Chris@50: // Copyright (c) 2015 Sandstorm Development Group, Inc. and contributors Chris@50: // Licensed under the MIT License: Chris@50: // Chris@50: // Permission is hereby granted, free of charge, to any person obtaining a copy Chris@50: // of this software and associated documentation files (the "Software"), to deal Chris@50: // in the Software without restriction, including without limitation the rights Chris@50: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell Chris@50: // copies of the Software, and to permit persons to whom the Software is Chris@50: // furnished to do so, subject to the following conditions: Chris@50: // Chris@50: // The above copyright notice and this permission notice shall be included in Chris@50: // all copies or substantial portions of the Software. Chris@50: // Chris@50: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR Chris@50: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, Chris@50: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE Chris@50: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER Chris@50: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, Chris@50: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN Chris@50: // THE SOFTWARE. Chris@50: Chris@50: #ifndef CAPNP_MEMBRANE_H_ Chris@50: #define CAPNP_MEMBRANE_H_ Chris@50: // In capability theory, a "membrane" is a wrapper around a capability which (usually) forwards Chris@50: // calls but recursively wraps capabilities in those calls in the same membrane. The purpose of a Chris@50: // membrane is to enforce a barrier between two capabilities that cannot be bypassed by merely Chris@50: // introducing new objects. Chris@50: // Chris@50: // The most common use case for a membrane is revocation: Say Alice wants to give Bob a capability Chris@50: // to access Carol, but wants to be able to revoke this capability later. Alice can accomplish this Chris@50: // by wrapping Carol in a revokable wrapper which passes through calls until such a time as Alice Chris@50: // indicates it should be revoked, after which all calls through the wrapper will throw exceptions. Chris@50: // However, a naive wrapper approach has a problem: if Bob makes a call to Carol and sends a new Chris@50: // capability in that call, or if Carol returns a capability to Bob in the response to a call, then Chris@50: // the two are now able to communicate using this new capability, which Alice cannot revoke. In Chris@50: // order to avoid this problem, Alice must use not just a wrapper but a "membrane", which Chris@50: // recursively wraps all objects that pass through it in either direction. Thus, all connections Chris@50: // formed between Bob and Carol (originating from Alice's original introduction) can be revoked Chris@50: // together by revoking the membrane. Chris@50: // Chris@50: // Note that when a capability is passed into a membrane and then passed back out, the result is Chris@50: // the original capability, not a double-membraned capability. This means that in our revocation Chris@50: // example, if Bob uses his capability to Carol to obtain another capability from her, then send Chris@50: // it back to her, the capability Carol receives back will NOT be revoked when Bob's access to Chris@50: // Carol is revoked. Thus Bob can create long-term irrevocable connections. In most practical use Chris@50: // cases, this is what you want. APIs commonly rely on the fact that a capability obtained and then Chris@50: // passed back can be recognized as the original capability. Chris@50: // Chris@50: // Mark Miller on membranes: http://www.eros-os.org/pipermail/e-lang/2003-January/008434.html Chris@50: Chris@50: #include "capability.h" Chris@50: Chris@50: namespace capnp { Chris@50: Chris@50: class MembranePolicy { Chris@50: // Applications may implement this interface to define a membrane policy, which allows some Chris@50: // calls crossing the membrane to be blocked or redirected. Chris@50: Chris@50: public: Chris@50: virtual kj::Maybe inboundCall( Chris@50: uint64_t interfaceId, uint16_t methodId, Capability::Client target) = 0; Chris@50: // Given an inbound call (a call originating "outside" the membrane destined for an object Chris@50: // "inside" the membrane), decides what to do with it. The policy may: Chris@50: // Chris@50: // - Return null to indicate that the call should proceed to the destination. All capabilities Chris@50: // in the parameters or result will be properly wrapped in the same membrane. Chris@50: // - Return a capability to have the call redirected to that capability. Note that the redirect Chris@50: // capability will be treated as outside the membrane, so the params and results will not be Chris@50: // auto-wrapped; however, the callee can easily wrap the returned capability in the membrane Chris@50: // itself before returning to achieve this effect. Chris@50: // - Throw an exception to cause the call to fail with that exception. Chris@50: // Chris@50: // `target` is the underlying capability (*inside* the membrane) for which the call is destined. Chris@50: // Generally, the only way you should use `target` is to wrap it in some capability which you Chris@50: // return as a redirect. The redirect capability may modify the call in some way and send it to Chris@50: // `target`. Be careful to use `copyIntoMembrane()` and `copyOutOfMembrane()` as appropriate when Chris@50: // copying parameters or results across the membrane. Chris@50: // Chris@50: // Note that since `target` is inside the capability, if you were to directly return it (rather Chris@50: // than return null), the effect would be that the membrane would be broken: the call would Chris@50: // proceed directly and any new capabilities introduced through it would not be membraned. You Chris@50: // generally should not do that. Chris@50: Chris@50: virtual kj::Maybe outboundCall( Chris@50: uint64_t interfaceId, uint16_t methodId, Capability::Client target) = 0; Chris@50: // Like `inboundCall()`, but applies to calls originating *inside* the membrane and terminating Chris@50: // outside. Chris@50: // Chris@50: // Note: It is strongly recommended that `outboundCall()` returns null in exactly the same cases Chris@50: // that `inboundCall()` return null. Conversely, for any case where `inboundCall()` would Chris@50: // redirect or throw, `outboundCall()` should also redirect or throw. Otherwise, you can run Chris@50: // into inconsistent behavion when a promise is returned across a membrane, and that promise Chris@50: // later resolves to a capability on the other side of the membrane: calls on the promise Chris@50: // will enter and then exit the membrane, but calls on the eventual resolution will not cross Chris@50: // the membrane at all, so it is important that these two cases behave the same. Chris@50: Chris@50: virtual kj::Own addRef() = 0; Chris@50: // Return a new owned pointer to the same policy. Chris@50: // Chris@50: // Typically an implementation of MembranePolicy should also inherit kj::Refcounted and implement Chris@50: // `addRef()` as `return kj::addRef(*this);`. Chris@50: // Chris@50: // Note that the membraning system considers two membranes created with the same MembranePolicy Chris@50: // object actually to be the *same* membrane. This is relevant when an object passes into the Chris@50: // membrane and then back out (or out and then back in): instead of double-wrapping the object, Chris@50: // the wrapping will be removed. Chris@50: }; Chris@50: Chris@50: Capability::Client membrane(Capability::Client inner, kj::Own policy); Chris@50: // Wrap `inner` in a membrane specified by `policy`. `inner` is considered "inside" the membrane, Chris@50: // while the returned capability should only be called from outside the membrane. Chris@50: Chris@50: Capability::Client reverseMembrane(Capability::Client outer, kj::Own policy); Chris@50: // Like `membrane` but treat the input capability as "outside" the membrane, and return a Chris@50: // capability appropriate for use inside. Chris@50: // Chris@50: // Applications typically won't use this directly; the membraning code automatically sets up Chris@50: // reverse membranes where needed. Chris@50: Chris@50: template Chris@50: ClientType membrane(ClientType inner, kj::Own policy); Chris@50: template Chris@50: ClientType reverseMembrane(ClientType inner, kj::Own policy); Chris@50: // Convenience templates which return the same interface type as the input. Chris@50: Chris@50: template Chris@50: typename ServerType::Serves::Client membrane( Chris@50: kj::Own inner, kj::Own policy); Chris@50: template Chris@50: typename ServerType::Serves::Client reverseMembrane( Chris@50: kj::Own inner, kj::Own policy); Chris@50: // Convenience templates which input a capability server type and return the appropriate client Chris@50: // type. Chris@50: Chris@50: template Chris@50: Orphan::Reads> copyIntoMembrane( Chris@50: Reader&& from, Orphanage to, kj::Own policy); Chris@50: // Copy a Cap'n Proto object (e.g. struct or list), adding the given membrane to any capabilities Chris@50: // found within it. `from` is interpreted as "outside" the membrane while `to` is "inside". Chris@50: Chris@50: template Chris@50: Orphan::Reads> copyOutOfMembrane( Chris@50: Reader&& from, Orphanage to, kj::Own policy); Chris@50: // Like copyIntoMembrane() except that `from` is "inside" the membrane and `to` is "outside". Chris@50: Chris@50: // ======================================================================================= Chris@50: // inline implementation details Chris@50: Chris@50: template Chris@50: ClientType membrane(ClientType inner, kj::Own policy) { Chris@50: return membrane(Capability::Client(kj::mv(inner)), kj::mv(policy)) Chris@50: .castAs(); Chris@50: } Chris@50: template Chris@50: ClientType reverseMembrane(ClientType inner, kj::Own policy) { Chris@50: return reverseMembrane(Capability::Client(kj::mv(inner)), kj::mv(policy)) Chris@50: .castAs(); Chris@50: } Chris@50: Chris@50: template Chris@50: typename ServerType::Serves::Client membrane( Chris@50: kj::Own inner, kj::Own policy) { Chris@50: return membrane(Capability::Client(kj::mv(inner)), kj::mv(policy)) Chris@50: .castAs(); Chris@50: } Chris@50: template Chris@50: typename ServerType::Serves::Client reverseMembrane( Chris@50: kj::Own inner, kj::Own policy) { Chris@50: return reverseMembrane(Capability::Client(kj::mv(inner)), kj::mv(policy)) Chris@50: .castAs(); Chris@50: } Chris@50: Chris@50: namespace _ { // private Chris@50: Chris@50: OrphanBuilder copyOutOfMembrane(PointerReader from, Orphanage to, Chris@50: kj::Own policy, bool reverse); Chris@50: OrphanBuilder copyOutOfMembrane(StructReader from, Orphanage to, Chris@50: kj::Own policy, bool reverse); Chris@50: OrphanBuilder copyOutOfMembrane(ListReader from, Orphanage to, Chris@50: kj::Own policy, bool reverse); Chris@50: Chris@50: } // namespace _ (private) Chris@50: Chris@50: template Chris@50: Orphan::Reads> copyIntoMembrane( Chris@50: Reader&& from, Orphanage to, kj::Own policy) { Chris@50: return _::copyOutOfMembrane( Chris@50: _::PointerHelpers::Reads>::getInternalReader(from), Chris@50: to, kj::mv(policy), true); Chris@50: } Chris@50: Chris@50: template Chris@50: Orphan::Reads> copyOutOfMembrane( Chris@50: Reader&& from, Orphanage to, kj::Own policy) { Chris@50: return _::copyOutOfMembrane( Chris@50: _::PointerHelpers::Reads>::getInternalReader(from), Chris@50: to, kj::mv(policy), false); Chris@50: } Chris@50: Chris@50: } // namespace capnp Chris@50: Chris@50: #endif // CAPNP_MEMBRANE_H_