Flow Access API Specification

The Access API is implemented as a gRPC service.

A language-agnostic specification for this API is defined using Protocol Buffers, which can be used to generate client libraries in a variety of programming languages.

• Flow Access API protobuf source files

Ping

Ping will return a successful response if the Access API is ready and available.

rpc Ping(PingRequest) returns (PingResponse)

If a ping request returns an error or times out, it can be assumed that the Access API is unavailable.

message PingRequest {}

message PingResponse {}

Block Headers

The following methods query information about block headers.

GetLatestBlockHeader

GetLatestBlockHeader gets the latest sealed or unsealed block header.

rpc GetLatestBlockHeader (GetLatestBlockHeaderRequest) returns (BlockHeaderResponse)

message GetLatestBlockHeaderRequest {
  bool is_sealed
}

message BlockHeaderResponse {
  flow.BlockHeader block
}

GetBlockHeaderByID

GetBlockHeaderByID gets a block header by ID.

rpc GetBlockHeaderByID (GetBlockHeaderByIDRequest) returns (BlockHeaderResponse)

message GetBlockHeaderByIDRequest {
  bytes id
}

message BlockHeaderResponse {
  flow.BlockHeader block
}

GetBlockHeaderByHeight

GetBlockHeaderByHeight gets a block header by height.

rpc GetBlockHeaderByHeight (GetBlockHeaderByHeightRequest) returns (BlockHeaderResponse)

message GetBlockHeaderByHeightRequest {
  uint64 height
}

message BlockHeaderResponse {
  flow.BlockHeader block
}

Blocks

The following methods query information about full blocks.

GetLatestBlock

GetLatestBlock gets the full payload of the latest sealed or unsealed block.

rpc GetLatestBlock (GetLatestBlockRequest) returns (BlockResponse)

message GetLatestBlockRequest {
  bool is_sealed
}

message BlockResponse {
  flow.Block block
}

GetBlockByID

GetBlockByID gets a full block by ID.

rpc GetBlockByID (GetBlockByIDRequest) returns (BlockResponse)

message GetBlockByIDRequest {
  bytes id
}

message BlockResponse {
  flow.Block block
}

GetBlockByHeight

GetBlockByHeight gets a full block by height.

rpc GetBlockByHeight (GetBlockByHeightRequest) returns (BlockResponse)

message GetBlockByHeightRequest {
  uint64 height
}

message BlockResponse {
  flow.Block block
}

Collections

The following methods query information about collections.

GetCollectionByID

GetCollectionByID gets a collection by ID.

rpc GetCollectionByID (GetCollectionByIDRequest) returns (CollectionResponse)

message GetCollectionByIDRequest {
  bytes id
}

message CollectionResponse {
  flow.Collection collection
}

Transactions

The following methods can be used to submit transactions and fetch their results.

SendTransaction

SendTransaction submits a transaction to the network.

rpc SendTransaction (SendTransactionRequest) returns (SendTransactionResponse)

SendTransaction determines the correct cluster of collector nodes that is responsible for collecting the transaction based on the hash of the transaction and forwards the transaction to that cluster.

message SendTransactionRequest {
  flow.Transaction transaction
}

message SendTransactionResponse {
  bytes id
}

GetTransaction

GetTransaction gets a transaction by ID.

If the transaction is not found in the access node cache, the request is forwarded to a collection node.

Currently, only transactions within the current epoch can be queried.

rpc GetTransaction (GetTransactionRequest) returns (TransactionResponse)

message GetTransactionRequest {
  bytes id
}

message TransactionResponse {
  flow.Transaction transaction
}

GetTransactionResult

GetTransactionResult gets the execution result of a transaction.

rpc GetTransactionResult (GetTransactionRequest) returns (TransactionResultResponse)

message GetTransactionRequest {
  bytes id
}

message TransactionResultResponse {
  flow.TransactionStatus status
  uint32 status_code
  string error_message
  repeated flow.Event events
}

Accounts

GetAccount

GetAccount gets an account by address at the latest sealed block.

⚠️ Warning: this function is deprecated. It behaves identically to GetAccountAtLatestBlock and will be removed in a future version.

rpc GetAccount(GetAccountRequest) returns (GetAccountResponse)

message GetAccountRequest {
  bytes address
}

message GetAccountResponse {
  Account account
}

GetAccountAtLatestBlock

GetAccountAtLatestBlock gets an account by address.

The access node queries an execution node for the account details, which are stored as part of the sealed execution state.

rpc GetAccountAtLatestBlock(GetAccountAtLatestBlockRequest) returns (AccountResponse)

message GetAccountAtLatestBlockRequest {
  bytes address
}

message AccountResponse {
  Account account
}

GetAccountAtBlockHeight

GetAccountAtBlockHeight gets an account by address at the given block height.

The access node queries an execution node for the account details, which are stored as part of the execution state.

rpc GetAccountAtBlockHeight(GetAccountAtBlockHeightRequest) returns (AccountResponse)

message GetAccountAtBlockHeightRequest {
  bytes address
  uint64 block_height
}

message AccountResponse {
  Account account
}

Scripts

ExecuteScriptAtLatestBlock

ExecuteScriptAtLatestBlock executes a read-only Cadence script against the latest sealed execution state.

This method can be used to read execution state from the blockchain. The script is executed on an execution node and the return value is encoded using the JSON-Cadence data interchange format.

rpc ExecuteScriptAtLatestBlock (ExecuteScriptAtLatestBlockRequest) returns (ExecuteScriptResponse)

This method is a shortcut for the following:

header = GetLatestBlockHeader()
value = ExecuteScriptAtBlockID(header.ID, script)

message ExecuteScriptAtLatestBlockRequest {
  bytes script
}

message ExecuteScriptResponse {
  bytes value
}

ExecuteScriptAtBlockID

ExecuteScriptAtBlockID executes a ready-only Cadence script against the execution state at the block with the given ID.

This method can be used to read account state from the blockchain. The script is executed on an execution node and the return value is encoded using the JSON-Cadence data interchange format.

rpc ExecuteScriptAtBlockID (ExecuteScriptAtBlockIDRequest) returns (ExecuteScriptResponse)

message ExecuteScriptAtBlockIDRequest {
  bytes block_id
  bytes script
}

message ExecuteScriptResponse {
  bytes value
}

ExecuteScriptAtBlockHeight

ExecuteScriptAtBlockHeight executes a ready-only Cadence script against the execution state at the given block height.

This method can be used to read account state from the blockchain. The script is executed on an execution node and the return value is encoded using the JSON-Cadence data interchange format.

rpc ExecuteScriptAtBlockHeight (ExecuteScriptAtBlockHeightRequest) returns (ExecuteScriptResponse)

message ExecuteScriptAtBlockHeightRequest {
  uint64 block_height
  bytes script
}

message ExecuteScriptResponse {
  bytes value
}

Events

The following methods can be used to query for on-chain events.

GetEventsForHeightRange

GetEventsForHeightRange retrieves events emitted within the specified block range.

rpc GetEventsForHeightRange(GetEventsForHeightRangeRequest) returns (GetEventsForHeightRangeResponse)

Events can be requested for a specific sealed block range via the start_height and end_height (inclusive) fields and further filtered by event type via the type field.

If end_height is greater than the current sealed chain height, then this method will return events up to and including the latest sealed block.

The event results are grouped by block, with each group specifying a block ID, height and block timestamp.

Event types are name-spaced with the address of the account and contract in which they are declared.

message GetEventsForHeightRangeRequest {
  string type
  uint64 start_height = 2;
  uint64 end_height = 3;
}

message EventsResponse {
  message Result {
    bytes block_id = 1;
    uint64 block_height = 2;
    repeated entities.Event events = 3;
    google.protobuf.Timestamp block_timestamp = 4;
  }
  repeated Result results = 1;
}

GetEventsForBlockIDs

GetEventsForBlockIDs retrieves events for the specified block IDs and event type.

rpc GetEventsForBlockIDs(GetEventsForBlockIDsRequest) returns (GetEventsForBlockIDsResponse)

Events can be requested for a list of block IDs via the block_ids field and further filtered by event type via the type field.

The event results are grouped by block, with each group specifying a block ID, height and block timestamp.

message GetEventsForBlockIDsRequest {
  string type = 1;
  repeated bytes block_ids = 2;
}

message EventsResponse {
  message Result {
    bytes block_id = 1;
    uint64 block_height = 2;
    repeated entities.Event events = 3;
    google.protobuf.Timestamp block_timestamp = 4;
  }
  repeated Result results = 1;
}

Network Parameters

Network parameters provide information about the Flow network. Currently, it only includes the chain ID. The following method can be used to query for network parameters.

GetNetworkParameters

GetNetworkParameters retrieves the network parameters.

rpc GetNetworkParameters (GetNetworkParametersRequest) returns (GetNetworkParametersResponse)

message GetNetworkParametersRequest {}

message GetNetworkParametersResponse {
  string chain_id = 1;
}

Entities

Below are in-depth descriptions of each of the data entities returned or accepted by the Access API.

Block

message Block {
  bytes id
  bytes parent_id
  uint64 height
  google.protobuf.Timestamp timestamp
  repeated CollectionGuarantee collection_guarantees
  repeated BlockSeal block_seals
  repeated bytes signatures
}

The detailed semantics of block formation are covered in the block formation guide.

Block Header

A block header is a summary of a block and contains only the block ID, height, and parent block ID.

message BlockHeader {
  bytes id
  bytes parent_id
  uint64 height
}

Block Seal

A block seal is an attestation that the execution result of a specific block has been verified and approved by a quorum of verification nodes.

message BlockSeal {
  bytes block_id
  bytes execution_receipt_id
  repeated bytes execution_receipt_signatures
  repeated bytes result_approval_signatures
}

Collection

A collection is a batch of transactions that have been included in a block. Collections are used to improve consensus throughput by increasing the number of transactions per block.

message Collection {
  bytes id
  repeated bytes transaction_ids
}

Collection Guarantee

A collection guarantee is a signed attestation that specifies the collection nodes that have guaranteed to store and respond to queries about a collection.

message CollectionGuarantee {
  bytes collection_id
  repeated bytes signatures
}

Transaction

A transaction represents a unit of computation that is submitted to the Flow network.

message Transaction {
  bytes script
  repeated bytes arguments
  bytes reference_block_id
  uint64 gas_limit
  TransactionProposalKey proposal_key
  bytes payer
  repeated bytes authorizers
  repeated TransactionSignature payload_signatures
  repeated TransactionSignature envelope_signatures
}

message TransactionProposalKey {
  bytes address
  uint32 key_id
  uint64 sequence_number
}

message TransactionSignature {
  bytes address
  uint32 key_id
  bytes signature
}

The detailed semantics of transaction creation, signing and submission are covered in the transaction submission guide.

Proposal Key

The proposal key is used to specify a sequence number for the transaction. Sequence numbers are covered in more detail here.

Transaction Signature

Transaction Status

enum TransactionStatus {
  UNKNOWN = 0;
  PENDING = 1;
  FINALIZED = 2;
  EXECUTED = 3;
  SEALED = 4;
  EXPIRED = 5;
}

Account

An account is a user's identity on Flow. It contains a unique address, a balance, a list of public keys and the code that has been deployed to the account.

message Account {
  bytes address
  uint64 balance
  bytes code
  repeated AccountKey keys
  map<string, bytes> contracts
}

The code and contracts fields contain the raw Cadence source code, encoded as UTF-8 bytes.

More information on accounts can be found here.

Account Key

An account key is a reference to a public key associated with a Flow account. Accounts can be configured with zero or more public keys, each of which can be used for signature verification when authorizing a transaction.

message AccountKey {
  uint32 id
  bytes public_key
  uint32 sign_algo
  uint32 hash_algo
  uint32 weight
  uint32 sequence_number
  bool revoked
}

More information on account keys, key weights and sequence numbers can be found here.

Event

An event is emitted as the result of a transaction execution. Events are either user-defined events originating from a Cadence smart contract, or built-in Flow system events.

message Event {
  string type
  bytes transaction_id
  uint32 transaction_index
  uint32 event_index
  bytes payload
}