Thursday, October 30, 2014

Deploying iOS applications with the Nix package manager revisited

Previously, I have written a couple of blog posts about iOS application deployment. For example, I have developed a Nix function that can be used to build apps for the iOS simulator and real iOS devices, made some testability improvements, and implemented a dirty trick to make wireless ad-hoc distributions of iOS apps possible with Hydra, the Nix-based continuous integration server.

Recently, I made a some major changes to the Nix build function which I will describe in this blog post.

Supporting multiple Xcode versions

Xcode version 6.0 and beyond do not support iOS SDK versions below 8.0. Sometimes, it might still be desirable to build apps against older SDKs, such as 7.0. To be able to do that, we must also install older Xcode versions alongside newer versions.

As with recent Xcode versions, we must also install older Xcode versions manually first and use a Nix proxy function to use it. DMG files for older Xcode versions can be obtained from Apple's developer portal.

When installing a second Xcode DMG, you typically get a warning that looks as follows:

The installer attempts to put Xcode in its standard location (/Applications/, but if you click on 'Keep Both' then it is installed in a different path, such as /Applications/Xcode

I modified the proxy function (described in the first blog post) in such a way that the version number and path to Xcode are configurable:

{ stdenv
, version ? "6.0.1"
, xcodeBaseDir ? "/Applications/"

stdenv.mkDerivation {
  name = "xcode-wrapper-"+version;
  buildCommand = ''
    mkdir -p $out/bin
    cd $out/bin
    ln -s /usr/bin/xcode-select
    ln -s /usr/bin/security
    ln -s /usr/bin/codesign
    ln -s "${xcodeBaseDir}/Contents/Developer/usr/bin/xcodebuild"
    ln -s "${xcodeBaseDir}/Contents/Developer/usr/bin/xcrun"
    ln -s "${xcodeBaseDir}/Contents/Developer/Applications/iOS\
Contents/MacOS/iOS Simulator"

    cd ..
    ln -s "${xcodeBaseDir}/Contents/Developer/Platforms/\

    # Check if we have the xcodebuild version that we want
    if [ -z "$($out/bin/xcodebuild -version | grep -x 'Xcode ${version}')" ]
        echo "We require xcodebuild version: ${version}"
        exit 1

As can be seen in the expression, two parameters have been added to the function definition. Moreover, only tools that a particular installation of Xcode does not provide are referenced from /usr/bin. The rest of the executables are linked to the specified Xcode installation.

We can configure an alternative Xcode version by modifying the composition expression shown in the first blog post:

rec {
  stdenv = ...;

  xcodeenv = import ./xcode-wrapper.nix {
    version = "5.0.2";
    xcodeBaseDir = "/Applications/Xcode";
    inherit stdenv;

  helloworld = import ./pkgs/helloworld {
    inherit xcodeenv;

As may be observed, we pass a different Xcode version number and path as parameters to the Xcode wrapper which correspond to an alternative Xcode 5.0.2 installation.

The app can be built with Nix as follows:

$ nix-build default.nix -A helloworld
$ cd result
$ ls

Simulating iOS apps

Previously, I also developed a Nix function that generates build scripts that automatically spawn iOS simulator instances in which apps are deployed, which is quite useful for testing purposes.

Unfortunately, things have changed considerably in the new Xcode 6 and the old method no longer works.

I created a new kind of script that is based on details described in the following Stack overflow article:

First, simulator instances must be created through Xcode. This can be done by starting Xcode and opening Window -> Devices in the Xcode menu:

A new simulator instance can be added by clicking on the '+' button on the bottom left in the window:

In the above example, I create a new instance with a name 'iPhone 6' that simulates an iPhone 6 running iOS 8.0.

After creating the instance, it should appear in the device list:

Furthermore, each simulator instance has a unique device identifier (UDID). In this particular example, the UDID is: 0AD5FC1C-A360-4D05-9D6A-FD719C46A149

We can launch the simulator instance we just created from the command-line as follows:

$ open -a "$(readlink "${xcodewrapper}/bin/iOS Simulator")" --args \
    -CurrentDeviceUDID 0AD5FC1C-A360-4D05-9D6A-FD719C46A149

We can provide the UDID of the simulator instance as a parameter to automatically launch it. If we don't know the UDID of a simulator instance, we can obtain a list from the command line by running:

$ xcrun simctl list
== Device Types ==
iPhone 4s (
iPhone 5 (
iPhone 5s (
iPhone 6 Plus (
iPhone 6 (
iPad 2 (
iPad Retina (
iPad Air (
Resizable iPhone (
Resizable iPad (
== Runtimes ==
iOS 7.0 (7.0.3 - 11B507) (
iOS 7.1 (7.1 - 11D167) (
iOS 8.0 (8.0 - 12A365) (
== Devices ==
-- iOS 7.0 --
-- iOS 7.1 --
-- iOS 8.0 --
    iPhone 4s (868D3066-A7A2-4FD1-AF6A-25A90F480A30) (Shutdown)
    iPhone 5 (7C672CBE-5A08-481A-A5EF-2EA834E3FCD4) (Shutdown)
    iPhone 6 (0AD5FC1C-A360-4D05-9D6A-FD719C46A149) (Shutdown)
    Resizable iPhone (E95FC563-8748-4547-BD2C-B6333401B381) (Shutdown)

We can also install an app into the simulator instance from the command-line. However, to be able to install any app produced by Nix, we must first copy the app to a temp directory and restore write permissions:

$ appTmpDir=$(mktemp -d -t appTmpDir)
$ cp -r "$(echo ${app}/*.app)" $appTmpDir
$ chmod -R 755 "$(echo $appTmpDir/*.app)"

The reason why we need to do this is because Nix makes a package immutable after it has been built by removing the write permission bits. After restoring the permissions, we can install it in the simulator by running:

$ xcrun simctl install 0AD5FC1C-A360-4D05-9D6A-FD719C46A149 \
    "$(echo $appTmpDir/*.app)"

And launch the app in the simulator with the following command:

$ xcrun simctl launch 0AD5FC1C-A360-4D05-9D6A-FD719C46A149 \

Like the old simulator function, I have encapsulated the earlier described steps in a Nix function that generates a script spawning the simulator instance automatically. The example app can be deployed by writing the following expression:

{xcodeenv, helloworld}:

xcodeenv.simulateApp {
  name = "HelloWorld";
  bundleId = "MyCompany.HelloWorld";
  app = helloworld;

By running the following command-line instructions, we can automatically deploy an app in a simulator instance:

$ nix-build -A simulate_helloworld
./result/bin/run-test-simulator 0AD5FC1C-A360-4D05-9D6A-FD719C46A149

And this is what the result looks like:

The UDID parameter passed to the script is not required. If a UDID has been provided, it deploys the app to that particular simulator instance. If the UDID parameter is omitted, it displays a list of simulator instances and asks the user to select one.


In this blog post, I have described an addition to the Nix function that builds iOS application to support multiple versions of Xcode. Furthermore, I have implemented a new simulator spawning script that works with Xcode 6.

The example case can be obtained from my GitHub page.

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