Support for parsing encrypted WebM streams by src.

media/webm/webm_crypt_helpers.cc

Index: media/webm/webm_crypt_helpers.cc
diff --git a/media/webm/webm_crypt_helpers.cc b/media/webm/webm_crypt_helpers.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8896cbca20544942f35b0b876c53ca62397daf0d
--- /dev/null
+++ b/media/webm/webm_crypt_helpers.cc
@@ -0,0 +1,49 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/webm/webm_crypt_helpers.h"

[xhwang, 2012/08/29 05:08:14]

How about rename this to "webm_crypto_helpers.h", to be consistent with
"base/crypto" and "media/crypto"?

[ddorwin, 2012/09/01 16:46:41]

Agreed. Is there a reason you chose "crypt"?

[fgalligan1, 2013/03/09 01:10:59]

Done.

[fgalligan1, 2013/03/09 01:10:59]

Done.

+
+#include "base/logging.h"

[ddorwin, 2012/09/01 16:46:41]

Not needed?

+#include "base/sys_byteorder.h"
+#include "media/base/decrypt_config.h"
+#include "media/crypto/decryptor_helpers.h"
+#include "media/webm/webm_constants.h"
+
+namespace media {
+
+scoped_refptr<DecoderBuffer> WebMCopyBufferCheckIfEncrypted(

[ddorwin, 2012/09/01 16:46:41]

This function does not "check if encrypted". So, it won't work for unencrypted
WebM (or ISO). Right now, it's being called in all cases, which means anything
but encrypted WebM is broken.

[fgalligan1, 2013/03/09 01:10:59]

Renamed.

+    const uint8* data, int data_size,
+    const uint8* key_id, int key_id_size) {
+  scoped_refptr<DecoderBuffer> encrypted_buffer = DecoderBuffer::CopyFrom(
+      data + kWebMHmacSize, data_size - kWebMHmacSize);

[ddorwin, 2012/09/01 16:46:41]

line breaks and alignment seem questionable.

[fgalligan1, 2013/03/09 01:10:59]

Removed.

+  CHECK(encrypted_buffer);
+
+  uint8 signal_byte = data[kWebMHmacSize];
+  int data_offset = sizeof(signal_byte);

[ddorwin, 2012/09/01 16:46:41]

const int kDataOffset?
"data_offset" is not directly related to "data", which is confusing. Is there a
better name?

[fgalligan1, 2013/03/09 01:10:59]

Changed to frame_offset.

+
+  // Setting the DecryptConfig object of the buffer while leaving the
+  // initialization vector empty will tell the decryptor that the frame is
+  // unencrypted but integrity should still be checked.
+  std::string counter_block_str;
+
+  if (signal_byte & kWebMFlagEncryptedFrame) {
+    uint64 network_iv;

[ddorwin, 2012/09/01 16:46:41]

Might comment "IV is only present for encrypted frames" somewhere.

[fgalligan1, 2013/03/09 01:10:59]

Done.

+    memcpy(&network_iv, data + kWebMHmacSize + data_offset, sizeof(network_iv));
+    const uint64 iv = base::NetToHost64(network_iv);
+    counter_block_str =
+        GenerateCounterBlock(iv);

[ddorwin, 2012/09/01 16:46:41]

on same line as above

+    data_offset += sizeof(iv);
+  }
+
+  encrypted_buffer->SetDecryptConfig(
+      scoped_ptr<DecryptConfig>(new DecryptConfig(
+          std::string(reinterpret_cast<const char*>(key_id), key_id_size),
+          counter_block_str,
+          std::string(reinterpret_cast<const char*>(data), kWebMHmacSize),
+          data_offset,
+          std::vector<SubsampleEntry>())));
+  return encrypted_buffer;
+}
+
+}  // media

[xhwang, 2012/08/29 05:08:14]

// namespace media

[fgalligan1, 2013/03/09 01:10:59]

Done.