[bun.js] Fix bug with headers not being sent in `fetch`

2 files changed, 23 insertions, 0 deletions

diff --git a/integration/bunjs-only-snippets/serve.test.ts b/integration/bunjs-only-snippets/serve.test.ts
index 323caf1f8..653454cc3 100644
--- a/integration/bunjs-only-snippets/serve.test.ts
+++ b/integration/bunjs-only-snippets/serve.test.ts
@@ -32,6 +32,28 @@ it("should work for a file", async () => {
   server.stop();
 });
 
+it("fetch should work with headers", async () => {
+  const fixture = resolve(import.meta.dir, "./fetch.js.txt");
+
+  const server = serve({
+    port: port++,
+    fetch(req) {
+      if (req.headers.get("X-Foo") !== "bar") {
+        return new Response("X-Foo header not set", { status: 500 });
+      }
+      return new Response(file(fixture));
+    },
+  });
+  const response = await fetch(`http://localhost:${server.port}`, {
+    headers: {
+      "X-Foo": "bar",
+    },
+  });
+
+  expect(response.status).toBe(200);
+  server.stop();
+});
+
 var count = 200;
 it(`should work for a file ${count} times`, async () => {
   const fixture = resolve(import.meta.dir, "./fetch.js.txt");
diff --git a/src/javascript/jsc/webcore/response.zig b/src/javascript/jsc/webcore/response.zig
index 1d4703bc1..bd6d05bcc 100644
--- a/src/javascript/jsc/webcore/response.zig
+++ b/src/javascript/jsc/webcore/response.zig
@@ -1041,6 +1041,7 @@ pub const Headers = struct {
             .allocator = allocator,
         };
         headers.entries.ensureTotalCapacity(allocator, header_count) catch unreachable;
+        headers.entries.len = header_count;
         headers.buf.ensureTotalCapacity(allocator, buf_len) catch unreachable;
         headers.buf.items.len = buf_len;
         var sliced = headers.entries.slice();