Design and Features of the Polkadot API Server

This page will present the inner workings of the API Server as well as the features that one is able to interact with and how. The following points will be presented and discussed:

• Design
• Complete List of Endpoints
• Using the API

Design

The components involved in the API Server are the following:

• The Polkadot Nodes from which the API retrieves information
• This API Server which uses the @polkadot/api JavaScript package to retrieve data from the Polkadot Nodes
• The User/Program which sends GET Requests to the API Server as per the defined Endpoints, and receives JSON formatted responses from the API Server

The diagram below gives an idea of the various components at play when the API Server is running, and how they interact with each other and the user/program:

The API Server works as follows:

• The API Server connects to each of these nodes one by one, as specified in the config/user_config_nodes.ini file.
• The API connections to each node exist within JS as promise objects.
• The API Server opens a port, as specified in the config/user_config_main.ini file.
• By communicating through this port, the API Server receives the endpoints specified in the Complete List of Endpoints section below, and requests information from the nodes it is connected to accordingly.
• Once the requested information is received from the node, it is formatted as a JSON, and returned.

Complete List of Endpoints

API Endpoint	Required Inputs	Optional Inputs	Output
Miscellaneous
/api/pingApi	None	None	pong if the API is accessible
/api/pingNode	websocket	None	pong if the API could access the Node
/api/getConnectionsList	None	None	List of nodes (websocket_ips) the API is connected to
RPC
/api/rpc/chain/getBlockHash	websocket	block_number	block hash of the specified block, or of the latest block if one is not specified
/api/rpc/chain/getFinalizedHead	websocket	None	block hash
/api/rpc/chain/getHeader	websocket	hash	header of the specified block hash, or of the latest block if the hash is not specified
/api/rpc/rpc/methods	websocket	None	version and methods, a list of RPC methods that are exposed by the node
/api/rpc/system/chain	websocket	None	system chain
/api/rpc/system/health	websocket	None	system health - peers, isSyncing
/api/rpc/system/networkState	websocket	None	peerId, listenedAddresses, externalAddresses and connectedPeers for the specified node. The current state of the network
/api/rpc/system/properties	websocket	None	ss58Format, tokenDecimals and tokenSymbol for the network of the specified node. Properties defined in the chain spec
Query
/api/query/balances/totalIssuance	websocket	None	The total amount of units issued in the chain. Value may be in Hex
/api/query/council/members	websocket	None	List of council members
/api/query/council/proposalCount	websocket	None	Number of proposals
/api/query/council/proposalOf	websocket, hash	None	proposal info - end, proposalHash, treshold, delay
/api/query/council/proposals	websocket	None	List of proposals
/api/query/democracy/publicPropCount	websocket	None	Number of public proposals
/api/query/democracy/referendumCount	websocket	None	Number of referendums
/api/query/democracy/referendumInfoOf	websocket, referendum_index	None	referendum info - end, proposalHash, treshold, delay
/api/query/imOnline/authoredBlocks	websocket, session_index, validator_id	None	Number of blocks authored by the specified validatorId in the specified sessionIndex
/api/query/imOnline/receivedHeartbeats	websocket, session_index, auth_index	None	Any data which shows that it is still online, despite not having signed any blocks
/api/query/session/currentIndex	websocket	None	current index
/api/query/session/disabledValidators	websocket	None	List of disabled validators
/api/query/session/validators	websocket	None	List of validators
/api/query/staking/activeEra	websocket	None	index and start of the active era
/api/query/staking/bonded	websocket, account_id	None	Controller account assigned to the stash account with the specified account_id. Will return null if the stash doesn't have a controller assigned.
/api/query/staking/erasRewardPoints	websocket	era_index	The total and individual rewards in the specified era index, or in the active one if it is not specified
/api/query/staking/erasStakers	websocket, account_id	era_index	stakers info - total balance nominated, balance nominated belonging to the owner, List of stakers who have nominated and how much they have nominated in the specified era index, or in the active one if it is not specified
/api/query/staking/erasTotalStake	websocket	era_index	The total amount staked in the specified era index, or in the active one if it is not specified. Value may be in Hex
/api/query/staking/erasValidatorReward	websocket	era_index	The total validator era payout in the specified era index, or in the last finished era (active era - 1) if it is not specified
/api/query/staking/payee	websocket, account_id	None	Reward destination address assigned to the stash with the specified account_id. Returns json with different keys depending on the type of reward destination: staked: null - when reward destination is a stash, controller: addr - when reward destination is a controller, and result: addr when reward destination is any other address.
/api/query/staking/unappliedSlashes	websocket	era_index	List of slashed validators (unapplied) in the specified era, or the current era if an era index is not specified.
/api/query/staking/validators	websocket, account_id	Preferences of the validator whose stash is the specified account_id (validator commission and blocked status).
/api/query/system/events	websocket	block_hash	events that happened in the specified block hash, or in the latest block if the block hash is not specified
Custom
/api/custom/getSlashAmount	websocket, account_address	block_hash	The balance slashed (if any) of the specified account address in the specified block hash, or in the latest block if the block hash is not specified
Derive
/api/derive/staking/validators	websocket	None	nextElected - List of validators which will be active in the next session and validators - List of validators which are currently active

Using the API

For example, the endpoint /api/rpc/system/health can be called as follows: http://localhost:3000/api/rpc/system/health?websocket=ws://1.2.3.4:9944. If successful, this will return:

{
    "result": {
        "peers": 92,
        "isSyncing": false,
        "shouldHavePeers": true
    }
}

If an API connection for the node specified in the websocket field is not set up, this will return:

{
    "error": "An API for ws://1.2.3.4:9944 needs to be setup before it can be queried"
}

If an API call without all the required fields is sent, such as http://localhost:3000/api/query/imOnline/authoredBlocks?websocket=ws://1.2.3.4:9944&session_index=3, this will return:

{
    "error": "You did not enter the stash account address of the validator that needs to be queried"
}

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