problem: RPC method names are undocumented and hardcoded

solution: single class to reference and document all methods

polkaj-api-base/src/main/java/io/emeraldpay/polkaj/api/PolkadotApi.java

@@ -2,6 +2,9 @@
 
 import java.util.concurrent.CompletableFuture;
 
+/**
+ * @see PolkadotMethod
+ */
 public interface PolkadotApi {
 
     /**

polkaj-api-base/src/main/java/io/emeraldpay/polkaj/api/PolkadotMethod.java

@@ -0,0 +1,278 @@
+package io.emeraldpay.polkaj.api;
+
+public class PolkadotMethod {
+
+    /**
+     * Get list of available methods.
+     * <br>
+     * RPC Method: rpc_methods
+     */
+    public static final String RPC_METHODS = "rpc_methods";
+
+    /**
+     * Get header and body of a relay chain block
+     * <br>
+     * RPC Method: chain_getBlock
+     */
+    public static final String CHAIN_GET_BLOCK = "chain_getBlock";
+
+    /**
+     * Get the block hash for a specific block
+     * <br>
+     * RPC Method: chain_getBlockHash <br>
+     * Alias: chain_getHead
+     */
+    public static final String CHAIN_GET_BLOCK_HASH = "chain_getBlockHash";
+
+    /**
+     * Get hash of the last finalized block in the canon chain
+     * <br>
+     * RPC Method: chain_getFinalizedHead <br>
+     * Alias: chain_getFinalisedHead
+     */
+    public static final String CHAIN_GET_FINALIZED_HEAD = "chain_getFinalizedHead";
+
+    /**
+     * Retrieves the header for a specific block
+     * <br>
+     * RPC Method: chain_getHeader
+     */
+    public static final String CHAIN_GET_HEADER = "chain_getHeader";
+
+    /**
+     * Retrieves the newest header via subscription
+     * <br>
+     * RPC Method: chain_subscribeAllHeads <br>
+     * Alias: subscribe_newHead, chain_subscribeNewHead
+     *
+     * @see #CHAIN_UNSUBSCRIBE_ALL_HEADS
+     */
+    public static final String CHAIN_SUBSCRIBE_ALL_HEADS = "chain_subscribeAllHeads";
+
+    /**
+     * Cancel subscription
+     * <br>
+     * RPC Method: chain_unsubscribeAllHeads
+     *
+     * @see #CHAIN_SUBSCRIBE_ALL_HEADS
+     */
+    public static final String CHAIN_UNSUBSCRIBE_ALL_HEADS = "chain_unsubscribeAllHeads";
+
+    /**
+     * Retrieves the best finalized header via subscription
+     * <br>
+     * RPC Method: chain_subscribeFinalizedHeads <br>
+     * Alias: chain_subscribeFinalisedHeads
+     *
+     * @see #CHAIN_UNSUBSCRIBE_FINALIZED_HEADS
+     */
+    public static final String CHAIN_SUBSCRIBE_FINALIZED_HEADS = "chain_subscribeFinalizedHeads";
+
+    /**
+     * Cancel subscription
+     * <br>
+     * RPC Method: chain_unsubscribeFinalizedHeads
+     *
+     * @see #CHAIN_SUBSCRIBE_FINALIZED_HEADS
+     */
+    public static final String CHAIN_UNSUBSCRIBE_FINALIZED_HEADS = "chain_unsubscribeFinalizedHeads";
+
+    /**
+     * Retrieves the best header via subscription
+     * <br>
+     * RPC Method: chain_subscribeNewHeads <br>
+     * Alias: subscribe_newHead, chain_subscribeNewHead
+     *
+     * @see #CHAIN_UNSUBSCRIBE_NEW_HEADS
+     */
+    public static final String CHAIN_SUBSCRIBE_NEW_HEADS = "chain_subscribeNewHeads";
+
+    /**
+     * Cancel subscription
+     * <br>
+     * RPC Method: chain_unsubscribeNewHeads
+     *
+     * @see #CHAIN_SUBSCRIBE_NEW_HEADS
+     */
+    public static final String CHAIN_UNSUBSCRIBE_NEW_HEADS = "chain_unsubscribeNewHeads";
+
+    // ----- STATE ----
+
+    /**
+     * Perform a call to a builtin on the chain
+     * <br>
+     * RPC Method: state_call <br>
+     * Alias: state_callAt
+     */
+    public static final String STATE_CALL = "state_call";
+
+    /**
+     * Returns the keys with prefix, leave empty to get all the keys
+     * <br>
+     * RPC Method: state_getPairs
+     */
+    public static final String STATE_GET_PAIRS = "state_getPairs";
+
+    /**
+     * Returns the keys with prefix with pagination support
+     * <br>
+     * RPC Method: state_getKeysPaged <br>
+     * Alias: state_getKeysPagedAt, state_getKeys
+     */
+    public static final String STATE_KEYS_PAGED = "state_getKeysPaged";
+
+    /**
+     * Returns a storage entry at a specific block's state. <br>
+     * RPC Method: state_getStorage <br>
+     * Alias: state_getStorageAt
+     */
+    public static final String STATE_GET_STORAGE = "state_getStorage";
+
+    /**
+     * Returns the hash of a storage entry at a block's state. <br>
+     * RPC Method: state_getStorageHash <br>
+     * Alias: state_getStorageHashAt
+     */
+    public static final String STATE_GET_STORAGE_HASH = "state_getStorageHash";
+
+    /**
+     * Returns the size of a storage entry at a block's state. <br>
+     * RPC Method: state_getStorageSize <br>
+     * Alias: state_getStorageSizeAt
+     */
+    public static final String STATE_GET_STORAGE_SIZE = "state_getStorageSize";
+
+    /**
+     * Returns the runtime metadata as an opaque blob. <br>
+     * RPC Method: state_getMetadata
+     */
+    public static final String STATE_GET_METADATA = "state_getMetadata";
+
+    /**
+     * Get the runtime version. <br>
+     * RPC Method: state_getRuntimeVersion <br>
+     * Alias: chain_getRuntimeVersion
+     */
+    public static final String STATE_GET_RUNTIME_VERSION = "state_getRuntimeVersion";
+
+    /**
+     * Query historical storage entries (by key) starting from a start block <br>
+     * RPC Method: state_queryStorage
+     */
+    public static final String STATE_QUERY_STORAGE = "state_queryStorage";
+
+    /**
+     * Query storage entries (by key) starting at block hash given as the second parameter <br>
+     * RPC Method: state_queryStorageAt
+     */
+    public static final String STATE_QUERY_STORAGE_AT = "state_queryStorageAt";
+
+    /**
+     * Returns proof of storage entries at a specific block's state. <br>
+     * RPC Method: state_getReadProof
+     */
+    public static final String STATE_GET_READ_PROOF = "state_getReadProof";
+
+    /**
+     * New runtime version subscription <br>
+     * RPC Method: state_subscribeRuntimeVersion <br>
+     * Alias: chain_subscribeRuntimeVersion
+     *
+     * @see #STATE_UNSUBSCRIBE_RUNTIME_VERSION
+     */
+    public static final String STATE_SUBSCRIBE_RUNTIME_VERSION = "state_subscribeRuntimeVersion";
+
+    /**
+     * Cancel subscription <br>
+     * RPC Method: state_subscribeRuntimeVersion
+     *
+     * @see #STATE_SUBSCRIBE_RUNTIME_VERSION
+     */
+    public static final String STATE_UNSUBSCRIBE_RUNTIME_VERSION = "state_unsubscribeRuntimeVersion";
+
+    /**
+     * New storage subscription <br>
+     * RPC Method: state_subscribeStorage
+     *
+     * @see #STATE_UNSUBSCRIBE_STORAGE
+     */
+    public static final String STATE_SUBSCRIBE_STORAGE = "state_subscribeStorage";
+
+    /**
+     * Cancel subscription <br>
+     * RPC Method: state_unsubscribeStorage
+     *
+     * @see #STATE_SUBSCRIBE_STORAGE
+     */
+    public static final String STATE_UNSUBSCRIBE_STORAGE = "state_unsubscribeStorage";
+
+    // ----- SYSTEM ----
+
+    /**
+     * Get the node's implementation name.
+     */
+    public static final String SYSTEM_NAME = "system_name";
+
+    /**
+     * Get the node implementation's version. Should be a semver string.
+     */
+    public static final String SYSTEM_VERSION = "system_version";
+
+    /**
+     * Get the chain's name. Given as a string identifier.
+     */
+    public static final String SYSTEM_CHAIN = "system_chain";
+
+    /**
+     * Get the chain's type.
+     */
+    public static final String SYSTEM_CHAIN_TYPE = "system_chainType";
+
+    /**
+     * Get a custom set of properties as a JSON object, defined in the chain spec.
+     */
+    public static final String SYSTEM_PROPERTIES = "system_properties";
+
+    /**
+     * Return health status of the node.
+     * <br>
+     * Node is considered healthy if it is:
+     * <ol>
+     *     <li>connected to some peers (unless running in dev mode)</li>
+     *     <li>not performing a major sync</li>
+     * </ol>
+     */
+    public static final String SYSTEM_HEALTH = "system_health";
+
+    /**
+     * Returns the base58-encoded PeerId of the node.
+     */
+    public static final String SYSTEM_LOCAL_PEER_ID = "system_localPeerId";
+
+    /**
+     * Returns the multiaddresses that the local node is listening on
+     */
+    public static final String SYSTEM_LOCAL_LISTEN_ADDRESSES = "system_localListenAddresses";
+
+    /**
+     * Returns currently connected peers
+     */
+    public static final String SYSTEM_PEERS = "system_peers";
+
+    /**
+     * Adds a reserved peer. Returns the empty string or an error. The string
+     * parameter should encode a `p2p` multiaddr.
+     */
+    public static final String SYSTEM_ADD_RESERVED_PEER = "system_addReservedPeer";
+
+    /**
+     * Remove a reserved peer. Returns the empty string or an error. The string
+     * should encode only the PeerId e.g. <code>QmSk5HQbn6LhUwDiNMseVUjuRYhEtYj4aUZ6WfWoGURpdV</code>
+     */
+    public static final String SYSTEM_REMOVE_RESERVED_PEER = "system_removeReservedPeer";
+
+    /**
+     * Returns the roles the node is running as.
+     */
+    public static final String SYSTEM_NODE_ROLES = "system_nodeRoles";
+}

polkaj-api-base/src/main/java/io/emeraldpay/polkaj/api/PolkadotSubscriptionApi.java

@@ -2,6 +2,9 @@
 
 import java.util.concurrent.CompletableFuture;
 
+/**
+ * @see PolkadotMethod
+ */
 public interface PolkadotSubscriptionApi {
 
     /**