[PATCH 1 of 2] QUIC: update stream flow control credit on STREAM_DATA_BLOCKED

[Roman Arutyunyan]

# HG changeset patch
# User Roman Arutyunyan <arut at nginx.com>
# Date 1637133234 -10800
#      Wed Nov 17 10:13:54 2021 +0300
# Branch quic
# Node ID 4e3a7fc0533192f51a01042a1e9dd2b595881420
# Parent  4ad8fc79cb33257c928a9098a87324b350576551
QUIC: update stream flow control credit on STREAM_DATA_BLOCKED.

Previously, after receiving STREAM_DATA_BLOCKED, current flow control limit
was sent to client.  Now, if the limit can be updated to the full window size,
it is updated and the new value is sent to client, otherwise nothing is sent.

The change lets client update flow control credit on demand.  Also, it saves
traffic by not sending MAX_STREAM_DATA with the same value twice.

diff --git a/src/event/quic/ngx_event_quic_streams.c b/src/event/quic/ngx_event_quic_streams.c
--- a/src/event/quic/ngx_event_quic_streams.c
+++ b/src/event/quic/ngx_event_quic_streams.c
@@ -31,6 +31,7 @@ static size_t ngx_quic_max_stream_flow(n
 static void ngx_quic_stream_cleanup_handler(void *data);
 static ngx_int_t ngx_quic_control_flow(ngx_connection_t *c, uint64_t last);
 static ngx_int_t ngx_quic_update_flow(ngx_connection_t *c, uint64_t last);
+static ngx_int_t ngx_quic_update_max_stream_data(ngx_connection_t *c);
 
 
 ngx_connection_t *
@@ -1190,8 +1191,6 @@ ngx_int_t
 ngx_quic_handle_stream_data_blocked_frame(ngx_connection_t *c,
     ngx_quic_header_t *pkt, ngx_quic_stream_data_blocked_frame_t *f)
 {
-    uint64_t                limit;
-    ngx_quic_frame_t       *frame;
     ngx_quic_stream_t      *qs;
     ngx_quic_connection_t  *qc;
 
@@ -1217,29 +1216,10 @@ ngx_quic_handle_stream_data_blocked_fram
             return NGX_OK;
         }
 
-        limit = qs->recv_max_data;
-
-        if (ngx_quic_init_stream(qs) != NGX_OK) {
-            return NGX_ERROR;
-        }
-
-    } else {
-        limit = qs->recv_max_data;
+        return ngx_quic_init_stream(qs);
     }
 
-    frame = ngx_quic_alloc_frame(c);
-    if (frame == NULL) {
-        return NGX_ERROR;
-    }
-
-    frame->level = pkt->level;
-    frame->type = NGX_QUIC_FT_MAX_STREAM_DATA;
-    frame->u.max_stream_data.id = f->id;
-    frame->u.max_stream_data.limit = limit;
-
-    ngx_quic_queue_frame(qc, frame);
-
-    return NGX_OK;
+    return ngx_quic_update_max_stream_data(qs->connection);
 }
 
 
@@ -1587,22 +1567,9 @@ ngx_quic_update_flow(ngx_connection_t *c
     if (!rev->pending_eof && !rev->error
         && qs->recv_max_data <= qs->recv_offset + qs->recv_window / 2)
     {
-        qs->recv_max_data = qs->recv_offset + qs->recv_window;
-
-        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, c->log, 0,
-                       "quic flow update msd:%uL", qs->recv_max_data);
-
-        frame = ngx_quic_alloc_frame(pc);
-        if (frame == NULL) {
+        if (ngx_quic_update_max_stream_data(c) != NGX_OK) {
             return NGX_ERROR;
         }
-
-        frame->level = ssl_encryption_application;
-        frame->type = NGX_QUIC_FT_MAX_STREAM_DATA;
-        frame->u.max_stream_data.id = qs->id;
-        frame->u.max_stream_data.limit = qs->recv_max_data;
-
-        ngx_quic_queue_frame(qc, frame);
     }
 
     qc->streams.recv_offset += len;
@@ -1632,6 +1599,44 @@ ngx_quic_update_flow(ngx_connection_t *c
 }
 
 
+static ngx_int_t
+ngx_quic_update_max_stream_data(ngx_connection_t *c)
+{
+    uint64_t                recv_max_data;
+    ngx_quic_frame_t       *frame;
+    ngx_quic_stream_t      *qs;
+    ngx_quic_connection_t  *qc;
+
+    qs = c->quic;
+    qc = ngx_quic_get_connection(qs->parent);
+
+    recv_max_data = qs->recv_offset + qs->recv_window;
+
+    if (qs->recv_max_data == recv_max_data) {
+        return NGX_OK;
+    }
+
+    qs->recv_max_data = recv_max_data;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "quic flow update msd:%uL", qs->recv_max_data);
+
+    frame = ngx_quic_alloc_frame(c);
+    if (frame == NULL) {
+        return NGX_ERROR;
+    }
+
+    frame->level = ssl_encryption_application;
+    frame->type = NGX_QUIC_FT_MAX_STREAM_DATA;
+    frame->u.max_stream_data.id = qs->id;
+    frame->u.max_stream_data.limit = qs->recv_max_data;
+
+    ngx_quic_queue_frame(qc, frame);
+
+    return NGX_OK;
+}
+
+
 ngx_int_t
 ngx_quic_handle_read_event(ngx_event_t *rev, ngx_uint_t flags)
 {