Using standard capabilities

Using existing capabilities from within an actor is quick and easy. If an actor interface exists for the type of capability contract you’re looking to use, then it’s just a matter of declaring a reference to it from inside your code. Remember that your actors depend only on the interface. The implementation of a contract is entirely up to the provider. For instance, once your actor is designed to work against the wasmcloud:keyvalue contract, it automatically works with any provider that implements that contract.

Find an interface

If you’re looking to see which types of supported, first-party capability provider contracts are available, you’ll want to take a look at the interfaces repository. Here you will find links to documentation as well as a list of which language-specific interfaces are available, and links to multiple implementations of the same contract (e.g. file system and S3 are two different implementations of wasmcloud:blobstore).

Add the interface as a dependency

It should also be very easy to simply declare a dependency on the interface from within your actor project. Remember that you’re taking a dependency on the abstract contract, and not the concrete implementation. You might be declaring a dependency on the wasmcloud:keyvalue contract, and not on Redis or Cassandra.

By convention, all of our first-party actor interface crates start with the prefix wasmcloud-interface and should be easy to find on

As an example, here’s what it looks like to add a dependency on the key-value actor interface. In Cargo.toml, there needs to be an entry under [dependencies]:

wasmcloud-interface-keyvalue = "0.5.0"

And in the Rust source (src/, it needs to be imported:

use wasmcloud_interface_keyvalue::*;

Sign the actor

Before an actor can use a capability provider, it needs to be signed with the capability id. The signing process takes a WebAssembly file (with .wasm extension), generates a JWT containing the list of capability claims, signs the JWT with your private signing key, and generates a file ending in _s.wasm containing the original WebAssembly plus the JWT.

Using the wasmCloud Makefiles (which you can get from a project in the examples repository, or a from project generated with wash new actor), the signing is done automatically for you, using the claims declared in the Makefile

CLAIMS = wasmcloud:httpserver

Whenever you type make, the Makefile’s rules execute the command wash claims sign ... to sign the actor module.

You can use the command wash claims inspect to show the capability claims of a signed actor.