feat: getInflation() RPC (needs better documentation pending book terms) (#473)

* feat: getInflation() RPC (needs better documentation pending book terms)

* feat: add test

web3.js/src/connection.js

@@ -66,6 +66,30 @@ type VoteAccountStatus = {
   delinquent: Array<VoteAccountInfo>,
 };
 
+/**
+ * Network Inflation parameters
+ *
+ * @typedef {Object} Inflation TODO - link to book terminology?
+ * @property {number} foundation TODO - link to book terminology?
+ * @property {number} foundation_term TODO - link to book terminology?
+ * @property {number} grant TODO - link to book terminology?
+ * @property {number} grant_term TODO - link to book terminology?
+ * @property {number} initial TODO - link to book terminology?
+ * @property {number} storage TODO - link to book terminology?
+ * @property {number} taper TODO - link to book terminology?
+ * @property {number} terminal TODO - link to book terminology?
+ */
+const GetInflationResult = struct({
+  foundation: 'number',
+  foundation_term: 'number',
+  grant: 'number',
+  grant_term: 'number',
+  initial: 'number',
+  storage: 'number',
+  taper: 'number',
+  terminal: 'number',
+});
+
 function createRpcRequest(url): RpcRequest {
   const server = jayson(async (request, callback) => {
     const options = {
@@ -98,6 +122,16 @@ function createRpcRequest(url): RpcRequest {
   };
 }
 
+/**
+ * Expected JSON RPC response for the "getInflation" message
+ */
+const GetInflationRpcResult = struct({
+  jsonrpc: struct.literal('2.0'),
+  id: 'string',
+  error: 'any?',
+  result: GetInflationResult,
+});
+
 /**
  * Expected JSON RPC response for the "getBalance" message
  */
@@ -638,6 +672,19 @@ export class Connection {
     return Number(res.result);
   }
 
+  /**
+   * Fetch the cluster Inflation parameters (TODO - book link/terminology?)
+   */
+  async getInflation(): Promise<GetInflationRpcResult> {
+    const unsafeRes = await this._rpcRequest('getInflation', []);
+    const res = GetInflationRpcResult(unsafeRes);
+    if (res.error) {
+      throw new Error(res.error.message);
+    }
+    assert(typeof res.result !== 'undefined');
+    return GetInflationResult(res.result);
+  }
+
   /**
    * Fetch a recent blockhash from the cluster
    */

web3.js/test/connection.test.js

@@ -128,6 +128,36 @@ test('get balance', async () => {
   expect(balance).toBeGreaterThanOrEqual(0);
 });
 
+test('get inflation', async () => {
+  const connection = new Connection(url);
+
+  mockRpc.push([
+    url,
+    {
+      method: 'getInflation',
+      params: [],
+    },
+    {
+      error: null,
+      result: {
+        foundation: 0.05,
+        foundation_term: 7.0,
+        grant: 0.05,
+        grant_term: 7.0,
+        initial: 0.15,
+        storage: 0.1,
+        taper: 0.15,
+        terminal: 0.015,
+      },
+    },
+  ]);
+
+  const inflation = await connection.getInflation();
+  expect(inflation.initial).toBeGreaterThan(0);
+  expect(inflation.storage).toBeGreaterThan(0);
+  expect(inflation.terminal).toBeGreaterThan(0);
+});
+
 test('get slot', async () => {
   const connection = new Connection(url);