[pyth-evm-price-pusher]: Enable polling in evm WS RPC (#68)

* Add polling in evm ws rpc as an addition to the existing subscription

Author: ali-behjati

pyth-evm-price-pusher/README.md

@@ -62,10 +62,11 @@ docker run public.ecr.aws/pyth-network/xc-evm-price-pusher:v<version> -- <above-
 
 The program accepts the following command line arguments:
 
-- `evm-endpoint`: RPC endpoint URL for the EVM network. If you provide a websocket RPC endpoint (`ws[s]://...`),
-  the price pusher will use event subscriptions to read the current EVM price. If you provide a normal
-  HTTP endpoint, the pusher will periodically poll for updates. The polling interval is configurable via
-  the `evm-polling-frequency` command-line argument (described below).
+- `evm-endpoint`: RPC endpoint URL for the EVM network. If you provide a normal HTTP endpoint,
+  the pusher will periodically poll for updates. The polling interval is configurable via the
+  `evm-polling-frequency` command-line argument (described below). If you provide a websocket RPC endpoint
+  (`ws[s]://...`), the price pusher will use event subscriptions to read the current EVM
+  price in addition to polling.
 - `mnemonic-file`: Path to payer mnemonic (private key) file.
 - `pyth-contract`: The Pyth contract address. Provide the network name on which Pyth is deployed
   or the Pyth contract address if you use a local network.

pyth-evm-price-pusher/docker-compose.mainnet.sample.yaml

@@ -1,6 +1,6 @@
 services:
   spy:
-    image: ghcr.io/wormhole-foundation/guardiand:v2.10.3
+    image: ghcr.io/wormhole-foundation/guardiand:v2.13.1
     command:
       - "spy"
       - "--nodeKey"

pyth-evm-price-pusher/docker-compose.testnet.sample.yaml

@@ -1,6 +1,6 @@
 services:
   spy:
-    image: ghcr.io/wormhole-foundation/guardiand:v2.10.3
+    image: ghcr.io/wormhole-foundation/guardiand:v2.13.1
     command:
       - "spy"
       - "--nodeKey"

pyth-evm-price-pusher/package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@pythnetwork/pyth-evm-price-pusher",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "description": "Pyth EVM Price Pusher",
   "homepage": "https://pyth.network",
   "main": "lib/index.js",

pyth-evm-price-pusher/package.json

@@ -54,15 +54,14 @@ export class EvmPriceListener implements PriceListener {
       this.startSubscription();
     } else {
       console.log(
-        "The target network RPC endpoint is not Websocket. Using polling instead..."
+        "The target network RPC endpoint is not Websocket. " +
+          "Listening for updates only via polling...."
       );
-      setInterval(this.pollPrices.bind(this), this.pollingFrequency * 1000);
     }
 
-    // Poll the prices to have values in the beginning until updates arrive.
-    console.log(
-      "Polling the prices in the beginning in order to set the initial values."
-    );
+    console.log(`Polling the prices every ${this.pollingFrequency} seconds...`);
+    setInterval(this.pollPrices.bind(this), this.pollingFrequency * 1000);
+
     await this.pollPrices();
   }
 
@@ -100,15 +99,15 @@ export class EvmPriceListener implements PriceListener {
       publishTime: Number(event.returnValues.publishTime),
     };
 
-    this.latestPriceInfo.set(priceId, priceInfo);
+    this.updateLatestPriceInfo(priceId, priceInfo);
   }
 
   private async pollPrices() {
     console.log("Polling evm prices...");
     for (const priceId of this.priceIds) {
       const currentPriceInfo = await this.getOnChainPriceInfo(priceId);
       if (currentPriceInfo !== undefined) {
-        this.latestPriceInfo.set(priceId, currentPriceInfo);
+        this.updateLatestPriceInfo(priceId, currentPriceInfo);
       }
     }
   }
@@ -134,7 +133,23 @@ export class EvmPriceListener implements PriceListener {
     return {
       conf: priceRaw.conf,
       price: priceRaw.price,
-      publishTime: priceRaw.publishTime,
+      publishTime: Number(priceRaw.publishTime),
     };
   }
+
+  private updateLatestPriceInfo(priceId: HexString, observedPrice: PriceInfo) {
+    const cachedLatestPriceInfo = this.getLatestPriceInfo(priceId);
+
+    // Ignore the observed price if the cache already has newer
+    // price. This could happen because we are using polling and
+    // subscription at the same time.
+    if (
+      cachedLatestPriceInfo !== undefined &&
+      cachedLatestPriceInfo.publishTime > observedPrice.publishTime
+    ) {
+      return;
+    }
+
+    this.latestPriceInfo.set(priceId, observedPrice);
+  }
 }

pyth-evm-price-pusher/src/evm-price-listener.ts

@@ -15,10 +15,11 @@ import { readPriceConfigFile } from "./price-config";
 const argv = yargs(hideBin(process.argv))
   .option("evm-endpoint", {
     description:
-      "RPC endpoint URL for the EVM network. If you provide a websocket RPC endpoint (`ws[s]://...`), " +
-      "the price pusher will use event subscriptions to read the current EVM price. If you provide " +
-      "a normal HTTP endpoint, the pusher will periodically poll for updates. The polling interval " +
-      "is configurable via the `evm-polling-frequency` command-line argument",
+      "RPC endpoint URL for the EVM network. If you provide a normal HTTP endpoint, the pusher " +
+      "will periodically poll for updates. The polling interval is configurable via the " +
+      "`evm-polling-frequency` command-line argument. If you provide a websocket RPC " +
+      "endpoint (`ws[s]://...`), the price pusher will use event subscriptions to read " +
+      "the current EVM price in addition to polling. ",
     type: "string",
     required: true,
   })

pyth-evm-price-pusher/src/index.ts

@@ -201,6 +201,9 @@ export class Pusher {
 
     console.log(`Analyzing price ${priceConfig.alias} (${priceId})`);
 
+    console.log("Source latest price: ", sourceLatestPrice);
+    console.log("Target latest price: ", targetLatestPrice);
+
     console.log(
       `Time difference: ${timeDifference} (< ${priceConfig.timeDifference}?)`
     );