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// Copyright 2020 The LUCI Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// Package module defines a framework for extending server.Server with optional
// reusable bundles of functionality (called "modules", naturally).
package module
import (
// Module represents some optional part of a server.
// It is generally a stateful object constructed from some configuration. It can
// be hooked to the server in server.New(...) or server.Main(...).
type Module interface {
// Name is a name of this module for logs and dependency relations.
// Usually a package that implements the module registers module's name as
// a public global variable (so other packages can refer to it) and this
// method just returns it.
Name() Name
// Dependencies returns dependencies (required and optional) of this module.
Dependencies() []Dependency
// Initialize is called during the server startup after the core functionality
// is initialized, but before the server enters the serving loop.
// The method receives the global server context and can return a derived
// context which will become the new global server context. That way the
// module may inject additional state into the context inherited by all
// requests. If it returns nil, the server context won't be changed.
// The module may use the context (with all values available there) and the
// given Host interface to register itself in various server systems. It must
// not retain 'host': the object it points to becomes invalid after Initialize
// finishes and using it causes panics. This is intentional.
// Modules are initialized sequentially in order they are registered. A module
// observes effects of initialization of all prior modules, e.g. via
// context.Context.
// An error causes the process to crash with the corresponding message.
Initialize(ctx context.Context, host Host, opts HostOptions) (context.Context, error)
// HostOptions are options the server was started with.
// It is a subset of global server.Options that modules are allowed to use to
// tweak their behavior.
type HostOptions struct {
Prod bool // set when running in production (not on a dev workstation)
GAE bool // set when running on Appengine, implies Prod
CloudProject string // name of hosting Google Cloud Project if running in GCP
CloudRegion string // name of a hosting region (e.g. 'us-central1') if known
// Host is part of server.Server API that modules are allowed to use during
// their initialization to inject useful functionality into the server.
// TODO(vadimsh):
// * Allow adding a middleware to the default middleware chain.
type Host interface {
// ServiceRegistrar is a registrar that can be used to register gRPC services.
ServiceRegistrar() grpc.ServiceRegistrar
// Routes returns a router that servers HTTP requests hitting the main port.
// The module can use it to register additional request handlers.
// Note that users of server.Server can register more routers through
// server.AddPort(...) and server.VirtualHost(...). Such application-specific
// routers are not accessible to modules.
Routes() *router.Router
// RunInBackground launches the given callback in a separate goroutine right
// before starting the serving loop.
// Should be used for background asynchronous activities like reloading
// configs.
// All logs lines emitted by the callback are annotated with "activity" field
// which can be arbitrary, but by convention has format "<namespace>.<name>",
// where "luci" namespace is reserved for internal activities.
// The context passed to the callback is derived from the global server
// context and it is canceled when the server is shutting down. It is expected
// the goroutine will exit soon after the context is canceled.
RunInBackground(activity string, f func(context.Context))
// RegisterWarmup registers a callback that is run in server's ListenAndServe
// right before the serving loop.
// It receives the global server context (including all customizations made
// by the user code in server.Main). Intended for best-effort warmups: there's
// no way to gracefully abort the server startup from a warmup callback.
// All module's essential initialization should happen in its Initialize
// method instead. The downside is that Initialize runs before the user code
// in server.Main and it can't depend on modifications done there.
RegisterWarmup(cb func(context.Context))
// RegisterCleanup registers a callback that is run in server's ListenAndServe
// after the server exits the serving loop.
// It receives the global server context.
RegisterCleanup(cb func(context.Context))
// RegisterUnaryServerInterceptor registers an grpc.UnaryServerInterceptor
// applied to all unary RPCs that hit the server.
// Interceptors are chained in order they are registered, which matches
// the order of modules in the list of modules. The first registered
// interceptor becomes the outermost.
RegisterUnaryServerInterceptor(intr grpc.UnaryServerInterceptor)
// RegisterCookieAuth registers an implementation of a cookie-based
// authentication scheme.
// If there are multiple such schemes registered, the server will refuse to
// start.
RegisterCookieAuth(method auth.Method)