package consul import ( "context" "crypto/tls" "encoding/binary" "errors" "fmt" "io" "net" "strings" "sync/atomic" "time" "github.com/armon/go-metrics" "github.com/armon/go-metrics/prometheus" "github.com/hashicorp/consul/acl" "github.com/hashicorp/consul/agent/consul/state" "github.com/hashicorp/consul/agent/consul/wanfed" "github.com/hashicorp/consul/agent/metadata" "github.com/hashicorp/consul/agent/pool" "github.com/hashicorp/consul/agent/structs" "github.com/hashicorp/consul/lib" "github.com/hashicorp/consul/logging" connlimit "github.com/hashicorp/go-connlimit" "github.com/hashicorp/go-hclog" memdb "github.com/hashicorp/go-memdb" "github.com/hashicorp/go-raftchunking" "github.com/hashicorp/memberlist" msgpackrpc "github.com/hashicorp/net-rpc-msgpackrpc" "github.com/hashicorp/raft" "github.com/hashicorp/yamux" ) var RPCCounters = []prometheus.CounterDefinition{ { Name: []string{"rpc", "accept_conn"}, Help: "Increments when a server accepts an RPC connection.", }, { Name: []string{"rpc", "raft_handoff"}, Help: "Increments when a server accepts a Raft-related RPC connection.", }, { Name: []string{"rpc", "request_error"}, Help: "Increments when a server returns an error from an RPC request.", }, { Name: []string{"rpc", "request"}, Help: "Increments when a server receives a Consul-related RPC request.", }, { Name: []string{"rpc", "cross-dc"}, Help: "Increments when a server sends a (potentially blocking) cross datacenter RPC query.", }, { Name: []string{"rpc", "query"}, Help: "Increments when a server receives a new blocking RPC request, indicating the rate of new blocking query calls.", }, } var RPCGauges = []prometheus.GaugeDefinition{ { Name: []string{"rpc", "queries_blocking"}, Help: "Shows the current number of in-flight blocking queries the server is handling.", }, } var RPCSummaries = []prometheus.SummaryDefinition{ { Name: []string{"rpc", "consistentRead"}, Help: "Measures the time spent confirming that a consistent read can be performed.", }, } const ( // jitterFraction is a the limit to the amount of jitter we apply // to a user specified MaxQueryTime. We divide the specified time by // the fraction. So 16 == 6.25% limit of jitter. This same fraction // is applied to the RPCHoldTimeout jitterFraction = 16 // Warn if the Raft command is larger than this. // If it's over 1MB something is probably being abusive. raftWarnSize = 1024 * 1024 // enqueueLimit caps how long we will wait to enqueue // a new Raft command. Something is probably wrong if this // value is ever reached. However, it prevents us from blocking // the requesting goroutine forever. enqueueLimit = 30 * time.Second ) var ( ErrChunkingResubmit = errors.New("please resubmit call for rechunking") ) func (s *Server) rpcLogger() hclog.Logger { return s.loggers.Named(logging.RPC) } // listen is used to listen for incoming RPC connections func (s *Server) listen(listener net.Listener) { for { // Accept a connection conn, err := listener.Accept() if err != nil { if s.shutdown { return } s.rpcLogger().Error("failed to accept RPC conn", "error", err) continue } free, err := s.rpcConnLimiter.Accept(conn) if err != nil { s.rpcLogger().Error("rejecting RPC conn from because rpc_max_conns_per_client exceeded", "conn", logConn(conn)) conn.Close() continue } // Wrap conn so it will be auto-freed from conn limiter when it closes. conn = connlimit.Wrap(conn, free) go s.handleConn(conn, false) metrics.IncrCounter([]string{"rpc", "accept_conn"}, 1) } } // logConn is a wrapper around memberlist's LogConn so that we format references // to "from" addresses in a consistent way. This is just a shorter name. func logConn(conn net.Conn) string { return memberlist.LogConn(conn) } // handleConn is used to determine if this is a Raft or // Consul type RPC connection and invoke the correct handler func (s *Server) handleConn(conn net.Conn, isTLS bool) { // Limit how long the client can hold the connection open before they send the // magic byte (and authenticate when mTLS is enabled). If `isTLS == true` then // this also enforces a timeout on how long it takes for the handshake to // complete since tls.Conn.Read implicitly calls Handshake(). if s.config.RPCHandshakeTimeout > 0 { conn.SetReadDeadline(time.Now().Add(s.config.RPCHandshakeTimeout)) } if !isTLS && s.tlsConfigurator.MutualTLSCapable() { // See if actually this is native TLS multiplexed onto the old // "type-byte" system. peekedConn, nativeTLS, err := pool.PeekForTLS(conn) if err != nil { if err != io.EOF { s.rpcLogger().Error( "failed to read first byte", "conn", logConn(conn), "error", err, ) } conn.Close() return } if nativeTLS { s.handleNativeTLS(peekedConn) return } conn = peekedConn } // Read a single byte buf := make([]byte, 1) if _, err := conn.Read(buf); err != nil { if err != io.EOF { s.rpcLogger().Error("failed to read byte", "conn", logConn(conn), "error", err, ) } conn.Close() return } typ := pool.RPCType(buf[0]) // Reset the deadline as we aren't sure what is expected next - it depends on // the protocol. if s.config.RPCHandshakeTimeout > 0 { conn.SetReadDeadline(time.Time{}) } // Enforce TLS if VerifyIncoming is set if s.tlsConfigurator.VerifyIncomingRPC() && !isTLS && typ != pool.RPCTLS && typ != pool.RPCTLSInsecure { s.rpcLogger().Warn("Non-TLS connection attempted with VerifyIncoming set", "conn", logConn(conn)) conn.Close() return } // Switch on the byte switch typ { case pool.RPCConsul: s.handleConsulConn(conn) case pool.RPCRaft: metrics.IncrCounter([]string{"rpc", "raft_handoff"}, 1) s.raftLayer.Handoff(conn) case pool.RPCTLS: // Don't allow malicious client to create TLS-in-TLS for ever. if isTLS { s.rpcLogger().Error("TLS connection attempting to establish inner TLS connection", "conn", logConn(conn)) conn.Close() return } conn = tls.Server(conn, s.tlsConfigurator.IncomingRPCConfig()) s.handleConn(conn, true) case pool.RPCMultiplexV2: s.handleMultiplexV2(conn) case pool.RPCSnapshot: s.handleSnapshotConn(conn) case pool.RPCTLSInsecure: // Don't allow malicious client to create TLS-in-TLS for ever. if isTLS { s.rpcLogger().Error("TLS connection attempting to establish inner TLS connection", "conn", logConn(conn)) conn.Close() return } conn = tls.Server(conn, s.tlsConfigurator.IncomingInsecureRPCConfig()) s.handleInsecureConn(conn) case pool.RPCGRPC: s.grpcHandler.Handle(conn) default: if !s.handleEnterpriseRPCConn(typ, conn, isTLS) { s.rpcLogger().Error("unrecognized RPC byte", "byte", typ, "conn", logConn(conn), ) conn.Close() } } } func (s *Server) handleNativeTLS(conn net.Conn) { s.rpcLogger().Trace( "detected actual TLS over RPC port", "conn", logConn(conn), ) tlscfg := s.tlsConfigurator.IncomingALPNRPCConfig(pool.RPCNextProtos) tlsConn := tls.Server(conn, tlscfg) // Force the handshake to conclude. if err := tlsConn.Handshake(); err != nil { s.rpcLogger().Error( "TLS handshake failed", "conn", logConn(conn), "error", err, ) conn.Close() return } // Reset the deadline as we aren't sure what is expected next - it depends on // the protocol. if s.config.RPCHandshakeTimeout > 0 { conn.SetReadDeadline(time.Time{}) } var ( cs = tlsConn.ConnectionState() sni = cs.ServerName nextProto = cs.NegotiatedProtocol transport = s.memberlistTransportWAN ) s.rpcLogger().Trace( "accepted nativeTLS RPC", "sni", sni, "protocol", nextProto, "conn", logConn(conn), ) switch nextProto { case pool.ALPN_RPCConsul: s.handleConsulConn(tlsConn) case pool.ALPN_RPCRaft: metrics.IncrCounter([]string{"rpc", "raft_handoff"}, 1) s.raftLayer.Handoff(tlsConn) case pool.ALPN_RPCMultiplexV2: s.handleMultiplexV2(tlsConn) case pool.ALPN_RPCSnapshot: s.handleSnapshotConn(tlsConn) case pool.ALPN_RPCGRPC: s.grpcHandler.Handle(conn) case pool.ALPN_WANGossipPacket: if err := s.handleALPN_WANGossipPacketStream(tlsConn); err != nil && err != io.EOF { s.rpcLogger().Error( "failed to ingest RPC", "sni", sni, "protocol", nextProto, "conn", logConn(conn), "error", err, ) } case pool.ALPN_WANGossipStream: // No need to defer the conn.Close() here, the Ingest methods do that. if err := transport.IngestStream(tlsConn); err != nil { s.rpcLogger().Error( "failed to ingest RPC", "sni", sni, "protocol", nextProto, "conn", logConn(conn), "error", err, ) } default: if !s.handleEnterpriseNativeTLSConn(nextProto, conn) { s.rpcLogger().Error( "discarding RPC for unknown negotiated protocol", "failed to ingest RPC", "protocol", nextProto, "conn", logConn(conn), ) conn.Close() } } } // handleMultiplexV2 is used to multiplex a single incoming connection // using the Yamux multiplexer func (s *Server) handleMultiplexV2(conn net.Conn) { defer conn.Close() conf := yamux.DefaultConfig() // override the default because LogOutput conflicts with Logger conf.LogOutput = nil // TODO: should this be created once and cached? conf.Logger = s.logger.StandardLogger(&hclog.StandardLoggerOptions{InferLevels: true}) server, _ := yamux.Server(conn, conf) for { sub, err := server.Accept() if err != nil { if err != io.EOF { s.rpcLogger().Error("multiplex conn accept failed", "conn", logConn(conn), "error", err, ) } return } // In the beginning only RPC was supposed to be multiplexed // with yamux. In order to add the ability to multiplex network // area connections, this workaround was added. // This code peeks the first byte and checks if it is // RPCGossip, in which case this is handled by enterprise code. // Otherwise this connection is handled like before by the RPC // handler. // This wouldn't work if a normal RPC could start with // RPCGossip(6). In messagepack a 6 encodes a positive fixint: // https://github.com/msgpack/msgpack/blob/master/spec.md. // None of the RPCs we are doing starts with that, usually it is // a string for datacenter. peeked, first, err := pool.PeekFirstByte(sub) if err != nil { s.rpcLogger().Error("Problem peeking connection", "conn", logConn(sub), "err", err) sub.Close() return } sub = peeked switch first { case pool.RPCGossip: buf := make([]byte, 1) sub.Read(buf) go func() { if !s.handleEnterpriseRPCConn(pool.RPCGossip, sub, false) { s.rpcLogger().Error("unrecognized RPC byte", "byte", pool.RPCGossip, "conn", logConn(conn), ) sub.Close() } }() default: go s.handleConsulConn(sub) } } } // handleConsulConn is used to service a single Consul RPC connection func (s *Server) handleConsulConn(conn net.Conn) { defer conn.Close() rpcCodec := msgpackrpc.NewCodecFromHandle(true, true, conn, structs.MsgpackHandle) for { select { case <-s.shutdownCh: return default: } if err := s.rpcServer.ServeRequest(rpcCodec); err != nil { if err != io.EOF && !strings.Contains(err.Error(), "closed") { s.rpcLogger().Error("RPC error", "conn", logConn(conn), "error", err, ) metrics.IncrCounter([]string{"rpc", "request_error"}, 1) } return } metrics.IncrCounter([]string{"rpc", "request"}, 1) } } // handleInsecureConsulConn is used to service a single Consul INSECURERPC connection func (s *Server) handleInsecureConn(conn net.Conn) { defer conn.Close() rpcCodec := msgpackrpc.NewCodecFromHandle(true, true, conn, structs.MsgpackHandle) for { select { case <-s.shutdownCh: return default: } if err := s.insecureRPCServer.ServeRequest(rpcCodec); err != nil { if err != io.EOF && !strings.Contains(err.Error(), "closed") { s.rpcLogger().Error("INSECURERPC error", "conn", logConn(conn), "error", err, ) metrics.IncrCounter([]string{"rpc", "request_error"}, 1) } return } metrics.IncrCounter([]string{"rpc", "request"}, 1) } } // handleSnapshotConn is used to dispatch snapshot saves and restores, which // stream so don't use the normal RPC mechanism. func (s *Server) handleSnapshotConn(conn net.Conn) { go func() { defer conn.Close() if err := s.handleSnapshotRequest(conn); err != nil { s.rpcLogger().Error("Snapshot RPC error", "conn", logConn(conn), "error", err, ) } }() } func (s *Server) handleALPN_WANGossipPacketStream(conn net.Conn) error { defer conn.Close() transport := s.memberlistTransportWAN for { select { case <-s.shutdownCh: return nil default: } // Note: if we need to change this format to have additional header // information we can just negotiate a different ALPN protocol instead // of needing any sort of version field here. prefixLen, err := readUint32(conn, wanfed.GossipPacketMaxIdleTime) if err != nil { return err } // Avoid a memory exhaustion DOS vector here by capping how large this // packet can be to something reasonable. if prefixLen > wanfed.GossipPacketMaxByteSize { return fmt.Errorf("gossip packet size %d exceeds threshold of %d", prefixLen, wanfed.GossipPacketMaxByteSize) } lc := &limitedConn{ Conn: conn, lr: io.LimitReader(conn, int64(prefixLen)), } if err := transport.IngestPacket(lc, conn.RemoteAddr(), time.Now(), false); err != nil { return err } } } func readUint32(conn net.Conn, timeout time.Duration) (uint32, error) { // Since requests are framed we can easily just set a deadline on // reading that frame and then disable it for the rest of the body. if err := conn.SetReadDeadline(time.Now().Add(timeout)); err != nil { return 0, err } var v uint32 if err := binary.Read(conn, binary.BigEndian, &v); err != nil { return 0, err } if err := conn.SetReadDeadline(time.Time{}); err != nil { return 0, err } return v, nil } type limitedConn struct { net.Conn lr io.Reader } func (c *limitedConn) Read(b []byte) (n int, err error) { return c.lr.Read(b) } // canRetry returns true if the given situation is safe for a retry. func canRetry(args interface{}, err error) bool { // No leader errors are always safe to retry since no state could have // been changed. if structs.IsErrNoLeader(err) { return true } // If we are chunking and it doesn't seem to have completed, try again intErr, ok := args.(error) if ok && strings.Contains(intErr.Error(), ErrChunkingResubmit.Error()) { return true } // Reads are safe to retry for stream errors, such as if a server was // being shut down. info, ok := args.(structs.RPCInfo) if ok && info.IsRead() && lib.IsErrEOF(err) { return true } return false } // ForwardRPC is used to forward an RPC request to a remote DC or to the local leader // Returns a bool of if forwarding was performed, as well as any error func (s *Server) ForwardRPC(method string, info structs.RPCInfo, args interface{}, reply interface{}) (bool, error) { var firstCheck time.Time // Handle DC forwarding dc := info.RequestDatacenter() if dc != s.config.Datacenter { // Local tokens only work within the current datacenter. Check to see // if we are attempting to forward one to a remote datacenter and strip // it, falling back on the anonymous token on the other end. if token := info.TokenSecret(); token != "" { done, ident, err := s.ResolveIdentityFromToken(token) if done { if err != nil && !acl.IsErrNotFound(err) { return false, err } if ident != nil && ident.IsLocal() { // Strip it from the request. info.SetTokenSecret("") defer info.SetTokenSecret(token) } } } err := s.forwardDC(method, dc, args, reply) return true, err } // Check if we can allow a stale read, ensure our local DB is initialized if info.IsRead() && info.AllowStaleRead() && !s.raft.LastContact().IsZero() { return false, nil } CHECK_LEADER: // Fail fast if we are in the process of leaving select { case <-s.leaveCh: return true, structs.ErrNoLeader default: } // Find the leader isLeader, leader := s.getLeader() // Handle the case we are the leader if isLeader { return false, nil } // Handle the case of a known leader rpcErr := structs.ErrNoLeader if leader != nil { rpcErr = s.connPool.RPC(s.config.Datacenter, leader.ShortName, leader.Addr, method, args, reply) if rpcErr != nil && canRetry(info, rpcErr) { goto RETRY } return true, rpcErr } RETRY: // Gate the request until there is a leader if firstCheck.IsZero() { firstCheck = time.Now() } if time.Since(firstCheck) < s.config.RPCHoldTimeout { jitter := lib.RandomStagger(s.config.RPCHoldTimeout / jitterFraction) select { case <-time.After(jitter): goto CHECK_LEADER case <-s.leaveCh: case <-s.shutdownCh: } } // No leader found and hold time exceeded return true, rpcErr } // getLeader returns if the current node is the leader, and if not then it // returns the leader which is potentially nil if the cluster has not yet // elected a leader. func (s *Server) getLeader() (bool, *metadata.Server) { // Check if we are the leader if s.IsLeader() { return true, nil } // Get the leader leader := s.raft.Leader() if leader == "" { return false, nil } // Lookup the server server := s.serverLookup.Server(leader) // Server could be nil return false, server } // forwardDC is used to forward an RPC call to a remote DC, or fail if no servers func (s *Server) forwardDC(method, dc string, args interface{}, reply interface{}) error { manager, server, ok := s.router.FindRoute(dc) if !ok { if s.router.HasDatacenter(dc) { s.rpcLogger().Warn("RPC request to DC is currently failing as no server can be reached", "datacenter", dc) return structs.ErrDCNotAvailable } s.rpcLogger().Warn("RPC request for DC is currently failing as no path was found", "datacenter", dc, "method", method, ) return structs.ErrNoDCPath } metrics.IncrCounterWithLabels([]string{"rpc", "cross-dc"}, 1, []metrics.Label{{Name: "datacenter", Value: dc}}) if err := s.connPool.RPC(dc, server.ShortName, server.Addr, method, args, reply); err != nil { manager.NotifyFailedServer(server) s.rpcLogger().Error("RPC failed to server in DC", "server", server.Addr, "datacenter", dc, "method", method, "error", err, ) return err } return nil } // keyringRPCs is used to forward an RPC request to a server in each dc. This // will only error for RPC-related errors. Otherwise, application-level errors // can be sent in the response objects. func (s *Server) keyringRPCs(method string, args interface{}, dcs []string) (*structs.KeyringResponses, error) { errorCh := make(chan error, len(dcs)) respCh := make(chan *structs.KeyringResponses, len(dcs)) for _, dc := range dcs { go func(dc string) { rr := &structs.KeyringResponses{} if err := s.forwardDC(method, dc, args, &rr); err != nil { errorCh <- err return } respCh <- rr }(dc) } responses := &structs.KeyringResponses{} for i := 0; i < len(dcs); i++ { select { case err := <-errorCh: return nil, err case rr := <-respCh: responses.Add(rr) } } return responses, nil } type raftEncoder func(structs.MessageType, interface{}) ([]byte, error) // raftApply is used to encode a message, run it through raft, and return // the FSM response along with any errors func (s *Server) raftApply(t structs.MessageType, msg interface{}) (interface{}, error) { return s.raftApplyMsgpack(t, msg) } // raftApplyMsgpack will msgpack encode the request and then run it through raft, // then return the FSM response along with any errors. func (s *Server) raftApplyMsgpack(t structs.MessageType, msg interface{}) (interface{}, error) { return s.raftApplyWithEncoder(t, msg, structs.Encode) } // raftApplyProtobuf will protobuf encode the request and then run it through raft, // then return the FSM response along with any errors. func (s *Server) raftApplyProtobuf(t structs.MessageType, msg interface{}) (interface{}, error) { return s.raftApplyWithEncoder(t, msg, structs.EncodeProtoInterface) } // raftApplyWithEncoder is used to encode a message, run it through raft, // and return the FSM response along with any errors. Unlike raftApply this // takes the encoder to use as an argument. func (s *Server) raftApplyWithEncoder(t structs.MessageType, msg interface{}, encoder raftEncoder) (interface{}, error) { if encoder == nil { return nil, fmt.Errorf("Failed to encode request: nil encoder") } buf, err := encoder(t, msg) if err != nil { return nil, fmt.Errorf("Failed to encode request: %v", err) } // Warn if the command is very large if n := len(buf); n > raftWarnSize { s.rpcLogger().Warn("Attempting to apply large raft entry", "size_in_bytes", n) } var chunked bool var future raft.ApplyFuture switch { case len(buf) <= raft.SuggestedMaxDataSize || t != structs.KVSRequestType: future = s.raft.Apply(buf, enqueueLimit) default: chunked = true future = raftchunking.ChunkingApply(buf, nil, enqueueLimit, s.raft.ApplyLog) } if err := future.Error(); err != nil { return nil, err } resp := future.Response() if chunked { // In this case we didn't apply all chunks successfully, possibly due // to a term change; resubmit if resp == nil { // This returns the error in the interface because the raft library // returns errors from the FSM via the future, not via err from the // apply function. Downstream client code expects to see any error // from the FSM (as opposed to the apply itself) and decide whether // it can retry in the future's response. return ErrChunkingResubmit, nil } // We expect that this conversion should always work chunkedSuccess, ok := resp.(raftchunking.ChunkingSuccess) if !ok { return nil, errors.New("unknown type of response back from chunking FSM") } // Return the inner wrapped response return chunkedSuccess.Response, nil } return resp, nil } // queryFn is used to perform a query operation. If a re-query is needed, the // passed-in watch set will be used to block for changes. The passed-in state // store should be used (vs. calling fsm.State()) since the given state store // will be correctly watched for changes if the state store is restored from // a snapshot. type queryFn func(memdb.WatchSet, *state.Store) error // blockingQuery is used to process a potentially blocking query operation. func (s *Server) blockingQuery(queryOpts structs.QueryOptionsCompat, queryMeta structs.QueryMetaCompat, fn queryFn) error { var cancel func() var ctx context.Context = &lib.StopChannelContext{StopCh: s.shutdownCh} var queriesBlocking uint64 var queryTimeout time.Duration // Instrument all queries run metrics.IncrCounter([]string{"rpc", "query"}, 1) minQueryIndex := queryOpts.GetMinQueryIndex() // Fast path right to the non-blocking query. if minQueryIndex == 0 { goto RUN_QUERY } queryTimeout = queryOpts.GetMaxQueryTime() // Restrict the max query time, and ensure there is always one. if queryTimeout > s.config.MaxQueryTime { queryTimeout = s.config.MaxQueryTime } else if queryTimeout <= 0 { queryTimeout = s.config.DefaultQueryTime } // Apply a small amount of jitter to the request. queryTimeout += lib.RandomStagger(queryTimeout / jitterFraction) // wrap the base context with a deadline ctx, cancel = context.WithDeadline(ctx, time.Now().Add(queryTimeout)) defer cancel() // instrument blockingQueries // atomic inc our server's count of in-flight blockingQueries and store the new value queriesBlocking = atomic.AddUint64(&s.queriesBlocking, 1) // atomic dec when we return from blockingQuery() defer atomic.AddUint64(&s.queriesBlocking, ^uint64(0)) // set the gauge directly to the new value of s.blockingQueries metrics.SetGauge([]string{"rpc", "queries_blocking"}, float32(queriesBlocking)) RUN_QUERY: // Setup blocking loop // Update the query metadata. s.setQueryMeta(queryMeta) // Validate // If the read must be consistent we verify that we are still the leader. if queryOpts.GetRequireConsistent() { if err := s.consistentRead(); err != nil { return err } } // Run query // Operate on a consistent set of state. This makes sure that the // abandon channel goes with the state that the caller is using to // build watches. state := s.fsm.State() // We can skip all watch tracking if this isn't a blocking query. var ws memdb.WatchSet if minQueryIndex > 0 { ws = memdb.NewWatchSet() // This channel will be closed if a snapshot is restored and the // whole state store is abandoned. ws.Add(state.AbandonCh()) } // Execute the queryFn err := fn(ws, state) // Note we check queryOpts.MinQueryIndex is greater than zero to determine if // blocking was requested by client, NOT meta.Index since the state function // might return zero if something is not initialized and care wasn't taken to // handle that special case (in practice this happened a lot so fixing it // systematically here beats trying to remember to add zero checks in every // state method). We also need to ensure that unless there is an error, we // return an index > 0 otherwise the client will never block and burn CPU and // requests. if err == nil && queryMeta.GetIndex() < 1 { queryMeta.SetIndex(1) } // block up to the timeout if we don't see anything fresh. if err == nil && minQueryIndex > 0 && queryMeta.GetIndex() <= minQueryIndex { if err := ws.WatchCtx(ctx); err == nil { // a non-nil error only occurs when the context is cancelled // If a restore may have woken us up then bail out from // the query immediately. This is slightly race-ey since // this might have been interrupted for other reasons, // but it's OK to kick it back to the caller in either // case. select { case <-state.AbandonCh(): default: // loop back and look for an update again goto RUN_QUERY } } } return err } // setQueryMeta is used to populate the QueryMeta data for an RPC call func (s *Server) setQueryMeta(m structs.QueryMetaCompat) { if s.IsLeader() { m.SetLastContact(0) m.SetKnownLeader(true) } else { m.SetLastContact(time.Since(s.raft.LastContact())) m.SetKnownLeader(s.raft.Leader() != "") } } // consistentRead is used to ensure we do not perform a stale // read. This is done by verifying leadership before the read. func (s *Server) consistentRead() error { defer metrics.MeasureSince([]string{"rpc", "consistentRead"}, time.Now()) future := s.raft.VerifyLeader() if err := future.Error(); err != nil { return err //fail fast if leader verification fails } // poll consistent read readiness, wait for up to RPCHoldTimeout milliseconds if s.isReadyForConsistentReads() { return nil } jitter := lib.RandomStagger(s.config.RPCHoldTimeout / jitterFraction) deadline := time.Now().Add(s.config.RPCHoldTimeout) for time.Now().Before(deadline) { select { case <-time.After(jitter): // Drop through and check before we loop again. case <-s.shutdownCh: return fmt.Errorf("shutdown waiting for leader") } if s.isReadyForConsistentReads() { return nil } } return structs.ErrNotReadyForConsistentReads }