Invoke#

This guide explains how to invoke a smart contract instance, which means triggering a receive function and viewing its return value. Invoking an instance is not a transaction and it does not change the state of a contract. Invoking can be useful to either view information about the instance or to test a receive method before running an update. Because invoking is not a transaction, there is no fee to run invoke. The view functions are regular receive functions that return information about the contract, ideally with schemas on the return values.

There is no limit to the number of logs per invocation (apart from energy).

Preparation#

Make sure that you are running a node using the latest Concordium software and that you have a smart-contract instance on-chain to inspect.

See also

For how to deploy a smart contract module see Deploy a smart contract module and for how to create an instance Initialize.

Invocation#

To invoke an instance with address index 0 (the subindex defaults to 0) using the parameterless entrypoint my_receive, run the following command:

$concordium-client contract invoke 0 --entrypoint my_receive

If successful, the output should be similar to the following:

Invocation resulted in success:
- Energy used: 595 NRG
- Return value:
    <some-return-value>

The contract state is updated, but the changes are not persisted to the chain and are discarded. The energy used value represents a simulation of how much NRG is needed when making the smart contract call.

Note

By default, the invocation is sent by a fictional account with address 2wkBET2rRgE8pahuaczxKbmv7ciehqsne57F9gtzf1PVdr2VP3 (the byte representation is [0u8; 32]). This account has unbounded funds. However, when specifying a custom sender account or contract, both of which must exist on the chain, these must have sufficient funds to cover the transfer that will be made to the contract. Please note that no funds will be withdrawn on the account or contract as it is not a transaction. This design allows you to try invoking an entrypoint with your own account or contract for free to ensure that the result is as expected before pay for the transaction on chain.

Use the invoker-account parameter to invoke an entrypoint with a specific sender account:

$concordium-client contract invoke 0 --entrypoint my_receive --invoker-account <account-address>

Use the invoker-contract parameter to invoke an entrypoint with a sender contract:

$concordium-client contract invoke 0 --entrypoint my_receive --invoker-contract <contract-index>

Use the amount parameter to invoke an entrypoint with the specified amount of CCD.

$concordium-client contract invoke 0 --entrypoint my_receive --amount <CCD>

Note

By default, an invoked entrypoint will have the same state and balance as if it was an update transaction at the very end of the current best block on the chain.

Use the block parameter to specify a different block to run the invocation in:

$concordium-client contract invoke 0 --entrypoint my_receive --block <block-hash>

Passing parameters in JSON format#

A parameter in JSON format can be passed if a smart contract schema is supplied, either as a file or embedded in the module. The schema is used to serialize the JSON into binary. You can read more about JSON parameters here

See also

Read more about why and how to use smart contract schemas.

To invoke an instance with address index 0 using the receive function my_parameter_receive with a parameter file my_parameter.json in JSON format, run the following command:

$concordium-client contract invoke 0 --entrypoint my_parameter_receive \
         --parameter-json my_parameter.json

If successful, the output should be similar to the following:

Invocation resulted in success:
 - Energy used: 595 NRG
 - Return value:
      <some-return-value>

Otherwise, an error describing the problem is displayed.

See also

For more information about contract instance addresses, see References on-chain.

Note

If the parameter provided in JSON format does not conform to the type specified in the schema, an error message will be displayed. For example:

Error: Could not decode parameters from file 'my_parameter.json' as JSON:
Expected value of type "UInt64", but got: "hello".
In field 'first_field'.
In {
    "first_field": "hello",
    "second_field": 42
}.

Note

If a given module does not contain an embedded schema, it can be supplied using the --schema /path/to/schema.bin parameter.

Passing parameters in binary format#

When passing parameters in binary format, a contract schema is not needed.

To invoke an instance with address index 0 using the receive function my_parameter_receive with a parameter file my_parameter.bin in binary format, run the following command:

$concordium-client contract invoke 0 --entrypoint my_parameter_receive \
         --parameter-bin my_parameter.bin

If successful, the output should be similar to the following:

Invocation resulted in success:
 - Energy used: 595 NRG
 - Return value:
      <some-return-value>

See also

For information on how to work with parameters in smart contracts, see Work with parameters.

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