tls: stop the event-loop spin when a handshake stalls on WANT_READ

packages/bun-usockets/src/crypto/openssl.c

@@ -2032,7 +2032,19 @@ static void ssl_update_handshake(struct us_socket_t *s) {
     }
     s->ssl_handshake_state = HANDSHAKE_PENDING;
     s->ssl_write_wants_read = 1;
-    s->flags.last_write_failed = 1;
+    /* Only a blocked write justifies keeping writable interest armed. For
+     * WANT_READ no write failed — progress comes from the read side — and
+     * setting last_write_failed here kept EPOLLOUT / the EVFILT_WRITE
+     * one-shot re-armed on an always-writable socket: every tick re-entered
+     * this function with zero progress, spinning the loop at 100% CPU
+     * whenever writable interest existed while the handshake stalled
+     * (us_socket_pause arms writable, so pause() mid-handshake spun until
+     * resume). WANT_WRITE's blocked BIO write already set the flag inside
+     * us_socket_raw_write; keep this for the BIO retry paths that buffer
+     * without issuing a send. */
+    if (err == SSL_ERROR_WANT_WRITE) {
+      s->flags.last_write_failed = 1;
+    }
     return;
   }
 

test/js/bun/net/socket.test.ts

@@ -362,6 +362,13 @@ describe.concurrent("socket", () => {
     expect(await bunRun(fileURLToPath(new URL("./kqueue-filter-coalesce-fixture.ts", import.meta.url)))).toSpawn();
   });
 
+  // ssl_update_handshake set last_write_failed on SSL_ERROR_WANT_READ, so a
+  // paused (writable-armed) socket with a stalled handshake re-fired writable
+  // every tick at 100% CPU until the peer's handshake bytes arrived.
+  it("paused TLS socket with a stalled handshake must not spin the event loop", async () => {
+    expect(await bunRun(fileURLToPath(new URL("./tls-handshake-pause-spin-fixture.ts", import.meta.url)))).toSpawn();
+  });
+
   it("reload() should preserve active_connections (no UAF / counter underflow)", async () => {
     await using proc = Bun.spawn({
       cmd: [bunExe(), fileURLToPath(new URL("./socket-reload-fixture.ts", import.meta.url))],