fix(ext/fetch): do not truncate field value in EventSource (#22368)

Depends on #22493. Closes #22367.

ext/fetch/27_eventsource.js

@@ -15,7 +15,6 @@ const {
   StringPrototypeIncludes,
   StringPrototypeIndexOf,
   StringPrototypeSlice,
-  StringPrototypeSplit,
   StringPrototypeStartsWith,
   StringPrototypeToLowerCase,
   SymbolFor,
@@ -268,8 +267,10 @@ class EventSource extends EventTarget {
         } else {
           let field = chunk;
           let value = "";
-          if (StringPrototypeIncludes(chunk, ":")) {
+          const colonIndex = StringPrototypeIndexOf(chunk, ":");
-            ({ 0: field, 1: value } = StringPrototypeSplit(chunk, ":"));
+          if (colonIndex !== -1) {
+            field = StringPrototypeSlice(chunk, 0, colonIndex);
+            value = StringPrototypeSlice(chunk, colonIndex + 1);
             if (StringPrototypeStartsWith(value, " ")) {
               value = StringPrototypeSlice(value, 1);
             }

tests/integration/js_unit_tests.rs

@@ -30,6 +30,7 @@ util::unit_test_factory!(
     error_stack_test,
     error_test,
     esnext_test,
+    event_source_test,
     event_target_test,
     event_test,
     fetch_test,

tests/unit/event_source_test.ts

@@ -0,0 +1,27 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+import { assertStrictEquals } from "./test_util.ts";
+
+Deno.test(
+  { permissions: { net: ["127.0.0.1"] } },
+  async function eventSourceColonInMessage() {
+    const portDeferred = Promise.withResolvers<number>();
+
+    await using _server = Deno.serve({
+      handler: () =>
+        new Response('data: {"key":"value"}\n\n', {
+          headers: { "content-type": "text/event-stream" },
+        }),
+      onListen: ({ port }) => portDeferred.resolve(port),
+      hostname: "127.0.0.1",
+      port: 0,
+    });
+
+    const port = await portDeferred.promise;
+    const eventSource = new EventSource(`http://127.0.0.1:${port}/`);
+    const event = await new Promise<MessageEvent>((resolve) =>
+      eventSource.onmessage = resolve
+    );
+    eventSource.close();
+    assertStrictEquals(event.data, '{"key":"value"}');
+  },
+);