package agent /* The agent exposes an RPC mechanism that is used for both controlling Consul as well as providing a fast streaming mechanism for events. This allows other applications to easily leverage Consul without embedding. We additionally make use of the RPC layer to also handle calls from the CLI to unify the code paths. This results in a split Request/Response as well as streaming mode of operation. The system is fairly simple, each client opens a TCP connection to the agent. The connection is initialized with a handshake which establishes the protocol version being used. This is to allow for future changes to the protocol. Once initialized, clients send commands and wait for responses. Certain commands will cause the client to subscribe to events, and those will be pushed down the socket as they are received. This provides a low-latency mechanism for applications to send and receive events, while also providing a flexible control mechanism for Consul. */ import ( "bufio" "fmt" "github.com/hashicorp/logutils" "github.com/hashicorp/serf/serf" "github.com/hashicorp/go-msgpack/codec" "io" "log" "net" "os" "strings" "sync" ) const ( MinRPCVersion = 1 MaxRPCVersion = 1 ) const ( handshakeCommand = "handshake" forceLeaveCommand = "force-leave" joinCommand = "join" membersLANCommand = "members-lan" membersWANCommand = "members-wan" stopCommand = "stop" monitorCommand = "monitor" leaveCommand = "leave" statsCommand = "stats" reloadCommand = "reload" ) const ( unsupportedCommand = "Unsupported command" unsupportedRPCVersion = "Unsupported RPC version" duplicateHandshake = "Handshake already performed" handshakeRequired = "Handshake required" monitorExists = "Monitor already exists" ) // msgpackHandle is a shared handle for encoding/decoding of // messages var msgpackHandle = &codec.MsgpackHandle{ RawToString: true, WriteExt: true, } // Request header is sent before each request type requestHeader struct { Command string Seq uint64 } // Response header is sent before each response type responseHeader struct { Seq uint64 Error string } type handshakeRequest struct { Version int32 } type eventRequest struct { Name string Payload []byte Coalesce bool } type forceLeaveRequest struct { Node string } type joinRequest struct { Existing []string WAN bool } type joinResponse struct { Num int32 } type membersResponse struct { Members []Member } type monitorRequest struct { LogLevel string } type streamRequest struct { Type string } type stopRequest struct { Stop uint64 } type logRecord struct { Log string } type userEventRecord struct { Event string LTime serf.LamportTime Name string Payload []byte Coalesce bool } type Member struct { Name string Addr net.IP Port uint16 Tags map[string]string Status string ProtocolMin uint8 ProtocolMax uint8 ProtocolCur uint8 DelegateMin uint8 DelegateMax uint8 DelegateCur uint8 } type memberEventRecord struct { Event string Members []Member } type AgentRPC struct { sync.Mutex agent *Agent clients map[string]*rpcClient listener net.Listener logger *log.Logger logWriter *logWriter reloadCh chan struct{} stop bool stopCh chan struct{} } type rpcClient struct { name string conn net.Conn reader *bufio.Reader writer *bufio.Writer dec *codec.Decoder enc *codec.Encoder writeLock sync.Mutex version int32 // From the handshake, 0 before logStreamer *logStream } // send is used to send an object using the MsgPack encoding. send // is serialized to prevent write overlaps, while properly buffering. func (c *rpcClient) Send(header *responseHeader, obj interface{}) error { c.writeLock.Lock() defer c.writeLock.Unlock() if err := c.enc.Encode(header); err != nil { return err } if obj != nil { if err := c.enc.Encode(obj); err != nil { return err } } if err := c.writer.Flush(); err != nil { return err } return nil } func (c *rpcClient) String() string { return fmt.Sprintf("rpc.client: %v", c.conn) } // NewAgentRPC is used to create a new Agent RPC handler func NewAgentRPC(agent *Agent, listener net.Listener, logOutput io.Writer, logWriter *logWriter) *AgentRPC { if logOutput == nil { logOutput = os.Stderr } rpc := &AgentRPC{ agent: agent, clients: make(map[string]*rpcClient), listener: listener, logger: log.New(logOutput, "", log.LstdFlags), logWriter: logWriter, reloadCh: make(chan struct{}, 1), stopCh: make(chan struct{}), } go rpc.listen() return rpc } // Shutdown is used to shutdown the RPC layer func (i *AgentRPC) Shutdown() { i.Lock() defer i.Unlock() if i.stop { return } i.stop = true close(i.stopCh) i.listener.Close() // Close the existing connections for _, client := range i.clients { client.conn.Close() } } // ReloadCh returns a channel that can be watched for // when a reload is being triggered. func (i *AgentRPC) ReloadCh() <-chan struct{} { return i.reloadCh } // listen is a long running routine that listens for new clients func (i *AgentRPC) listen() { for { conn, err := i.listener.Accept() if err != nil { if i.stop { return } i.logger.Printf("[ERR] agent.rpc: Failed to accept client: %v", err) continue } i.logger.Printf("[INFO] agent.rpc: Accepted client: %v", conn.RemoteAddr()) // Wrap the connection in a client client := &rpcClient{ name: conn.RemoteAddr().String(), conn: conn, reader: bufio.NewReader(conn), writer: bufio.NewWriter(conn), } client.dec = codec.NewDecoder(client.reader, msgpackHandle) client.enc = codec.NewEncoder(client.writer, msgpackHandle) if err != nil { i.logger.Printf("[ERR] agent.rpc: Failed to create decoder: %v", err) conn.Close() continue } // Register the client i.Lock() if !i.stop { i.clients[client.name] = client go i.handleClient(client) } else { conn.Close() } i.Unlock() } } // deregisterClient is called to cleanup after a client disconnects func (i *AgentRPC) deregisterClient(client *rpcClient) { // Close the socket client.conn.Close() // Remove from the clients list i.Lock() delete(i.clients, client.name) i.Unlock() // Remove from the log writer if client.logStreamer != nil { i.logWriter.DeregisterHandler(client.logStreamer) client.logStreamer.Stop() } } // handleClient is a long running routine that handles a single client func (i *AgentRPC) handleClient(client *rpcClient) { defer i.deregisterClient(client) var reqHeader requestHeader for { // Decode the header if err := client.dec.Decode(&reqHeader); err != nil { if !i.stop { // The second part of this if is to block socket // errors from Windows which appear to happen every // time there is an EOF. if err != io.EOF && !strings.Contains(err.Error(), "WSARecv") { i.logger.Printf("[ERR] agent.rpc: failed to decode request header: %v", err) } } return } // Evaluate the command if err := i.handleRequest(client, &reqHeader); err != nil { i.logger.Printf("[ERR] agent.rpc: Failed to evaluate request: %v", err) return } } } // handleRequest is used to evaluate a single client command func (i *AgentRPC) handleRequest(client *rpcClient, reqHeader *requestHeader) error { // Look for a command field command := reqHeader.Command seq := reqHeader.Seq // Ensure the handshake is performed before other commands if command != handshakeCommand && client.version == 0 { respHeader := responseHeader{Seq: seq, Error: handshakeRequired} client.Send(&respHeader, nil) return fmt.Errorf(handshakeRequired) } // Dispatch command specific handlers switch command { case handshakeCommand: return i.handleHandshake(client, seq) case membersLANCommand: return i.handleMembersLAN(client, seq) case membersWANCommand: return i.handleMembersWAN(client, seq) case monitorCommand: return i.handleMonitor(client, seq) case stopCommand: return i.handleStop(client, seq) case forceLeaveCommand: return i.handleForceLeave(client, seq) case joinCommand: return i.handleJoin(client, seq) case leaveCommand: return i.handleLeave(client, seq) case statsCommand: return i.handleStats(client, seq) case reloadCommand: return i.handleReload(client, seq) default: respHeader := responseHeader{Seq: seq, Error: unsupportedCommand} client.Send(&respHeader, nil) return fmt.Errorf("command '%s' not recognized", command) } } func (i *AgentRPC) handleHandshake(client *rpcClient, seq uint64) error { var req handshakeRequest if err := client.dec.Decode(&req); err != nil { return fmt.Errorf("decode failed: %v", err) } resp := responseHeader{ Seq: seq, Error: "", } // Check the version if req.Version < MinRPCVersion || req.Version > MaxRPCVersion { resp.Error = unsupportedRPCVersion } else if client.version != 0 { resp.Error = duplicateHandshake } else { client.version = req.Version } return client.Send(&resp, nil) } func (i *AgentRPC) handleForceLeave(client *rpcClient, seq uint64) error { var req forceLeaveRequest if err := client.dec.Decode(&req); err != nil { return fmt.Errorf("decode failed: %v", err) } // Attempt leave err := i.agent.ForceLeave(req.Node) // Respond resp := responseHeader{ Seq: seq, Error: errToString(err), } return client.Send(&resp, nil) } func (i *AgentRPC) handleJoin(client *rpcClient, seq uint64) error { var req joinRequest if err := client.dec.Decode(&req); err != nil { return fmt.Errorf("decode failed: %v", err) } // Attempt the join var num int var err error if req.WAN { num, err = i.agent.JoinWAN(req.Existing) } else { num, err = i.agent.JoinLAN(req.Existing) } // Respond header := responseHeader{ Seq: seq, Error: errToString(err), } resp := joinResponse{ Num: int32(num), } return client.Send(&header, &resp) } func (i *AgentRPC) handleMembersLAN(client *rpcClient, seq uint64) error { raw := i.agent.LANMembers() return formatMembers(raw, client, seq) } func (i *AgentRPC) handleMembersWAN(client *rpcClient, seq uint64) error { raw := i.agent.WANMembers() return formatMembers(raw, client, seq) } func formatMembers(raw []serf.Member, client *rpcClient, seq uint64) error { members := make([]Member, 0, len(raw)) for _, m := range raw { sm := Member{ Name: m.Name, Addr: m.Addr, Port: m.Port, Tags: m.Tags, Status: m.Status.String(), ProtocolMin: m.ProtocolMin, ProtocolMax: m.ProtocolMax, ProtocolCur: m.ProtocolCur, DelegateMin: m.DelegateMin, DelegateMax: m.DelegateMax, DelegateCur: m.DelegateCur, } members = append(members, sm) } header := responseHeader{ Seq: seq, Error: "", } resp := membersResponse{ Members: members, } return client.Send(&header, &resp) } func (i *AgentRPC) handleMonitor(client *rpcClient, seq uint64) error { var req monitorRequest if err := client.dec.Decode(&req); err != nil { return fmt.Errorf("decode failed: %v", err) } resp := responseHeader{ Seq: seq, Error: "", } // Upper case the log level req.LogLevel = strings.ToUpper(req.LogLevel) // Create a level filter filter := LevelFilter() filter.MinLevel = logutils.LogLevel(req.LogLevel) if !ValidateLevelFilter(filter.MinLevel, filter) { resp.Error = fmt.Sprintf("Unknown log level: %s", filter.MinLevel) goto SEND } // Check if there is an existing monitor if client.logStreamer != nil { resp.Error = monitorExists goto SEND } // Create a log streamer client.logStreamer = newLogStream(client, filter, seq, i.logger) // Register with the log writer. Defer so that we can respond before // registration, avoids any possible race condition defer i.logWriter.RegisterHandler(client.logStreamer) SEND: return client.Send(&resp, nil) } func (i *AgentRPC) handleStop(client *rpcClient, seq uint64) error { var req stopRequest if err := client.dec.Decode(&req); err != nil { return fmt.Errorf("decode failed: %v", err) } // Remove a log monitor if any if client.logStreamer != nil && client.logStreamer.seq == req.Stop { i.logWriter.DeregisterHandler(client.logStreamer) client.logStreamer.Stop() client.logStreamer = nil } // Always succeed resp := responseHeader{Seq: seq, Error: ""} return client.Send(&resp, nil) } func (i *AgentRPC) handleLeave(client *rpcClient, seq uint64) error { i.logger.Printf("[INFO] agent.rpc: Graceful leave triggered") // Do the leave err := i.agent.Leave() if err != nil { i.logger.Printf("[ERR] agent.rpc: leave failed: %v", err) } resp := responseHeader{Seq: seq, Error: errToString(err)} // Send and wait err = client.Send(&resp, nil) // Trigger a shutdown! if err := i.agent.Shutdown(); err != nil { i.logger.Printf("[ERR] agent.rpc: shutdown failed: %v", err) } return err } // handleStats is used to get various statistics func (i *AgentRPC) handleStats(client *rpcClient, seq uint64) error { header := responseHeader{ Seq: seq, Error: "", } resp := i.agent.Stats() return client.Send(&header, resp) } func (i *AgentRPC) handleReload(client *rpcClient, seq uint64) error { // Push to the reload channel select { case i.reloadCh <- struct{}{}: default: } // Always succeed resp := responseHeader{Seq: seq, Error: ""} return client.Send(&resp, nil) } // Used to convert an error to a string representation func errToString(err error) string { if err == nil { return "" } return err.Error() }