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/metrics/vars/report.go

@@ -0,0 +1,62 @@
+package vars
+
+import (
+	"time"
+
+	"github.com/coredns/coredns/request"
+
+	"github.com/miekg/dns"
+)
+
+// Report reports the metrics data associcated with request.
+func Report(req request.Request, zone, rcode string, size int, start time.Time) {
+	// Proto and Family.
+	net := req.Proto()
+	fam := "1"
+	if req.Family() == 2 {
+		fam = "2"
+	}
+
+	typ := req.QType()
+
+	RequestCount.WithLabelValues(zone, net, fam).Inc()
+	RequestDuration.WithLabelValues(zone).Observe(float64(time.Since(start) / time.Millisecond))
+
+	if req.Do() {
+		RequestDo.WithLabelValues(zone).Inc()
+	}
+
+	if _, known := monitorType[typ]; known {
+		RequestType.WithLabelValues(zone, dns.Type(typ).String()).Inc()
+	} else {
+		RequestType.WithLabelValues(zone, other).Inc()
+	}
+
+	ResponseSize.WithLabelValues(zone, net).Observe(float64(size))
+	RequestSize.WithLabelValues(zone, net).Observe(float64(req.Len()))
+
+	ResponseRcode.WithLabelValues(zone, rcode).Inc()
+}
+
+var monitorType = map[uint16]bool{
+	dns.TypeAAAA:   true,
+	dns.TypeA:      true,
+	dns.TypeCNAME:  true,
+	dns.TypeDNSKEY: true,
+	dns.TypeDS:     true,
+	dns.TypeMX:     true,
+	dns.TypeNSEC3:  true,
+	dns.TypeNSEC:   true,
+	dns.TypeNS:     true,
+	dns.TypePTR:    true,
+	dns.TypeRRSIG:  true,
+	dns.TypeSOA:    true,
+	dns.TypeSRV:    true,
+	dns.TypeTXT:    true,
+	// Meta Qtypes
+	dns.TypeIXFR: true,
+	dns.TypeAXFR: true,
+	dns.TypeANY:  true,
+}
+
+const other = "other"

plugin/metrics/vars/vars.go

@@ -0,0 +1,69 @@
+package vars
+
+import (
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// Request* and Response* are the prometheus counters and gauges we are using for exporting metrics.
+var (
+	RequestCount = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: subsystem,
+		Name:      "request_count_total",
+		Help:      "Counter of DNS requests made per zone, protocol and family.",
+	}, []string{"zone", "proto", "family"})
+
+	RequestDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: subsystem,
+		Name:      "request_duration_milliseconds",
+		Buckets:   append(prometheus.DefBuckets, []float64{50, 100, 200, 500, 1000, 2000, 3000, 4000, 5000, 10000}...),
+		Help:      "Histogram of the time (in milliseconds) each request took.",
+	}, []string{"zone"})
+
+	RequestSize = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: subsystem,
+		Name:      "request_size_bytes",
+		Help:      "Size of the EDNS0 UDP buffer in bytes (64K for TCP).",
+		Buckets:   []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
+	}, []string{"zone", "proto"})
+
+	RequestDo = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: subsystem,
+		Name:      "request_do_count_total",
+		Help:      "Counter of DNS requests with DO bit set per zone.",
+	}, []string{"zone"})
+
+	RequestType = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: subsystem,
+		Name:      "request_type_count_total",
+		Help:      "Counter of DNS requests per type, per zone.",
+	}, []string{"zone", "type"})
+
+	ResponseSize = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: subsystem,
+		Name:      "response_size_bytes",
+		Help:      "Size of the returned response in bytes.",
+		Buckets:   []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
+	}, []string{"zone", "proto"})
+
+	ResponseRcode = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: subsystem,
+		Name:      "response_rcode_count_total",
+		Help:      "Counter of response status codes.",
+	}, []string{"zone", "rcode"})
+)
+
+const (
+	subsystem = "dns"
+
+	// Dropped indicates we dropped the query before any handling. It has no closing dot, so it can not be a valid zone.
+	Dropped = "dropped"
+)