Fix llhttp_get_error_pos usage

It returns NULL if return value is HPE_OK.

src/h2load_http1_session.cc

@@ -203,8 +203,11 @@ int Http1Session::submit_request() {
 int Http1Session::on_read(const uint8_t *data, size_t len) {
   auto htperr =
       llhttp_execute(&htp_, reinterpret_cast<const char *>(data), len);
-  auto nread = static_cast<size_t>(
-      reinterpret_cast<const uint8_t *>(llhttp_get_error_pos(&htp_)) - data);
+  auto nread = htperr == HPE_OK
+                   ? len
+                   : static_cast<size_t>(reinterpret_cast<const uint8_t *>(
+                                             llhttp_get_error_pos(&htp_)) -
+                                         data);
 
   if (client_->worker->config->verbose) {
     std::cout.write(reinterpret_cast<const char *>(data), nread);

src/nghttp.cc

@@ -1035,9 +1035,11 @@ int HttpClient::on_upgrade_read(const uint8_t *data, size_t len) {
 
   auto htperr =
       llhttp_execute(htp.get(), reinterpret_cast<const char *>(data), len);
-  auto nread = static_cast<size_t>(
-      reinterpret_cast<const uint8_t *>(llhttp_get_error_pos(htp.get())) -
-      data);
+  auto nread = htperr == HPE_OK
+                   ? len
+                   : static_cast<size_t>(reinterpret_cast<const uint8_t *>(
+                                             llhttp_get_error_pos(htp.get())) -
+                                         data);
 
   if (config.verbose) {
     std::cout.write(reinterpret_cast<const char *>(data), nread);

src/shrpx_http_downstream_connection.cc

@@ -1402,9 +1402,12 @@ int HttpDownstreamConnection::process_input(const uint8_t *data,
 
   auto htperr = llhttp_execute(&response_htp_,
                                reinterpret_cast<const char *>(data), datalen);
-  auto nproc = static_cast<size_t>(
-      reinterpret_cast<const uint8_t *>(llhttp_get_error_pos(&response_htp_)) -
-      data);
+  auto nproc =
+      htperr == HPE_OK
+          ? datalen
+          : static_cast<size_t>(reinterpret_cast<const uint8_t *>(
+                                    llhttp_get_error_pos(&response_htp_)) -
+                                data);
 
   if (htperr != HPE_OK &&
       (!downstream_->get_upgraded() || htperr != HPE_PAUSED_UPGRADE)) {

src/shrpx_https_upstream.cc

@@ -629,8 +629,11 @@ int HttpsUpstream::on_read() {
   auto htperr = llhttp_execute(&htp_, reinterpret_cast<const char *>(rb->pos()),
                                rb->rleft());
 
-  auto nread = reinterpret_cast<const uint8_t *>(llhttp_get_error_pos(&htp_)) -
-               rb->pos();
+  auto nread =
+      htperr == HPE_OK
+          ? rb->rleft()
+          : reinterpret_cast<const uint8_t *>(llhttp_get_error_pos(&htp_)) -
+                rb->pos();
   rb->drain(nread);
   rlimit->startw();