update PythConnection to subscribe to single accounts and add new ws …

…example with SOL/USDC feed (#64)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@pythnetwork/client",
-  "version": "2.13.1",
+  "version": "2.14.0",
   "description": "Client for consuming Pyth price data",
   "homepage": "https://pyth.network",
   "main": "lib/index.js",
@@ -20,6 +20,7 @@
     "version": "npm run format && git add -A src",
     "postversion": "git push && git push --tags",
     "ws_example": "npm run build && node lib/example_ws_usage.js",
+    "ws_single_example": "npm run build && node lib/example_ws_usage.js",
     "http_example": "npm run build && node lib/example_http_usage.js"
   },
   "keywords": [

src/PythConnection.ts

@@ -30,6 +30,7 @@ export class PythConnection {
   connection: Connection
   pythProgramKey: PublicKey
   commitment: Commitment
+  feedIds?: PublicKey[]
 
   productAccountKeyToProduct: Record<string, AccountUpdate<ProductData>> = {}
   priceAccountKeyToProductAccountKey: Record<string, string> = {}
@@ -104,29 +105,49 @@ export class PythConnection {
   /** Create a PythConnection that reads its data from an underlying solana web3 connection.
    *  pythProgramKey is the public key of the Pyth program running on the chosen solana cluster.
    */
-  constructor(connection: Connection, pythProgramKey: PublicKey, commitment: Commitment = 'finalized') {
+  constructor(connection: Connection, pythProgramKey: PublicKey, commitment: Commitment = 'finalized', feedIds?: PublicKey[]) {
     this.connection = connection
     this.pythProgramKey = pythProgramKey
     this.commitment = commitment
+    this.feedIds = feedIds
   }
 
   /** Start receiving price updates. Once this method is called, any registered callbacks will be invoked
    *  each time a Pyth price account is updated.
    */
   public async start() {
-    const accounts = await this.connection.getProgramAccounts(this.pythProgramKey, this.commitment)
+    let accounts = await this.connection.getProgramAccounts(this.pythProgramKey, this.commitment)
     const currentSlot = await this.connection.getSlot(this.commitment)
+    // Handle all accounts once since we need to handle product accounts
+    // at least once
     for (const account of accounts) {
       this.handleAccount(account.pubkey, account.account, true, currentSlot)
     }
 
-    this.connection.onProgramAccountChange(
-      this.pythProgramKey,
-      (keyedAccountInfo, context) => {
-        this.handleAccount(keyedAccountInfo.accountId, keyedAccountInfo.accountInfo, false, context.slot)
-      },
-      this.commitment,
-    )
+    if(this.feedIds) {
+      // Filter down to only the feeds we want
+      const rawIDs = this.feedIds.map((feed) => feed.toString())
+      accounts = accounts.filter((feed) => rawIDs.includes(feed.pubkey.toString()))
+      for (const account of accounts){
+        this.connection.onAccountChange(
+        account.pubkey,
+
+        (accountInfo, context) => {
+          this.handleAccount(account.pubkey, accountInfo, false, context.slot)
+        },
+        this.commitment,
+          )
+      }
+
+    } else {
+      this.connection.onProgramAccountChange(
+        this.pythProgramKey,
+        (keyedAccountInfo, context) => {
+          this.handleAccount(keyedAccountInfo.accountId, keyedAccountInfo.accountInfo, false, context.slot)
+        },
+        this.commitment,
+      )
+    }
   }
 
   /** Register callback to receive price updates. */

src/example_ws_single_feed.ts

@@ -0,0 +1,30 @@
+import { Connection, PublicKey } from '@solana/web3.js'
+import { PythConnection } from './PythConnection'
+import { getPythClusterApiUrl, getPythProgramKeyForCluster, PythCluster, PriceStatus } from '.'
+
+const PYTHNET_CLUSTER_NAME: PythCluster = 'pythnet'
+const connection = new Connection(getPythClusterApiUrl(PYTHNET_CLUSTER_NAME))
+const pythPublicKey = getPythProgramKeyForCluster(PYTHNET_CLUSTER_NAME)
+// This feed ID comes from this list: https://pyth.network/developers/price-feed-ids#solana-mainnet-beta
+// This example shows Crypto.SOL/USD
+const feeds = [new PublicKey('H6ARHf6YXhGYeQfUzQNGk6rDNnLBQKrenN712K4AQJEG')]
+
+const pythConnection = new PythConnection(connection, pythPublicKey, "confirmed", feeds)
+pythConnection.onPriceChangeVerbose((productAccount, priceAccount) => {
+  // The arguments to the callback include solana account information / the update slot if you need it.
+  const product = productAccount.accountInfo.data.product
+  const price = priceAccount.accountInfo.data
+  // sample output:
+  // SOL/USD: $14.627930000000001 ±$0.01551797
+  if (price.price && price.confidence) {
+    // tslint:disable-next-line:no-console
+    console.log(`${product.symbol}: $${price.price} \xB1$${price.confidence}`)
+  } else {
+    // tslint:disable-next-line:no-console
+    console.log(`${product.symbol}: price currently unavailable. status is ${PriceStatus[price.status]}`)
+  }
+})
+
+// tslint:disable-next-line:no-console
+console.log('Reading from Pyth price feed...')
+pythConnection.start()