Keep unknown BBR bandwidth from imposing a one-byte pacing stall

src/transport_layer/etcp_bbr.c

@@ -723,6 +723,7 @@ static void bbr_init_pacing_rate_from_rtt(struct bbr* bbr, uint32_t mss, uint32_
 
 static void bbr_set_pacing_rate(struct bbr* bbr, uint32_t bw, int gain, uint32_t* pacing_rate_out)
 {
+    if (!bw) return; // Нет измерения полосы: сохраняем начальное состояние/ставку от достоверного RTT.
     uint32_t rate = bbr_bw_to_pacing_rate(bw, gain);
 
     if (bbr->full_bw_reached || rate > *pacing_rate_out)

tests/test_etcp_bbr.c

@@ -358,9 +358,12 @@ static int test_initial_pacing(void) {
     const uint32_t sizes[] = {576, 1400}, rtts[] = {20000, 200000};
     for (unsigned i = 0; i < 2; i++) for (unsigned j = 0; j < 2; j++) {
         struct bbr s = { .now_tb = 10000 }; bbr_init(&s);
-        uint32_t cwnd = 4 * sizes[i], pacing = 123;
+        uint32_t cwnd = 4 * sizes[i], pacing = 0;
         struct bbr_rate_sample rs = { .acked_sacked = 16, .delivered = 16, .is_app_limited = 1 };
         bbr_main(&s, &rs, &cwnd, &pacing, sizes[i], 0, 0);
+        if (s.has_seen_rtt || pacing) FAIL("unknown RTT and rate must not fabricate a 1B/s pacing stall");
+        pacing = 123;
+        bbr_main(&s, &rs, &cwnd, &pacing, sizes[i], 0, 0);
         if (s.has_seen_rtt || pacing != 123) FAIL("unknown RTT must not seed pacing with a guessed duration");
         rs.rtt_us = rs.interval_us = rtts[j]; s.now_tb += rtts[j] / 100;
         bbr_main(&s, &rs, &cwnd, &pacing, sizes[i], 0, 0);

tests/test_etcp_stcp.c

@@ -6,6 +6,7 @@
 #include "etcp_api.h"
 #include "etcp_connections.h"
 #include "etcp_session.h"
+#include "etcp_bbr.h"
 #include "node_conn_direct.h"
 #include "topo_group.h"
 #include "topo_node.h"
@@ -188,6 +189,22 @@ static void exchange_messages(void) {
         }
         if (drained) break;
     }
+    if (failed || endpoints[0].received != FULL_MASK || endpoints[1].received != FULL_MASK) {
+        for (int i = 0; i < 2; i++) {
+            struct ETCP_CONN* conn = endpoints[i].conn;
+            DEBUG_ERROR(DEBUG_CATEGORY_GENERAL, "Delivery stalled: side=%d phase=%u mask=%04x expected=%04x tx=%u till=%u "
+                "need=%u send=%d wait=%d receive=%d input=%d unacked=%u", i, phase, endpoints[i].received, FULL_MASK,
+                conn->next_tx_id, conn->rx_ack_till, conn->last_delivered_id + 1, conn->input_send_q->count,
+                conn->input_wait_ack->count, conn->recv_q->count, conn->input_queue->count, conn->unacked_bytes);
+            for (struct ETCP_LINK* link = conn->links; link; link = link->next)
+                DEBUG_ERROR(DEBUG_CATEGORY_GENERAL, "Delivery path: side=%d link=%u UP=%u rate=%u shaper=%d deadline=%llu now=%llu "
+                    "flight=%u/%u RTT_tb=%u BBR_mode=%u BBR_RTT_us=%u delivered=%llu model_delivered=%u", i,
+                    link->local_link_id, link->link_status, link->bbr_pacing_rate, link->shaper_timer != NULL,
+                    (unsigned long long)link->shaper_load_time_tb, (unsigned long long)get_time_tb(), link->inflight_bytes,
+                    link->inflight_lim_bytes, link->rtt_last, link->bbr->mode, link->bbr->min_rtt_us,
+                    (unsigned long long)link->delivered_bytes, link->bbr->delivered);
+        }
+    }
     CHECK(!failed && endpoints[0].received == FULL_MASK && endpoints[1].received == FULL_MASK);
     for (int i = 0; i < 2; i++) CHECK(!endpoints[i].conn->input_wait_ack->count && !endpoints[i].conn->input_send_q->count);
 }