test(app/webrtc): M3 unit tests for error matrix + Register + CORS

Covers each new code path that the design's §6 table requires:
- Subscribe -> 406 on non-H264 / non-Opus offer (TestHandler_Subscribe_406OnCodecMismatch)
- Subscribe -> 503 when total cap exhausted (TestHandler_Subscribe_503OnTotalCap)
- Subscribe -> 503 when per-stream cap exhausted (TestHandler_Subscribe_503OnPerStreamCap)
- Trickle -> 404 on unknown resource (TestHandler_Trickle_404WhenUnknown)
- preflight -> 204 + CORS headers (TestHandler_PreflightCORS)
- Register installs all 5 routes (TestHandler_RegisterMountsAllRoutes)
- Close drains the index without panicking (TestHandler_Close_DrainsPeers)
- requireH264AndOpus table-driven (TestRequireH264AndOpus)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/webrtc/handler_m3_test.go

@@ -0,0 +1,251 @@
+package webrtc
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync/atomic"
+	"testing"
+
+	"github.com/labstack/echo/v4"
+
+	corewebrtc "github.com/datarhei/core/v16/core/webrtc"
+)
+
+// minimalH264OpusOffer returns an SDP offer that includes both H264
+// and Opus rtpmap lines — passes requireH264AndOpus but is otherwise
+// nonsense, so CreatePeerFromSources will fail downstream when this
+// is wired through. Use it only in tests that don't reach the
+// PeerConnection path.
+func minimalH264OpusOffer() string {
+	return "v=0\r\n" +
+		"o=- 0 0 IN IP4 0.0.0.0\r\ns=-\r\nt=0 0\r\n" +
+		"m=video 9 UDP/TLS/RTP/SAVPF 102\r\n" +
+		"a=rtpmap:102 H264/90000\r\n" +
+		"m=audio 9 UDP/TLS/RTP/SAVPF 111\r\n" +
+		"a=rtpmap:111 opus/48000/2\r\n"
+}
+
+// nonH264Offer is missing H264 entirely. Triggers requireH264AndOpus.
+func nonH264Offer() string {
+	return "v=0\r\n" +
+		"m=video 9 UDP/TLS/RTP/SAVPF 96\r\n" +
+		"a=rtpmap:96 VP8/90000\r\n" +
+		"m=audio 9 UDP/TLS/RTP/SAVPF 111\r\n" +
+		"a=rtpmap:111 opus/48000/2\r\n"
+}
+
+// TestHandler_Subscribe_406OnCodecMismatch verifies an offer that
+// doesn't include H264 yields 406, per the design's error matrix.
+func TestHandler_Subscribe_406OnCodecMismatch(t *testing.T) {
+	sub := newTestSubsystem(t)
+	sub.mu.Lock()
+	sub.streams["s"] = &processStream{id: "s"}
+	sub.mu.Unlock()
+	h := NewHandler(sub, 0)
+
+	e := echo.New()
+	req := httptest.NewRequest(http.MethodPost, "/whep/s", strings.NewReader(nonH264Offer()))
+	rec := httptest.NewRecorder()
+	c := e.NewContext(req, rec)
+	c.SetParamNames("id")
+	c.SetParamValues("s")
+
+	if err := h.Subscribe(c); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+	if rec.Code != http.StatusNotAcceptable {
+		t.Fatalf("expected 406, got %d: %s", rec.Code, rec.Body.String())
+	}
+	if !strings.Contains(rec.Body.String(), "H264") {
+		t.Errorf("body should mention missing codec: %q", rec.Body.String())
+	}
+}
+
+// TestHandler_Subscribe_503OnTotalCap simulates the total cap being
+// exhausted by another subscriber. We don't actually create real peers
+// (would need a real PeerConnection); instead we pre-load the atomic
+// counter so the cap check fires.
+func TestHandler_Subscribe_503OnTotalCap(t *testing.T) {
+	sub := newTestSubsystem(t)
+	sub.mu.Lock()
+	sub.streams["s"] = &processStream{id: "s"}
+	sub.mu.Unlock()
+	h := NewHandlerWithCaps(sub, 1, 100)
+	atomic.StoreInt64(&h.count, 1) // simulate one in-flight peer
+
+	e := echo.New()
+	req := httptest.NewRequest(http.MethodPost, "/whep/s", strings.NewReader(minimalH264OpusOffer()))
+	rec := httptest.NewRecorder()
+	c := e.NewContext(req, rec)
+	c.SetParamNames("id")
+	c.SetParamValues("s")
+	_ = h.Subscribe(c)
+	if rec.Code != http.StatusServiceUnavailable {
+		t.Fatalf("expected 503, got %d: %s", rec.Code, rec.Body.String())
+	}
+	if !strings.Contains(rec.Body.String(), corewebrtc.ErrPeerCapReached.Error()) {
+		t.Errorf("body should mention peer cap: %q", rec.Body.String())
+	}
+}
+
+// TestHandler_Subscribe_503OnPerStreamCap simulates the per-stream cap
+// being exhausted. Same trick as above but populating the per-stream
+// index directly.
+func TestHandler_Subscribe_503OnPerStreamCap(t *testing.T) {
+	sub := newTestSubsystem(t)
+	sub.mu.Lock()
+	sub.streams["s"] = &processStream{id: "s"}
+	sub.mu.Unlock()
+	h := NewHandlerWithCaps(sub, 100, 1)
+	// Drop a placeholder peer into the per-stream bucket so the cap
+	// arithmetic trips on the next subscribe.
+	h.mu.Lock()
+	h.peersByStream["s"] = map[string]*corewebrtc.Peer{"existing": nil}
+	h.mu.Unlock()
+
+	e := echo.New()
+	req := httptest.NewRequest(http.MethodPost, "/whep/s", strings.NewReader(minimalH264OpusOffer()))
+	rec := httptest.NewRecorder()
+	c := e.NewContext(req, rec)
+	c.SetParamNames("id")
+	c.SetParamValues("s")
+	_ = h.Subscribe(c)
+	if rec.Code != http.StatusServiceUnavailable {
+		t.Fatalf("expected 503, got %d: %s", rec.Code, rec.Body.String())
+	}
+	if !strings.Contains(rec.Body.String(), "per-stream") {
+		t.Errorf("body should mention per-stream cap: %q", rec.Body.String())
+	}
+}
+
+// TestHandler_Trickle_404WhenUnknown verifies a PATCH for an unknown
+// resource returns 404 (we still treat the resource as authoritative
+// here; only DELETE is idempotent per spec).
+func TestHandler_Trickle_404WhenUnknown(t *testing.T) {
+	h := NewHandler(newTestSubsystem(t), 0)
+
+	e := echo.New()
+	req := httptest.NewRequest(http.MethodPatch, "/whep/id/unknown", strings.NewReader(""))
+	rec := httptest.NewRecorder()
+	c := e.NewContext(req, rec)
+	c.SetParamNames("id", "resource")
+	c.SetParamValues("id", "unknown")
+
+	if err := h.Trickle(c); err != nil {
+		t.Fatalf("Trickle: %v", err)
+	}
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("expected 404, got %d", rec.Code)
+	}
+}
+
+// TestHandler_PreflightCORS verifies OPTIONS returns 204 with the
+// browser-friendly CORS headers.
+func TestHandler_PreflightCORS(t *testing.T) {
+	h := NewHandler(newTestSubsystem(t), 0)
+
+	e := echo.New()
+	req := httptest.NewRequest(http.MethodOptions, "/whep/x", nil)
+	rec := httptest.NewRecorder()
+	c := e.NewContext(req, rec)
+	c.SetParamNames("id")
+	c.SetParamValues("x")
+
+	if err := h.preflight(c); err != nil {
+		t.Fatalf("preflight: %v", err)
+	}
+	if rec.Code != http.StatusNoContent {
+		t.Fatalf("expected 204, got %d", rec.Code)
+	}
+	hh := rec.Header()
+	for _, k := range []string{
+		"Access-Control-Allow-Origin",
+		"Access-Control-Allow-Methods",
+		"Access-Control-Allow-Headers",
+		"Access-Control-Expose-Headers",
+	} {
+		if hh.Get(k) == "" {
+			t.Errorf("missing CORS header %q", k)
+		}
+	}
+}
+
+// TestHandler_RegisterMountsAllRoutes is a sanity check that
+// Handler.Register installs OPTIONS / POST / DELETE / PATCH on the
+// expected paths. Echo's Group has no public route enumerator, so we
+// dispatch synthetic requests and assert the right methods are
+// reachable.
+func TestHandler_RegisterMountsAllRoutes(t *testing.T) {
+	h := NewHandler(newTestSubsystem(t), 0)
+	e := echo.New()
+	g := e.Group("")
+	h.Register(g)
+
+	cases := []struct {
+		method, path string
+		want         int
+	}{
+		{http.MethodOptions, "/whep/foo", http.StatusNoContent},
+		{http.MethodOptions, "/whep/foo/bar", http.StatusNoContent},
+		{http.MethodPost, "/whep/foo", http.StatusNotFound}, // stream missing -> 404
+		{http.MethodDelete, "/whep/foo/bar", http.StatusNoContent},
+		{http.MethodPatch, "/whep/foo/bar", http.StatusNotFound},
+	}
+	for _, tc := range cases {
+		req := httptest.NewRequest(tc.method, tc.path, strings.NewReader(""))
+		rec := httptest.NewRecorder()
+		e.ServeHTTP(rec, req)
+		if rec.Code != tc.want {
+			t.Errorf("%s %s: got %d want %d (%s)", tc.method, tc.path, rec.Code, tc.want, rec.Body.String())
+		}
+	}
+}
+
+// TestHandler_Close_DrainsPeers seeds a fake peer into the index and
+// verifies Close clears it without panicking.
+func TestHandler_Close_DrainsPeers(t *testing.T) {
+	h := NewHandler(newTestSubsystem(t), 0)
+	h.mu.Lock()
+	h.peersByStream["s"] = map[string]*corewebrtc.Peer{"r1": nil}
+	h.peerStream["r1"] = "s"
+	atomic.StoreInt64(&h.count, 1)
+	h.mu.Unlock()
+
+	h.Close()
+	if got := atomic.LoadInt64(&h.count); got != 0 {
+		t.Errorf("count after Close = %d, want 0", got)
+	}
+	h.mu.Lock()
+	if len(h.peersByStream) != 0 || len(h.peerStream) != 0 {
+		t.Errorf("indexes not cleared")
+	}
+	h.mu.Unlock()
+}
+
+// TestRequireH264AndOpus covers the SDP scanner's positive +
+// negative cases.
+func TestRequireH264AndOpus(t *testing.T) {
+	cases := []struct {
+		name string
+		sdp  string
+		ok   bool
+	}{
+		{"both", minimalH264OpusOffer(), true},
+		{"missing h264", nonH264Offer(), false},
+		{"missing opus", "m=video 9 UDP/TLS/RTP/SAVPF 102\r\na=rtpmap:102 H264/90000\r\n", false},
+		{"capitalized", "a=rtpmap:111 OPUS/48000\r\na=rtpmap:102 H264/90000", true},
+		{"empty", "", false},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			err := requireH264AndOpus(c.sdp)
+			if c.ok && err != nil {
+				t.Errorf("expected ok, got %v", err)
+			}
+			if !c.ok && err == nil {
+				t.Errorf("expected error")
+			}
+		})
+	}
+}