http2: get trailers working with the compat api

PR-URL: nodejs#14239
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/http2/compat.js

@@ -328,16 +328,12 @@ class Http2ServerResponse extends Stream {
   addTrailers(headers) {
     let trailers = this[kTrailers];
     const keys = Object.keys(headers);
-    let key = '';
-    if (keys.length > 0)
+    if (keys.length === 0)
       return;
     if (trailers === undefined)
       trailers = this[kTrailers] = Object.create(null);
     for (var i = 0; i < keys.length; i++) {
-      key = String(keys[i]).trim().toLowerCase();
-      const value = headers[key];
-      assertValidHeader(key, value);
-      trailers[key] = String(value);
+      trailers[keys[i]] = String(headers[keys[i]]);
     }
   }
 
@@ -508,12 +504,16 @@ class Http2ServerResponse extends Stream {
 
   [kBeginSend](options) {
     const stream = this[kStream];
+    options = options || Object.create(null);
     if (stream !== undefined && stream.headersSent === false) {
       const state = this[kState];
       const headers = this[kHeaders] || Object.create(null);
       headers[constants.HTTP2_HEADER_STATUS] = state.statusCode;
       if (stream.finished === true)
         options.endStream = true;
+      options.getTrailers = (trailers) => {
+        Object.assign(trailers, this[kTrailers]);
+      };
       if (stream.destroyed === false) {
         stream.respond(headers, options);
       }

test/parallel/test-http2-compat-serverresponse-trailers.js

@@ -0,0 +1,30 @@
+// Flags: --expose-http2
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const http2 = require('http2');
+
+const server = http2.createServer();
+server.listen(0, common.mustCall(() => {
+  const port = server.address().port;
+  server.once('request', common.mustCall((request, response) => {
+    response.addTrailers({
+      ABC: 123
+    });
+    response.end('hello');
+  }));
+
+  const url = `http://localhost:${port}`;
+  const client = http2.connect(url, common.mustCall(() => {
+    const request = client.request();
+    request.on('trailers', common.mustCall((headers) => {
+      assert.strictEqual(headers.abc, '123');
+    }));
+    request.resume();
+    request.on('end', common.mustCall(() => {
+      client.destroy();
+      server.close();
+    }));
+  }));
+}));