type DecoratedRegistration struct {
    // Service is the service to decorate.
    Service RegistrationServer
    // Prelude is called for each method before forwarding the call to Service.
    // If Prelude returns an error, then the call is skipped and the error is
    // processed via the Postlude (if one is defined), or it is returned directly.
    Prelude func(c context.Context, methodName string, req proto.Message) (context.Context, error)
    // Postlude is called for each method after Service has processed the call, or
    // after the Prelude has returned an error. This takes the the Service's
    // response proto (which may be nil) and/or any error. The decorated
    // service will return the response (possibly mutated) and error that Postlude
    // returns.
    Postlude func(c context.Context, methodName string, rsp proto.Message, err error) error
}

type RegisterPrefixRequest struct {
    // The log stream's project.
    Project string `protobuf:"bytes,1,opt,name=project" json:"project,omitempty"`
    // The log stream prefix to register.
    Prefix string `protobuf:"bytes,2,opt,name=prefix" json:"prefix,omitempty"`
    // Optional information about the registering agent.
    SourceInfo []string `protobuf:"bytes,3,rep,name=source_info,json=sourceInfo" json:"source_info,omitempty"`
    // Optional nonce to allow retries of this RPC. ALL CLIENTS SHOULD PROVIDE
    // THIS. The client should generate the nonce once while preparing the request
    // message, and then re-use the same nonce for retries of the request.
    //
    // The nonce should be 32 bytes of random data.
    // The nonce must not be reused between different requests (only for retries
    //   of the same request).
    //
    // NOTE: This is currently optional, but once all clients have upgraded to
    // this scheme, it will become mandatory. During the transition if this is
    // omitted, then NO RETRIES will be allowed for this request, if the server
    // processes it correctly but the client fails to get the response from the
    // server.
    OpNonce []byte `protobuf:"bytes,4,opt,name=op_nonce,json=opNonce,proto3" json:"op_nonce,omitempty"`
    // The prefix expiration time. If <= 0, the project's default prefix
    // expiration period will be applied.
    //
    // The prefix will be closed by the Coordinator after its expiration period.
    // Once closed, new stream registration requests will no longer be accepted.
    //
    // If supplied, this value should exceed the timeout of the local task, else
    // some of the task's streams may be dropped due to failing registration.
    Expiration           *duration.Duration `protobuf:"bytes,10,opt,name=expiration" json:"expiration,omitempty"`
    XXX_NoUnkeyedLiteral struct{}           `json:"-"`
    XXX_unrecognized     []byte             `json:"-"`
    XXX_sizecache        int32              `json:"-"`
}

type RegisterPrefixResponse struct {
    // Secret is the prefix's secret. This must be included verbatim in Butler
    // bundles to assert ownership of this prefix.
    Secret []byte `protobuf:"bytes,1,opt,name=secret,proto3" json:"secret,omitempty"`
    // The name of the Pub/Sub topic to publish butlerproto-formatted Butler log
    // bundles to.
    LogBundleTopic       string   `protobuf:"bytes,2,opt,name=log_bundle_topic,json=logBundleTopic" json:"log_bundle_topic,omitempty"`
    XXX_NoUnkeyedLiteral struct{} `json:"-"`
    XXX_unrecognized     []byte   `json:"-"`
    XXX_sizecache        int32    `json:"-"`
}

type RegistrationClient interface {
    // RegisterStream allows a Butler instance to register a log stream with the
    // Coordinator. Upon success, the Coordinator will return registration
    // information and streaming parameters to the Butler.
    //
    // This should be called by a Butler instance to gain the ability to publish
    // to a prefix space. The caller must have WRITE access to its project's
    // stream space. If WRITE access is not present, this will fail with the
    // "PermissionDenied" gRPC code.
    //
    // A stream prefix may be registered at most once. Additional registration
    // requests will fail with the "AlreadyExists" gRPC code.
    RegisterPrefix(ctx context.Context, in *RegisterPrefixRequest, opts ...grpc.CallOption) (*RegisterPrefixResponse, error)
}

type RegistrationServer interface {
    // RegisterStream allows a Butler instance to register a log stream with the
    // Coordinator. Upon success, the Coordinator will return registration
    // information and streaming parameters to the Butler.
    //
    // This should be called by a Butler instance to gain the ability to publish
    // to a prefix space. The caller must have WRITE access to its project's
    // stream space. If WRITE access is not present, this will fail with the
    // "PermissionDenied" gRPC code.
    //
    // A stream prefix may be registered at most once. Additional registration
    // requests will fail with the "AlreadyExists" gRPC code.
    RegisterPrefix(context.Context, *RegisterPrefixRequest) (*RegisterPrefixResponse, error)
}