Category: Programming

One of the most popular articles on this blog is “Notarize a Command Line Tool with notarytool.” In that post I introduced a workflow for Xcode to build and notarize a custom installer package for a command line tool. This workflow also works with apps and other projects that require a customized installer package building workflow. I use it in many of my own projects.

But Xcode is not the only way to build Swift binaries. Especially for command line tools, you can also use Swift Package Manager. This provides a mostly command line based interface to building and organizing your project, which you might prefer if you want to use an IDE that is not Xcode, or have Swift projects that need to run cross-platform.

I also have an older article on building a command line tool with Swift Package Manager. But then, I did not create an installer package or notarize the resulting binary.

Placing the binary in an installer package file is the best way to distribute a binary as you can control where in the file system the binary is installed. Notarizing the pkg file is necessary when you are distributing a command line tool, since it enables installations without scary dialogs or handling quarantine flags.

Also, some of the behavior of Swift Package Manager (SPM) and Xcode have changed since the previous posts. So, this article will introduce an updated workflow using Swift Package Manager tools and how to sign, package and notarize a command line tool for distribution.

Note on nomenclature: Swift Package Manager projects are called ‘packages.’ On macOS, installer files (with the pkg file extension) are also called ‘packages.’ We will be using SPM to build a notarized installation package (a pkg file) from a Swift package project. This is confusing. There is not much I can do about that other than using ‘installer package’ and ‘Swift package project’ to help distinguish.

Prerequisites

I wrote this article using Xcode 14.3.1 and Swift 5.8.1. It should also work with somewhat older or newer versions of Xcode and Swift, but I have not tested any explicitly.

Since I said earlier that using Swift Package Manager allows us to not use Xcode and maybe even build a cross-platform project, you may be wondering why we need Xcode. While we don’t need Xcode for our project, it is one way of installing all the tools we need, most importantly the swift and notarytool binaries. You get those from Developer Command Line tools, as well. We will also see that we can combine Xcode with the command line Swift Package Manager workflow, which I find a very useful setup.

To submit a binary to Apple’s notarization process you will need a Personal or Enterprise Apple Developer account, and access to the Developer ID Application and Developer ID Installer certificates from that account. A free Apple Developer account does not provide those certificates, but they are necessary for notarization

You can follow the instructions in the Xcode article on how to get the certificates and how to configure notarytool with an application specific password. If you had already done this previously you should be able to re-use all of that here. When you reach the ‘Preparing the Xcode Project’ section in that article, you can stop and continue here. Apple also has some documentation on how to configure notarytool.

The sample code we will be using will only work on macOS as it uses CoreFoundation functions. Installer packages and notarization are features of macOS, too, so this is not really a problem here. You can use this workflow to build macOS specific signed binaries and notarized installation pkg files from a cross-platform Swift package project. This will work as long as you keep in mind that the tools to sign, package and notarize only exist and/or work on macOS.

The sample code

We will build the same simple sample tool as in the last article. The prf command (short for ‘pref’ or ‘preference’) reads a default setting’s effective value using the CFPreferencesCopyAppValue function.

The macOS defaults command will read preferences, but only from the user level, or from a specified file path. This ignores one of the main features of macOS’ preferences system as it will not show if a value is being managed by a different preference level, such as the global domain, a file in /Library/Preferences, or (most importantly for MacAdmins) a configuration profile.

You can learn all about preferences and profiles in my book “Property Lists, Preferences and Profiles for Apple Administrators.”

We will build a really simple command line tool, named prf which shows the effective value of a setting, no matter where the value comes from. You could make this tool far more elaborate, but we will keep it simple, since the code is not the actual topic for this article.

We will also be using the Swift Argument Parser package to parse command line arguments and provide a help message. We could build this simple tool without using Argument Parser, but using an external package module is one of the strengths of using Swift Package Manager.

Create the Swift Package project

With all the preparations done, it is time to create our Swift package. We will do all the work in the shell, so open Terminal or your other favorite terminal app and navigate to the directory where you want to create the project.

> cd ~/Projects

Then create a new directory with the name swift-prf. This will contain all the files from the Swift package project. Change directory into that new directory. All following commands will assume this project directory is the current working directory.

> mkdir swift-prf
> cd swift-prf

Then run the swift tool to setup the template structure for our command line tool or ‘executable.’

> swift package init --type executable 
Creating executable package: swift-prf
Creating Package.swift
Creating .gitignore
Creating Sources/
Creating Sources/main.swift

You can inspect the hierarchy of files that the init tool created in the Finder (open .) or in your preferred editor or IDE.

.gitignore
Package.swift
Sources
    main.swift

`

You can open this package project in Xcode. In older versions of Xcode you had to run a special swift package command to generate the Xcode project, but now, Xcode can open Swift package projects directly. Use xed (the ‘Xcode text editor invocation tool’) to open the current directory in Xcode.

> xed .

There is a pre-filled .gitignore (which will be hidden in Finder and probably your IDE), a Package.swift, and a Sources directory with a single main.swift inside. If you want to use git (or another version control) system, now is the time to initialize with git init.

Build the project with swift build and/or run it with swift run. Not surprisingly, the template prints Hello, world!.

> swift build
Building for debugging...
[3/3] Linking swift-prf
Build complete! (0.92s)
> swift run  
Building for debugging...
Build complete! (0.11s)
Hello, world!

After building, there will also be a .build directory (also hidden in Finder, unless you toggle the visibility of invisible files using shift-command-.) which contains all the interim files. In the debug folder, you can find the swift-prf executable. You can run it directly:

> .build/debug/swift-prf
Hello, world!

You can clean all the generated pieces from the .build directory with swift package clean. This will leave some empty folders behind but remove all the interim and final products. This means the next build is going to take much longer, but this can be helpful after reconfiguring the Package.swift file or when the compiler gets confused.

Sidenote: when you use Xcode to edit your Swift package project, and choose Build or Run from the Xcode interface, then it will build and run in a different location (~/Library/Developer/Xcode/DerivedData/swift-prf-<random-letters>/Build). You need to be aware of this when you alternate between Xcode and the command line.

Configuring the Package

The Package.swift file contains the configuration for a Swift package project. You can see that the executable package template has a single target named swift-prf that builds from the files in Sources.

To change the name of the executable file, change the value of the name: of the .executableTarget to just prf. There is another name: earlier in the file, that sets the name of the entire project, you can leave that being swift-prf. They do not have to match.

Then build the project in the command line and run it directly:

> swift build
Building for debugging...
[3/3] Linking prf
Build complete! (0.51s)
> .build/debug/prf          
Hello, world!

We want to add the Swift Argument Parser package to our project as a dependency, so we can use its functionality in our code. For that, we will have to add a ‘dependency’ to the project and then to the target, as well. Modify the Package.swift file to match this:

// swift-tools-version: 5.8
// The swift-tools-version declares the minimum version of Swift required to build this package.
import PackageDescription
let package = Package(
  name: "swift-prf",
  products: [
    .executable(name: "prf", targets: ["prf"]),
  ],
  dependencies: [
    .package(url: "https://github.com/apple/swift-argument-parser", from: "1.2.0"),
  ],
  targets: [
    .executableTarget(
      name: "prf",
      dependencies: [.product(name: "ArgumentParser", package: "swift-argument-parser")],
      path: "Sources")
  ]
)

This means that our project uses the package available at the given URL, and our target is going to use the specific product (or module or framework) named ArgumentParser from that package. Some packages have several products combined out of several targets.

You can find more information on the format of the Package.swift file in this overview, and the full documentation.

The next time you build after this change, it will download the repository, build and link to toward your executable. That might take a while. The next build should be much faster again. Also, a Package.resolved file will appear in the project. This file caches the current versions of the included packages protecting you from unexpected changes when a package repo dependency updates. You can force Swift Package Manager to update the file with swift package update.

Sprinkle some code

Now that we have the Swift package project prepared, we can add the code to actually do something.

First, let’s keep the ‘Hello, world!’ for a moment, but put it in the right struct to use ArgumentParser. Change main.swift to:

import Foundation
import ArgumentParser
@main
struct PRF: ParsableCommand {
  func run() {
    print("Hello, world!")
  }
}

This should build and run fine from the command line with swift build and swift run. However, when you open this now in Xcode, you will see an error: 'main' attribute cannot be used in a module that contains top-level code

This comes from a long-running issue in Swift. In older versions of Swift it appears on the command line, as well. The work-around is easy though. It only seems to appear when the @main designator is the main.swift file. We can rename our main file to PRF.swift.

You may want to close the Xcode project window before you do this because this can confuse Xcode. If you manage to get Xcode into a confused state where the project in Xcode does not match what is on disk any more, quit Xcode and delete the .swiftpm/xcode directory, which is where Xcode keeps its generated files.

> mv Sources/main.swift Sources/PRF.swift

Now the project should build and run the same with the Swift Package Manager tools and in Xcode.

Now we can add the ‘full’ code for our tool. Keep in mind that the goal of this tutorial is not to learn how to write complex swift code for command line tools, but to learn the infrastructure requires to create and distribute them, so this code is intentionally simple and basic.

import Foundation
import ArgumentParser
@main
struct PRF: ParsableCommand {
  static var configuration = CommandConfiguration(
    commandName: "prf",
    abstract: "read effective preference value",
    version: "1.0"
  )
  @Argument(help: "the preference domain, e.g. 'com.apple.dock'")
  var domain: String
  @Argument(help: "the preference key, e.g. 'orientation'")
  var key: String
  func run() {
    let plist = CFPreferencesCopyAppValue(key as CFString, domain as CFString)
    print(plist?.description ?? "<no value>")
  }
}

When you compare that to the code from the last article, there are a few differences. We are using the @main attribute to designate the main entry point for the code (this was added in Swift 5.3) and I have added some help text to the tool and argument declarations.

When you use Swift Argument Parser, you should study the documentation on adding help to [commands](I have added some help text to the tool and argument declarations. ) and flags, arguments and options. (To be honest, you should read the entire documentation, a lot has changed since the last article.)

When you now run the tool:

> swift run  
Building for debugging...
[3/3] Linking prf
Build complete! (0.54s)
Error: Missing expected argument '<domain>'
OVERVIEW: read effective preference value
USAGE: prf <domain> <key>
ARGUMENTS:
  <domain>                the preference domain, e.g. 'com.apple.dock'
  <key>                   the preference key, e.g. 'orientation'
OPTIONS:
  --version               Show the version.
  -h, --help              Show help information.

We get the help text generated by Swift Argument Parser with the extra information we provided in the code.

If you want to provide the arguments to the swift run you have to add the executable name, as well:

> swift run prf com.apple.dock orientation       
Building for debugging...
Build complete! (0.11s)
left

Or you can run the executable directly from the .build/debug directory. (This will not automatically re-build the command like swift run does.

> .build/debug/prf com.apple.dock orientation
left

Since we provided a version in the CommandConfiguration, ArgumentParser automatically generates a --version option:

> .build/debug/prf --version       
1.0

Now that we have a simple but working tool, we can tackle the main part: we will package and notarize the tool for distribution.

Preparing the binary

When you run swift build or swift run it will compile the tool in a form that is optimized for debugging. This is not the form you want to distribute the binary in. Also, we want to compile the release binary as a ‘universal’ binary, which means it will contain the code for both Intel and Apple silicon, no matter which CPU architecture we are building this on.

The command to build a universal release binary is

> swift build --configuration release --arch arm64 --arch x86_64

When that command is finished, you will find the universal binary file in .build/apple/Products/Release/prf. we can check that it contains the Intel (x86_64) and Apple silicon (arm64) with the lipo tool:

> lipo -info .build/apple/Products/Release/prf
Architectures in the fat file: .build/apple/Products/Release/prf are: x86_64 arm64 

For comparison, the debug version of the binary only contains the platform you are currently on:

> lipo -info .build/debug/prf
Non-fat file: .build/debug/prf is architecture: arm64

Apple’s notarization process requires submitted binaries to fulfill a few restrictions. They need a timestamped signature with a valid Developer ID and have the ‘hardened runtime’ enabled.

Xcode will always sign code it generates, but the swift command line tool does not. We will have to sign it ourselves using the codesign tool. You will need the full name of your “Developer ID Application” certificate for this. (Don’t confuse it with the “Developer ID Installer” certificate, which we will need later.)

You can list the available certs with

> security find-identity -p basic -v

and copy the entire name (including the quotes) of your certificate. Then run codesign:

> codesign --sign "Developer ID Application: Your Name (ABCDEFGHJK)" --options runtime  --timestamp .build/apple/Products/Release/prf

You can verify the code signature with

> codesign --display --verbose .build/apple/Products/Release/prf

Build the installation package

Now that we have prepared the binary for distribution, we can wrap it in an package installer file.

To cover all deployment scenarios, we will create a signed ‘product archive.’ You can watch my MacDevOps presentation “The Encyclopedia of Packages” for all the gory details.

First, create a directory that will contain all the files we want put in the pkg. Then we copy the binary there.

> mkdir .build/pkgroot
> cp .build/apple/Products/Release/prf .build/pkgroot/

Then build a component pkg from the pkgroot:

> pkgbuild --root .build/pkgroot --identifier com.scriptingosx.prf --version 1.0 --install-location /usr/local/bin/ prf.pkg

The --identifier uses the common reverse domain notation. This is what the installer system on macOS uses to determine whether an installation is an upgrade, so you really need to pay attention to keep using the same identifier across different versions of the tool. The --version value should change on every update.

The --install-location determines where the contents of the payload (i.e. the contents of the pkgroot directory) get installed to. /usr/local/bin/ is a useful default for macOS, but you can choose other locations here.

Next, we need to wrap the component pkg inside a distribution package.

> productbuild --package prf.pkg --identifier com.scriptingosx.prf --version 1.0 --sign "Developer ID Installer: Your Name (ABCDEFGHJK)" prf-1.0.pkg

It is important that you use the “Developer ID Installer” certificate here. The --identifier and --version are optional with productbuild but this data required for some (admittedly rare) deployment scenarios, and we want to cover them all.

You can inspect the installer pkg file with a package inspection tool such as the amazing Suspicious Package. The package file should as a signed “Product Archive.”

We don’t need the component pkg anymore, and it’s presence might be confusing, so let’s remove it:

> rm prf.pkg

Note: If you want to learn more about building installation packages, check out my book “Packaging for Apple Administrators”

Notarization

We are nearly there, just two more steps.

It is important to notarize pkgs that will be installed by a user, because otherwise they will get a scary warning that Apple can’t verify the pkg for malicious software.

notarytool submits the installer package to Apple’s Notarization process and returns the results. Use the keychain profile name you set up, following the instructions in the previous article or the instructions from the Apple Developer page.

> xcrun notarytool submit prf-1.0.pkg --keychain-profile notary-example.com --wait

This will print a lot of logging, most of which is self-explanatory. The process might stall at the “waiting” step for a while, depending on how busy Apple’s servers are. You should eventually get status: Accepted.

If you got a different status, or if you are curious, you can get more detail about the process, including rejection reasons, with notarytool log. You will need the ‘Submission ID’ from the submission output:

xcrun notarytool log <submission-uuid> --keychain-profile notary-example.com

As the final step, you should ‘staple’ the notarization ticket to the pkg. This means that the (signed) notarization information is attached to the pkg-file, saving a round trip to Apple’s servers to verify the notarization status when a system evaluates the downloaded installer package file.

xcrun stapler staple prf-1.0.pkg
Processing: /Users/armin/Desktop/swift-prf/prf-1.0.pkg
Processing: /Users/armin/Desktop/swift-prf/prf-1.0.pkg
The staple and validate action worked!

And with that, we have a signed and notarized installation pkg file! You can verify this with spctl:

> spctl --assess --verbose -t install prf-1.0.pkg 
prf-1.0.pkg: accepted
source=Notarized Developer ID

Automation

While it is instructive to do this process manually, it is also quite complex and error-prone. If you have been following this blog for any time, you will know that I don’t stop at detailed step-by-step instructions with explanations.

You can find a script to automate all of these steps here. The enclosing repository includes the entire project (all three files) for your reference.

There is a section at the beginning with variables to modify with the information specific to your environment and project, such as your developer ID information and the name of the credential profile for notarytool. Then there are a few variables, such as the product name, and the installation package identifier.

Run the pkgAndNotarize.sh script from the root of the Swift package project directory.

./pkgAndNotarize.sh

The script creates the installer pkg file in the .build directory. The last line of output is the path to the final, signed, notarized and stapled pkg file.

The script mostly follows the process described above, with a few extras. For example, the script determines the version dynamically by running the tool with the --version option. It also uses the modern compression options I described in this post.

If any of the steps in the script fail, you can determine what exactly failed from the output, error message and error code.

(I belief that this could probably be a makefile, but I have no experience with that (yet). I guess I will need to ‘make’ time for this…)

Conclusion

Apple provides developers and MacAdmins with amazing platforms and tools to build all kinds of powerful apps, tools and automations. But then they don’t really document any of the processes or best practices at all. The amount of searching, guesswork, and frustrating trial and error necessary to piece all of this together for a workflow like this one is quite the shocking condemnation of Apple’s documentation.

There are glimmers of hope. The documentation for the notarization process and notarytool are exemplary.

But they only cover one piece of this puzzle. A developer building a tool has to still figure out how to

• sign all the binaries properly
• assemble the binaries and resources necessary into an installation package payload
• how (and when, and when not) to use pre- and postinstall scripts
• which kind of package installer to build and which tools to use
• securely manage the Developer ID certificates (this is especially challenging for developer teams)
• automate this workflow with Xcode or Swift Package Manager or a CI/CD system

MacAdmins often complain about poorly built installer pkgs, and often for good reasons. But to be fair, there are no best practices and little to no documentation for this from Apple. How are developers supposed to know all of this? Most MacAdmins can define what an installer package should do and not do, but wouldn’t be able to explain to a developer how to build such an installer package, let alone integrate that into their build automations. And most developers don’t even know a MacAdmin to ask about this.

Apple requires that developers create signed and notarized archives for software distribution. And I agree wholeheartedly with their motivations and goals here. But when impose requirements for distribution, you have to make the process of creating the installers the correct way easy, or at least well documented, whether you use Xcode or a different tool set, whether you want to distribute a simple self-contained app, a single command line tool, or a complex suite of tools and resources.

Apple has their work cut out to improve this. Official best practices and sample workflows for installer creation and distribution that consider and respect the requirements of MacAdmins for deployment, have been disgracefully lacking for a long time. The more requirements and security Apple piles on to application and tool distribution, the more desperately they need to provide documentation, best practices and guidance.

Until that happens, you have my paltry scripts.