From da34e3569e95357d9469209d926cb645f0750bfa Mon Sep 17 00:00:00 2001
From: Richard Moore <me@ricmoo.com>
Date: Thu, 23 Nov 2023 21:26:26 -0500
Subject: [PATCH] Account for provider config weight when kicking off a request
 in FallbackProvider (#4298).

---
 src.ts/_tests/test-providers-fallback.ts | 66 ++++++++++++++++++++++++
 src.ts/providers/provider-fallback.ts    | 10 ++--
 2 files changed, 73 insertions(+), 3 deletions(-)

diff --git a/src.ts/_tests/test-providers-fallback.ts b/src.ts/_tests/test-providers-fallback.ts
index 4b2716505..66627740a 100644
--- a/src.ts/_tests/test-providers-fallback.ts
+++ b/src.ts/_tests/test-providers-fallback.ts
@@ -4,6 +4,7 @@ import {
     isError, makeError,
 
     AbstractProvider, FallbackProvider, Network,
+    ZeroAddress
 } from "../index.js";
 
 import type {
@@ -93,3 +94,68 @@ describe("Test Fallback broadcast", function() {
         });
     });
 });
+
+describe("Test Inflight Quorum", function() {
+    // Fires the %%actions%% as providers which will delay before returning,
+    // and returns an array of arrays, where each sub-array indicates which
+    // providers were inflight at once.
+    async function test(actions: Array<{ delay: number, stallTimeout: number, priority: number, weight: number }>, quorum: number): Promise<Array<Array<number>>> {
+        const inflights: Array<Array<number>> = [ [ ] ];
+
+        const configs = actions.map(({ delay, stallTimeout, priority, weight }, index) => ({
+            provider: new MockProvider(async (r) => {
+                if (r.method === "getBlockNumber") { return 1; }
+                if (r.method === "getBalance") {
+                    // Add this as inflight
+                    let last = inflights.pop();
+                    if (last == null) { throw new Error("no elements"); }
+                    inflights.push(last);
+                    last = last.slice();
+                    last.push(index);
+                    inflights.push(last);
+
+                    // Do the thing
+                    await stall(delay);
+
+                    // Remove as inflight
+                    last = inflights.pop();
+                    if (last == null) { throw new Error("no elements"); }
+                    inflights.push(last);
+                    last = last.filter((v) => (v !== index));
+                    inflights.push(last);
+
+                    return 0;
+                }
+                console.log(r);
+                throw new Error(`unhandled method: ${ r.method }`);
+            }),
+            stallTimeout, priority, weight
+        }));
+
+        const provider = new FallbackProvider(configs, network, {
+            cacheTimeout: -1, pollingInterval: 100,
+            quorum
+        });
+        await provider.getBalance(ZeroAddress);
+
+        return inflights;
+    }
+
+    // See: #4298
+    it("applies weights against inflight requests", async function() {
+        this.timeout(2000);
+
+        const inflights = await test([
+            { delay: 50, stallTimeout: 1000, priority: 1, weight: 2 },
+            { delay: 50, stallTimeout: 1000, priority: 1, weight: 2 },
+        ], 2);
+
+        // Make sure there is never more than 1 inflight provider at once
+        for (const running of inflights) {
+            assert.ok(running.length <= 1, `too many inflight requests: ${ JSON.stringify(inflights) }`);
+        }
+    });
+
+    // @TODO: add lots more tests, checking on priority, weight and stall
+    //        configurations
+});
diff --git a/src.ts/providers/provider-fallback.ts b/src.ts/providers/provider-fallback.ts
index 7f8fc6eef..f5a00f7cf 100644
--- a/src.ts/providers/provider-fallback.ts
+++ b/src.ts/providers/provider-fallback.ts
@@ -684,7 +684,7 @@ export class FallbackProvider extends AbstractProvider {
         // Add any new runners, because a staller timed out or a result
         // or error response came in.
         for (let i = 0; i < newRunners; i++) {
-            this.#addRunner(running, req)
+            this.#addRunner(running, req);
         }
 
         // All providers have returned, and we have no result
@@ -759,8 +759,12 @@ export class FallbackProvider extends AbstractProvider {
 
         // Bootstrap enough runners to meet quorum
         const running: Set<RunnerState> = new Set();
-        for (let i = 0; i < this.quorum; i++) {
-            this.#addRunner(running, req);
+        let inflightQuorum = 0;
+        while (true) {
+            const runner = this.#addRunner(running, req);
+            if (runner == null) { break; }
+            inflightQuorum += runner.config.weight;
+            if (inflightQuorum >= this.quorum) { break; }
         }
 
         const result = await this.#waitForQuorum(running, req);