Functional configuration refactoring. Fixes alienscience#5

Inspired by @davecheney post: http://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis

README.md

@@ -8,9 +8,7 @@ This is an IMAP server written in Go. It is a work in progress.
 In the demo subdirectory is an example IMAP server that starts up on port 1193. To run this server:
 
 ```
-$ cd demo
-$ go build
-$ ./demo
+$ go run ./demo/main.go
 ```
 
 You can connect to this server using telnet or netcat. For example:
@@ -37,7 +35,11 @@ $ nc -C localhost 1193
 
 # Developing
 
-The server is not fully operational on its own. It defines an interface in session.go which describes the service it needs from a Mailstore. The Mailstore can be a database or filesystem or combination of both. The IMAP server does not care and it is up to the user to supply this service. 
+The server is not fully operational on its own. It requires a mailstore and an authentication mechanism. 
+
+It defines an interface in mailstore.go which describes the service it needs from a Mailstore. You can use multiple mailstores at the same time: database, filesystem, maildir, etc...
+
+There are plans to add basic support for maildir and a basic database storage.
 
 To add a new IMAP command the usual steps are:
 

demo/main.go

@@ -1,55 +1,53 @@
-
 package main
 
 import (
 	imap "github.com/alienscience/imapsrv"
 )
 
-// A dummy mailstore used for demonstrating the IMAP server
-type Mailstore struct {
-}
-
 func main() {
-	// Configure an IMAP server on localhost port 1193
-	config := imap.DefaultConfig()
-	config.Interface = "127.0.0.1:1193"
-
-	// Configure a dummy mailstore
-	mailstore := &Mailstore{}
-	config.Store = mailstore
-
-	// Start the server
-	server := imap.Create(config)
-	server.Start()
-
+	// The simplest possible server - zero config
+	// It will find a free tcp port, create some temporary directories.. - just give me a server!
+	//s := imap.NewServer()
+	//s.Start()
+
+	// More advanced config
+	m := &imap.DummyMailstore{}
+
+	s := imap.NewServer(
+		imap.Listen("127.0.0.1:1193"),
+		imap.Store(m),
+	)
+	s.Start()
 }
 
-//------ Dummy Mailstore -------------------------------------------------------
+// A dummy mailstore used for demonstrating the IMAP server
+type DummyMailstore struct {
+}
 
 // Get mailbox information
-func (m *Mailstore) GetMailbox(name string) (*imap.Mailbox, error) {
+func (m *DummyMailstore) GetMailbox(name string) (*imap.Mailbox, error) {
 	return &imap.Mailbox{
 		Name: "inbox",
-		Id: 1,
+		Id:   1,
 	}, nil
 }
 
 // Get the sequence number of the first unseen message
-func (m *Mailstore) FirstUnseen(mbox int64) (int64, error) {
+func (m *DummyMailstore) FirstUnseen(mbox int64) (int64, error) {
 	return 4, nil
 }
 
 // Get the total number of messages in an IMAP mailbox
-func (m *Mailstore) TotalMessages(mbox int64) (int64, error) {
+func (m *DummyMailstore) TotalMessages(mbox int64) (int64, error) {
 	return 8, nil
 }
 
 // Get the total number of unread messages in an IMAP mailbox
-func (m *Mailstore) RecentMessages(mbox int64) (int64, error) {
+func (m *DummyMailstore) RecentMessages(mbox int64) (int64, error) {
 	return 4, nil
 }
 
 // Get the next available uid in an IMAP mailbox
-func (m *Mailstore) NextUid(mbox int64) (int64, error) {
+func (m *DummyMailstore) NextUid(mbox int64) (int64, error) {
 	return 9, nil
 }

imap.go

@@ -1,4 +1,3 @@
-
 // An IMAP server
 package imapsrv
 
@@ -10,17 +9,22 @@ import (
 
 // IMAP server configuration
 type Config struct {
-	Interface  string
-	MaxClients int
-	Store      Mailstore
+	MaxClients uint
+	Listeners  []Listener
+	Mailstores []Mailstore
 }
 
 // An IMAP Server
 type Server struct {
 	// Server configuration
 	config *Config
 	// Number of active clients
-	activeClients int
+	activeClients uint
+}
+
+// A listener is listening on a given address. Ex: 0.0.0.0:193
+type Listener struct {
+	Addr string
 }
 
 // An IMAP Client as seen by an IMAP server
@@ -42,47 +46,131 @@ func Create(config *Config) *Server {
 
 // Return the default server configuration
 func DefaultConfig() *Config {
+	listeners := []Listener{
+		Listener{
+			Addr: "0.0.0.0:143",
+		},
+	}
+
 	return &Config{
-		Interface:  "0.0.0.0:193",
+		Listeners:  listeners,
 		MaxClients: 8,
 	}
 }
 
-// Start an IMAP server
-func (s *Server) Start() {
+// Add a mailstore to the config
+func Store(m Mailstore) func(*Server) error {
+	return func(s *Server) error {
+		s.config.Mailstores = append(s.config.Mailstores, m)
+		return nil
+	}
+}
 
-	// Start listening for IMAP connections
-	iface := s.config.Interface
-	listener, err := net.Listen("tcp", iface)
-	if err != nil {
-		log.Fatalf("IMAP cannot listen on %s, %v", iface, err)
+// test if 2 listeners are equal
+func equalListeners(l1, l2 []Listener) bool {
+	for i, l := range l1 {
+		if l != l2[i] {
+			return false
+		}
 	}
+	return true
+}
 
-	log.Print("IMAP server listening on ", iface)
+// Add an interface to listen to
+func Listen(Addr string) func(*Server) error {
+	return func(s *Server) error {
+		// if we only have the default config we should override it
+		dc := DefaultConfig()
+		l := Listener{
+			Addr: Addr,
+		}
+		if equalListeners(dc.Listeners, s.config.Listeners) {
+			s.config.Listeners = []Listener{l}
+		} else {
+			s.config.Listeners = append(s.config.Listeners, l)
+		}
 
-	clientNumber := 1
+		return nil
+	}
+}
 
-	for {
-		// Accept a connection from a new client
-		conn, err := listener.Accept()
+// Set MaxClients config
+func MaxClients(max uint) func(*Server) error {
+	return func(s *Server) error {
+		s.config.MaxClients = max
+		return nil
+	}
+}
+
+func NewServer(options ...func(*Server) error) *Server {
+	// set the default config
+	s := &Server{}
+	dc := DefaultConfig()
+	s.config = dc
+
+	// override the config with the functional options
+	for _, option := range options {
+		err := option(s)
 		if err != nil {
-			log.Print("IMAP accept error, ", err)
-			continue
+			panic(err)
 		}
+	}
+
+	//Check if we can listen on default ports, if not try to find a free port
+	if equalListeners(dc.Listeners, s.config.Listeners) {
+		listener := s.config.Listeners[0]
+		l, err := net.Listen("tcp", listener.Addr)
+		if err != nil {
+			l, err = net.Listen("tcp4", ":0") // this will ask the OS to give us a free port
+			if err != nil {
+				panic("Can't listen on any port")
+			}
+			l.Close()
+			s.config.Listeners[0].Addr = l.Addr().String()
+		} else {
+			l.Close()
+		}
+	}
+
+	return s
+}
 
-		// Handle the client
-		client := &client{
-			conn:   conn,
-			bufin:  bufio.NewReader(conn),
-			bufout: bufio.NewWriter(conn),
-			id:     clientNumber,
-			config: s.config,
+// Start an IMAP server
+func (s *Server) Start() error {
+	// Start listening for IMAP connections
+	for _, iface := range s.config.Listeners {
+		listener, err := net.Listen("tcp", iface.Addr)
+		if err != nil {
+			log.Fatalf("IMAP cannot listen on %s, %v", iface.Addr, err)
 		}
 
-		go client.handle()
+		log.Print("IMAP server listening on ", iface.Addr)
+
+		clientNumber := 1
 
-		clientNumber += 1
+		for {
+			// Accept a connection from a new client
+			conn, err := listener.Accept()
+			if err != nil {
+				log.Print("IMAP accept error, ", err)
+				continue
+			}
+
+			// Handle the client
+			client := &client{
+				conn:   conn,
+				bufin:  bufio.NewReader(conn),
+				bufout: bufio.NewWriter(conn),
+				id:     clientNumber,
+				config: s.config,
+			}
+
+			go client.handle()
+
+			clientNumber += 1
+		}
 	}
+	return nil
 }
 
 // Handle requests from an IMAP client

mailstore.go

@@ -0,0 +1,48 @@
+package imapsrv
+
+// A service that is needed to read mail messages
+type Mailstore interface {
+	// Get IMAP mailbox information
+	// Returns nil if the mailbox does not exist
+	GetMailbox(name string) (*Mailbox, error)
+	// Get the sequence number of the first unseen message
+	FirstUnseen(mbox int64) (int64, error)
+	// Get the total number of messages in an IMAP mailbox
+	TotalMessages(mbox int64) (int64, error)
+	// Get the total number of unread messages in an IMAP mailbox
+	RecentMessages(mbox int64) (int64, error)
+	// Get the next available uid in an IMAP mailbox
+	NextUid(mbox int64) (int64, error)
+}
+
+// A dummy mailstore used for demonstrating the IMAP server
+type DummyMailstore struct {
+}
+
+// Get mailbox information
+func (m *DummyMailstore) GetMailbox(name string) (*Mailbox, error) {
+	return &Mailbox{
+		Name: "inbox",
+		Id:   1,
+	}, nil
+}
+
+// Get the sequence number of the first unseen message
+func (m *DummyMailstore) FirstUnseen(mbox int64) (int64, error) {
+	return 4, nil
+}
+
+// Get the total number of messages in an IMAP mailbox
+func (m *DummyMailstore) TotalMessages(mbox int64) (int64, error) {
+	return 8, nil
+}
+
+// Get the total number of unread messages in an IMAP mailbox
+func (m *DummyMailstore) RecentMessages(mbox int64) (int64, error) {
+	return 4, nil
+}
+
+// Get the next available uid in an IMAP mailbox
+func (m *DummyMailstore) NextUid(mbox int64) (int64, error) {
+	return 9, nil
+}

parser.go

@@ -1,4 +1,3 @@
-
 package imapsrv
 
 import (