LibWeb/EME: Implement a KeySystem

Author: https://github.com/stelar7
Commit: cc50b30399
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5665
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/trflynn89

Libraries/LibWeb/EncryptedMediaExtensions/KeySystem.h

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2025, stelar7 <dudedbz@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Utf16String.h>
+#include <LibWeb/EncryptedMediaExtensions/EncryptedMediaExtensions.h>
+
+namespace Web::EncryptedMediaExtensions {
+
+class KeySystem {
+public:
+    virtual ~KeySystem() = default;
+
+    virtual bool supports_init_data_type(Utf16String const& init_data_type) const = 0;
+    virtual bool supports_encryption_scheme(Utf16String const& encryption_scheme) const = 0;
+    virtual bool supports_robustness(Utf16String const& robustness) const = 0;
+    virtual bool definitely_supports_playback(Utf16String const& container, Utf16String const& media_types, Optional<Utf16String> encryption_scheme, Utf16String const& robustness, Bindings::MediaKeySystemConfiguration const& accumulated_configuration, MediaKeyRestrictions const& restrictions) const = 0;
+
+private:
+};
+
+class ClearKeySystem : public KeySystem {
+public:
+    ClearKeySystem() = default;
+    virtual ~ClearKeySystem() override = default;
+
+    // https://w3c.github.io/encrypted-media/#clear-key-behavior
+    virtual bool supports_init_data_type(Utf16String const& init_data_type) const override
+    {
+        // Implementations SHOULD support the "keyids" type
+        // TODO: Implementations MAY support any combination of registered Initialization Data Types
+        // https://www.w3.org/TR/eme-initdata-registry/
+        constexpr Array<Utf16View, 1> registered_init_data_types = {
+            "keyids"sv,
+        };
+
+        return registered_init_data_types.contains_slow(init_data_type);
+    }
+
+    // https://w3c.github.io/encrypted-media/#clear-key-capabilities
+    virtual bool supports_encryption_scheme(Utf16String const& encryption_scheme) const override
+    {
+        // encryptionScheme: Implementations MUST support the "cenc" scheme, and MAY support other schemes.
+        return encryption_scheme == "cenc"sv;
+    }
+
+    // https://w3c.github.io/encrypted-media/#clear-key-capabilities
+    virtual bool supports_robustness(Utf16String const& robustness) const override
+    {
+        // robustness: Only the empty string is supported.
+        return robustness.is_empty();
+    }
+
+    virtual bool definitely_supports_playback(Utf16String const& container, Utf16String const& media_types, Optional<Utf16String> encryption_scheme, Utf16String const& robustness, Bindings::MediaKeySystemConfiguration const& accumulated_configuration, MediaKeyRestrictions const& restrictions) const override
+    {
+        (void)container;
+        (void)media_types;
+        (void)encryption_scheme;
+        (void)robustness;
+        (void)accumulated_configuration;
+        (void)restrictions;
+
+        // FIXME: Do some checks here
+        return true;
+    }
+};
+
+}