From 0052f3d8315e8cefb04a62a64cac17cbfbc6b8b6 Mon Sep 17 00:00:00 2001
From: Charlie Turner <chturne@gmail.com>
Date: Fri, 25 May 2018 09:43:30 +0100
Subject: [PATCH] Parse playready payload.

Look at the playready specific data payload to extract default key ids
for decrypting samples. The format of this payload seems to be
proprietary.

Signed-off-by: Xabier Rodriguez Calvar <calvaris@igalia.com>
---
 ext/smoothstreaming/gstmssdemux.c    |  14 ++-
 ext/smoothstreaming/gstmssmanifest.c | 138 +++++++++++++++++++++++++++
 ext/smoothstreaming/gstmssmanifest.h |   1 +
 3 files changed, 152 insertions(+), 1 deletion(-)

diff --git a/ext/smoothstreaming/gstmssdemux.c b/ext/smoothstreaming/gstmssdemux.c
index bcea8ca..4fa95b9 100644
--- a/ext/smoothstreaming/gstmssdemux.c
+++ b/ext/smoothstreaming/gstmssdemux.c
@@ -495,7 +495,19 @@ gst_mss_demux_setup_streams (GstAdaptiveDemux * demux)
           gst_event_new_protection (protection_system_id, protection_buffer,
           "smooth-streaming");
 
-      GST_LOG_OBJECT (stream, "Queueing Protection event on source pad");
+      GstBuffer *key_id = gst_mss_manifest_get_key_id (mssdemux->manifest);
+      if (!gst_buffer_get_size (key_id)) {
+        GST_WARNING_OBJECT (stream,
+            "protected manifest, but no key ids available");
+      } else {
+        GST_LOG_OBJECT (stream,
+            "Adding key id to the protection event of size %lu",
+            gst_buffer_get_size (key_id));
+        GstStructure *structure = gst_event_writable_structure (event);
+        gst_structure_set (structure, "key_id", GST_TYPE_BUFFER, key_id, NULL);
+      }
+
+      GST_LOG_OBJECT (stream, "Queuing Protection event on source pad");
       gst_adaptive_demux_stream_queue_event ((GstAdaptiveDemuxStream *) stream,
           event);
       gst_buffer_unref (protection_buffer);
diff --git a/ext/smoothstreaming/gstmssmanifest.c b/ext/smoothstreaming/gstmssmanifest.c
index c855cb3..df31330 100644
--- a/ext/smoothstreaming/gstmssmanifest.c
+++ b/ext/smoothstreaming/gstmssmanifest.c
@@ -28,6 +28,8 @@
 #include <ctype.h>
 #include <libxml/parser.h>
 #include <libxml/tree.h>
+#include <libxml/xpath.h>
+#include <libxml/xpathInternals.h>
 
 /* for parsing h264 codec data */
 #include <gst/codecparsers/gsth264parser.h>
@@ -109,6 +111,10 @@ struct _GstMssManifest
   GString *protection_system_id;
   gchar *protection_data;
 
+  // FIXME: There can be multiple key ids present in protected manifests.
+  gchar *key_id;
+  gsize key_id_len;
+
   GSList *streams;
 };
 
@@ -300,6 +306,122 @@ _gst_mss_stream_init (GstMssManifest * manifest, GstMssStream * stream,
   gst_mss_fragment_parser_init (&stream->fragment_parser);
 }
 
+static void
+_gst_mss_parse_protection_data (GstMssManifest * manifest)
+{
+  guchar *decoded_protection_data = NULL;
+  gsize decoded_protection_data_len = 0;
+  xmlChar *protection_data_text = NULL;
+  int protection_data_text_len = 0;
+  xmlDocPtr protection_data_xml = NULL;
+  // Note, this does not need to free'd, freeing the doc ptr will free this.
+  xmlNode *protection_data_root_element = NULL;
+  const xmlChar *protection_data_namespace = NULL;
+  xmlXPathContextPtr xpath_ctx = NULL;
+  xmlXPathObjectPtr xpath_obj = NULL;
+  xmlNodeSetPtr key_id_node = NULL;
+  gsize protection_data_xml_len = 0;
+  guchar *start_tag = NULL;
+
+  decoded_protection_data =
+      g_base64_decode (manifest->protection_data, &decoded_protection_data_len);
+
+  start_tag = decoded_protection_data;
+
+  // The protection data starts with a 10-byte PlayReady version
+  // header that needs to be skipped over to avoid XML parsing
+  // errors.
+  while (start_tag && *start_tag != '<')
+    start_tag++;
+
+  if (!start_tag) {
+    GST_ERROR ("failed to find a start tag in protection data payload");
+    goto beach;
+  }
+
+  protection_data_xml_len =
+      decoded_protection_data_len - (start_tag - decoded_protection_data);
+  protection_data_xml =
+      xmlReadMemory ((const gchar *) start_tag, protection_data_xml_len,
+      "protection_data", "utf-16", 0);
+
+  if (!protection_data_xml) {
+    GST_ERROR ("failed to parse protection data XML");
+    goto beach;
+  }
+
+  if (gst_debug_category_get_threshold (GST_CAT_DEFAULT) >= GST_LEVEL_MEMDUMP) {
+    xmlDocDumpMemoryEnc (protection_data_xml, &protection_data_text,
+        &protection_data_text_len, "utf8");
+    GST_MEMDUMP ("protection data XML", protection_data_text,
+        protection_data_text_len);
+    xmlFree (protection_data_text);
+  }
+
+  protection_data_root_element = xmlDocGetRootElement (protection_data_xml);
+  if (protection_data_root_element->type != XML_ELEMENT_NODE ||
+      xmlStrcmp (protection_data_root_element->name,
+          (const xmlChar *) "WRMHEADER") || !protection_data_root_element->ns) {
+    GST_ERROR ("invalid protection data XML");
+    goto beach;
+  }
+
+  xpath_ctx = xmlXPathNewContext (protection_data_xml);
+  if (!xpath_ctx) {
+    GST_ERROR ("failed to create xpath context");
+    goto beach;
+  }
+
+  protection_data_namespace = protection_data_root_element->ns->href;
+  if (xmlXPathRegisterNs (xpath_ctx, (const xmlChar *) "prhdr",
+          protection_data_namespace) < 0) {
+    GST_ERROR ("failed to register XML namespace");
+    goto beach;
+  }
+
+  xpath_obj =
+      xmlXPathEvalExpression ((const xmlChar *) "//prhdr:KID", xpath_ctx);
+  if (!xpath_obj) {
+    GST_DEBUG ("failed to eval XPath expression");
+    goto beach;
+  }
+
+  key_id_node = xpath_obj->nodesetval;
+  int num_key_ids = key_id_node ? key_id_node->nodeNr : 0;
+
+  GST_DEBUG ("found %d key ids", num_key_ids);
+
+  if (num_key_ids != 0 && (key_id_node->nodeTab[0]->type == XML_ELEMENT_NODE)) {
+    xmlChar *encoded_key_id = xmlNodeGetContent (key_id_node->nodeTab[0]);
+    gsize decoded_key_id_len;
+    guchar *decoded_key_id =
+        g_base64_decode ((const gchar *) encoded_key_id, &decoded_key_id_len);
+
+    GST_MEMDUMP ("key retrieved", decoded_key_id, decoded_key_id_len);
+
+    manifest->key_id = g_realloc (manifest->key_id, decoded_key_id_len);
+    memcpy (manifest->key_id, decoded_key_id, decoded_key_id_len);
+    manifest->key_id_len = decoded_key_id_len;
+
+    xmlFree (encoded_key_id);
+    g_free (decoded_key_id);
+  } else {
+    GST_ERROR ("invalid XML payload");
+    goto beach;
+  }
+
+beach:
+  if (decoded_protection_data)
+    g_free (decoded_protection_data);
+  if (xpath_ctx)
+    xmlXPathFreeContext (xpath_ctx);
+  if (xpath_obj)
+    xmlXPathFreeObject (xpath_obj);
+  if (protection_data_xml)
+    xmlFreeDoc (protection_data_xml);
+
+  return;
+}
 
 static void
 _gst_mss_parse_protection (GstMssManifest * manifest,
@@ -329,6 +451,7 @@ _gst_mss_parse_protection (GstMssManifest * manifest,
 
       manifest->protection_system_id = system_id;
       manifest->protection_data = (gchar *) xmlNodeGetContent (nodeiter);
+      _gst_mss_parse_protection_data (manifest);
       xmlFree (system_id_attribute);
       break;
     }
@@ -394,6 +517,9 @@ gst_mss_manifest_new (GstBuffer * data)
     }
   }
 
+  manifest->key_id = NULL;
+  manifest->key_id_len = 0;
+
   for (nodeiter = root->children; nodeiter; nodeiter = nodeiter->next) {
     if (nodeiter->type == XML_ELEMENT_NODE
         && (strcmp ((const char *) nodeiter->name, "StreamIndex") == 0)) {
@@ -440,6 +566,9 @@ gst_mss_manifest_free (GstMssManifest * manifest)
 
   g_slist_free_full (manifest->streams, (GDestroyNotify) gst_mss_stream_free);
 
+  if (manifest->key_id)
+    g_free (manifest->key_id);
+
   if (manifest->protection_system_id != NULL)
     g_string_free (manifest->protection_system_id, TRUE);
   xmlFree (manifest->protection_data);
@@ -462,6 +591,15 @@ gst_mss_manifest_get_protection_data (GstMssManifest * manifest)
   return manifest->protection_data;
 }
 
+GstBuffer *
+gst_mss_manifest_get_key_id (GstMssManifest * manifest)
+{
+  GstBuffer *key_id_buffer =
+      gst_buffer_new_allocate (NULL, manifest->key_id_len, NULL);
+  gst_buffer_fill (key_id_buffer, 0, manifest->key_id, manifest->key_id_len);
+  return key_id_buffer;
+}
+
 GSList *
 gst_mss_manifest_get_streams (GstMssManifest * manifest)
 {
diff --git a/ext/smoothstreaming/gstmssmanifest.h b/ext/smoothstreaming/gstmssmanifest.h
index 03b066a..4e6ad73 100644
--- a/ext/smoothstreaming/gstmssmanifest.h
+++ b/ext/smoothstreaming/gstmssmanifest.h
@@ -56,6 +56,7 @@ GstClockTime gst_mss_manifest_get_min_fragment_duration (GstMssManifest * manife
 const gchar * gst_mss_manifest_get_protection_system_id (GstMssManifest * manifest);
 const gchar * gst_mss_manifest_get_protection_data (GstMssManifest * manifest);
 gboolean gst_mss_manifest_get_live_seek_range (GstMssManifest * manifest, gint64 * start, gint64 * stop);
+GstBuffer * gst_mss_manifest_get_key_id (GstMssManifest * manifest);
 
 GstMssStreamType gst_mss_stream_get_type (GstMssStream *stream);
 GstCaps * gst_mss_stream_get_caps (GstMssStream * stream);
-- 
2.20.1