test: make http2 timeout test robust

Instead of using magic values for the server timeout in
test-http2-session-timeout, measure the duration of the first request
(which should be longer than subsequent requests) and use that value.
Fixes: #20628
PR-URL: #24877Fixes: #20628
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

Author: Trott

test/sequential/sequential.status

@@ -23,5 +23,3 @@ test-http2-large-file: PASS, FLAKY
 [$system==aix]
 
 [$arch==arm]
-# https://github.com/nodejs/node/issues/20628
-test-http2-session-timeout: PASS,FLAKY

test/sequential/test-http2-session-timeout.js

@@ -6,15 +6,15 @@ if (!common.hasCrypto)
 constassert=require('assert');
 consthttp2=require('http2');
 
-constserverTimeout=common.platformTimeout(200);
-
 letrequests=0;
 constmustNotCall=()=>{
 assert.fail(`Timeout after ${requests} request(s)`);
 };
 
 constserver=http2.createServer();
-server.timeout=serverTimeout;
+// Disable server timeout until first request. We will set the timeout based on
+// how long the first request takes.
+server.timeout=0;
 
 server.on('request',(req,res)=>res.end());
 server.on('timeout',mustNotCall);
@@ -24,7 +24,7 @@ server.listen(0, common.mustCall(() => {
 
 consturl=`http://localhost:${port}`;
 constclient=http2.connect(url);
-conststartTime=process.hrtime();
+letstartTime=process.hrtime();
 makeReq();
 
 functionmakeReq(){
@@ -42,7 +42,15 @@ server.listen(0, common.mustCall(() => {
 request.on('end',()=>{
 constdiff=process.hrtime(startTime);
 constmilliseconds=(diff[0]*1e3+diff[1]/1e6);
-if(milliseconds<serverTimeout*2){
+if(server.timeout===0){
+// Set the timeout now. First connection will take significantly longer
+// than subsequent connections, so using the duration of the first
+// connection as the timeout should be robust. Double it anyway for good
+// measure.
+server.timeout=milliseconds*2;
+startTime=process.hrtime();
+makeReq();
+}elseif(milliseconds<server.timeout*2){
 makeReq();
 }else{
 server.removeListener('timeout',mustNotCall);