=/usr/local/Cellar/apr-util/1.5.4_1/libexec/bin/apreq2-config to the line above (or wherever your apreq2-config is installed–to find this, you could make install | grep apreq2-config in the httpd-apreq-2 source folder).

You should also run make test and make itest then go to http://localhost:8181 and click on each of the links. To test R’s brew package, you’ll have to uncomment the <Directory> tags corresponding to the RHandler brew::brewin rapache/test/httpd.conf.

Importantly, the sendBin test script tests R’s ability to send binary data to the web server to allow plots to be displayed.

Notes

It’s useful to run brew update && brew upgrade to make sure you have the latest libpng, cairo, etc. If you don’t, the test script sendBin.R could crash and not give an Error 500 or even a 404. Not only that, but I was unable to find any mention of a crash in Apache’s error_log!

Putting it all together

You can edit your /usr/local/etc/apache2/2.2/httpd.conf (or wherever your Apache httpd.conf resides) to run individual R files or apply R functions to the files in a directory (like you’d want to do with R’s brew package) by adding directives like those in the testing httpd.conf Now you should be able to run $ sudo apachectl start or $ sudo apachectl restart and check out the web server running on your computer at http://localhost:8080.

Written on March 22, 2016