solana/ts: add parsed transaction to callback

solana/ts: make ArrayQueue dequeue safer

solana/ts/src/matchingEngine/index.ts

@@ -6,6 +6,7 @@ import {
     ConfirmOptions,
     Connection,
     Finality,
+    ParsedTransactionWithMeta,
     PublicKey,
     SYSVAR_CLOCK_PUBKEY,
     SYSVAR_EPOCH_SCHEDULE_PUBKEY,
@@ -267,6 +268,7 @@ export class MatchingEngineProgram {
             eventSlot: number,
             signature: string,
             currentSlotInfo?: SlotInfo,
+            parsedTransaction?: ParsedTransactionWithMeta,
         ) => void,
         commitment: Finality = "confirmed",
     ): number {
@@ -279,7 +281,17 @@ export class MatchingEngineProgram {
         connection.onSlotChange(async (slotInfo) => {
             // TODO: Make this more efficient by fetching multiple parsed transactions.
             while (!unprocessedTxs.isEmpty()) {
-                const { signature, eventSlot } = unprocessedTxs.head();
+                const head = unprocessedTxs.head();
+
+                // This check is superfluous. But we do it anyway to make sure the unprocessed
+                // transaction queue is actually empty.
+                //
+                // Once the ArrayQueue has been thoroughly tested, we can remove this check.
+                if (head === null) {
+                    break;
+                }
+
+                const { signature, eventSlot } = head;
 
                 const parsedTx = await connection.getParsedTransaction(signature, {
                     commitment,
@@ -316,6 +328,7 @@ export class MatchingEngineProgram {
                                 eventSlot,
                                 signature,
                                 slotInfo,
+                                parsedTx,
                             );
                         }
                     }

solana/ts/src/utils.ts

@@ -20,9 +20,9 @@ export class ArrayQueue<T> {
         this._data = new Array(capacity ?? 256).fill(null);
     }
 
-    head(): T {
+    head(): T | null {
         if (this.isEmpty()) {
-            throw new Error("queue is empty");
+            return null;
         }
 
         return this._data[this._index]!;
@@ -42,6 +42,10 @@ export class ArrayQueue<T> {
     }
 
     dequeue(): void {
+        if (this.isEmpty()) {
+            return;
+        }
+
         const data = this._data;
         const index = this._index;