ttmlparse: Handle whitespace before XML declaration

When ttmlparse is in, e.g., an MPEG-DASH pipeline, there may be
whitespace between successive TTML documents in ttmlparse's accumulated
input. As libxml2 will fail to parse documents that have whitespace
before the opening XML declaration, ensure that any preceding whitespace
is not passed to libxml2.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1859>

1 files changed, 8 insertions, 3 deletions

diff --git a/ext/ttml/ttmlparse.c b/ext/ttml/ttmlparse.c
index 4914910f7..3c7d8f07c 100644
--- a/ext/ttml/ttmlparse.c
+++ b/ext/ttml/ttmlparse.c
@@ -1926,6 +1926,7 @@ ttml_find_child (xmlNodePtr parent, const gchar * name)
   return child;
 }
 
+#define XML_START_TAG "<?xml"
 #define TTML_END_TAG "</tt>"
 
 guint
@@ -1941,7 +1942,8 @@ ttml_parse (const gchar * input, GstClockTime begin, GstClockTime duration,
   guint cellres_x, cellres_y;
   TtmlWhitespaceMode doc_whitespace_mode = TTML_WHITESPACE_MODE_DEFAULT;
   guint consumed = 0;
-  gchar *end_tt;
+  guint start_offset = 0;
+  gchar *start_xml, *end_tt;
 
   g_return_val_if_fail (parsed != NULL, 0);
 
@@ -1952,14 +1954,16 @@ ttml_parse (const gchar * input, GstClockTime begin, GstClockTime duration,
   }
   GST_CAT_LOG (ttmlparse_debug, "Input:\n%s", input);
 
+  start_xml = g_strstr_len (input, strlen (input), XML_START_TAG);
   end_tt = g_strstr_len (input, strlen (input), TTML_END_TAG);
 
-  if (!end_tt) {
+  if (!start_xml || !end_tt) {
     GST_CAT_DEBUG (ttmlparse_debug, "Need more data");
     return 0;
   }
 
   consumed = end_tt - input + strlen (TTML_END_TAG);
+  start_offset = start_xml - input;
 
   styles_table = g_hash_table_new_full (g_str_hash, g_str_equal, g_free,
       (GDestroyNotify) ttml_delete_element);
@@ -1967,7 +1971,8 @@ ttml_parse (const gchar * input, GstClockTime begin, GstClockTime duration,
       (GDestroyNotify) ttml_delete_element);
 
   /* Parse input. */
-  doc = xmlReadMemory (input, consumed, "any_doc_name", NULL, 0);
+  doc = xmlReadMemory (start_xml, consumed - start_offset, "any_doc_name",
+      NULL, 0);
   if (!doc) {
     GST_CAT_ERROR (ttmlparse_debug, "Failed to parse document.");
     return 0;