coredns/middleware/trace/setup.go

package trace

import (
	"fmt"
	"strconv"
	"strings"

	"github.com/coredns/coredns/core/dnsserver"
	"github.com/coredns/coredns/middleware"

	"github.com/mholt/caddy"
)

func init() {
	caddy.RegisterPlugin("trace", caddy.Plugin{
		ServerType: "dns",
		Action:     setup,
	})
}

func setup(c *caddy.Controller) error {
	t, err := traceParse(c)
	if err != nil {
		return middleware.Error("trace", err)
	}

	dnsserver.GetConfig(c).AddMiddleware(func(next middleware.Handler) middleware.Handler {
		t.Next = next
		return t
	})

	c.OnStartup(t.OnStartup)

	return nil
}

func traceParse(c *caddy.Controller) (*trace, error) {
	var (
		tr  = &trace{Endpoint: defEP, EndpointType: defEpType, every: 1, serviceName: defServiceName}
		err error
	)

	cfg := dnsserver.GetConfig(c)
	tr.ServiceEndpoint = cfg.ListenHost + ":" + cfg.Port
	for c.Next() { // trace
		var err error
		args := c.RemainingArgs()
		switch len(args) {
		case 0:
			tr.Endpoint, err = normalizeEndpoint(tr.EndpointType, defEP)
		case 1:
			tr.Endpoint, err = normalizeEndpoint(defEpType, args[0])
		case 2:
			tr.EndpointType = strings.ToLower(args[0])
			tr.Endpoint, err = normalizeEndpoint(tr.EndpointType, args[1])
		default:
			err = c.ArgErr()
		}
		if err != nil {
			return tr, err
		}
		for c.NextBlock() {
			switch c.Val() {
			case "every":
				args := c.RemainingArgs()
				if len(args) != 1 {
					return nil, c.ArgErr()
				}
				tr.every, err = strconv.ParseUint(args[0], 10, 64)
				if err != nil {
					return nil, err
				}
			case "service":
				args := c.RemainingArgs()
				if len(args) != 1 {
					return nil, c.ArgErr()
				}
				tr.serviceName = args[0]
			case "client_server":
				args := c.RemainingArgs()
				if len(args) > 1 {
					return nil, c.ArgErr()
				}
				tr.clientServer = true
				if len(args) == 1 {
					tr.clientServer, err = strconv.ParseBool(args[0])
				}
				if err != nil {
					return nil, err
				}
			}
		}
	}
	return tr, err
}

func normalizeEndpoint(epType, ep string) (string, error) {
	switch epType {
	case "zipkin":
		if strings.Index(ep, "http") == -1 {
			ep = "http://" + ep + "/api/v1/spans"
		}
		return ep, nil
	default:
		return "", fmt.Errorf("tracing endpoint type '%s' is not supported", epType)
	}
}

const (
	defEP          = "localhost:9411"
	defEpType      = "zipkin"
	defServiceName = "coredns"
)