Rust for Functions

You can write your functions in Rust. This guide describes the shopify_function Rust crate that Shopify provides to help developers build with Shopify Functions.

Requirements

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You need to have graphql_client installed as a dependency in your project:

How it works

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The shopify_function Rust crate bundles graphql_client-based type generation, reduces boilerplate code, and makes it easier to test various function inputs. It includes the following components:

Component	Description
`shopify_function_target`	An attribute macro that transforms the following function to: Generate structs and output types for the Function API target from the specified input query and GraphQL schema. Export a WebAssembly function with the specified name, which must match the target export in the function extension configuration. Automatically handle input parsing from `STDIN` and output serialization to `STDOUT`.
`run_function_with_input`	A utility for unit testing that enables you to add new tests based on a given JSON input string.

Viewing the generated types

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To preview the types generated by the shopify_function Rust crate, use the cargo doc command.

You can also use the cargo-expand crate to view the generated source, or use the rust-analyzer VSCode extension to get IntelliSense for Rust and the generated types.

Example implementations

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Explore example implementations using the shopify_function Rust crate.

For API versions 2023-07 and earlier, the generate_types and shopify_function macros can be used directly to conform to previous WebAssembly requirements.

Rust Shopify Function example

Explore an example of how to use the shopify_function crate to implement a Shopify Function in Rust.

Rust Shopify Function example for earlier versions

Explore an example of how to use the shopify_function crate to implement a Shopify Function in Rust compatible with API versions 2023-07 and earlier.

Binary size tips

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Shopify Functions compiled Wasm file must be under 256 kB. Here are a few tips to keep binary size small when using Rust:

Update the shopify_function crate to the latest version.
For regular expressions, use the regex_lite crate.
Follow tips and documentation in the johnthagen/min-sized-rust GitHub repository.
Use wasm-snip to remove the panicking code, then wasm-opt to strip debug information. For example:
Use to_ascii_uppercase and to_ascii_lowercase when possible to avoid pulling in Unicode tables, unless needed.
Only query for data you need.

Code generation happens for all types and fields included in the input queries (for example, run.graphql). Review and remove any unused parts of the queries.
Keep JSON metafields that require deserialization as small as possible.

Code generated for deserialization increases the binary size. The smaller the metafield is, the less code needs to be generated.
Bring your own types and deserializers.

Instead of using the generated structs from the shopify_function_macro crate, write the appropropriate struct definitions and derive the deserializsers using mini_serde.

The structs from shopify_function_macro can be used as a starting point, see them with cargo expand.

Alternative serializers are generally less efficient than serde, make sure to benchmark the instruction count when going down this path.

Next steps

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Explore the reference documentation for the shopify_function Rust crate.