swarm: integrate OpenTracing; propagate ctx to internal APIs (#17169)

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured

vendor/github.com/uber/jaeger-client-go/utils/localip.go

@@ -0,0 +1,84 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package utils
+
+import (
+	"errors"
+	"net"
+)
+
+// This code is borrowed from https://github.com/uber/tchannel-go/blob/dev/localip.go
+
+// scoreAddr scores how likely the given addr is to be a remote address and returns the
+// IP to use when listening. Any address which receives a negative score should not be used.
+// Scores are calculated as:
+// -1 for any unknown IP addresses.
+// +300 for IPv4 addresses
+// +100 for non-local addresses, extra +100 for "up" interaces.
+func scoreAddr(iface net.Interface, addr net.Addr) (int, net.IP) {
+	var ip net.IP
+	if netAddr, ok := addr.(*net.IPNet); ok {
+		ip = netAddr.IP
+	} else if netIP, ok := addr.(*net.IPAddr); ok {
+		ip = netIP.IP
+	} else {
+		return -1, nil
+	}
+
+	var score int
+	if ip.To4() != nil {
+		score += 300
+	}
+	if iface.Flags&net.FlagLoopback == 0 && !ip.IsLoopback() {
+		score += 100
+		if iface.Flags&net.FlagUp != 0 {
+			score += 100
+		}
+	}
+	return score, ip
+}
+
+// HostIP tries to find an IP that can be used by other machines to reach this machine.
+func HostIP() (net.IP, error) {
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	bestScore := -1
+	var bestIP net.IP
+	// Select the highest scoring IP as the best IP.
+	for _, iface := range interfaces {
+		addrs, err := iface.Addrs()
+		if err != nil {
+			// Skip this interface if there is an error.
+			continue
+		}
+
+		for _, addr := range addrs {
+			score, ip := scoreAddr(iface, addr)
+			if score > bestScore {
+				bestScore = score
+				bestIP = ip
+			}
+		}
+	}
+
+	if bestScore == -1 {
+		return nil, errors.New("no addresses to listen on")
+	}
+
+	return bestIP, nil
+}