Support SVG sources (closes #68)

The fetcher accepts image/svg+xml; internal/magic detects SVG. orig of
an SVG at the orig size is the SVG unchanged, cached, with a
Content-Security-Policy allowing only its styles and data: images; at
another size, ErrSVGNotOriginalSize (400). Any other format renders it
at the least size covering the output, at most 8192 on a side.
Rendering refuses an SVG with a side over 8192 times the other
(ErrSVGTooThin, 415), and the orig size of one above 8192 on a side
(ErrSVGTooLargeForOrigSize, 400). Child processes of pixad read an
SVG's size and render it, killed after 20 seconds and limited to 1 GiB;
any failure there is ErrSVGRenderFailed (415). Tests pinning the SVG
refusal now expect SVG.

Model: opus-5-5

internal/handlers/unsupported_source_internal_test.go

@@ -15,7 +15,7 @@ import (
 
 // TestUnsupportedSourceFormatAnswers415 checks that respondImageError, which
 // answers the errors of both image routes, answers 415 with a clear error when
-// the upstream answers with a content type pixa does not accept, such as SVG,
+// the upstream answers with a content type pixa does not accept, such as TIFF,
 // and when libvips does not read a source as the format its first bytes
 // show, wrapped as the service wraps them.
 func TestUnsupportedSourceFormatAnswers415(t *testing.T) {
@@ -23,11 +23,11 @@ func TestUnsupportedSourceFormatAnswers415(t *testing.T) {
 
 	h := &Handlers{log: slog.New(slog.DiscardHandler)}
 	req := &imagerequest.Request{
-		Source: imagerequest.Source{Host: "img.example.com", Path: "/a.svg"},
+		Source: imagerequest.Source{Host: "img.example.com", Path: "/a.tiff"},
 	}
 
 	for _, err := range []error{
-		fmt.Errorf("upstream fetch failed: %w: image/svg+xml",
+		fmt.Errorf("upstream fetch failed: %w: image/tiff",
 			httpfetcher.ErrInvalidContentType),
 		fmt.Errorf("image processing failed: %w: libvips does not read the input as avif",
 			imageprocessor.ErrUnsupportedInputFormat),
@@ -47,3 +47,67 @@ func TestUnsupportedSourceFormatAnswers415(t *testing.T) {
 		}
 	}
 }
+
+// TestSVGTooThinAnswers415 checks that respondImageError answers 415 with a
+// clear error for an SVG source too thin to render, wrapped as the service
+// wraps it.
+func TestSVGTooThinAnswers415(t *testing.T) {
+	t.Parallel()
+
+	h := &Handlers{log: slog.New(slog.DiscardHandler)}
+	req := &imagerequest.Request{
+		Source: imagerequest.Source{Host: "svg.example.com", Path: "/a.svg"},
+	}
+	err := fmt.Errorf("image processing failed: %w: 81930x10",
+		imageprocessor.ErrSVGTooThin)
+
+	rec := httptest.NewRecorder()
+	h.respondImageError(rec, req, err)
+	t.Logf("for %v: %d %s", err, rec.Code, rec.Body.String())
+
+	if rec.Code != http.StatusUnsupportedMediaType {
+		t.Errorf("status = %d, want %d", rec.Code,
+			http.StatusUnsupportedMediaType)
+	}
+
+	if !strings.Contains(rec.Body.String(), "SVG source too thin to render") {
+		t.Errorf("body = %q, want the SVG too thin error", rec.Body.String())
+	}
+}
+
+// TestSVGRenderFailedAnswers415 checks that respondImageError answers 415,
+// naming the limits, for an SVG source that a child process could not read
+// or render, wrapped as the service wraps it.
+func TestSVGRenderFailedAnswers415(t *testing.T) {
+	t.Parallel()
+
+	h := &Handlers{log: slog.New(slog.DiscardHandler)}
+	err := fmt.Errorf("image processing failed: %w: it took more than 20s",
+		imageprocessor.ErrSVGRenderFailed)
+
+	rec := httptest.NewRecorder()
+	h.respondImageError(rec, &imagerequest.Request{}, err)
+	t.Logf("for %v: %d %s", err, rec.Code, rec.Body.String())
+
+	checkErrorBody(t, rec, http.StatusUnsupportedMediaType,
+		"SVG source could not be rendered: it is not valid, or it takes more "+
+			"than 20 seconds or 1 GiB of memory to render")
+}
+
+// TestSVGTooLargeForOrigSizeAnswers400 checks that respondImageError answers
+// 400, asking for a size, for an SVG source above 8192 on a side asked for at
+// the orig size in a raster format, wrapped as the service wraps it.
+func TestSVGTooLargeForOrigSizeAnswers400(t *testing.T) {
+	t.Parallel()
+
+	h := &Handlers{log: slog.New(slog.DiscardHandler)}
+	err := fmt.Errorf("image processing failed: %w: 10000x10 is above 8192",
+		imageprocessor.ErrSVGTooLargeForOrigSize)
+
+	rec := httptest.NewRecorder()
+	h.respondImageError(rec, &imagerequest.Request{}, err)
+	t.Logf("for %v: %d %s", err, rec.Code, rec.Body.String())
+
+	checkErrorBody(t, rec, http.StatusBadRequest,
+		"SVG source above 8192 on a side: give a size to render it at")
+}