perf: expand gateway capacity and prevent receipt replay

gateway/internal/upstream/pool_test.go

@@ -2,7 +2,9 @@ package upstream
 
 import (
 	"context"
+	cmpp "github.com/bigwhite/gocmpp"
 	"testing"
+	"time"
 
 	"cmpp-platform/gateway/internal/queue"
 )
@@ -10,8 +12,8 @@ import (
 func TestConnectionPoolAcquiresAcrossConnections(t *testing.T) {
 	pool := &connectionPool{
 		conns: []*connection{
-			{window: make(chan struct{}, 1)},
-			{window: make(chan struct{}, 1)},
+			{client: &cmpp.Client{}, window: make(chan struct{}, 64), windowLimit: 1},
+			{client: &cmpp.Client{}, window: make(chan struct{}, 64), windowLimit: 1},
 		},
 	}
 
@@ -40,6 +42,51 @@ func TestConnectionPoolAcquiresAcrossConnections(t *testing.T) {
 	releaseSecond()
 }
 
+func TestPoolContinuesOnHealthyConnectionWhenPeerIsDraining(t *testing.T) {
+	draining := &connection{client: &cmpp.Client{}, window: make(chan struct{}, 64), windowLimit: 16, draining: true}
+	healthy := &connection{client: &cmpp.Client{}, window: make(chan struct{}, 64), windowLimit: 16}
+	pool := &connectionPool{conns: []*connection{draining, healthy}}
+	selected, release := pool.tryAcquireConnection()
+	if selected != healthy {
+		t.Fatal("expected healthy peer connection")
+	}
+	release()
+}
+
+func TestRuntimeCapacityMatrixAndSmoothScaleDown(t *testing.T) {
+	for _, connections := range []int{1, 2, 4, 8} {
+		for _, window := range []int{1, 16, 32, 64} {
+			config := normalizeUpstreamConfig(queue.UpstreamConfig{GatewayHost: "127.0.0.1", GatewayPort: 17890, Account: "a", PasswordCipher: "p", CMPPVersion: "3.0", DesiredConnections: connections, WindowSize: window})
+			if config.DesiredConnections != connections || config.WindowSize != window {
+				t.Fatalf("matrix normalized incorrectly: %+v", config)
+			}
+		}
+	}
+	pool := &connectionPool{channelID: "channel-1", connectionID: "primary", config: normalizeUpstreamConfig(queue.UpstreamConfig{DesiredConnections: 2, WindowSize: 16, ConnectionDrainSeconds: 1}), stopCh: make(chan struct{}), reconnectSignal: make(chan struct{}, 1)}
+	pool.conns = []*connection{{pool: pool, window: make(chan struct{}, 64), windowLimit: 16}, {pool: pool, window: make(chan struct{}, 64), windowLimit: 16}}
+	pool.reconfigure(queue.UpstreamConfig{DesiredConnections: 1, WindowSize: 32, ConnectionDrainSeconds: 1})
+	deadline := time.Now().Add(time.Second)
+	for {
+		pool.mu.Lock()
+		count := len(pool.conns)
+		first := pool.conns[0]
+		pool.mu.Unlock()
+		if count == 1 {
+			first.mu.Lock()
+			limit := first.windowLimit
+			first.mu.Unlock()
+			if limit != 32 {
+				t.Fatalf("window limit=%d want32", limit)
+			}
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("scale down did not complete")
+		}
+		time.Sleep(time.Millisecond)
+	}
+}
+
 func TestManagerDisconnectChannelRemovesPoolAndStopsReconnects(t *testing.T) {
 	pool := &connectionPool{
 		channelID:       "channel-1",