From 29ae3264f32a8a36fc9b56374d76652119e5306a Mon Sep 17 00:00:00 2001
From: Sergei Gunchenko <26045362+sxgunchenko@users.noreply.github.com>
Date: Fri, 7 May 2021 15:22:16 +0300
Subject: [PATCH] Provide a possibility to confirm SETTINGS frames manually

---
 lib/includes/nghttp2/nghttp2.h | 43 ++++++++++++++++++++++++++++------
 lib/nghttp2_option.c           |  5 ++++
 lib/nghttp2_option.h           |  5 ++++
 lib/nghttp2_session.c          |  7 +++++-
 lib/nghttp2_session.h          |  3 ++-
 lib/nghttp2_submit.c           |  6 +++--
 6 files changed, 58 insertions(+), 11 deletions(-)

diff --git a/lib/includes/nghttp2/nghttp2.h b/lib/includes/nghttp2/nghttp2.h
index edc0defc..7501d285 100644
--- a/lib/includes/nghttp2/nghttp2.h
+++ b/lib/includes/nghttp2/nghttp2.h
@@ -2719,6 +2719,19 @@ NGHTTP2_EXTERN void nghttp2_option_set_max_outbound_ack(nghttp2_option *option,
 NGHTTP2_EXTERN void nghttp2_option_set_max_settings(nghttp2_option *option,
                                                     size_t val);
 
+/**
+ * @function
+ *
+ * This option prevents the library from sending empty SETTINGS frame with ACK
+ * flag set automatically when SETTINGS frame is received.
+ * If this option is set to nonzero, the library won't send empty
+ * SETTINGS frame with ACK flag set in the response for incoming SETTINGS
+ * frame.  The application can send SETTINGS frame with ACK flag set using
+ * `nghttp2_submit_settings()` with :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK`
+ * as flags parameter.
+ */
+NGHTTP2_EXTERN void nghttp2_option_set_no_auto_settings_ack(nghttp2_option *option, int val);
+
 /**
  * @function
  *
@@ -4228,8 +4241,21 @@ NGHTTP2_EXTERN int nghttp2_submit_rst_stream(nghttp2_session *session,
  * pointer to the array of :type:`nghttp2_settings_entry`.  The |niv|
  * indicates the number of :type:`nghttp2_settings_entry`.
  *
- * The |flags| is currently ignored and should be
- * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.
+ * The |flags| must be one of the following values:
+ *
+ * * :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`
+ * * :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK`
+ *
+ * Unless `nghttp2_option_set_no_auto_settings_ack()` is used, the |flags|
+ * should be :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE` and
+ * SETTINGS with :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK` is
+ * automatically submitted by the library and application could not
+ * send it at its will.
+ *
+ * Otherwise the application must confirm the received settings by
+ * calling `nghttp2_submit_settings` with the flags set to
+ * :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK` and empty settings
+ * (e.g. the |niv| must be 0).
  *
  * This function does not take ownership of the |iv|.  This function
  * copies all the elements in the |iv|.
@@ -4238,16 +4264,19 @@ NGHTTP2_EXTERN int nghttp2_submit_rst_stream(nghttp2_session *session,
  * size becomes strictly larger than NGHTTP2_MAX_WINDOW_SIZE,
  * RST_STREAM is issued against such a stream.
  *
- * SETTINGS with :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK` is
- * automatically submitted by the library and application could not
- * send it at its will.
- *
  * This function returns 0 if it succeeds, or one of the following
  * negative error codes:
  *
  * :enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
  *     The |iv| contains invalid value (e.g., initial window size
- *     strictly greater than (1 << 31) - 1.
+ *     strictly greater than (1 << 31) - 1;
+ *     or the |flags| is set to :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK`
+ *     but the manual SETTINGS confirmation was not configured with
+ *     `nghttp2_option_set_no_auto_settings_ack()`;
+ *     or the |flags| is set to :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK`
+ *     and the |niv| is non-zero;
+ *     or the |flags| is neither :enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`
+ *     nor :enum:`nghttp2_flag.NGHTTP2_FLAG_ACK`.
  * :enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
  *     Out of memory.
  */
diff --git a/lib/nghttp2_option.c b/lib/nghttp2_option.c
index 34348e66..19a48eee 100644
--- a/lib/nghttp2_option.c
+++ b/lib/nghttp2_option.c
@@ -126,3 +126,8 @@ void nghttp2_option_set_max_settings(nghttp2_option *option, size_t val) {
   option->opt_set_mask |= NGHTTP2_OPT_MAX_SETTINGS;
   option->max_settings = val;
 }
+
+void nghttp2_option_set_no_auto_settings_ack(nghttp2_option *option, int val) {
+    option->opt_set_mask |= NGHTTP2_OPT_NO_AUTO_SETTINGS_ACK;
+    option->no_auto_settings_ack = val;
+}
diff --git a/lib/nghttp2_option.h b/lib/nghttp2_option.h
index 939729fd..b2668e80 100644
--- a/lib/nghttp2_option.h
+++ b/lib/nghttp2_option.h
@@ -68,6 +68,7 @@ typedef enum {
   NGHTTP2_OPT_NO_CLOSED_STREAMS = 1 << 10,
   NGHTTP2_OPT_MAX_OUTBOUND_ACK = 1 << 11,
   NGHTTP2_OPT_MAX_SETTINGS = 1 << 12,
+  NGHTTP2_OPT_NO_AUTO_SETTINGS_ACK = 1 << 13,
 } nghttp2_option_flag;
 
 /**
@@ -131,6 +132,10 @@ struct nghttp2_option {
    * NGHTTP2_OPT_USER_RECV_EXT_TYPES
    */
   uint8_t user_recv_ext_types[32];
+  /**
+   * NGHTTP2_OPT_NO_AUTO_SETTINGS_ACK
+   */
+  int no_auto_settings_ack;
 };
 
 #endif /* NGHTTP2_OPTION_H */
diff --git a/lib/nghttp2_session.c b/lib/nghttp2_session.c
index 2e7e907f..736e3efb 100644
--- a/lib/nghttp2_session.c
+++ b/lib/nghttp2_session.c
@@ -527,6 +527,11 @@ static int session_new(nghttp2_session **session_ptr,
         option->max_settings) {
       (*session_ptr)->max_settings = option->max_settings;
     }
+
+    if ((option->opt_set_mask & NGHTTP2_OPT_NO_AUTO_SETTINGS_ACK) &&
+        option->no_auto_settings_ack) {
+      (*session_ptr)->opt_flags |= NGHTTP2_OPTMASK_NO_AUTO_SETTINGS_ACK;
+    }
   }
 
   rv = nghttp2_hd_deflate_init2(&(*session_ptr)->hd_deflater,
@@ -4546,7 +4551,7 @@ int nghttp2_session_on_settings_received(nghttp2_session *session,
     }
   }
 
-  if (!noack && !session_is_closing(session)) {
+  if (!(session->opt_flags & NGHTTP2_OPTMASK_NO_AUTO_SETTINGS_ACK) && !noack && !session_is_closing(session)) {
     rv = nghttp2_session_add_settings(session, NGHTTP2_FLAG_ACK, NULL, 0);
 
     if (rv != 0) {
diff --git a/lib/nghttp2_session.h b/lib/nghttp2_session.h
index 07bfbb6c..6f6e626a 100644
--- a/lib/nghttp2_session.h
+++ b/lib/nghttp2_session.h
@@ -52,7 +52,8 @@ typedef enum {
   NGHTTP2_OPTMASK_NO_RECV_CLIENT_MAGIC = 1 << 1,
   NGHTTP2_OPTMASK_NO_HTTP_MESSAGING = 1 << 2,
   NGHTTP2_OPTMASK_NO_AUTO_PING_ACK = 1 << 3,
-  NGHTTP2_OPTMASK_NO_CLOSED_STREAMS = 1 << 4
+  NGHTTP2_OPTMASK_NO_CLOSED_STREAMS = 1 << 4,
+  NGHTTP2_OPTMASK_NO_AUTO_SETTINGS_ACK = 1 << 5,
 } nghttp2_optmask;
 
 /*
diff --git a/lib/nghttp2_submit.c b/lib/nghttp2_submit.c
index 744a49cf..ea14d7da 100644
--- a/lib/nghttp2_submit.c
+++ b/lib/nghttp2_submit.c
@@ -303,8 +303,10 @@ int nghttp2_submit_shutdown_notice(nghttp2_session *session) {
 
 int nghttp2_submit_settings(nghttp2_session *session, uint8_t flags,
                             const nghttp2_settings_entry *iv, size_t niv) {
-  (void)flags;
-  return nghttp2_session_add_settings(session, NGHTTP2_FLAG_NONE, iv, niv);
+  if (flags == NGHTTP2_FLAG_ACK && !(session->opt_flags & NGHTTP2_OPTMASK_NO_AUTO_SETTINGS_ACK)) {
+    return NGHTTP2_ERR_INVALID_ARGUMENT;
+  }
+  return nghttp2_session_add_settings(session, flags, iv, niv);
 }
 
 int32_t nghttp2_submit_push_promise(nghttp2_session *session, uint8_t flags,