Hello, Linera

This section is about interacting with the Devnet, running a local development network, then compiling and deploying your first application from scratch.

By the end of this section, you'll have a microchain on the Devnet and/or on your local network, and a working application that can be queried using GraphQL.

Using the Devnet

The Linera Devnet is a deployment of the Linera protocol that's useful for developers. It should not be considered stable, and can be restarted from a clean slate and new genesis at any time.

To interact with the Devnet, some tokens are needed. A Faucet service is available to create new microchains and obtain some test tokens. To do so, this must be configured when initializing the wallet:

linera wallet init --with-new-chain --faucet https://faucet.devnet-2024-03-26.linera.net

This creates a new microchain on Devnet with some initial test tokens, and the chain is automatically added to the newly instantiated wallet.

Make sure to use a Linera toolchain compatible with the current Devnet.

Starting a Local Test Network

Another option is to start your own local development network. A development network consists of a number of validators, each of which consist of an ingress proxy (aka. a "load balancer") and a number of workers (aka. "physical shards").

To start a local network, run the following command:

linera net up

This will start a validator with the default number of shards and create a temporary directory storing the entire network state.

This will set up a number of initial chains and create an initial wallet to operate them.

Using the Initial Test Wallet

linera net up prints Bash statements on its standard output to help you configure your terminal to use the initial wallet of the new test network, for instance:

export LINERA_WALLET="/var/folders/3d/406tbklx3zx2p3_hzzpfqdbc0000gn/T/.tmpvJ6lJI/wallet.json"
export LINERA_STORAGE="rocksdb:/var/folders/3d/406tbklx3zx2p3_hzzpfqdbc0000gn/T/.tmpvJ6lJI/linera.db"

This wallet is only valid for the lifetime of a single network. Every time a local network is restarted, the wallet needs to be reconfigured.

Interacting with the Network

In the following examples, we assume that either the wallet was initialized to interact with the Devnet or the variables LINERA_WALLET and LINERA_STORAGE are both set and point to the initial wallet of the running local network.

The main way of interacting with the network and deploying applications is using the linera client.

To check that the network is working, you can synchronize your default chain with the rest of the network and display the chain balance as follows:

linera sync
linera query-balance

You should see an output number, e.g. 10.

Building an Example Application

Applications running on Linera are Wasm bytecode. Each validator and client has a built-in Wasm virtual machine (VM) which can execute bytecode.

Let's build the counter application from the examples/ subdirectory:

cd examples/counter && cargo build --release

Note: This will automatically build Wasm, not native code, thanks to the configuration file examples/.cargo/config.toml.

Publishing your Application

You can publish the bytecode and create an application using it on your local network using the linera client's publish-and-create command and provide:

  1. The location of the contract bytecode
  2. The location of the service bytecode
  3. The JSON encoded initialization arguments
linera publish-and-create \
  ../target/wasm32-unknown-unknown/release/counter_{contract,service}.wasm \
  --json-argument "42"

Congratulations! You've published your first application on Linera!

Querying your Application

Now let's query your application to get the current counter value. To do that, we need to use the client running in service mode. This will expose a bunch of APIs locally which we can use to interact with applications on the network.

linera service

Navigate to http://localhost:8080 in your browser to access the GraphiQL, the GraphQL IDE. We'll look at this in more detail in a later section; for now, list the applications deployed on your default chain e476… by running:

query {
  applications(
    chainId: "e476187f6ddfeb9d588c7b45d3df334d5501d6499b3f9ad5595cae86cce16a65"
  ) {
    id
    description
    link
  }
}

Since we've only deployed one application, the results returned have a single entry.

At the bottom of the returned JSON there is a field link. To interact with your application copy and paste the link into a new browser tab.

Finally, to query the counter value, run:

query {
  value
}

This will return a value of 42, which is the initialization argument we specified when deploying our application.