perf(ext/http): Use flat list of headers for multiple set/get methods (#19336)

This PR attempts to resolve the first item on the list from
https://github.com/denoland/deno/issues/19330 which is about using a
flat list of interleaved key/value pairs, instead of a nested array of
tuples.

I can tackle some more if you can provide a quick example of using raw
v8 arrays, cc @mmastrac

1 files changed, 7 insertions, 2 deletions

diff --git a/ext/http/00_serve.js b/ext/http/00_serve.js
index d84244ee4..dbdc22705 100644
--- a/ext/http/00_serve.js
+++ b/ext/http/00_serve.js
@@ -334,7 +334,12 @@ class InnerRequest {
     if (this.#slabId === undefined) {
       throw new TypeError("request closed");
     }
-    return op_http_get_request_headers(this.#slabId);
+    const headers = [];
+    const reqHeaders = op_http_get_request_headers(this.#slabId);
+    for (let i = 0; i < reqHeaders.length; i += 2) {
+      headers.push([reqHeaders[i], reqHeaders[i + 1]]);
+    }
+    return headers;
   }
 
   get slabId() {
@@ -570,7 +575,7 @@ function mapToCallback(context, callback, onError) {
       if (headers.length == 1) {
         op_http_set_response_header(req, headers[0][0], headers[0][1]);
       } else {
-        op_http_set_response_headers(req, headers);
+        op_http_set_response_headers(req, headers.flat());
       }
     }