Bound a TLS handshake by its timeout as a whole

The handshake loops gave every wait for the socket the full timeout
again, so a peer that sent a byte now and then kept a handshake going,
and the worker serving it, for as long as it liked. Work out the
deadline once and wait only for what is left of it, on both sides and in
every backend.

test/test.cc

@@ -10220,6 +10220,30 @@ static bool send_request(time_t read_timeout_sec, const std::string &req,
   return send_request_in_parts(read_timeout_sec, {req}, resp, port);
 }
 
+#ifdef CPPHTTPLIB_SSL_ENABLED
+TEST(SSLClientServerTest, ReadTimeoutBoundsTheWholeHandshake) {
+  SSLServer svr(SERVER_CERT_FILE, SERVER_PRIVATE_KEY_FILE);
+  ASSERT_TRUE(svr.is_valid());
+  svr.set_read_timeout(1, 0);
+
+  thread t = thread([&]() { ASSERT_TRUE(svr.listen(HOST, PORT)); });
+  auto se = detail::scope_exit([&] {
+    svr.stop();
+    t.join();
+    ASSERT_FALSE(svr.is_running());
+  });
+
+  svr.wait_until_ready();
+
+  // The start of a TLS record, then the rest of it a byte every 100 ms, which
+  // keeps each wait well within the read timeout. The server gives up a
+  // second in, so the bytes sent after that fail.
+  std::vector<std::string> parts{std::string("\x16\x03\x01\x00\xff", 5)};
+  parts.resize(26, std::string(1, '\0'));
+  EXPECT_FALSE(send_request_in_parts(5, parts));
+}
+#endif
+
 TEST(ServerRequestParsingTest, TrimWhitespaceFromHeaderValues) {
   Server svr;
   std::string header_value;