comparison win64-msvc/include/capnp/persistent.capnp @ 47:d93140aac40b

Current Capnp libs and headers from git

+# Copyright (c) 2014 Sandstorm Development Group, Inc. and contributors
+# Licensed under the MIT License:
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+@0xb8630836983feed7;
+
+$import "/capnp/c++.capnp".namespace("capnp");
+
+interface Persistent@0xc8cb212fcd9f5691(SturdyRef, Owner) {
+  # Interface implemented by capabilities that outlive a single connection. A client may save()
+  # the capability, producing a SturdyRef. The SturdyRef can be stored to disk, then later used to
+  # obtain a new reference to the capability on a future connection.
+  #
+  # The exact format of SturdyRef depends on the "realm" in which the SturdyRef appears. A "realm"
+  # is an abstract space in which all SturdyRefs have the same format and refer to the same set of
+  # resources. Every vat is in exactly one realm. All capability clients within that vat must
+  # produce SturdyRefs of the format appropriate for the realm.
+  #
+  # Similarly, every VatNetwork also resides in a particular realm. Usually, a vat's "realm"
+  # corresponds to the realm of its main VatNetwork. However, a Vat can in fact communicate over
+  # a VatNetwork in a different realm -- in this case, all SturdyRefs need to be transformed when
+  # coming or going through said VatNetwork. The RPC system has hooks for registering
+  # transformation callbacks for this purpose.
+  #
+  # Since the format of SturdyRef is realm-dependent, it is not defined here. An application should
+  # choose an appropriate realm for itself as part of its design. Note that under Sandstorm, every
+  # application exists in its own realm and is therefore free to define its own SturdyRef format;
+  # the Sandstorm platform handles translating between realms.
+  #
+  # Note that whether a capability is persistent is often orthogonal to its type. In these cases,
+  # the capability's interface should NOT inherit `Persistent`; instead, just perform a cast at
+  # runtime. It's not type-safe, but trying to be type-safe in these cases will likely lead to
+  # tears. In cases where a particular interface only makes sense on persistent capabilities, it
+  # still should not explicitly inherit Persistent because the `SturdyRef` and `Owner` types will
+  # vary between realms (they may even be different at the call site than they are on the
+  # implementation). Instead, mark persistent interfaces with the $persistent annotation (defined
+  # below).
+  #
+  # Sealing
+  # -------
+  #
+  # As an added security measure, SturdyRefs may be "sealed" to a particular owner, such that
+  # if the SturdyRef itself leaks to a third party, that party cannot actually restore it because
+  # they are not the owner. To restore a sealed capability, you must first prove to its host that
+  # you are the rightful owner. The precise mechanism for this authentication is defined by the
+  # realm.
+  #
+  # Sealing is a defense-in-depth mechanism meant to mitigate damage in the case of catastrophic
+  # attacks. For example, say an attacker temporarily gains read access to a database full of
+  # SturdyRefs: it would be unfortunate if it were then necessary to revoke every single reference
+  # in the database to prevent the attacker from using them.
+  #
+  # In general, an "owner" is a course-grained identity. Because capability-based security is still
+  # the primary mechanism of security, it is not necessary nor desirable to have a separate "owner"
+  # identity for every single process or object; that is exactly what capabilities are supposed to
+  # avoid! Instead, it makes sense for an "owner" to literally identify the owner of the machines
+  # where the capability is stored. If untrusted third parties are able to run arbitrary code on
+  # said machines, then the sandbox for that code should be designed using Distributed Confinement
+  # such that the third-party code never sees the bits of the SturdyRefs and cannot directly
+  # exercise the owner's power to restore refs. See:
+  #
+  #     http://www.erights.org/elib/capability/dist-confine.html
+  #
+  # Resist the urge to represent an Owner as a simple public key. The whole point of sealing is to
+  # defend against leaked-storage attacks. Such attacks can easily result in the owner's private
+  # key being stolen as well. A better solution is for `Owner` to contain a simple globally unique
+  # identifier for the owner, and for everyone to separately maintain a mapping of owner IDs to
+  # public keys. If an owner's private key is compromised, then humans will need to communicate
+  # and agree on a replacement public key, then update the mapping.
+  #
+  # As a concrete example, an `Owner` could simply contain a domain name, and restoring a SturdyRef
+  # would require signing a request using the domain's private key. Authenticating this key could
+  # be accomplished through certificate authorities or web-of-trust techniques.
+
+  save @0 SaveParams -> SaveResults;
+  # Save a capability persistently so that it can be restored by a future connection.  Not all
+  # capabilities can be saved -- application interfaces should define which capabilities support
+  # this and which do not.
+
+  struct SaveParams {
+    sealFor @0 :Owner;
+    # Seal the SturdyRef so that it can only be restored by the specified Owner. This is meant
+    # to mitigate damage when a SturdyRef is leaked. See comments above.
+    #
+    # Leaving this value null may or may not be allowed; it is up to the realm to decide. If a
+    # realm does allow a null owner, this should indicate that anyone is allowed to restore the
+    # ref.
+  }
+  struct SaveResults {
+    sturdyRef @0 :SturdyRef;
+  }
+}
+
+interface RealmGateway(InternalRef, ExternalRef, InternalOwner, ExternalOwner) {
+  # Interface invoked when a SturdyRef is about to cross realms. The RPC system supports providing
+  # a RealmGateway as a callback hook when setting up RPC over some VatNetwork.
+
+  import @0 (cap :Persistent(ExternalRef, ExternalOwner),
+             params :Persistent(InternalRef, InternalOwner).SaveParams)
+         -> Persistent(InternalRef, InternalOwner).SaveResults;
+  # Given an external capability, save it and return an internal reference. Used when someone
+  # inside the realm tries to save a capability from outside the realm.
+
+  export @1 (cap :Persistent(InternalRef, InternalOwner),
+             params :Persistent(ExternalRef, ExternalOwner).SaveParams)
+         -> Persistent(ExternalRef, ExternalOwner).SaveResults;
+  # Given an internal capability, save it and return an external reference. Used when someone
+  # outside the realm tries to save a capability from inside the realm.
+}
+
+annotation persistent(interface, field) :Void;
+# Apply this annotation to interfaces for objects that will always be persistent, instead of
+# extending the Persistent capability, since the correct type parameters to Persistent depend on
+# the realm, which is orthogonal to the interface type and therefore should not be defined
+# along-side it.
+#
+# You may also apply this annotation to a capability-typed field which will always contain a
+# persistent capability, but where the capability's interface itself is not already marked
+# persistent.
+#
+# Note that absence of the $persistent annotation doesn't mean a capability of that type isn't
+# persistent; it just means not *all* such capabilities are persistent.