perf(jsonl): add reusable zstd frame decoders

2026-08-05 17:27:02 +08:00
parent 906ab15490
commit 353226246e
3 changed files with 230 additions and 1 deletions
@@ -0,0 +1,38 @@
+/**
+ * Public-API synchronous Zstandard frame decoder fallback.
+ * @module dsh-session-persistence-jsonl/zstd-public-decoder
+ */
+
+import { zstdDecompressSync } from 'node:zlib'
+import type { ZstdFrameDecoder, ZstdFrameRange } from './zstd.ts'
+
+/** Multi-frame adapter built exclusively from Node's supported one-shot API. */
+export class PublicZstdFrameDecoder implements ZstdFrameDecoder {
+  private started = false
+  private closed = false
+
+  /** @inheritdoc */
+  public *decode(source: Buffer, frames: readonly ZstdFrameRange[]): Generator<Buffer, void, void> {
+    if (this.started) throw new Error('Zstandard frame decoder was already started')
+    if (this.closed) throw new Error('cannot start a closed Zstandard frame decoder')
+    this.started = true
+    try {
+      for (const frame of frames) {
+        try {
+          yield zstdDecompressSync(source.subarray(frame.start, frame.end))
+        } catch (error) {
+          throw new Error(`corrupt Zstandard session log: frame at byte ${frame.start} failed validation`, {
+            cause: error,
+          })
+        }
+      }
+    } finally {
+      this.close()
+    }
+  }
+
+  /** @inheritdoc */
+  close(): void {
+    this.closed = true
+  }
+}