2. Hosted Services

In the previous example, we used a local, browser-native service to facilitate the string generation and communication with another browser. The real power of the Fluence solution, however, is that services can be hosted on one or more nodes, easily reused and composed into decentralized applications with Aqua.

Creating A WebAssembly Module

In this section, we develop a simple HelloWorld service and host it on a peer-to-peer node of the Fluence testnet. In your VSCode IDE, change to the 2-hosted-services directory and open the src/main.rs file:

Rust code for HelloWorld hosted service module

Fluence hosted services are comprised of WebAssembly modules implemented in Rust and compiled to wasm32-wasi. Let's have look at our code:

// quickstart/2-hosted-services/src/main.rs
use marine_rs_sdk::marine;
use marine_rs_sdk::module_manifest;
pub fn main() {}
pub struct HelloWorld {
pub msg: String,
pub reply: String,
pub fn hello(from: String) -> HelloWorld {
HelloWorld {
msg: format!("Hello from: \n{}", from),
reply: format!("Hello back to you, \n{}", from),

At the core of our implementation is the hello function which takes a string parameter and returns the HelloWorld struct consisting of the msg and reply field, respectively. We can use the build.sh script in the scripts directory, ./scripts/build.sh , to compile the code to the Wasm target from the VSCode terminal:

Aside from some housekeeping, the build.sh script gives the compile instructions with marine, marine build --release , and copies the resulting Wasm module, hello_world.wasm, to the artifacts directory for easy access.

Testing And Exploring Wasm Code

So far, so good. Of course, we want to test our code and we have a couple of test functions in our main.rs file:

// quickstart/2-hosted-services/src/main.rs
use marine_rs_sdk::marine;
use marine_rs_sdk::module_manifest;
mod tests {
use marine_rs_sdk_test::marine_test;
#[marine_test(config_path = "../configs/Config.toml", modules_dir = "../artifacts")]
fn non_empty_string(hello_world: marine_test_env::hello_world::ModuleInterface) {
let actual = hello_world.hello("SuperNode".to_string());
assert_eq!(actual.msg, "Hello from: \nSuperNode".to_string());
#[marine_test(config_path = "../configs/Config.toml", modules_dir = "../artifacts")]
fn empty_string(hello_world: marine_test_env::hello_world::ModuleInterface) {
let actual = hello_world.hello("".to_string());
assert_eq!(actual.msg, "Hello from: \n");

To run our tests, we can use the familiarcargo test . However, we don't really care all that much about our native Rust functions being tested but want to test our WebAssembly functions. This is where the extra code in the test module comes into play. In short., we are running cargo test against the exposed interfaces of the hello_world.wasm module and in order to do that, we need the marine_test macro and provide it with both the modules directory, i.e., the artifacts directory, and the location of the Config.toml file. Note that the Config.toml file specifies the module metadata and optional module linking data. Moreover, we need to call our Wasm functions from the module namespace, i.e. hello_world.hello instead of the standard hello -- see lines 13 and 19 above, which we specify as an argument in the test function signature (lines 11 and 17, respectively).

In order to able able to use the macro, install the marine-rs-sdk-test crate as a dev dependency:

[dev-dependencies] marine-rs-sdk-test = "<version>"

From the VSCode terminal, we now run our tests with thecargo +nightly test --release command. Please note that if nightly is your default, you don't need it in your cargo test command.

Cargo test using Wasm module

Well done -- our tests check out. Before we deploy our service to the network, we can interact with it locally using the Marine REPL. In your VSCode terminal the 2-hosted-services directory run:

mrepl configs/Config.toml

which puts us in the REPL:

mrepl configs/Config.toml
Welcome to the Marine REPL (version 0.9.1)
Minimal supported versions
sdk: 0.6.0
interface-types: 0.20.0
app service was created with service id = 8a2d946d-b474-468c-8c56-9e970ee64743
elapsed time 53.593404ms
1> i
Loaded modules interface:
data HelloWorld:
msg: string
reply: string
fn hello(from: string) -> HelloWorld
2> call hello_world hello ["Fluence"]
result: Object({"msg": String("Hello from: \nFluence"), "reply": String("Hello back to you, \nFluence")})
elapsed time: 278.5µs

We can explore the available interfaces with the i command and see that the interfaces we marked with the marine macro in our Rust code above are indeed exposed and available for consumption. Using the call command, still in the REPL, we can access any available function in the module namespace, e.g., call hello_word hello [<string arg>]. You can exit the REPL with the ctrl-c command.

Exporting WebAssembly Interfaces To Aqua

In anticipation of future needs, note that marine allows us to export the Wasm interfaces ready for use in Aqua. In your VSCode terminal, navigate to the `` directory

marine aqua artifacts/hello_world.wasm

Which gives us the Aqua-ready interfaces:

data HelloWorld:
msg: string
reply: string
service HelloWorld:
hello(from: string) -> HelloWorld

That can be piped directly into an aqua file , e.g., `marine aqua my_wasm.wasm >> my_aqua.aqua.

Deploying A Wasm Module To The Network

Looks like all is in order with our module and we are ready to deploy our HelloWorld service to the world by means of the Fluence peer-to-peer network. For this to happen, we need two things: the peer id of our target node(s) and a way to deploy the service. The latter can be accomplished with the fldist command line tool and with respect to the former, we can get a peer from one of the Fluence testnets also with fldist . In your VSCode terminal:

fldist env

Which gets us a list of network peers:


Let's use the peer12D3KooWFEwNWcHqi9rtsmDhsYcDbRUCDXH84RC4FW6UfsFWaoHi as our deployment target and deploy our service from the VSCode terminal. In the quickstart/2-hosted-services directory run:

fldist --node-id 12D3KooWFEwNWcHqi9rtsmDhsYcDbRUCDXH84RC4FW6UfsFWaoHi \
new_service \
--ms artifacts/hello_world.wasm:configs/hello_world_cfg.json \
--name hello-world

Which gives us a unique service id:

service id: 1e740ce4-81f6-4dd4-9bed-8d86e9c2fa50
service created successfully

Take note of the service id, 1e740ce4-81f6-4dd4-9bed-8d86e9c2fa50 in this example but different for you, as we need it to use the service with Aqua.

Congratulations, we just deployed our first reusable service to the Fluence network and we can admire our handiwork on the Fluence Developer Hub:

HelloWorld service deployed to peer 12D3Koo...WaoHi

With our newly created service ready to roll, let's move on and put it to work.