Scratch Link

Scratch Link is a helper application which allows Scratch 3.0 to communicate with hardware peripherals. Scratch Link replaces the Scratch Device Manager and Scratch Device Plug-in.

System Requirements:

Using Scratch Link with Scratch 3.0

To use Scratch Link with Scratch 3.0:

1. Install and run Scratch Link
2. Open Scratch 3.0
3. Select the "Add Extension" button (looks like Scratch blocks with a + at the bottom of the block categories list)
4. Select a compatible extension such as the micro:bit or LEGO EV3 extension.
5. Follow the prompts to connect your peripheral.
6. Build a project with the new extension blocks. Scratch Link will help Scratch communicate with your peripheral.

Development: Getting started

Documentation

The general network protocol and all supported hardware protocols are documented in Markdown files in the Documentation subdirectory. Please note that network protocol stability and compatibility are high priorities for this project. Changes to the protocol are unlikely to be accepted without very strong justification combined with thorough documentation.

Please use markdownlint to check documentation changes before submitting a pull request.

Secure WebSockets

Previous versions of Scratch Link used Secure WebSockets (wss://) to communicate with Scratch. This is no longer the case: new versions of Scratch Link use regular WebSockets (ws://). It is no longer necessary to prepare an SSL certificate for Scratch Link.

This change causes an incompatibility with some browsers, including Safari. An upcoming version of Scratch Link will resolve this incompatibility.

macOS

The macOS version of this project is in the macOS subdirectory. It uses Swift 5.2 and the Swift Package Manager.

Developer prerequisites on macOS, most of which are available through Homebrew:

• Xcode Command Line Tools
  • Install with xcode-select --install
• git
• pngcrush
• swiftlint (optional)
• Swift Version Manager swiftenv (optional)

The build is primarily controlled through make:

• Build the app bundle with make, which will automatically:
  1. Compile Scratch Link code using swift build
  2. Create an app bundle at dist/Scratch Link.app
  3. Copy all necessary frameworks and dylibs into the app bundle
  4. Generate and/or copy other resources, such as icons, into the app bundle
• Build PKG installers with make dist, which runs both of these:
  • Build a PKG for the Mac App Store with make dist-mas
  • Build a PKG for non-Store distribution ("Developer ID") with make dist-devid
• Run the app in any of these ways:
  • Use Finder to activate the Scratch Link bundle in the dist directory
  • Run "dist/Scratch Link.app/Contents/MacOS/scratch-link"
  • Debug output will appear in the terminal
  • Type open "dist/Scratch Link.app" in a terminal
  • Debug output will not appear in the terminal
• Create an Xcode project file with make xcodeproj
  • If your workflow uses the Xcode project file (Xcode, AppCode, etc.) you should re-run this command each time you add or remove source files.
  • Any changes you make to the Xcode project file will be discarded when you run this command.
  • You may not be able to run the project using the Xcode project file, but completion and building should work.

Windows

The Windows version of this project is in the Windows subdirectory.

Prerequisites:

• Visual Studio 2017 or newer (Community Edition is sufficient)
• Windows 10.0.16299 SDK (install with Visual Studio)
• Some of the Scratch Link project files depend on NuGet packages. Visual Studio should prompt you to install these packages when you open the Solution file. Without these packages, Scratch Link may fail to build or run.

Optional:

• MSBuildStructuredLog is a huge help for debugging MSBuild.
• Wix Toolset Visual Studio Extension (install through "Manage Extensions") is required for ScratchLinkSetup work.

Build, run, and debug by opening the Solution (*.sln) file in Visual Studio.

Signing the MSI installer

This section applies to Scratch Team members only.

To build and sign the ScratchLinkSetup installer (MSI), you must install the appropriate signing certificate. Contact another Scratch Team member to obtain the certificate, then install it with these steps:

1. Open "Manage User Certificates"
2. Expand "Personal"
3. Right-click "Certificates" under "Personal"
4. Select "Import..."
5. Follow the steps to import the signing certificate.
   • You may need to change the file browser to Personal Information Exchange (*.pfx;*.p12).
   • When prompted, enter the password for the certificate file you're importing.
   • On the last step, make sure the certificate store is listed as "Personal"

You can verify that you've installed the correct certificate by comparing the thumbprint in the Certificate Manager to the one listed in the post-build event in the ScratchLinkSetup project.

Known Issues for Developers

1. Building the ScratchLinkSetup project may fail with a System.IO.DirectoryNotFoundException if the Windows case sensitivity flag is enabled on any directory in the path to the Scratch Link project files. This flag can become enabled when WSL is used to create or manipulate directories.
   • Solution: Use fsutil file queryCaseSensitiveInfo myDirName to check if myDirName has its case sensitivity flag set. If so, use fsutil file setCaseSensitiveInfo myDirName disable to clear the flag.
   • More detail: https://github.com/wixtoolset/issues/issues/5809
2. The make step may fail if the path to the Scratch Link directory contains whitespace.
   • Solution: Move Scratch Link to a directory without whitespace in the path.
   • More detail: http://savannah.gnu.org/bugs/?712 and https://github.com/LLK/scratch-link/issues/66