etcd/etcdserver/server.go

package etcdserver

import (
	"errors"
	"time"

	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
	"github.com/coreos/etcd/raft"
	"github.com/coreos/etcd/raft/raftpb"
	"github.com/coreos/etcd/store"
	"github.com/coreos/etcd/third_party/code.google.com/p/go.net/context"
	"github.com/coreos/etcd/wait"
)

var (
	ErrUnknownMethod = errors.New("etcdserver: unknown method")
	ErrStopped       = errors.New("etcdserver: server stopped")
)

type SendFunc func(m []raftpb.Message)
type SaveFunc func(st raftpb.State, ents []raftpb.Entry)

type Response struct {
	Event   *store.Event
	Watcher store.Watcher
	err     error
}

type Server interface {
	// Start performs any initialization of the Server necessary for it to
	// begin serving requests. It must be called before Do or Process.
	// Start must be non-blocking; any long-running server functionality
	// should be implemented in goroutines.
	Start()
	// Stop terminates the Server and performs any necessary finalization.
	// Do and Process cannot be called after Stop has been invoked.
	Stop()
	// Do takes a request and attempts to fulfil it, returning a Response.
	Do(ctx context.Context, r pb.Request) (Response, error)
	// Process takes a raft message and applies it to the server's raft state
	// machine, respecting any timeout of the given context.
	Process(ctx context.Context, m raftpb.Message) error
}

// EtcdServer is the production implementation of the Server interface
type EtcdServer struct {
	w    wait.Wait
	done chan struct{}

	Node  raft.Node
	Store store.Store

	// Send specifies the send function for sending msgs to peers. Send
	// MUST NOT block. It is okay to drop messages, since clients should
	// timeout and reissue their messages.  If Send is nil, server will
	// panic.
	Send SendFunc

	// Save specifies the save function for saving ents to stable storage.
	// Save MUST block until st and ents are on stable storage.  If Send is
	// nil, server will panic.
	Save func(st raftpb.State, ents []raftpb.Entry)

	Ticker <-chan time.Time
}

// Start prepares and starts server in a new goroutine. It is no longer safe to
// modify a server's fields after it has been sent to Start.
func (s *EtcdServer) Start() {
	s.w = wait.New()
	s.done = make(chan struct{})
	go s.run()
}

func (s *EtcdServer) Process(ctx context.Context, m raftpb.Message) error {
	return s.Node.Step(ctx, m)
}

func (s *EtcdServer) run() {
	for {
		select {
		case <-s.Ticker:
			s.Node.Tick()
		case rd := <-s.Node.Ready():
			s.Save(rd.State, rd.Entries)
			s.Send(rd.Messages)

			// TODO(bmizerany): do this in the background, but take
			// care to apply entries in a single goroutine, and not
			// race them.
			for _, e := range rd.CommittedEntries {
				var r pb.Request
				if err := r.Unmarshal(e.Data); err != nil {
					panic("TODO: this is bad, what do we do about it?")
				}
				s.w.Trigger(r.Id, s.apply(r))
			}
		case <-s.done:
			return
		}
	}
}

// Stop stops the server, and shuts down the running goroutine. Stop should be
// called after a Start(s), otherwise it will block forever.
func (s *EtcdServer) Stop() {
	s.Node.Stop()
	close(s.done)
}

// Do interprets r and performs an operation on s.Store according to r.Method
// and other fields. If r.Method is "POST", "PUT", "DELETE", or a "GET with
// Quorum == true, r will be sent through consensus before performing its
// respective operation. Do will block until an action is performed or there is
// an error.
func (s *EtcdServer) Do(ctx context.Context, r pb.Request) (Response, error) {
	if r.Id == 0 {
		panic("r.Id cannot be 0")
	}
	if r.Method == "GET" && r.Quorum {
		r.Method = "QGET"
	}
	switch r.Method {
	case "POST", "PUT", "DELETE", "QGET":
		data, err := r.Marshal()
		if err != nil {
			return Response{}, err
		}
		ch := s.w.Register(r.Id)
		s.Node.Propose(ctx, data)
		select {
		case x := <-ch:
			resp := x.(Response)
			return resp, resp.err
		case <-ctx.Done():
			s.w.Trigger(r.Id, nil) // GC wait
			return Response{}, ctx.Err()
		case <-s.done:
			return Response{}, ErrStopped
		}
	case "GET":
		switch {
		case r.Wait:
			wc, err := s.Store.Watch(r.Path, r.Recursive, false, r.Since)
			if err != nil {
				return Response{}, err
			}
			return Response{Watcher: wc}, nil
		default:
			ev, err := s.Store.Get(r.Path, r.Recursive, r.Sorted)
			if err != nil {
				return Response{}, err
			}
			return Response{Event: ev}, nil
		}
	default:
		return Response{}, ErrUnknownMethod
	}
}

// apply interprets r as a call to store.X and returns an Response interpreted from store.Event
func (s *EtcdServer) apply(r pb.Request) Response {
	f := func(ev *store.Event, err error) Response {
		return Response{Event: ev, err: err}
	}
	expr := time.Unix(0, r.Expiration)
	switch r.Method {
	case "POST":
		return f(s.Store.Create(r.Path, r.Dir, r.Val, true, expr))
	case "PUT":
		exists, existsSet := getBool(r.PrevExists)
		switch {
		case existsSet:
			if exists {
				return f(s.Store.Update(r.Path, r.Val, expr))
			} else {
				return f(s.Store.Create(r.Path, r.Dir, r.Val, false, expr))
			}
		case r.PrevIndex > 0 || r.PrevValue != "":
			return f(s.Store.CompareAndSwap(r.Path, r.PrevValue, r.PrevIndex, r.Val, expr))
		default:
			return f(s.Store.Set(r.Path, r.Dir, r.Val, expr))
		}
	case "DELETE":
		switch {
		case r.PrevIndex > 0 || r.PrevValue != "":
			return f(s.Store.CompareAndDelete(r.Path, r.PrevValue, r.PrevIndex))
		default:
			return f(s.Store.Delete(r.Path, r.Recursive, r.Dir))
		}
	case "QGET":
		return f(s.Store.Get(r.Path, r.Recursive, r.Sorted))
	default:
		// This should never be reached, but just in case:
		return Response{err: ErrUnknownMethod}
	}
}

func getBool(v *bool) (vv bool, set bool) {
	if v == nil {
		return false, false
	}
	return *v, true
}