Counter Example Application

This example application implements a simple counter contract, it is initialized with an unsigned integer that can be increased by the increment operation.

How It Works

It is a simple Linera application, which is initialized by a u64 which can be incremented by a u64.

For example, if the contract was initialized with 1, querying the contract would give us 1. Now if we want to increment it by 3, we will have to perform an operation with the parameter being 3. Now querying the application would give us 4 (1+3 = 4).

Setup and Deployment

Before getting started, make sure that the binary tools linera* corresponding to your version of linera-sdk are in your PATH. For scripting purposes, we also assume that the BASH function linera_spawn is defined.

From the root of Linera repository, this can be achieved as follows:

bash

export PATH="$PWD/target/debug:$PATH"
eval "$(linera net helper 2>/dev/null)"

Next, start the local Linera network and run a faucet:

bash

LINERA_FAUCET_PORT=8079
LINERA_FAUCET_URL=http://localhost:$LINERA_FAUCET_PORT
linera_spawn linera net up --with-faucet --faucet-port $LINERA_FAUCET_PORT

# If you're using a testnet, run this instead:
#   LINERA_TMP_DIR=$(mktemp -d)
#   export LINERA_FAUCET_URL=https://faucet.testnet-XXX.linera.net  # for some value XXX

Enable logs for user applications:

bash

export LINERA_APPLICATION_LOGS=true

Create the user wallet and add chains to it:

bash

export LINERA_WALLET="$LINERA_TMP_DIR/wallet.json"
export LINERA_KEYSTORE="$LINERA_TMP_DIR/keystore.json"
export LINERA_STORAGE="rocksdb:$LINERA_TMP_DIR/client.db"

linera wallet init --faucet $LINERA_FAUCET_URL

INFO=($(linera wallet request-chain --faucet $LINERA_FAUCET_URL))
CHAIN="${INFO[0]}"
OWNER="${INFO[1]}"

Now, compile the counter application WebAssembly binaries, publish and create an application instance.

bash

cd examples/counter
cargo build --release --target wasm32-unknown-unknown

LINERA_APPLICATION_ID=$(linera publish-and-create \
  ../target/wasm32-unknown-unknown/release/counter_{contract,service}.wasm \
  --json-argument "1")

We have saved the LINERA_APPLICATION_ID as it will be useful later.

Connecting with the Web Frontend

If you install the dependencies for the Web frontend and export the necessary variables you can run a local development server using Vite:

bash,ignore

export LINERA_APPLICATION_ID LINERA_FAUCET_URL
pnpm install
pnpm dev

This will start a server and print its address; access that URL to use the application frontend.

Alternatively, there is a frontend in metamask that signs transactions using the user's MetaMask wallet; it can be accessed the same way.

Connecting with the GraphQL Client

Alternatively, you can connect to the application using the GraphQL client. This is useful for inspecting and debugging the backend APIs.

First, a node service for the current wallet has to be started:

bash

PORT=8080
linera service --port $PORT &
echo "http://localhost:8080/chains/$CHAIN/applications/$LINERA_APPLICATION_ID"

Clicking the printed URL will take you to a GraphiQL environment connected to your app.

To get the current value of counter, you can run the query:

gql,uri=http://localhost:8080/chains/$CHAIN/applications/$LINERA_APPLICATION_ID

query {
  value
}

To increase the value of the counter, you can run the increment mutation. Note that the result of a mutation is the hash of the resulting block, if any.

gql,uri=http://localhost:8080/chains/$CHAIN/applications/$LINERA_APPLICATION_ID

mutation {
  increment(value: 3)
}

If you run the query again, you'll now see a value of 4.