From 3a86677126615a163b5c42b2234fdbb6404a07fd Mon Sep 17 00:00:00 2001
From: Aaron O'Mullan <aaron.omullan@gmail.com>
Date: Thu, 15 Aug 2024 17:09:40 +0900
Subject: [PATCH] perf(ts): simple monomorphic message parse

---
 typescript/core/src/McapStreamReader.ts | 12 ++++++++++--
 typescript/core/src/parse.ts            | 25 +++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/typescript/core/src/McapStreamReader.ts b/typescript/core/src/McapStreamReader.ts
index 6ed8292ce..e32c5a7e6 100644
--- a/typescript/core/src/McapStreamReader.ts
+++ b/typescript/core/src/McapStreamReader.ts
@@ -2,7 +2,7 @@ import { crc32 } from "@foxglove/crc";
 
 import Reader from "./Reader";
 import { MCAP_MAGIC } from "./constants";
-import { parseMagic, parseRecord } from "./parse";
+import { monoParseMessage, parseMagic, parseRecord } from "./parse";
 import { Channel, DecompressHandlers, McapMagic, TypedMcapRecord, TypedMcapRecords } from "./types";
 
 type McapReaderOptions = {
@@ -233,7 +233,15 @@ export default class McapStreamReader {
           const view = new DataView(buffer.buffer, buffer.byteOffset, buffer.byteLength);
           const chunkReader = new Reader(view);
           let chunkRecord;
-          while ((chunkRecord = parseRecord(chunkReader, this.#validateCrcs))) {
+          while (true) {
+            if (chunkRecord = monoParseMessage(chunkReader)) {
+              yield chunkRecord;
+              continue;
+            }
+            chunkRecord = parseRecord(chunkReader, this.#validateCrcs)
+            if (!chunkRecord) {
+              break;
+            }
             switch (chunkRecord.type) {
               case "Unknown":
                 break;
diff --git a/typescript/core/src/parse.ts b/typescript/core/src/parse.ts
index 95d010575..026fd2bda 100644
--- a/typescript/core/src/parse.ts
+++ b/typescript/core/src/parse.ts
@@ -417,3 +417,28 @@ function parseDataEnd(reader: Reader, recordLength: number): TypedMcapRecord {
     dataSectionCrc,
   };
 }
+
+
+export function monoParseMessage(reader: Reader): TypedMcapRecord | undefined | null {
+  const RECORD_HEADER_SIZE = 1 /*opcode*/ + 8; /*record content length*/
+  if (reader.bytesRemaining() < RECORD_HEADER_SIZE) {
+    return undefined;
+  }
+  const start = reader.offset;
+  const opcode = reader.uint8();
+  const recordLength = reader.uint64();
+
+  if (opcode !== Opcode.MESSAGE) {
+    reader.offset = start; // Rewind to the start of the record
+    return null;
+  }
+
+  const recordLengthNum = Number(recordLength);
+
+  if (reader.bytesRemaining() < recordLengthNum) {
+    reader.offset = start; // Rewind to the start of the record
+    return undefined;
+  }
+
+  return parseMessage(reader, recordLengthNum);
+}