Create the gated discount function

• How to build a Shopify Function to apply the discount specified in the GateConfiguration
• Read and validate the HMAC signature stored as a cart attribute to verify your app's evaluation has not been tampered with. This will ensure your exclusive discount only goes to those who have met your gate requirements, as deemed by your app's evaluation.

• You've installed Rust.

  On Windows, Rust requires the Microsoft C++ Build Tools. Make sure to select the Desktop development with C++ workload when installing the tools.

• You've installed cargo-wasi:

To automatically apply exclusive discounts for buyers at checkout, add a product discount function as an extension to your app.

1. Navigate to your app directory.

2. Run the following command to create a new product discount extension:

   Choose the Rust language option.

3. Navigate to extensions/tokengating-function

4. Replace your Cargo.toml file with the following:

5. Build the function's Wasm module.

If you encounter any errors, ensure that you've installed Rust and cargo-wasi.

The function logic uses the input from the metafield that was defined when you created the GateConfiguration. The following _shopify_gate_context cart attribute key is the gate context that was created in the previous tutorial. This gate context is added here so that the function can determine whether the tokengated discount should be applied.

Copy the following code into extensions/tokengating-function/input.graphql. This file defines the input for the function. Replace tokengating-example-app with the namespace that you used when creating your GateConfiguration.

Your main discounting logic is located in extensions/tokengating-function/src/main.rs directory and written in Rust. By the time the code in this file executes, the input query above will have resolved and we have everything we need to accomplish our tasks within the function which are:

• Check that the automatic discount is relevant by reading its metafield for the GateConfiguration and only evaluating further if it matches the line item's GateConfiguration
• Verify the attached HMAC value, which is your app's attestation that this buyer has met the requirements to unlock the gate.
• If the above HMAC is verified, apply the discount by adding the corresponding discount object and returning it as the function's output. Otherwise, the function will not apply the discount.

The following code will set up the function logic to determine if the gate is unlocked. Replace the code in src/main.rs with the following:

The code checks that your automatic discount is relevant to the cart's line items, and that your app has attested that the buyer has unlocked the gate. You can review the culmination of this logic by looking at the definition of gate_unlocked.

1. Before deploying, ensure that the api_version in your extensions/tokengating-function/shopify.extension.toml is set to unstable. In the end, it should look like the following:

2. Because the api_version is unstable, you need to update the schema.graphql file. Navigate to the extensions/tokengating-function/ directory and run the following code:

3. Deploy your app along with the function.

To test your function, you need to make it available to your development store.

1. If you're developing a function in a language other than JavaScript or TypeScript, ensure you have configured build.watch in your function extension configuration.

2. Navigate back to your app root:

3. Use the Shopify CLI dev command to start app preview:

   You can keep the preview running as you work on your function. When you make changes to a watched file, Shopify CLI rebuilds your function and updates the function extension's drafts, so you can immediately test your changes.

4. Follow the CLI prompts to preview your app, and install it on your development store.

1. Install the Shopify GraphiQL app on your store.

2. In the GraphiQL app, in the API Version field, select the unstable version.

3. Find the ID of your function by executing the following query:

   The result contains a node with your function's ID:

4. Copy the ID and navigate to /web/api/create-discount.js to replace the YOUR_FUNCTION_ID.

You've now:

• built an admin app for merchants to configure gates and the corresponding discount
• deployed a theme app extension to display those gate requirements to buyers along with a wallet connection experience
• used Shopify Functions to apply the discount when gated products are added to the cart

To see the function in action:

1. Navigate to your gated product's detail page and unlock the product.
2. Add the product to your cart.
3. View your cart and check that the exclusive discount is applied. Note that the discount should be visibile in the cart, even before initiating the checkout process.

To view all of the code used for the tokengating example app, you can download the source code.

Tokengating example app

Explore an example app that enables merchants to tokengate products.