feat: add block author example

effects/rpc_known_methods.ts

@@ -31,6 +31,7 @@ export namespace chain {
   export const getBlockHash = rpcCall<[height?: known.ListOrValue<known.NumberOrHex>], U.HexHash>(
     "chain_getBlockHash",
   )
+  export const getBlockHeader = rpcCall<[hash?: U.HexHash], known.Header>("chain_getHeader")
 }
 export namespace system {
   export const accountNextIndex = rpcCall<[accountId: known.AccountId], number>(

examples/block_author.ts

@@ -0,0 +1,42 @@
+import * as C from "http://localhost:5646/@local/mod.ts"
+import {
+  Session,
+  System,
+} from "http://localhost:5646/@local/proxy/wss:rpc.polkadot.io/pallets/mod.ts"
+import { $preDigest } from "http://localhost:5646/@local/proxy/wss:rpc.polkadot.io/types/sp_consensus_babe/digests.ts"
+import {
+  $digestItem,
+  DigestItem,
+} from "http://localhost:5646/@local/proxy/wss:rpc.polkadot.io/types/sp_runtime/generic/digest.ts"
+import * as U from "http://localhost:5646/@local/util/mod.ts"
+
+const blockHeader = C.chain.getBlockHeader(C.polkadot)()
+const header = U.throwIfError(await blockHeader.run())
+const digestedLogs = header.digest.logs.map(C.hex.decode).map($digestItem.decode.bind($digestItem))
+
+function preRuntimeGuard(digestItem: DigestItem): digestItem is DigestItem.PreRuntime {
+  return digestItem.type === "PreRuntime"
+}
+
+const digest = digestedLogs.find(preRuntimeGuard)
+if (!digest) {
+  throw new Error("Missing PreRuntime log")
+}
+
+const utf8decoder = new TextDecoder()
+const consensusEngineId = utf8decoder.decode(digest.value[0])
+
+if (consensusEngineId !== "BABE") {
+  throw new Error(`Unsupported consensus engine id: ${consensusEngineId}. Only BABE is supported.`)
+}
+
+const preDigest = $preDigest.decode(digest.value[1])
+const validators = U.throwIfError(await Session.Validators.entry().read().run())
+const pubKey = validators.value[preDigest.value.authorityIndex]!
+
+const ss58EncodedPubKey = U.ss58.encode(
+  System.SS58Prefix,
+  pubKey,
+)
+
+console.log(ss58EncodedPubKey)

examples/mod.ts

@@ -5,6 +5,7 @@
 
 export * from "./balance.ts"
 export * from "./batch.ts"
+export * from "./block_author.ts"
 export * from "./derived.ts"
 export * from "./fee_estimate.ts"
 export * from "./first_ten_keys.ts"
@@ -19,6 +20,7 @@ export * from "./read_era_rewards.ts"
 export * from "./read_events.ts"
 export * from "./rpc_call.ts"
 export * from "./rpc_subscription.ts"
+export * from "./smart_contract.ts"
 export * from "./ticker.ts"
 export * from "./transfer.ts"
 export * from "./watch_blocks.ts"