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Wasm

Detailed documentation on the WebAssembly binding component

/operations/components/setup-bindings/supported-bindings/wasm/

Overview

WebAssembly is a way to 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 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, a user must specify a Wasm binary compiled with the canonical WASI version wasi_snapshot_preview1 a.k.a. wasip1, often abbreviated to wasi.

If compiling yourself in Go 1.21+, this is GOOS=wasip1 GOARCH=wasm, whereas 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, a URL "file://rewrite.wasm" loads "rewrite.wasm" from the current directory of the process. On Kubernetes, see [mounting volumes to the Dapr sidecar]({{< ref kubernetes-volume-mounts.md >}}) to configure a filesystem mount that can contain Wasm binaries.

Dapr embeds wazero which loads programs compiled with the WebAssembly System Interface (WASI), obviating platform dependencies or forking otherwise needed to accomplish something like this.

Component format

To configure a WebAssembly (Wasm) binding, create a component of type bindings.wasm. See [this guide]({{< ref "howto-bindings.md#1-create-a-binding" >}}) on how to create and apply a binding configuration.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: wasm
spec:
  type: bindings.wasm
  version: v1
  metadata:
  - name: url
    value: "file://uppercase.wasm"

Spec metadata fields

Field	Details	Required	Example
url	The 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 '/'.	true	"file://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 your Wasm binary is ruby.wasm, the following request would have the response data "Hello, salaboy"

{
  "operation": "execute",
  "metadata": {
    "args": "-ne,'print \"Hello, \"; print'"
  },
  "data": "salaboy"
}

[Basic schema for a Dapr component]({{< ref component-schema >}})
[Bindings building block]({{< ref bindings >}})
[How-To: Trigger application with input binding]({{< ref howto-triggers.md >}})
[How-To: Use bindings to interface with external resources]({{< ref howto-bindings.md >}})
[Bindings API reference]({{< ref bindings_api.md >}})

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