Implement Chromium side of MediaKeys.isTypeSupported().

content/renderer/media/webcontentdecryptionmodule_impl.cc

Index: content/renderer/media/webcontentdecryptionmodule_impl.cc
diff --git a/content/renderer/media/webcontentdecryptionmodule_impl.cc b/content/renderer/media/webcontentdecryptionmodule_impl.cc
index 9dcb39ee9ca98931c5f49c05035f805ed883e846..8ab053175dda19a63bb9b0ffcf62ef7923635fb1 100644
--- a/content/renderer/media/webcontentdecryptionmodule_impl.cc
+++ b/content/renderer/media/webcontentdecryptionmodule_impl.cc
@@ -16,6 +16,7 @@
 #include "content/renderer/media/crypto/key_systems.h"
 #include "content/renderer/media/webcontentdecryptionmodulesession_impl.h"
 #include "media/base/media_keys.h"
+#include "net/base/mime_util.h"
 #include "third_party/WebKit/public/platform/WebString.h"
 #include "third_party/WebKit/public/web/WebSecurityOrigin.h"
 #include "url/gurl.h"
@@ -83,6 +84,103 @@ WebContentDecryptionModuleImpl::WebContentDecryptionModuleImpl(
 WebContentDecryptionModuleImpl::~WebContentDecryptionModuleImpl() {
 }
 
+// static
+blink::WebContentDecryptionModule::SupportsKeySystem
+WebContentDecryptionModuleImpl::IsKeySystemSupported(
+    const blink::WebString& key_system,
+    const blink::WebString& init_data_type,
+    const blink::WebString& container,
+    const blink::WebString& codecs,
+    const blink::WebString& capability) {
+  // 15-18.

[ddorwin, 2014/09/13 01:20:46]

It might help to say something like:
// Continue the MediaKeys.isTypeSupported() algorithm.
<empty line>

[sandersd (OOO until July 31), 2014/09/22 23:45:54]

Done.

+  if (!capability.isEmpty())

[ddorwin, 2014/09/13 01:20:46]

I believe we need the following:
// Not currently supported.
// TODO: Implement support.

[sandersd (OOO until July 31), 2014/09/22 23:45:53]

Done.

+    return blink::WebContentDecryptionModule::IsNotSupported;

[ddorwin, 2014/09/13 01:20:46]

Should we move this to the end where it will be eventually? There's no reason
for it to be here, right?

[sandersd (OOO until July 31), 2014/09/22 23:45:54]

The only reason was that an early exit seemed like less of a waste. (Done.)

+
+  // 1. If keySystem is an empty string or contains an unrecognized or

[ddorwin, 2014/09/13 01:20:46]

Half of step 1 is handled in Blink. The other half is really handled by step 2.

[sandersd (OOO until July 31), 2014/09/22 23:45:53]

Done.

+  //    unsupported Key System, return the empty string and abort these steps.
+  //    String comparison is case-sensitive.
+  // 2. If the keySystem implementation is not available and usable, return the
+  //    empty string and abort these steps.
+  const std::string key_system_ascii = key_system.utf8();

[ddorwin, 2014/09/13 01:20:46]

Are we checking and rejecting non-ascii values in Blink? That was the plan, but
I'm not sure we've implemented that yet. See [1]. If not, I'm not sure whether
this is safe. This might be sufficiently high enough to do the conversion
(rather than in Blink), but we should return the empty string if any of the
parameters are not ASCII. See [2] for an example.

On the other hand, the ASCII check fits better in step 1, which is mostly in
Blink.

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/m...

[2]
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/m...

[sandersd (OOO until July 31), 2014/09/22 23:45:54]

Because the spec didn't say to do that check, this CL avoids the problem by
re-coding to UTF-8. It's not a great solution, but it's efficient if the strings
are ASCII and I believe correct if they are not (the lookups just won't find
anything).

It makes sense to do an ASCII check in Blink, and then just assume it here. I've
added a TODO for now.

[ddorwin, 2014/09/23 22:48:15]

FWIW, there is a note in the spec that lower-case ascii is recommended.

+  if (!IsSupportedKeySystem(key_system_ascii))
+    return blink::WebContentDecryptionModule::IsNotSupported;
+
+  // 3. Follow the steps for the first matching condition from the following
+  //    list:
+  //    - If keySystem is a value that may be successfully passed to create()
+  //        Let probably result be "probably"
+  //    - Otherwise (as may be the case for strings that are only used for
+  //      discovery)
+  //        Let probably result be "maybe".
+  blink::WebContentDecryptionModule::SupportsKeySystem probably_result =
+      blink::WebContentDecryptionModule::MayBeSupported;
+  if (IsConcreteSupportedKeySystem(key_system_ascii))

[ddorwin, 2014/09/13 01:20:46]

nit: Convert to ? :.

[sandersd (OOO until July 31), 2014/09/22 23:45:53]

Done.

+    probably_result = blink::WebContentDecryptionModule::IsSupported;
+
+  // 4. If initDataType was not provided, follow the steps for the first
+  //    matching condition from the following list and abort these steps:
+  //    - If the user agent is not confident that the keySystem implementation
+  //      is available and usable
+  //        Return "maybe"
+  //    - Otherwise
+  //        Return probably result.
+  if (init_data_type.isEmpty())
+    return probably_result;
+
+  // 5. If initDataType is an empty string or contains an unrecognized or
+  //    unsupported initialization data type, return the empty string and abort
+  //    these steps. String comparison is case-sensitive.
+  // 6. If initDataType is not an initialization data type supported by the
+  //    keySystem implementation, return the empty string and abort these steps.
+  // 7. If the keySystem implementation supporting initDataType is not available
+  //    and usable, return the empty string and abort these steps.
+  const std::string init_data_type_ascii = init_data_type.utf8();
+  if (!IsSupportedKeySystemWithInitDataType(key_system_ascii,
+                                            init_data_type_ascii))
+    return blink::WebContentDecryptionModule::IsNotSupported;
+
+  // Exclude some specific combinations that don't make much sense.
+  if ((key_system_ascii == "mp4" && init_data_type_ascii == "webm") ||

[ddorwin, 2014/09/13 01:20:46]

This should be comparing the container.

[sandersd (OOO until July 31), 2014/09/22 23:45:53]

Whoops, thanks!

+      (key_system_ascii == "webm" && init_data_type_ascii == "cenc"))

[ddorwin, 2014/09/13 01:20:46]

Let's move this code to key_systems.cc into a function like
VerifyIsSaneCombination().

Also, I would structure these as:
if (container-specific-IDT)
  if (!matching-container)
    return false;

The location allows us to have a single place to track these issues and update
it if a new container or IDT is added. The helper function allows us to
structure code as above. The name makes it clear what we're doing.

[sandersd (OOO until July 31), 2014/09/22 23:45:53]

Done.

+    return blink::WebContentDecryptionModule::IsNotSupported;
+
+  // 8. If contentType was not provided, follow the steps for the first matching
+  //    condition from the following list and abort these steps:
+  //    - If the user agent is not confident that the keySystem implementation
+  //      supporting initDataType is available and usable
+  //        Return "maybe"
+  //    - Otherwise
+  //        Return probably result.
+  if (container.isEmpty())
+    return probably_result;
+
+  // 9.  If contentType is an empty string or contains an invalid or

[ddorwin, 2014/09/13 01:20:46]

As noted in the Blink CL, these should be there, except maybe the "unrecognized
MIME type" part of 9 - but we can just assume it's handled in step 13.

[sandersd (OOO until July 31), 2014/09/22 23:45:54]

Done.

+  //     unrecognized MIME type, return the empty string and abort these steps.
+  // 10. Let container be the container type specified by contentType.
+  // 11. Let parameters be the RFC 6381 parameters, if any, specified by
+  //     contentType.
+  // 12. Let media types be the set of media types specified by parameters. It
+  //     may be empty. The case-sensitivity of string comparisons is determined
+  //     by the appropriate RFC or other specification.
+  // 13. If the user agent does not support container, return the empty string
+  //     and abort these steps. The case-sensitivity of string comparisons is
+  //     determined by the appropriate RFC.
+  // 14. If the user agent and keySystem implementation do not support playback
+  //     of encrypted media data for all media types, return the empty string
+  //     and abort these steps.
+  const std::string container_ascii = container.utf8();
+  bool strip_codec_suffixes = !net::IsStrictMediaMimeType(container_ascii);

[ddorwin, 2014/09/13 01:20:46]

TODO: Do a better job validating codecs: crbug.com/374751

[sandersd (OOO until July 31), 2014/09/22 23:45:54]

Done.

+  std::vector<std::string> codec_vector;
+  net::ParseCodecString(codecs.utf8(), &codec_vector, strip_codec_suffixes);

[ddorwin, 2014/09/13 01:20:46]

note: need to ensure we have checked ASCII before here

[sandersd (OOO until July 31), 2014/09/22 23:45:54]

Acknowledged.

+  if (!IsSupportedKeySystemWithMediaMimeType(
+      container_ascii, codec_vector, key_system_ascii))
+    return blink::WebContentDecryptionModule::IsNotSupported;
+
+  // TODO(sandersd): If the codecs are all unambiguous and supported, return
+  // IsSupported.

[ddorwin, 2014/09/13 01:20:46]

probably_result, right?

[sandersd (OOO until July 31), 2014/09/22 23:45:54]

That's correct, but because we don't check that the codecs are unambiguous, we
can't actually return "probably" yet, so it's always "maybe".

+  return blink::WebContentDecryptionModule::MayBeSupported;
+}
+
 // The caller owns the created session.
 blink::WebContentDecryptionModuleSession*
 WebContentDecryptionModuleImpl::createSession() {