Locally simulate contract functions#

This guide is about how to locally simulate an invocation of some init or receive function from a Wasm smart contract module in a given context and state. This simulation is useful for inspecting a smart contract and the outcome in specific scenarios.

Preparation#

Make sure you have cargo-concordium installed, if not follow the guide Install tools for development. You will also need a smart contract module in Wasm to simulate.

Simulating instantiation#

To simulate the instantiation of a smart contract instance using cargo-concordium, run the following command:

$cargo concordium run init --module contract.wasm.v1 \
                            --contract "my_contract" \
                            --context init-context.json \
                            --amount 123456.789 \
                            --parameter-bin parameter.bin \
                            --out-bin state.bin

Note

If using contract schemas, it is possible to pass the parameter as JSON instead of binary by using the --parameter-json flag.

init-context.json (used with the --context parameter) is a file that contains context information such as the current state of the chain, the sender of the transaction, and which account invoked this function. It is only necessary to specify the fields that your contract function actually uses. cargo-concordium returns an error if the function tries to access an unspecified context field. An example of a fully specified init context could be:

{
    "metadata": {
        "slotTime": "2021-01-01T00:00:01Z"
    },
    "initOrigin": "3uxeCZwa3SxbksPWHwXWxCsaPucZdzNaXsRbkztqUUYRo1MnvF",
    "senderPolicies": [{
        "identityProvider": 1,
        "createdAt": "202012",
        "validTo": "202109"
    }]
}

Simulating updates#

To simulate an update to a smart contract instance using cargo-concordium, run:

$cargo concordium run update --module contract.wasm.v1 \
                              --contract "my_contract" \
                              --entrypoint "some_receive" \
                              --context receive-context.json \
                              --amount 123456.789 \
                              --parameter-bin parameter.bin \
                              --state-bin state-in.bin \
                              --out-bin state-out.bin

Note

If using contract schemas, it is possible to pass the parameter as JSON instead of binary by using the --parameter-json flag.

Note

The simulation of the init function in the previous paragraph produced an output state.bin file. This state.bin file can be used as the input state-in.bin file in this paragraph.

receive-context.json (used with the --context parameter) is a file that contains context information such as the current state of the chain, the sender of the transaction, which account invoked this function, and which account or address that sent the current message. It is only necessary to specify the fields that your contract function actually uses. cargo-concordium returns an error if the function tries to access an unspecified context field. An example of a fully specified receive context could be:

{
    "metadata": {
        "slotTime": "2021-01-01T00:00:01Z"
    },
    "invoker": "3uxeCZwa3SxbksPWHwXWxCsaPucZdzNaXsRbkztqUUYRo1MnvF",
    "selfAddress": {"index": 0, "subindex": 0},
    "selfBalance": "0",
    "sender": {
        "type": "account",
        "address": "3uxeCZwa3SxbksPWHwXWxCsaPucZdzNaXsRbkztqUUYRo1MnvF"
    },
    "senderPolicies": [{
        "identityProvider": 1,
        "createdAt": "202012",
        "validTo": "202109"
    }],
    "owner": "3uxeCZwa3SxbksPWHwXWxCsaPucZdzNaXsRbkztqUUYRo1MnvF"
}