Wasm

Detailed documentation on the WebAssembly binding component

Overview

With WebAssembly, you can safely run code compiled in other languages. Runtimes execute WebAssembly Modules (Wasm), which are most often binaries with a .wasm extension.

The Wasm Binding allows you to invoke a program compiled to Wasm by passing commandline args or environment variables to it, similar to how you would with a normal subprocess. For example, you can satisfy an invocation using Python, even though Dapr is written in Go and is running on a platform that doesn’t have Python installed!

The Wasm binary must be a program compiled with the WebAssembly System Interface (WASI). The binary can be a program you’ve written such as in Go, or an interpreter you use to run inlined scripts, such as Python.

Minimally, you must specify a Wasm binary compiled with the canonical WASI version wasi_snapshot_preview1 (a.k.a. wasip1), often abbreviated to wasi.

Note: If compiling in Go 1.21+, this is GOOS=wasip1 GOARCH=wasm. In TinyGo, Rust, and Zig, this is the target wasm32-wasi.

You can also re-use an existing binary. For example, Wasm Language Runtimes distributes interpreters (including PHP, Python, and Ruby) already compiled to WASI.

Wasm binaries are loaded from a URL. For example, the URL file://rewrite.wasm loads rewrite.wasm from the current directory of the process. On Kubernetes, see How to: Mount Pod volumes to the Dapr sidecar to configure a filesystem mount that can contain Wasm binaries.

Dapr uses wazero to run these binaries, because it has no dependencies. This allows use of WebAssembly with no installation process except Dapr itself.

Component format

To configure a Wasm binding, create a component of type bindings.wasm. See this guide on how to create and apply a binding configuration.

  1. apiVersion: dapr.io/v1alpha1
  2. kind: Component
  3. metadata:
  4.   name: wasm
  5. spec:
  6.   type: bindings.wasm
  7.   version: v1
  8.   metadata:
  9.   - name: url
  10.     value: "file://uppercase.wasm"

Spec metadata fields

FieldDetailsRequiredExample
urlThe URL of the resource including the Wasm binary to instantiate. The supported schemes include file://. The path of a file:// URL is relative to the Dapr process unless it begins with /.truefile://hello.wasm

Binding support

This component supports output binding with the following operations:

  • execute

Example request

The data field, if present will be the program’s STDIN. You can optionally pass metadata properties with each request:

  • args any CLI arguments, comma-separated. This excludes the program name.

For example, if the binding url was a Ruby interpreter, such as from webassembly-language-runtimes, the following request would respond back with “Hello, salaboy”:

  1. {
  2.   "operation": "execute",
  3.   "metadata": {
  4.     "args": "-ne,'print \"Hello, \"; print'"
  5.   },
  6.   "data": "salaboy"
  7. }

Last modified June 19, 2023: Merge pull request #3565 from dapr/aacrawfi/skip-secrets-close (b1763bf)