Add support for getFeeStats endpoint (#1006)

Signed-off-by: George <george@stellar.org>

CHANGELOG.md

@@ -6,6 +6,36 @@ A breaking change will get clearly marked in this log.
 
 ## Unreleased
 
+### Added
+- `rpc.Server` now has a `getFeeStats` method which retrieves fee statistics for a previous chunk of ledgers to provide users with a way to provide informed decisions about getting their transactions included in the following ledgers ([#998](https://github.com/stellar/js-stellar-sdk/issues/998)):
+
+```typescript
+export interface GetFeeStatsResponse {
+  sorobanInclusionFee: FeeDistribution;
+  inclusionFee: FeeDistribution;
+  latestLedger: number; // uint32
+}
+
+interface FeeDistribution {
+  max: string;  // uint64
+  min: string;  // uint64
+  mode: string; // uint64
+  p10: string;  // uint64
+  p20: string;  // uint64
+  p30: string;  // uint64
+  p40: string;  // uint64
+  p50: string;  // uint64
+  p60: string;  // uint64
+  p70: string;  // uint64
+  p80: string;  // uint64
+  p90: string;  // uint64
+  p95: string;  // uint64
+  p99: string;  // uint64
+  transactionCount: string; // uint32
+  ledgerCount: number;      // uint32
+}
+```
+
 
 ## [v12.1.0](https://github.com/stellar/js-stellar-sdk/compare/v12.0.1...v12.1.0)
 

src/rpc/api.ts

@@ -362,4 +362,30 @@ export namespace Api {
     /** State Difference information */
     stateChanges?: RawLedgerEntryChange[];
   }
+
+  export interface GetFeeStatsResponse {
+    sorobanInclusionFee: FeeDistribution;
+    inclusionFee: FeeDistribution;
+    latestLedger: number; // uint32
+  }
+
+  interface FeeDistribution {
+    max: string;    // uint64
+    min: string;    // uint64
+    mode: string;   // uint64
+    p10: string;    // uint64
+    p20: string;    // uint64
+    p30: string;    // uint64
+    p40: string;    // uint64
+    p50: string;    // uint64
+    p60: string;    // uint64
+    p70: string;    // uint64
+    p80: string;    // uint64
+    p90: string;    // uint64
+    p95: string;    // uint64
+    p99: string;    // uint64
+
+    transactionCount: string; // uint32
+    ledgerCount: number; // uint32
+  }
 }

src/rpc/server.ts

@@ -854,4 +854,15 @@ export class Server {
       throw error;
     }
   }
+
+  /**
+   * Provides an analysis of the recent fee stats for regular and smart 
+   * contract operations.
+   * 
+   * @returns {Promise<Api.GetFeeStatsResponse>}  the fee stats
+   * @see https://soroban.stellar.org/api/methods/getFeeStats
+   */
+  public async getFeeStats(): Promise<Api.GetFeeStatsResponse> {
+    return jsonrpc.postObject(this.serverURL.toString(), 'getFeeStats');
+  }
 }

test/unit/server/soroban/get_fee_stats_test.js

@@ -0,0 +1,57 @@
+const { Server, AxiosClient } = StellarSdk.rpc;
+
+describe("Server#getFeeStats", function () {
+  beforeEach(function () {
+    this.server = new Server(serverUrl);
+    this.axiosMock = sinon.mock(AxiosClient);
+  });
+
+  afterEach(function () {
+    this.axiosMock.verify();
+    this.axiosMock.restore();
+  });
+
+  it("requests the correct endpoint", function (done) {
+    const innerFeeStat = {
+      max: "100000000000000000000", // just > uint32
+      min: "100",
+      mode: "100",
+      p10: "100",
+      p20: "100",
+      p30: "100",
+      p40: "100",
+      p50: "100",
+      p60: "100",
+      p70: "100",
+      p80: "100",
+      p90: "100",
+      p95: "100",
+      p99: "100",
+      transactionCount: "200",
+      ledgerCount: "300",
+    };
+    const result = {
+      sorobanInclusionFee: innerFeeStat,
+      inclusionFee: innerFeeStat,
+      latestLedger: "12345678",
+    };
+
+    this.axiosMock
+      .expects("post")
+      .withArgs(serverUrl, {
+        jsonrpc: "2.0",
+        id: 1,
+        method: "getFeeStats",
+        params: null,
+      })
+      .returns(Promise.resolve({ data: { result } }));
+
+    this.server
+      .getFeeStats()
+      .then(function (response) {
+        expect(response).to.be.deep.equal(result);
+        done();
+      })
+      .catch((err) => done(err));
+  });
+});