h3: replenish bidi stream credit on stream close

src/http3/http3_callbacks.c

@@ -1290,7 +1290,7 @@ static int stream_close_cb(ngtcp2_conn *conn, uint32_t flags,
                            int64_t stream_id, uint64_t app_error_code,
                            void *user_data, void *stream_user_data)
 {
-    (void)conn; (void)stream_user_data;
+    (void)stream_user_data;
     http3_connection_t *c = (http3_connection_t *)user_data;
 
     if (c == NULL || c->nghttp3_conn == NULL) {
@@ -1308,6 +1308,12 @@ static int stream_close_cb(ngtcp2_conn *conn, uint32_t flags,
 
     if (stats != NULL) stats->h3_stream_close++;
 
+    /* ngtcp2 never auto-extends MAX_STREAMS on close, so without this each
+     * connection caps at initial_max_streams_bidi. id&3==0 = client bidi. */
+    if ((stream_id & 0x03) == 0) {
+        ngtcp2_conn_extend_max_streams_bidi(conn, 1);
+    }
+
     if (rv != 0 && rv != NGHTTP3_ERR_STREAM_NOT_FOUND) {
         return NGTCP2_ERR_CALLBACK_FAILURE;
     }

tests/phpt/server/h3/036-h3-stream-credit-replenish.phpt

@@ -0,0 +1,92 @@
+--TEST--
+HttpServer: HTTP/3 replenishes bidi stream credit beyond initial_max_streams_bidi
+--EXTENSIONS--
+true_async_server
+true_async
+--ENV--
+PHP_HTTP3_DISABLE_RETRY=1
+--SKIPIF--
+<?php
+require __DIR__ . '/_h3_skipif.inc';
+h3_skipif(['openssl_cli' => true, 'h3client' => true]);
+?>
+--FILE--
+<?php
+/* Regression: a QUIC connection must keep serving requests past the
+ * advertised initial_max_streams_bidi (default 100). ngtcp2 never
+ * auto-extends MAX_STREAMS on stream close, so the server must call
+ * ngtcp2_conn_extend_max_streams_bidi() in its stream_close callback.
+ * Without that, every connection is permanently capped at 100 bidi
+ * request streams — each one served fast, then the connection stalls
+ * (this is what crushed the HttpArena baseline-h3 result to ~20 req/s
+ * per connection).
+ *
+ * Drive 150 sequential request streams (> the 100 default) over a
+ * single reused QUIC connection. Pre-fix: completed stalls at 100.
+ * Post-fix: all 150 complete and the connection is accepted once. */
+
+use TrueAsync\HttpServer;
+use TrueAsync\HttpServerConfig;
+use function Async\spawn;
+use function Async\await;
+
+$tmp = __DIR__ . '/tmp-036';
+@mkdir($tmp, 0700, true);
+$cert = $tmp . '/cert.pem';
+$key  = $tmp . '/key.pem';
+$rc = 0;
+exec(sprintf('openssl req -x509 -newkey rsa:2048 -sha256 -days 1 -nodes '
+    . '-subj "/CN=localhost" -keyout %s -out %s 2>/dev/null',
+    escapeshellarg($key), escapeshellarg($cert)), $_, $rc);
+if ($rc !== 0) { echo "cert gen failed\n"; exit(1); }
+
+$port = 20400 + (getmypid() % 40) + 16;
+
+$config = (new HttpServerConfig())
+    ->addListener('127.0.0.1', $port + 1)
+    ->addHttp3Listener('127.0.0.1', $port)
+    ->enableTls(true)->setCertificate($cert)->setPrivateKey($key);
+$server = new HttpServer($config);
+$server->addHttpHandler(function ($req, $res) {
+    $res->setStatusCode(200)
+        ->setHeader('content-type', 'text/plain')
+        ->setBody('ok');
+});
+
+$client_bin = __DIR__ . '/../../../h3client/h3client';
+
+$client = spawn(function () use ($server, $port, $client_bin) {
+    usleep(80000);
+
+    $cmd = sprintf('H3CLIENT_REQUEST_COUNT=150 H3CLIENT_QUIET=1 %s 127.0.0.1 %d / GET 2>&1',
+        escapeshellarg($client_bin), $port);
+    $out = shell_exec($cmd) ?? '';
+
+    $completed = -1;
+    if (preg_match('/^COMPLETED=(\d+)$/m', $out, $m)) $completed = (int)$m[1];
+    echo "completed=", $completed, "\n";
+
+    $s = $server->getHttp3Stats()[0] ?? [];
+    echo "streams_opened=",     (int)($s['h3_streams_opened']     ?? -1), "\n";
+    echo "request_received=",   (int)($s['h3_request_received']   ?? -1), "\n";
+    echo "response_submitted=", (int)($s['h3_response_submitted'] ?? -1), "\n";
+    /* One connection, 150 streams — reuse must hold (no per-request
+     * handshake) or the credit-replenish path isn't what's exercised. */
+    echo "conn_accepted=",      (int)($s['quic_conn_accepted'] ?? -1), "\n";
+
+    $server->stop();
+});
+
+$server->start();
+await($client);
+
+@unlink($cert); @unlink($key); @rmdir($tmp);
+echo "done\n";
+?>
+--EXPECT--
+completed=150
+streams_opened=150
+request_received=150
+response_submitted=150
+conn_accepted=1
+done