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diff --git a/js/public/Principals.h b/js/public/Principals.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* JSPrincipals and related interfaces. */
+
+#ifndef js_Principals_h
+#define js_Principals_h
+
+#include "mozilla/Atomics.h"
+
+#include <stdint.h>
+
+#include "jspubtd.h"
+
+struct JSStructuredCloneReader;
+struct JSStructuredCloneWriter;
+
+struct JSPrincipals {
+  /* Don't call "destroy"; use reference counting macros below. */
+  mozilla::Atomic<int32_t, mozilla::SequentiallyConsistent> refcount{0};
+
+#ifdef JS_DEBUG
+  /* A helper to facilitate principals debugging. */
+  uint32_t debugToken;
+#endif
+
+  JSPrincipals() = default;
+
+  void setDebugToken(uint32_t token) {
+#ifdef JS_DEBUG
+    debugToken = token;
+#endif
+  }
+
+  /*
+   * Write the principals with the given |writer|. Return false on failure,
+   * true on success.
+   */
+  virtual bool write(JSContext* cx, JSStructuredCloneWriter* writer) = 0;
+
+  /*
+   * Whether the principal corresponds to a System or AddOn Principal.
+   * Technically this also checks for an ExpandedAddonPrincipal.
+   */
+  virtual bool isSystemOrAddonPrincipal() = 0;
+
+  /*
+   * This is not defined by the JS engine but should be provided by the
+   * embedding.
+   */
+  JS_PUBLIC_API void dump();
+};
+
+extern JS_PUBLIC_API void JS_HoldPrincipals(JSPrincipals* principals);
+
+extern JS_PUBLIC_API void JS_DropPrincipals(JSContext* cx,
+                                            JSPrincipals* principals);
+
+// Return whether the first principal subsumes the second. The exact meaning of
+// 'subsumes' is left up to the browser. Subsumption is checked inside the JS
+// engine when determining, e.g., which stack frames to display in a backtrace.
+typedef bool (*JSSubsumesOp)(JSPrincipals* first, JSPrincipals* second);
+
+/*
+ * Used to check if a CSP instance wants to disable eval() and friends.
+ * See GlobalObject::isRuntimeCodeGenEnabled() in vm/GlobalObject.cpp.
+ */
+typedef bool (*JSCSPEvalChecker)(JSContext* cx, JS::HandleString code);
+
+struct JSSecurityCallbacks {
+  JSCSPEvalChecker contentSecurityPolicyAllows;
+  JSSubsumesOp subsumes;
+};
+
+extern JS_PUBLIC_API void JS_SetSecurityCallbacks(
+    JSContext* cx, const JSSecurityCallbacks* callbacks);
+
+extern JS_PUBLIC_API const JSSecurityCallbacks* JS_GetSecurityCallbacks(
+    JSContext* cx);
+
+/*
+ * Code running with "trusted" principals will be given a deeper stack
+ * allocation than ordinary scripts. This allows trusted script to run after
+ * untrusted script has exhausted the stack. This function sets the
+ * runtime-wide trusted principal.
+ *
+ * This principals is not held (via JS_HoldPrincipals/JS_DropPrincipals).
+ * Instead, the caller must ensure that the given principals stays valid for as
+ * long as 'cx' may point to it. If the principals would be destroyed before
+ * 'cx', JS_SetTrustedPrincipals must be called again, passing nullptr for
+ * 'prin'.
+ */
+extern JS_PUBLIC_API void JS_SetTrustedPrincipals(JSContext* cx,
+                                                  JSPrincipals* prin);
+
+typedef void (*JSDestroyPrincipalsOp)(JSPrincipals* principals);
+
+/*
+ * Initialize the callback that is called to destroy JSPrincipals instance
+ * when its reference counter drops to zero. The initialization can be done
+ * only once per JS runtime.
+ */
+extern JS_PUBLIC_API void JS_InitDestroyPrincipalsCallback(
+    JSContext* cx, JSDestroyPrincipalsOp destroyPrincipals);
+
+/*
+ * Read a JSPrincipals instance from the given |reader| and initialize the out
+ * paratemer |outPrincipals| to the JSPrincipals instance read.
+ *
+ * Return false on failure, true on success. The |outPrincipals| parameter
+ * should not be modified if false is returned.
+ *
+ * The caller is not responsible for calling JS_HoldPrincipals on the resulting
+ * JSPrincipals instance, the JSReadPrincipalsOp must increment the refcount of
+ * the resulting JSPrincipals on behalf of the caller.
+ */
+using JSReadPrincipalsOp = bool (*)(JSContext* cx,
+                                    JSStructuredCloneReader* reader,
+                                    JSPrincipals** outPrincipals);
+
+/*
+ * Initialize the callback that is called to read JSPrincipals instances from a
+ * buffer. The initialization can be done only once per JS runtime.
+ */
+extern JS_PUBLIC_API void JS_InitReadPrincipalsCallback(
+    JSContext* cx, JSReadPrincipalsOp read);
+
+namespace JS {
+
+class MOZ_RAII AutoHoldPrincipals {
+  JSContext* cx_;
+  JSPrincipals* principals_ = nullptr;
+
+ public:
+  explicit AutoHoldPrincipals(JSContext* cx, JSPrincipals* principals = nullptr)
+      : cx_(cx) {
+    reset(principals);
+  }
+
+  ~AutoHoldPrincipals() { reset(nullptr); }
+
+  void reset(JSPrincipals* principals) {
+    if (principals) {
+      JS_HoldPrincipals(principals);
+    }
+    if (principals_) {
+      JS_DropPrincipals(cx_, principals_);
+    }
+    principals_ = principals;
+  }
+
+  JSPrincipals* get() const { return principals_; }
+};
+
+}  // namespace JS
+
+#endif /* js_Principals_h */