Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/trace/README.md

@@ -0,0 +1,73 @@
+# trace
+
+This module enables OpenTracing-based tracing of DNS requests as they go through the
+plugin chain.
+
+## Syntax
+
+The simplest form is just:
+
+~~~
+trace [ENDPOINT-TYPE] [ENDPOINT]
+~~~
+
+* **ENDPOINT-TYPE** is the type of tracing destination. Currently only `zipkin` is supported
+  and that is what it defaults to.
+* **ENDPOINT** is the tracing destination, and defaults to `localhost:9411`. For Zipkin, if
+  ENDPOINT does not begin with `http`, then it will be transformed to `http://ENDPOINT/api/v1/spans`.
+
+With this form, all queries will be traced.
+
+Additional features can be enabled with this syntax:
+
+~~~
+trace [ENDPOINT-TYPE] [ENDPOINT] {
+	every AMOUNT
+	service NAME
+	client_server
+}
+~~~
+
+* `every` **AMOUNT** will only trace one query of each AMOUNT queries. For example, to trace 1 in every
+  100 queries, use AMOUNT of 100. The default is 1.
+* `service` **NAME** allows you to specify the service name reported to the tracing server.
+  Default is `coredns`.
+* `client_server` will enable the `ClientServerSameSpan` OpenTracing feature.
+
+## Zipkin
+You can run Zipkin on a Docker host like this:
+
+```
+docker run -d -p 9411:9411 openzipkin/zipkin
+```
+
+## Examples
+
+Use an alternative Zipkin address:
+
+~~~
+trace tracinghost:9253
+~~~
+
+or
+
+~~~
+trace zipkin tracinghost:9253
+~~~
+
+If for some reason you are using an API reverse proxy or something and need to remap
+the standard Zipkin URL you can do something like:
+
+~~~
+trace http://tracinghost:9411/zipkin/api/v1/spans
+~~~
+
+Trace one query every 10000 queries, rename the service, and enable same span:
+
+~~~
+trace tracinghost:9411 {
+	every 10000
+	service dnsproxy
+	client_server
+}
+~~~

plugin/trace/setup.go

@@ -0,0 +1,113 @@
+package trace
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+
+	"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 plugin.Error("trace", err)
+	}
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.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.Contains(ep, "http") {
+			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"
+)

plugin/trace/setup_test.go

@@ -0,0 +1,60 @@
+package trace
+
+import (
+	"testing"
+
+	"github.com/mholt/caddy"
+)
+
+func TestTraceParse(t *testing.T) {
+	tests := []struct {
+		input        string
+		shouldErr    bool
+		endpoint     string
+		every        uint64
+		serviceName  string
+		clientServer bool
+	}{
+		// oks
+		{`trace`, false, "http://localhost:9411/api/v1/spans", 1, `coredns`, false},
+		{`trace localhost:1234`, false, "http://localhost:1234/api/v1/spans", 1, `coredns`, false},
+		{`trace http://localhost:1234/somewhere/else`, false, "http://localhost:1234/somewhere/else", 1, `coredns`, false},
+		{`trace zipkin localhost:1234`, false, "http://localhost:1234/api/v1/spans", 1, `coredns`, false},
+		{`trace zipkin http://localhost:1234/somewhere/else`, false, "http://localhost:1234/somewhere/else", 1, `coredns`, false},
+		{"trace {\n every 100\n}", false, "http://localhost:9411/api/v1/spans", 100, `coredns`, false},
+		{"trace {\n every 100\n service foobar\nclient_server\n}", false, "http://localhost:9411/api/v1/spans", 100, `foobar`, true},
+		{"trace {\n every 2\n client_server true\n}", false, "http://localhost:9411/api/v1/spans", 2, `coredns`, true},
+		{"trace {\n client_server false\n}", false, "http://localhost:9411/api/v1/spans", 1, `coredns`, false},
+		// fails
+		{`trace footype localhost:4321`, true, "", 1, "", false},
+		{"trace {\n every 2\n client_server junk\n}", true, "", 1, "", false},
+	}
+	for i, test := range tests {
+		c := caddy.NewTestController("dns", test.input)
+		m, err := traceParse(c)
+		if test.shouldErr && err == nil {
+			t.Errorf("Test %v: Expected error but found nil", i)
+			continue
+		} else if !test.shouldErr && err != nil {
+			t.Errorf("Test %v: Expected no error but found error: %v", i, err)
+			continue
+		}
+
+		if test.shouldErr {
+			continue
+		}
+
+		if test.endpoint != m.Endpoint {
+			t.Errorf("Test %v: Expected endpoint %s but found: %s", i, test.endpoint, m.Endpoint)
+		}
+		if test.every != m.every {
+			t.Errorf("Test %v: Expected every %d but found: %d", i, test.every, m.every)
+		}
+		if test.serviceName != m.serviceName {
+			t.Errorf("Test %v: Expected service name %s but found: %s", i, test.serviceName, m.serviceName)
+		}
+		if test.clientServer != m.clientServer {
+			t.Errorf("Test %v: Expected client_server %t but found: %t", i, test.clientServer, m.clientServer)
+		}
+	}
+}

plugin/trace/trace.go

@@ -0,0 +1,84 @@
+// Package trace implements OpenTracing-based tracing
+package trace
+
+import (
+	"fmt"
+	"sync"
+	"sync/atomic"
+
+	"github.com/coredns/coredns/plugin"
+	// Plugin the trace package.
+	_ "github.com/coredns/coredns/plugin/pkg/trace"
+
+	"github.com/miekg/dns"
+	ot "github.com/opentracing/opentracing-go"
+	zipkin "github.com/openzipkin/zipkin-go-opentracing"
+	"golang.org/x/net/context"
+)
+
+type trace struct {
+	Next            plugin.Handler
+	ServiceEndpoint string
+	Endpoint        string
+	EndpointType    string
+	tracer          ot.Tracer
+	serviceName     string
+	clientServer    bool
+	every           uint64
+	count           uint64
+	Once            sync.Once
+}
+
+func (t *trace) Tracer() ot.Tracer {
+	return t.tracer
+}
+
+// OnStartup sets up the tracer
+func (t *trace) OnStartup() error {
+	var err error
+	t.Once.Do(func() {
+		switch t.EndpointType {
+		case "zipkin":
+			err = t.setupZipkin()
+		default:
+			err = fmt.Errorf("unknown endpoint type: %s", t.EndpointType)
+		}
+	})
+	return err
+}
+
+func (t *trace) setupZipkin() error {
+
+	collector, err := zipkin.NewHTTPCollector(t.Endpoint)
+	if err != nil {
+		return err
+	}
+
+	recorder := zipkin.NewRecorder(collector, false, t.ServiceEndpoint, t.serviceName)
+	t.tracer, err = zipkin.NewTracer(recorder, zipkin.ClientServerSameSpan(t.clientServer))
+
+	return err
+}
+
+// Name implements the Handler interface.
+func (t *trace) Name() string {
+	return "trace"
+}
+
+// ServeDNS implements the plugin.Handle interface.
+func (t *trace) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	trace := false
+	if t.every > 0 {
+		queryNr := atomic.AddUint64(&t.count, 1)
+
+		if queryNr%t.every == 0 {
+			trace = true
+		}
+	}
+	if span := ot.SpanFromContext(ctx); span == nil && trace {
+		span := t.Tracer().StartSpan("servedns")
+		defer span.Finish()
+		ctx = ot.ContextWithSpan(ctx, span)
+	}
+	return plugin.NextOrFailure(t.Name(), t.Next, ctx, w, r)
+}

plugin/trace/trace_test.go

@@ -0,0 +1,33 @@
+package trace
+
+import (
+	"testing"
+
+	"github.com/mholt/caddy"
+)
+
+// createTestTrace creates a trace plugin to be used in tests
+func createTestTrace(config string) (*caddy.Controller, *trace, error) {
+	c := caddy.NewTestController("dns", config)
+	m, err := traceParse(c)
+	return c, m, err
+}
+
+func TestTrace(t *testing.T) {
+	_, m, err := createTestTrace(`trace`)
+	if err != nil {
+		t.Errorf("Error parsing test input: %s", err)
+		return
+	}
+	if m.Name() != "trace" {
+		t.Errorf("Wrong name from GetName: %s", m.Name())
+	}
+	err = m.OnStartup()
+	if err != nil {
+		t.Errorf("Error starting tracing plugin: %s", err)
+		return
+	}
+	if m.Tracer() == nil {
+		t.Errorf("Error, no tracer created")
+	}
+}