Bug 1356334: Part 1 - Add helpers for safely casting principals without COM overhead. r=bholley

MozReview-Commit-ID: EOtK17WiLZl

--HG--
extra : rebase_source : ac4a18a377d513d276df24f7e9e25903bc437084

caps/BasePrincipal.h

@@ -40,6 +40,19 @@ public:
 
   explicit BasePrincipal(PrincipalKind aKind);
 
+  template<typename T>
+  bool Is() const
+  {
+    return mKind == T::Kind();
+  }
+
+  template<typename T>
+  T* As()
+  {
+    MOZ_ASSERT(Is<T>());
+    return static_cast<T*>(this);
+  }
+
   enum DocumentDomainConsideration { DontConsiderDocumentDomain, ConsiderDocumentDomain};
   bool Subsumes(nsIPrincipal* aOther, DocumentDomainConsideration aConsideration);
 

caps/ContentPrincipal.h

@@ -30,6 +30,8 @@ public:
 
   ContentPrincipal();
 
+  static PrincipalKind Kind() { return eCodebasePrincipal; }
+
   // Init() must be called before the principal is in a usable state.
   nsresult Init(nsIURI* aCodebase,
                 const mozilla::OriginAttributes& aOriginAttributes,

caps/ExpandedPrincipal.h

@@ -20,6 +20,8 @@ public:
   Create(nsTArray<nsCOMPtr<nsIPrincipal>>& aWhiteList,
          const mozilla::OriginAttributes& aAttrs);
 
+  static PrincipalKind Kind() { return eExpandedPrincipal; }
+
   NS_DECL_NSIEXPANDEDPRINCIPAL
   NS_DECL_NSISERIALIZABLE
 

caps/NullPrincipal.h

@@ -41,6 +41,8 @@ public:
   {
   }
 
+  static PrincipalKind Kind() { return eNullPrincipal; }
+
   NS_DECL_NSISERIALIZABLE
 
   NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override;

caps/SystemPrincipal.h

@@ -30,6 +30,8 @@ class SystemPrincipal final : public mozilla::BasePrincipal
 public:
   static already_AddRefed<SystemPrincipal> Create();
 
+  static PrincipalKind Kind() { return eSystemPrincipal; }
+
   NS_DECL_NSISERIALIZABLE
   NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override;
   NS_IMETHOD GetHashValue(uint32_t* aHashValue) override;