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Rust actions


OpenWhisk requires a JSON object as output. Hence, serverless function cannot return arrays. It must return an object at the top level which can have arrays inside it.

The process of creating Rust actions is similar to that of other actions.

The following sections guide you through creating and invoking a single Rust action, and demonstrate how to bundle multiple Rust files and third party dependencies.

An example action Rust action is simply a top-level function.

For example, create a file called with the following source code:

extern crate serde_json;

use serde_derive::{Deserialize, Serialize};
use serde_json::{Error, Value};

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
struct Input {
#[serde(default = "stranger")]
name: String,

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
struct Output {
greeting: String,

fn stranger() -> String {

pub fn main(args: Value) -> Result<Value, Error> {
let input: Input = serde_json::from_value(args)?;
let output = Output {
greeting: format!("Hello, {}",,

Rust actions are mainly composed by a main function that accepts a JSON serdes Value as input and returns a Result including a JSON serde Value.

The entry method for the action is main by default but may be specified explicitly when creating the action with the wsk CLI using --main, as with any other action type.

You can create an OpenWhisk action called helloRust from this function as follows:

wsk action create helloRust --kind rust:1.34

The CLI automatically infers the type of the action from the source file extension. For .rs source files, the action runs using a Rust v1.34 runtime.

Action invocation is the same for Rust actions as it is for any other actions:

wsk action invoke --result helloRust --param name World
"greeting": "Hello World!"

Find out more about parameters in the Working with parameters section.

Packaging Rust actions in zip files

If your action needs external dependencies, you need to provide a zip file including your source and your cargo file with all your dependencies.

The filename of the source file containing the entry point (e.g., main) must be The folder structure should be as follows:

|- Cargo.toml
|- src

Here is an example of a Cargo.toml file

name = "actions"
version = "0.1.0"
authors = ["John Doe <[email protected]>"]
edition = "2018"

serde_json = "1.0"
serde = "1.0"
serde_derive = "1.0"

To zip your folder:

zip -r Cargo.toml src

and then create the action:

wsk action create helloRust --kind rust:1.34

Large portions of this page is copied from the Apache OpenWhisk documentation on April 23rd 2021 - where there have been customisations to match Hypi's deployment this has been noted. Apache OpenWhisk and the Apache name are the property of the Apache Foundation and licensed under the Apache V2 license .