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Runtime APIs

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Please read Substrate to Polkadot SDK page first.

As discussed in Architecture, Substrate nodes consist of outer node services and a runtime and this separation of responsibilities is an important concept for designing Substrate-based chains and building upgradeable logic. However, the outer node services and the runtime must communicate with each other to complete many critical operations, including reading and writing data and performing state transitions. The outer node services communicate with the runtime by calling runtime application programming interfaces to perform specific tasks. By default, the Substrate runtime provides the following traits for outer node services to call:

AccountNonceApi

Use the AccountNonceApi to get the nonce for a specified account identifier. The nonce for each account is incremented each time that account is used to complete a transaction. Therefore, the nonce is also sometimes referred to as a transaction index.

This API provides the following methods:

  • account_nonce to get the current account nonce for a specified AccountId.
  • account_nonce_with_context to get the current account nonce for a specified AccountId and execution context.

AuraApi

Use the AuraApi to manage block authoring with the slot-based consensus that uses a round-robin rotation of authorities. Although most consensus-related tasks are handled by outer node services, the runtime must provide this API for consensus-related tasks that are part of the state transition logic.

This API provides the following methods for authority-based round-robin scheduling (Aura):

  • slot_duration to get the slot duration for Aura consensus.
  • slot_duration_with_context to get the slot duration for Aura consensus within a specified execution context.
  • authorities to get the authorities set for Aura consensus.
  • authorities_with_context to get the authorities set for Aura consensus within a specified execution context.

Benchmark

Use the Benchmark API to provide the information required for benchmarking function execution in a FRAME runtime.

This API provides the following methods:

  • benchmark_metadata to get the benchmark metadata available for this runtime.
  • benchmark_metadata_with_context to get the benchmark metadata available for this runtime within a specified execution context.
  • dispatch_benchmark to dispatch the specified benchmark.
  • dispatch_benchmark_with_context to dispatch the specified benchmark within a specified execution context.

BlockBuilder

Use the BlockBuilder API to provide the functionality required for building and finalizing a block. The runtime is responsible for checking transaction validity and executing the transactions to construct blocks. For the outer node, transactions are an opaque vector array (Vec).

This API provides the following methods:

  • apply_extrinsic to include the specified extrinsic in the current block. The method also returns a result that indicates whether the transaction was included in the block or not.
  • apply_extrinsic_with_context to include the specified extrinsic in the current block and specified execution context. The method also returns a result that indicates whether the transaction was included in the block or not.
  • finalize_block to finish construction of the current block.
  • finalize_block_with_context to finish construction of the current block within the specified execution context.
  • inherent_extrinsics to include inherent extrinsic transactions in the current block. Inherent transaction types vary from chain to chain.
  • inherent_extrinsics_with_context to include inherent extrinsic transactions in the current block and specified execution context. Inherent transaction types vary from chain to chain.
  • check_inherents to check that the inherent transactions are valid.
  • check_inherents_with_context to check that the inherent transactions are valid within the specified execution contex.

GrandpaApi

Use the GrandpaApi to integrate authority-set changes from the GRANDPA finalization protocol into the runtime. The GRANDPA finalization protocol signals changes to the authority sets by specifying a delay of some number of blocks. The changes ar then automatically applied in the runtime after the specified number of blocks have been finalized.

This API provides the following methods:

  • grandpa_authorities to get the current authorities and weights for GRANDPA finalization.
  • grandpa_authorities_with_context to get the current authorities and weights for GRANDPA finalization in the specified execution context.
  • current_set_id to get the current GRANDPA authority set identifier.
  • current_set_id_with_context to get the current GRANDPA authority set identifier in the specified execution context.

The GrandpaApi also provides methods for submitting transactions to report evidence of misbehavior and related proof of key ownership. For information about these methods, see GrandpaApi.

NominationPoolsApi

Use the NominationPoolsApi to get information about about nomination pools and nomination pool members.

This API provides the following methods:

  • pending_rewards to get the pending rewards for the nomination pool member with the specified AccountId.
  • pending_rewards_with_context to get the pending rewards for the nomination pool member with the specified AccountId within the specified execution context.

OffchainWorkerApi

Use the OffchainWorkerApi to start offchain worker operations.

This API provides the following methods:

  • offchain_worker to start the off-chain task for a specified block header.
  • offchain_worker_with_context to start the off-chain task for a specified block header and execution context.

SessionKeys

Use the SessionKeys API to generate and decode session keys (https://paritytech.github.io/substrate/master/sp_session/trait.SessionKeys.html)

This API provides the following methods:

  • generate_session_keys to generate a set of session keys. If you generate the keys using a specified seed, the seed must to be a valid utf8 string. You should store the generated keys in the keystore exposed by the runtime externalities. The method returns the public keys as concatenated SCALE-encoded values.
  • generate_session_keys_with_context to generate a set of session keys within the specified execution context. If you generate the keys using a specified seed, the seed must to be a valid utf8 string. You should store the generated keys in the keystore exposed by the runtime externalities. The method returns the public keys as concatenated SCALE-encoded values.
  • decode_session_keys to decode the specified public session keys. The method returns the list of raw public keys and the key type.
  • decode_session_keys_with_context to decode the specified public session keys within the specified execution context. The method returns the list of raw public keys and the key type.

TaggedTransactionQueue

Use the TaggedTransactionQueue API to validate transactions in the transaction queue.

This API provides the following methods:

  • validate_transaction to verify the specified transaction is a valid transaction given the state specified by the block_hash parameter.
  • validate_transaction_with_context to verify the specified transaction is a valid transaction given the state specified by the block_hash parameter within the specified execution context.

TransactionPaymentApi

Use the TransactionPaymentApi to query the runtime for information about transactions and transaction fees.

This API provides the following methods:

  • query_info to return information about a specified transaction dispatched to the runtime.
  • query_info_with_context to return information about a specified transaction dispatched to the runtime within the specified execution context.
  • query_fee_details to return information about the transaction fees for a specified transaction.
  • query_fee_details_with_context to return information about the transaction fees for a specified transaction within the specified execution context.

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