http: reject addTrailers after finish

Fixes: #62809

Author: ryuhei shima

lib/_http_outgoing.js

@@ -977,6 +977,10 @@ function connectionCorkNT(conn) {
 }
 
 OutgoingMessage.prototype.addTrailers = function addTrailers(headers) {
+  if (this.finished) {
+    throw new ERR_HTTP_HEADERS_SENT('set trailing');
+  }
+
   this._trailer = '';
   const keys = ObjectKeys(headers);
   const isArray = ArrayIsArray(headers);

test/parallel/test-http-outgoing-proto.js

@@ -129,6 +129,16 @@ assert.throws(() => {
   message: 'Invalid character in trailer content ["404"]'
 });
 
+assert.throws(() => {
+  const outgoingMessage = new OutgoingMessage();
+  outgoingMessage.finished = true;
+  outgoingMessage.addTrailers({ 'x-foo': 'bar' });
+}, {
+  code: 'ERR_HTTP_HEADERS_SENT',
+  name: 'Error',
+  message: 'Cannot set trailing headers after they are sent to the client'
+});
+
 {
   const outgoingMessage = new OutgoingMessage();
   assert.strictEqual(outgoingMessage.destroyed, false);