Add base Module interface and global registry

module/module.go

@@ -0,0 +1,36 @@
+// Package module contians interfaces implemented by maddy modules.
+//
+// They are moved to separate package to prevent circular dependencies.
+//
+// Each interface required by maddy for operation is provided by some object
+// called "module".  This includes authentication, storage backends, DKIM,
+// email filters, etc.  Each module may serve multiple functions. I.e. it can
+// be IMAP storage backend, SMTP upstream and authentication provider at the
+// same moment.
+//
+// Each module gets its own unique name (sqlmail for go-sqlmail, proxy for
+// proxy module, local for local delivery perhaps, etc). Each module instance
+// also gets its own (unique too) name which is used to refer to it in
+// configuration.
+package module
+
+import "github.com/mholt/caddy/caddyfile"
+
+// Module is the interface implemented by all maddy module instances.
+//
+// It defines basic methods used to identify instances.
+type Module interface {
+	// Name method reports module name.
+	//
+	// It is used to reference module in the configuration and in logs.
+	Name() string
+
+	// InstanceName method reports unique name of this module instance.
+	InstanceName() string
+
+	// Module version. Reported in logs.
+	Version() string
+}
+
+// NewModule is function that creates new instance of module with specified name.
+type NewModule func(name string, cfg map[string]caddyfile.Token) (Module, error)

module/registry.go

@@ -0,0 +1,63 @@
+package module
+
+import "sync"
+
+var modules = make(map[string]NewModule)
+var modulesLck sync.RWMutex
+
+// Register adds module factory function to global registry.
+//
+// name must be unique. Register will panic if module with specified name
+// already exists in registry.
+//
+// You probably want to call this function from func init() of module package.
+func Register(name string, factory NewModule) {
+	modulesLck.Lock()
+	defer modulesLck.Unlock()
+
+	if _, ok := modules[name]; ok {
+		panic("Register: module with specified name is already registered: " + name)
+	}
+
+	modules[name] = factory
+}
+
+// GetMod returns module from global registry.
+//
+// Nil is returned if no module with specified name is registered.
+func GetMod(name string) NewModule {
+	modulesLck.RLock()
+	defer modulesLck.RUnlock()
+
+	return modules[name]
+}
+
+var instances = make(map[string]Module)
+var instancesLck sync.RWMutex
+
+// Register adds module factory function to global registry.
+//
+// name must be unique. Register will panic if module with specified name
+// already exists in registry.
+//
+// You probably want to call this function from func init() of module package.
+func RegisterInstance(inst Module) {
+	instancesLck.Lock()
+	defer instancesLck.Unlock()
+
+	if _, ok := instances[inst.InstanceName()]; ok {
+		panic("RegisterInstance: instance with specified name is already registered: " + inst.InstanceName())
+	}
+
+	instances[inst.InstanceName()] = inst
+}
+
+// GetInstance returns module instance from global registry.
+//
+// Nil is returned if no module instance with specified name is registered.
+func GetInstnace(name string) Module {
+	instancesLck.RLock()
+	defer instancesLck.RUnlock()
+
+	return instances[name]
+}