perf(cmpp): reserve transport for inbound submit

gateway/internal/inbound/http_client_test.go

@@ -1,7 +1,10 @@
 package inbound
 
 import (
+	"io"
+	"net"
 	"net/http"
+	"strings"
 	"testing"
 )
 
@@ -26,3 +29,32 @@ func TestNewAPIHTTPClientUsesSafeDefault(t *testing.T) {
 		t.Fatalf("expected default max connections 64, got %d", transport.MaxConnsPerHost)
 	}
 }
+
+func TestSubmitUsesDedicatedHTTPClient(t *testing.T) {
+	background := &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
+		t.Fatal("background client must not carry inbound Submit")
+		return nil, nil
+	})}
+	submit := &http.Client{Transport: roundTripFunc(func(request *http.Request) (*http.Response, error) {
+		if request.URL.Path != "/api/gateway/events/inbound/submit" {
+			t.Fatalf("unexpected submit path %s", request.URL.Path)
+		}
+		return &http.Response{
+			StatusCode: http.StatusCreated,
+			Status:     "201 Created",
+			Header:     make(http.Header),
+			Body:       io.NopCloser(strings.NewReader(`{"accepted":true,"messageId":"MSG-1"}`)),
+		}, nil
+	})}
+	server := Server{APIBaseURL: "http://api.test/api", HTTPClient: background, SubmitHTTPClient: submit}
+	result, err := server.submit(&net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 12000}, submitRequest{Account: "test"})
+	if err != nil || !result.Accepted {
+		t.Fatalf("expected dedicated submit success, result=%+v err=%v", result, err)
+	}
+}
+
+type roundTripFunc func(*http.Request) (*http.Response, error)
+
+func (fn roundTripFunc) RoundTrip(request *http.Request) (*http.Response, error) {
+	return fn(request)
+}

gateway/internal/inbound/server.go

@@ -15,6 +15,7 @@ type Server struct {
 	APIBaseURL           string
 	SecurityEventToken   string
 	HTTPClient           *http.Client
+	SubmitHTTPClient     *http.Client
 	LogWriter            io.Writer
 	PendingFlushInterval time.Duration
 	PresenceStore        PresenceStore

gateway/internal/inbound/submit.go

@@ -290,7 +290,13 @@ func setInboundSubmitResponse(packet any, messageID uint64, result uint32) {
 func (s Server) submit(remote net.Addr, payload submitRequest) (submitResponse, error) {
 	payload.RemoteIP = remoteIP(remote)
 	var result submitResponse
-	err := s.post(context.Background(), "/gateway/events/inbound/submit", payload, &result)
+	client := s.SubmitHTTPClient
+	if client == nil {
+		client = s.HTTPClient
+	}
+	// Submit has a dedicated transport so protocol logs, receipt recovery and
+	// presence traffic cannot occupy the connections needed for SubmitResp.
+	err := s.postWithClient(context.Background(), client, "/gateway/events/inbound/submit", payload, &result)
 	return result, err
 }
 

gateway/internal/inbound/transport.go

@@ -15,7 +15,10 @@ import (
 const maxAPIResponseBodyBytes int64 = 4 * 1024 * 1024
 
 func (s Server) post(ctx context.Context, path string, payload any, result any) error {
-	client := s.HTTPClient
+	return s.postWithClient(ctx, s.HTTPClient, path, payload, result)
+}
+
+func (s Server) postWithClient(ctx context.Context, client *http.Client, path string, payload any, result any) error {
 	if client == nil {
 		client = &http.Client{Timeout: defaultHTTPTimeout}
 	}