First workable server.

vendor/deno.land/std@0.191.0/streams/text_delimiter_stream.ts

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+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+// This module is browser compatible.
+
+import { createLPS } from "./_common.ts";
+
+import type {
+  DelimiterDisposition,
+  DelimiterStreamOptions,
+} from "./delimiter_stream.ts";
+
+/** Transform a stream into a stream where each chunk is divided by a given delimiter.
+ *
+ * ```ts
+ * import { TextDelimiterStream } from "https://deno.land/std@$STD_VERSION/streams/text_delimiter_stream.ts";
+ * const res = await fetch("https://example.com");
+ * const parts = res.body!
+ *   .pipeThrough(new TextDecoderStream())
+ *   .pipeThrough(new TextDelimiterStream("foo"));
+ * ```
+ */
+export class TextDelimiterStream extends TransformStream<string, string> {
+  #buf = "";
+  #delimiter: string;
+  #inspectIndex = 0;
+  #matchIndex = 0;
+  #delimLPS: Uint8Array;
+  #disp: DelimiterDisposition;
+
+  constructor(delimiter: string, options?: DelimiterStreamOptions) {
+    super({
+      transform: (chunk, controller) => {
+        this.#handle(chunk, controller);
+      },
+      flush: (controller) => {
+        controller.enqueue(this.#buf);
+      },
+    });
+
+    this.#delimiter = delimiter;
+    this.#delimLPS = createLPS(new TextEncoder().encode(delimiter));
+    this.#disp = options?.disposition ?? "discard";
+  }
+
+  #handle(
+    chunk: string,
+    controller: TransformStreamDefaultController<string>,
+  ) {
+    this.#buf += chunk;
+    let localIndex = 0;
+    while (this.#inspectIndex < this.#buf.length) {
+      if (chunk[localIndex] === this.#delimiter[this.#matchIndex]) {
+        this.#inspectIndex++;
+        localIndex++;
+        this.#matchIndex++;
+        if (this.#matchIndex === this.#delimiter.length) {
+          // Full match
+          const start = this.#inspectIndex - this.#delimiter.length;
+          const end = this.#disp === "suffix" ? this.#inspectIndex : start;
+          const copy = this.#buf.slice(0, end);
+          controller.enqueue(copy);
+          const shift = this.#disp == "prefix" ? start : this.#inspectIndex;
+          this.#buf = this.#buf.slice(shift);
+          this.#inspectIndex = this.#disp == "prefix"
+            ? this.#delimiter.length
+            : 0;
+          this.#matchIndex = 0;
+        }
+      } else {
+        if (this.#matchIndex === 0) {
+          this.#inspectIndex++;
+          localIndex++;
+        } else {
+          this.#matchIndex = this.#delimLPS[this.#matchIndex - 1];
+        }
+      }
+    }
+  }
+}