Zcash iOS Framework

A Zcash Lightweight Client SDK for iOS

This is an alpha build and is currently under active development. Please be advised of the following:

• This code currently is not audited by an external security auditor, use it at your own risk
• The code has not been subjected to thorough review by engineers at the Electric Coin Company
• We are actively changing the codebase and adding features where/when needed

🔒 Security Warnings

• The Zcash iOS Wallet SDK is experimental and a work in progress. Use it at your own risk.
• Developers using this SDK must familiarize themselves with the current threat model, especially the known weaknesses described there.

Build dependencies

ZcashLightClientKit uses a rust library called Librustzcash. In order to build it, you need to have rust and cargo installed on your environment.

Install Rust, and then cargo-lipo:

$ cargo install cargo-lipo
$ rustup target add aarch64-apple-ios x86_64-apple-ios

Cocoapods Support

Installing as a ZcashLightClientKit as a Contributor

use_frameworks!

pod 'ZcashLightClientKit', :path => '../../', :testspecs => ['Tests']  # include testspecs if you want to run the tests

Installing a wallet app developer

use_frameworks!

pod 'ZcashLightClientKit'

Set Testnet or Mainnet environment

Before building, make sure that your enviroment has the variable ZCASH_NETWORK_ENVIRONMENT set to MAINNET or TESTNET.

Custom build phases warning

When running pod install you will see this warning upon sucess:

[!] ZcashLightClientKit has added 2 script phases. Please inspect before executing a build. 
See `https://guides.cocoapods.org/syntax/podspec.html#script_phases` for more information.

Integrating Rust code with Swift code and delivering it in a consistent and (build) reproducible way, is hard. We’ve taken the lead to get that burden off your shoulders as much as possible by leveraging the prepare_command and script_phases features from Cocoapods to carefully generate the TESTNET and MAINNET builds as simple and less error prone as we could think it could be. Which started as some simple vanilla scripts, ended up being some kind of “Build System” on its own. Nothing is written on stone, and we accept collaborations and improvements in this matter too.

Build system

This section explains the ‘Build System’ that integrates the rust code and creates the corresponding environment

Overview

There are some basic steps to build ZcashLightClientKit. Even though they are ‘basic’ they can be cumbersome. So we automated them in scripts.

1. Pod install and prepare_command

ZcashLightClientKit needs files to be present at pod installation time, but that can’t be defined properly yet and depend on librustzcash building properly and for an environment to be set up at build time. For know we just need to let Cocoapods that these files exist:

• ${ZCASH_POD_SRCROOT}/zcashlc/libzcashlc.a this is the librustzcash build .a file itself
• lib/libzcashlc.a (as vendored library that will be added as an asset by xcodeproj)
• ZcashSDK.generated.swift which contains sensitive values for the SDK that change depending on the network environment we are building for
• WalletBirthday+saplingtree.generated.swift helper functions to import existing wallets.

2. Build Phase

The build Phase scripts executes withing the Xcode Build Step and has all the known variables of a traditional build at hand.

s.script_phase = {
      :name => 'Build generate constants and build librustzcash',
      :script => 'sh ${PODS_TARGET_SRCROOT}/Scripts/generate_zcashsdk_constants.sh && sh ${PODS_TARGET_SRCROOT}/Scripts/build_librustzcash_xcode.sh',
      :execution_position => :before_compile
   }

This step will generate files needed on the next steps and build the librustzcash with Xcode but not using cargo’s built-in xcode integration

a. Generating ZcashSDK constants

To run this you need Sourcery. We use Stencil templates to create this files based on the ZCASH_NETWORK_ENVIRONMENT value of your choice. You can either integrate sourcery with cocoapods or as part of your environment.

All generated files will be located in the Pods source root within the Generated folder. ZCASH_SDK_GENERATED_SOURCES_FOLDER represents that path in the build system

b. Building librust zcash and integrating it to the pod structure.

Where the magic happens. Here we will make sure that everything is set up properly to start building librustzcash. When on mainnet, the build will append a parameter to include mainnet features.

Safeguards points: if it appears that you are about to build something smelly, we will let you know. Combining testnet and mainnet values and artifacts and viceversa leads to unstable builds and may cause lost of funds if ran on production.

if [ existing_build_mismatch = true ]; then 
        # clean
        echo "build mismatch. You previously build a Different network environment. It appears that your build could be inconsistent if proceeding. Please clean your Pods/ folder and clean your build before running your next build."
        exit 1
fi

3. Xcode clean integration

When performing a clean, we will clean the rust build folders.

Scripts

On the Scripts folder you will find the following files:

 | Scripts
 |-/prepare_zcash_sdk.sh
 |-/generate_test_constants.sh
 |-/build_librustzcash_xcode.sh
 |-/build_librustzcash.sh
 |-/generate_zcashsdk_constants.sh
 |-/script_commons.sh

prepare_zcash_sdk.sh

This script is run by the Cocoapods ‘preapare_command’.

s.prepare_command = <<-CMD
      sh Scripts/prepare_zcash_sdk.sh
    CMD

It basically creates empty files that cocoapods needs to pick up on it’s pod structure but that are still not present in the file system and that will be generated in later build phases.

NOTE: pod install will only run this phase when no Pods/ folder is present or if your pod hash has changed or is not present on manifest.lock. When in doubt, just clean the Pods/ folder and start over. That usually gets rid of weirdness caused by Xcode caching a lot of stuff you are not aware of.

script_commons.sh

A lot of important environment variables and helper functions live in the script_commons.sh.

Testing

Currently tests depend on a lightwalletd server instance runnning locally or remotely to pass. To know more about running lightwalletd, refer to its repo https://github.com/zcash/lightwalletd

Pointing tests to a lightwalletd instance

Tests use Sourcery to generate a Constants file which injects the lightwalletd server address to the test themselves

Installing sourcery

refer to the official repo https://github.com/krzysztofzablocki/Sourcery

Setting env-var.sh file to run locally

create a file called env-var.sh on the project root to create the LIGHTWALLETD_ADDRESS environment variable on build time.

export LIGHTWALLETD_ADDRESS="localhost%3a9067"

Integrating with CD/CI

The LIGHTWALLETD_ADDRESS environment variable can also be added to your shell of choice and xcodebuild will pick it up accordingly.

We advice setting this value as a secret variable on your CD/CI environment when possible

Integrating with logging tools

There are a lots of good logging tools for iOS. So we’ll leave that choice to you. ZcashLightClientKit relies on a simple protocol to bubble up logs to client applications, which is called Logger (kudos for the naming originality…)

public protocol Logger {

    func debug(_ message: String, file: String, function: String, line: Int)

    func info(_ message: String, file: String, function: String, line: Int)

    func event(_ message: String, file: String, function: String, line: Int)

    func warn(_ message: String, file: String, function: String, line: Int)

    func error(_ message: String, file: String, function: String, line: Int)

}

To enable logging you need to do 2 simple steps:

1. have one class conform the Logger protocol
2. inject that logger when creating the Initializer

For more details look the Sample App’s AppDelegate code.

Swiftlint

We don’t like reinveing the wheel, so be gently borrowed swift lint rules from AirBnB which we find pretty cool and reasonable.

Troubleshooting

No network environment….

if you see this message when building: No network environment. Set ZCASH_NETWORK_ENVIRONMENT to MAINNET or TESTNET make sure your dev environment is has this variable set before the build starts. DO NOT CHANGE IT DURING THE BUILD PROCESS.

If the variable was properly set after you’ve seen this message, you will need to either a) set it manually on the pod’s target or b) doing a clean pod install and subsequent build.

a) setting the flag manually

1. on your workspace, select the Pods project.
2. on the Targets pane, select ZcashLightClientKit
3. go to build settings
4. scroll down to see ZCASH_NETWORK_ENVIRONMENT and complete with TESTNET or MAINNET

b) clean pod install

it’s not necessary to delete the whole Pods/ directory and download all of your dependencies again.

1. on your project root, locate the Pods/ directory
2. remove ZcashLightClientKit from it
3. clean derived data from xcode
4. close xcode
5. run pod install (run –verbose to see more details)
6. open xcode project
7. build

_function_name referenced from…

if you get a build error similar to _function_name referenced from...

• on your project root directory *
• remove the ‘Pods’ directory rm -rf Pods/
• delete derived data and clean
• run pod install
• build

ZcashLightClientKitSample missing .params

ZcashLightClientKit has an external dependency on 2 files containing Sapling parameters. Although you can provide those files as you seem fit, the sample app requires them on the main bundle.

You can download these files from https://z.cash/downloads/sapling-spend.params and https://z.cash/downloads/sapling-output.params and then move them to the correct folder, which is specified on the error itself.

Versioning

This project follows semantic versioning with pre-release versions. An example of a valid version number is 1.0.4-alpha11 denoting the 11th iteration of the alpha pre-release of version 1.0.4. Stable releases, such as 1.0.4 will not contain any pre-release identifiers. Pre-releases include the following, in order of stability: alpha, beta, rc. Version codes offer a numeric representation of the build name that always increases. The first six significant digits represent the major, minor and patch number (two digits each) and the last 3 significant digits represent the pre-release identifier. The first digit of the identifier signals the build type. Lastly, each new build has a higher version code than all previous builds. The following table breaks this down:

Build Types

Examples

This repo contains demos of isolated functionality that this SDK provides. They can be found in the examples folder

Examples can be found in the Demo App

License

Apache License Version 2.0