gsk: Avoid long lines in serialized nodes

When encoding big blobs of data in base64, insert newlines.
Base64 allows it, CSS allows it, so not need to make GtkTextView
struggle with multi-megabyte lines.

Update nodeparser tests to reflect this change.

gsk/gskrendernodeparser.c

@@ -2202,10 +2202,57 @@ cairo_destroy_array (gpointer array)
   g_byte_array_free (array, TRUE);
 }
 
+static void
+append_escaping_newlines (GString    *str,
+                          const char *string)
+{
+  gsize len;
+
+  do {
+    len = strcspn (string, "\n");
+    g_string_append_len (str, string, len);
+    string += len;
+    g_string_append (str, "\\\n");
+    string++;
+  } while (*string);
+}
+
+/* like g_base64 encode, but breaks lines
+ * in CSS-compatible way
+ */
+static char *
+base64_encode_with_linebreaks (const guchar *data,
+                               gsize         len)
+{
+  gsize max;
+  char *out;
+  int state = 0, outlen;
+  int save = 0;
+
+  g_return_val_if_fail (data != NULL || len == 0, NULL);
+
+  /* We can use a smaller limit here, since we know the saved state is 0,
+     +1 is needed for trailing \0, also check for unlikely integer overflow */
+  g_return_val_if_fail (len < ((G_MAXSIZE - 1) / 4 - 1) * 3, NULL);
+
+  max = (len / 3 + 1) * 4 + 1;
+  max += 2 * (max / 76);
+
+  out = g_malloc (max);
+
+  outlen = g_base64_encode_step (data, len, TRUE, out, &state, &save);
+  outlen += g_base64_encode_close (TRUE, out + outlen, &state, &save);
+  out[outlen] = '\0';
+
+  return out;
+}
+
 static void
 render_node_print (Printer       *p,
                    GskRenderNode *node)
 {
+  char *b64;
+
   switch (gsk_render_node_get_node_type (node))
     {
     case GSK_CONTAINER_NODE:
@@ -2518,7 +2565,6 @@ render_node_print (Printer       *p,
         GdkTexture *texture = gsk_texture_node_get_texture (node);
         cairo_surface_t *surface;
         GByteArray *array;
-        char *b64;
 
         start_node (p, "texture");
         append_rect_param (p, "bounds", &node->bounds);
@@ -2526,13 +2572,15 @@ render_node_print (Printer       *p,
         surface = gdk_texture_download_surface (texture);
         array = g_byte_array_new ();
         cairo_surface_write_to_png_stream (surface, cairo_write_array, array);
-        b64 = g_base64_encode (array->data, array->len);
 
         _indent (p);
-        g_string_append_printf (p->str, "texture: url(\"data:image/png;base64,%s\");\n", b64);
+        g_string_append (p->str, "texture: url(\"data:image/png;base64,");
+        b64 = base64_encode_with_linebreaks (array->data, array->len);
+        append_escaping_newlines (p->str, b64);
+        g_free (b64);
+        g_string_append (p->str, "\");\n");
         end_node (p);
 
-        g_free (b64);
         g_byte_array_free (array, TRUE);
         cairo_surface_destroy (surface);
       }
@@ -2828,7 +2876,6 @@ render_node_print (Printer       *p,
       {
         cairo_surface_t *surface = gsk_cairo_node_peek_surface (node);
         GByteArray *array;
-        char *b64;
 
         start_node (p, "cairo");
         append_rect_param (p, "bounds", &node->bounds);
@@ -2837,12 +2884,14 @@ render_node_print (Printer       *p,
           {
             array = g_byte_array_new ();
             cairo_surface_write_to_png_stream (surface, cairo_write_array, array);
-            b64 = g_base64_encode (array->data, array->len);
 
             _indent (p);
-            g_string_append_printf (p->str, "pixels: url(\"data:image/png;base64,%s\");\n", b64);
-
+            g_string_append (p->str, "pixels: url(\"data:image/png;base64,");
+            b64 = base64_encode_with_linebreaks (array->data, array->len);
+            append_escaping_newlines (p->str, b64);
             g_free (b64);
+            g_string_append (p->str, "\");\n");
+
             g_byte_array_free (array, TRUE);
 
 #ifdef CAIRO_HAS_SCRIPT_SURFACE
@@ -2856,10 +2905,12 @@ render_node_print (Printer       *p,
 
                 if (cairo_script_from_recording_surface (script, surface) == CAIRO_STATUS_SUCCESS)
                   {
-                    b64 = g_base64_encode (array->data, array->len);
                     _indent (p);
-                    g_string_append_printf (p->str, "script: url(\"data:;base64,%s\");\n", b64);
+                    g_string_append (p->str, "script: url(\"data:;base64,");
+                    b64 = base64_encode_with_linebreaks (array->data, array->len);
+                    append_escaping_newlines (p->str, b64);
                     g_free (b64);
+                    g_string_append (p->str, "\");\n");
                   }
 
                 /* because Cairo is stupid and writes to the device after we finished it,

testsuite/gsk/nodeparser/empty-texture.ref.node

@@ -1,4 +1,7 @@
 texture {
   bounds: 0 0 50 50;
-  texture: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAABmJLR0QA/wD/AP+gvaeTAAAAKUlEQVQYlWP8z3DmPwMaYGQwYUQXY0IXwAUGUCGGoxkYGBiweXAoeAYAz44F3e3U1xUAAAAASUVORK5CYII=");
+  texture: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAABmJLR0QA/wD/AP+gvaeTAAAAKUlE\
+QVQYlWP8z3DmPwMaYGQwYUQXY0IXwAUGUCGGoxkYGBiweXAoeAYAz44F3e3U1xUAAAAASUVORK5C\
+YII=\
+");
 }