Extract meshconn from raft-on-mesh experiment

This is independently useful, and will have a separate lifecycle.

examples/meshconn/README.md

@@ -0,0 +1,15 @@
+# meshconn
+
+meshconn implements [net.PacketConn](https://golang.org/pkg/net/#PacketConn) on top of mesh.
+Think of it as UDP with benefits:
+ NAT and bastion host (DMZ) traversal,
+ broadcast/multicast in networks where this is normally not possible e.g. EC2,
+ and an up-to-date, queryable memberlist.
+
+meshconn supports [net.Addr](https://golang.org/pkg/net/#Addr) of the form `weavemesh://<PeerName>`.
+By default, `<PeerName>` is a hardware address of the form `01:02:03:FD:FE:FF`.
+Other forms of PeerName e.g. hashes are supported.
+
+meshconn itself is largely stateless and has best-effort delivery semantics.
+As a future experiment, it could easily be amended to have basic resiliency guarantees.
+Also, at the moment, PacketConn read and write deadlines are not supported.

examples/meshconn/mesh_addr.go

@@ -0,0 +1,21 @@
+package meshconn
+
+import (
+	"fmt"
+	"net"
+
+	"github.com/weaveworks/mesh"
+)
+
+// MeshAddr implements net.Addr for mesh peers.
+type MeshAddr struct {
+	mesh.PeerName
+}
+
+var _ net.Addr = MeshAddr{}
+
+// Network returns weavemesh.
+func (a MeshAddr) Network() string { return "weavemesh" }
+
+// String returns weavemesh://<PeerName>.
+func (a MeshAddr) String() string { return fmt.Sprintf("%s://%s", a.Network(), a.PeerName.String()) }

examples/meshconn/peer.go

@@ -0,0 +1,181 @@
+package meshconn
+
+import (
+	"errors"
+	"log"
+	"net"
+	"time"
+
+	"github.com/weaveworks/mesh"
+)
+
+var (
+	// ErrShortRead is returned by ReadFrom when the
+	// passed buffer is too small for the packet.
+	ErrShortRead = errors.New("short read")
+
+	// ErrPeerClosed is returned by ReadFrom and WriteTo
+	// when the peer is closed during the operation.
+	ErrPeerClosed = errors.New("peer closed")
+
+	// ErrGossipNotRegistered is returned by Write to when attempting
+	// to write before a mesh.Gossip has been registered in the peer.
+	ErrGossipNotRegistered = errors.New("gossip not registered")
+
+	// ErrNotMeshAddr is returned by WriteTo when attempting
+	// to write to a non-mesh address.
+	ErrNotMeshAddr = errors.New("not a mesh addr")
+
+	// ErrNotSupported is returned by methods that are not supported.
+	ErrNotSupported = errors.New("not supported")
+)
+
+// Peer implements mesh.Gossiper and net.PacketConn.
+type Peer struct {
+	name    mesh.PeerName
+	gossip  mesh.Gossip
+	recv    chan pkt
+	actions chan func()
+	quit    chan struct{}
+	logger  *log.Logger
+}
+
+// NewPeer returns a Peer, which can be used as a net.PacketConn.
+// Clients must Register a mesh.Gossip before calling ReadFrom or WriteTo.
+// Clients should aggressively consume from ReadFrom.
+func NewPeer(name mesh.PeerName, logger *log.Logger) *Peer {
+	p := &Peer{
+		name:    name,
+		gossip:  nil, // initially no gossip
+		recv:    make(chan pkt),
+		actions: make(chan func()),
+		quit:    make(chan struct{}),
+		logger:  logger,
+	}
+	go p.loop()
+	return p
+}
+
+func (p *Peer) loop() {
+	for {
+		select {
+		case f := <-p.actions:
+			f()
+		case <-p.quit:
+			return
+		}
+	}
+}
+
+// Register injects the mesh.Gossip and enables full-duplex communication.
+// Clients should consume from ReadFrom without blocking.
+func (p *Peer) Register(gossip mesh.Gossip) {
+	p.actions <- func() { p.gossip = gossip }
+}
+
+// ReadFrom implements net.PacketConn.
+// Clients should consume from ReadFrom without blocking.
+func (p *Peer) ReadFrom(b []byte) (n int, remote net.Addr, err error) {
+	c := make(chan struct{})
+	p.actions <- func() {
+		go func() { // so as not to block loop
+			defer close(c)
+			select {
+			case pkt := <-p.recv:
+				n = copy(b, pkt.Buf)
+				remote = MeshAddr{pkt.Src}
+				if n < len(pkt.Buf) {
+					err = ErrShortRead
+				}
+			case <-p.quit:
+				err = ErrPeerClosed
+			}
+		}()
+	}
+	<-c
+	return n, remote, err
+}
+
+// WriteTo implements net.PacketConn.
+func (p *Peer) WriteTo(b []byte, dst net.Addr) (n int, err error) {
+	c := make(chan struct{})
+	p.actions <- func() {
+		defer close(c)
+		if p.gossip == nil {
+			err = ErrGossipNotRegistered
+			return
+		}
+		meshAddr, ok := dst.(MeshAddr)
+		if !ok {
+			err = ErrNotMeshAddr
+			return
+		}
+		pkt := pkt{Src: p.name, Buf: b}
+		if meshAddr.PeerName == p.name {
+			p.recv <- pkt
+			return
+		}
+		// TODO(pb): detect and support broadcast
+		buf := pkt.encode()
+		n = len(buf)
+		err = p.gossip.GossipUnicast(meshAddr.PeerName, buf)
+	}
+	<-c
+	return n, err
+}
+
+// Close implements net.PacketConn.
+func (p *Peer) Close() error {
+	close(p.quit)
+	return nil
+}
+
+// LocalAddr implements net.PacketConn.
+func (p *Peer) LocalAddr() net.Addr {
+	return MeshAddr{p.name}
+}
+
+// SetDeadline implements net.PacketConn.
+// SetDeadline is not supported.
+func (p *Peer) SetDeadline(time.Time) error {
+	return ErrNotSupported
+}
+
+// SetReadDeadline implements net.PacketConn.
+// SetReadDeadline is not supported.
+func (p *Peer) SetReadDeadline(time.Time) error {
+	return ErrNotSupported
+}
+
+// SetWriteDeadline implements net.PacketConn.
+// SetWriteDeadline is not supported.
+func (p *Peer) SetWriteDeadline(time.Time) error {
+	return ErrNotSupported
+}
+
+// Gossip implements mesh.Gossiper.
+func (p *Peer) Gossip() (complete mesh.GossipData) {
+	return pktSlice{} // we're stateless
+}
+
+// OnGossip implements mesh.Gossiper.
+// The buf is a single pkt.
+func (p *Peer) OnGossip(buf []byte) (delta mesh.GossipData, err error) {
+	return pktSlice{makePkt(buf)}, nil
+}
+
+// OnGossipBroadcast implements mesh.Gossiper.
+// The buf is a single pkt
+func (p *Peer) OnGossipBroadcast(_ mesh.PeerName, buf []byte) (received mesh.GossipData, err error) {
+	pkt := makePkt(buf)
+	p.recv <- pkt // to ReadFrom
+	return pktSlice{pkt}, nil
+}
+
+// OnGossipUnicast implements mesh.Gossiper.
+// The buf is a single pkt.
+func (p *Peer) OnGossipUnicast(_ mesh.PeerName, buf []byte) error {
+	pkt := makePkt(buf)
+	p.recv <- pkt // to ReadFrom
+	return nil
+}

examples/meshconn/pkt.go

@@ -0,0 +1,50 @@
+package meshconn
+
+import (
+	"bytes"
+	"encoding/gob"
+
+	"github.com/weaveworks/mesh"
+)
+
+type pkt struct {
+	Src mesh.PeerName
+	Buf []byte
+}
+
+func makePkt(buf []byte) pkt {
+	var p pkt
+	if err := gob.NewDecoder(bytes.NewBuffer(buf)).Decode(&p); err != nil {
+		panic(err)
+	}
+	return p
+}
+
+func (p pkt) encode() []byte {
+	var buf bytes.Buffer
+	if err := gob.NewEncoder(&buf).Encode(p); err != nil {
+		panic(err)
+	}
+	return buf.Bytes()
+}
+
+// pktSlice implements mesh.GossipData.
+type pktSlice []pkt
+
+var _ mesh.GossipData = &pktSlice{}
+
+func (s pktSlice) Encode() [][]byte {
+	bufs := make([][]byte, len(s))
+	for i, pkt := range s {
+		bufs[i] = pkt.encode()
+	}
+	return bufs
+}
+
+func (s pktSlice) Merge(other mesh.GossipData) mesh.GossipData {
+	o := other.(pktSlice)
+	merged := make(pktSlice, 0, len(s)+len(o))
+	merged = append(merged, s...)
+	merged = append(merged, o...)
+	return merged
+}