http2: do not modify explicity set date headers

Fixes: #30894
Refs: #29829

PR-URL: #33160
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/http2.md

@@ -1409,6 +1409,10 @@ and will throw an error.
 #### `http2stream.respond([headers[, options]])`
 <!-- YAML
 added: v8.4.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/33160
+    description: Allow explicity setting date headers.
 -->
 
 * `headers` {HTTP/2 Headers Object}
@@ -1453,6 +1457,9 @@ server.on('stream', (stream) => {
 <!-- YAML
 added: v8.4.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/33160
+    description: Allow explicity setting date headers.
   - version: v12.12.0
     pr-url: https://github.com/nodejs/node/pull/29876
     description: The `fd` option may now be a `FileHandle`.
@@ -1551,6 +1558,9 @@ server.on('stream', (stream) => {
 <!-- YAML
 added: v8.4.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/33160
+    description: Allow explicity setting date headers.
   - version: v10.0.0
     pr-url: https://github.com/nodejs/node/pull/18936
     description: Any readable file, not necessarily a

lib/internal/http2/core.js

@@ -2234,7 +2234,10 @@ function processHeaders(oldHeaders) {
   const statusCode =
     headers[HTTP2_HEADER_STATUS] =
       headers[HTTP2_HEADER_STATUS] | 0 || HTTP_STATUS_OK;
-  headers[HTTP2_HEADER_DATE] = utcDate();
+
+  if (headers[HTTP2_HEADER_DATE] === null ||
+      headers[HTTP2_HEADER_DATE] === undefined)
+    headers[HTTP2_HEADER_DATE] = utcDate();
 
   // This is intentionally stricter than the HTTP/1 implementation, which
   // allows values between 100 and 999 (inclusive) in order to allow for

test/parallel/test-http2-removed-header-stays-removed.js

@@ -0,0 +1,22 @@
+'use strict';
+const common = require('../common');
+if (!common.hasCrypto) { common.skip('missing crypto'); }
+const assert = require('assert');
+const http2 = require('http2');
+
+const server = http2.createServer(common.mustCall((request, response) => {
+  response.setHeader('date', 'snacks o clock');
+  response.end();
+}));
+
+server.listen(0, common.mustCall(() => {
+  const session = http2.connect(`http://localhost:${server.address().port}`);
+  const req = session.request();
+  req.on('response', (headers, flags) => {
+    assert.deepStrictEqual(headers.date, 'snacks o clock');
+  });
+  req.on('end', () => {
+    session.close();
+    server.close();
+  });
+}));