Test that an SVG source and orig of an unnamed input are refused

Failing tests, ahead of the fix: an upstream answering image/svg+xml is
answered 415 on the image route, also for orig; both image routes answer
415 for an unaccepted upstream content type and for orig of an input the
processor cannot name; and the processor refuses orig of a TIFF instead
of saving it as JPEG.

Model: opus-5-5

internal/server/svg_internal_test.go

@@ -0,0 +1,41 @@
+package server
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// TestImageProxyRefusesSVG requests an image the upstream answers as SVG,
+// in its own format (orig) and resized as PNG, through pixa's router,
+// upstream fetcher and image processor. pixa does not accept SVG as a
+// source, so each request is answered 415, never with an image.
+func TestImageProxyRefusesSVG(t *testing.T) {
+	t.Parallel()
+
+	upstream := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "image/svg+xml")
+			_, _ = io.WriteString(w, `<svg xmlns="http://www.w3.org/2000/svg" `+
+				`width="64" height="48"><rect width="64" height="48"/></svg>`)
+		}))
+	t.Cleanup(upstream.Close)
+
+	s, _, _ := startImageProxy(t, upstream)
+
+	for _, sizeFormat := range []string{"64x48.orig", "32x24.png"} {
+		target := "/v1/image/" + upstreamHost + "/drawing.svg/" + sizeFormat
+
+		rec := httptest.NewRecorder()
+		s.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, target, nil))
+		t.Logf("GET %s: %d, Content-Type %s, body %s",
+			target, rec.Code, rec.Header().Get("Content-Type"), rec.Body.String())
+
+		if rec.Code != http.StatusUnsupportedMediaType {
+			t.Errorf("GET %s status = %d, want %d",
+				target, rec.Code, http.StatusUnsupportedMediaType)
+		}
+	}
+}