Started to implement server

vendor/deno.land/std@0.178.0/streams/byte_slice_stream.ts

@@ -0,0 +1,44 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+import { assert } from "../_util/asserts.ts";
+
+/**
+ * A transform stream that only transforms from the zero-indexed `start` and `end` bytes (both inclusive).
+ *
+ * @example
+ * ```ts
+ * import { ByteSliceStream } from "https://deno.land/std@$STD_VERSION/streams/byte_slice_stream.ts";
+ * const response = await fetch("https://example.com");
+ * const rangedStream = response.body!
+ *   .pipeThrough(new ByteSliceStream(3, 8));
+ * ```
+ */
+export class ByteSliceStream extends TransformStream<Uint8Array, Uint8Array> {
+  #offsetStart = 0;
+  #offsetEnd = 0;
+
+  constructor(start = 0, end = Infinity) {
+    super({
+      start: () => {
+        assert(start >= 0, "`start` must be greater than 0");
+        end += 1;
+      },
+      transform: (chunk, controller) => {
+        this.#offsetStart = this.#offsetEnd;
+        this.#offsetEnd += chunk.byteLength;
+        if (this.#offsetEnd > start) {
+          if (this.#offsetStart < start) {
+            chunk = chunk.slice(start - this.#offsetStart);
+          }
+          if (this.#offsetEnd >= end) {
+            chunk = chunk.slice(0, chunk.byteLength - this.#offsetEnd + end);
+            controller.enqueue(chunk);
+            controller.terminate();
+          } else {
+            controller.enqueue(chunk);
+          }
+        }
+      },
+    });
+  }
+}