privval: Add IPCPV and fix SocketPV (#2568)

Ref: #2563

I added IPC as an unencrypted alternative to SocketPV.

Besides I fixed the following aspects of SocketPV:

Added locking since we are operating on a single socket
The connection deadline is extended every time a successful packet exchange happens; otherwise the connection would always die permanently x seconds after the connection was established.
Added a ping/heartbeat mechanism to keep the connection alive; native TCP keepalives do not work in this use-case


* Extend the SecureConn socket to extend its deadline
* Add locking & ping/heartbeat packets to SocketPV
* Implement IPC PV and abstract socket signing
* Refactored IPC and SocketPV
* Implement @melekes comments
* Fixes to rebase

privval/ipc.go

@@ -0,0 +1,120 @@
+package privval
+
+import (
+	"net"
+	"time"
+
+	cmn "github.com/tendermint/tendermint/libs/common"
+	"github.com/tendermint/tendermint/libs/log"
+	"github.com/tendermint/tendermint/types"
+)
+
+// IPCValOption sets an optional parameter on the SocketPV.
+type IPCValOption func(*IPCVal)
+
+// IPCValConnTimeout sets the read and write timeout for connections
+// from external signing processes.
+func IPCValConnTimeout(timeout time.Duration) IPCValOption {
+	return func(sc *IPCVal) { sc.connTimeout = timeout }
+}
+
+// IPCValHeartbeat sets the period on which to check the liveness of the
+// connected Signer connections.
+func IPCValHeartbeat(period time.Duration) IPCValOption {
+	return func(sc *IPCVal) { sc.connHeartbeat = period }
+}
+
+// IPCVal implements PrivValidator, it uses a unix socket to request signatures
+// from an external process.
+type IPCVal struct {
+	cmn.BaseService
+	*RemoteSignerClient
+
+	addr string
+
+	connTimeout   time.Duration
+	connHeartbeat time.Duration
+
+	conn       net.Conn
+	cancelPing chan struct{}
+	pingTicker *time.Ticker
+}
+
+// Check that IPCVal implements PrivValidator.
+var _ types.PrivValidator = (*IPCVal)(nil)
+
+// NewIPCVal returns an instance of IPCVal.
+func NewIPCVal(
+	logger log.Logger,
+	socketAddr string,
+) *IPCVal {
+	sc := &IPCVal{
+		addr:          socketAddr,
+		connTimeout:   connTimeout,
+		connHeartbeat: connHeartbeat,
+	}
+
+	sc.BaseService = *cmn.NewBaseService(logger, "IPCVal", sc)
+
+	return sc
+}
+
+// OnStart implements cmn.Service.
+func (sc *IPCVal) OnStart() error {
+	err := sc.connect()
+	if err != nil {
+		sc.Logger.Error("OnStart", "err", err)
+		return err
+	}
+
+	sc.RemoteSignerClient = NewRemoteSignerClient(sc.conn)
+
+	// Start a routine to keep the connection alive
+	sc.cancelPing = make(chan struct{}, 1)
+	sc.pingTicker = time.NewTicker(sc.connHeartbeat)
+	go func() {
+		for {
+			select {
+			case <-sc.pingTicker.C:
+				err := sc.Ping()
+				if err != nil {
+					sc.Logger.Error("Ping", "err", err)
+				}
+			case <-sc.cancelPing:
+				sc.pingTicker.Stop()
+				return
+			}
+		}
+	}()
+
+	return nil
+}
+
+// OnStop implements cmn.Service.
+func (sc *IPCVal) OnStop() {
+	if sc.cancelPing != nil {
+		close(sc.cancelPing)
+	}
+
+	if sc.conn != nil {
+		if err := sc.conn.Close(); err != nil {
+			sc.Logger.Error("OnStop", "err", err)
+		}
+	}
+}
+
+func (sc *IPCVal) connect() error {
+	la, err := net.ResolveUnixAddr("unix", sc.addr)
+	if err != nil {
+		return err
+	}
+
+	conn, err := net.DialUnix("unix", nil, la)
+	if err != nil {
+		return err
+	}
+
+	sc.conn = newTimeoutConn(conn, sc.connTimeout)
+
+	return nil
+}