plugin/metadata: add metadata plugin (#1894)

* plugin/metadata: add metadata plugin

* plugin/metadata: Add MD struct, refactor code, fix doc

* plugin/metadata: simplify metadata key

* plugin/metadata: improve setup_test

* Support of metadata by rewrite plugin. Move calculated variables to metadata.

* Move variables from metadata to pkg, add UTs, READMEs change, metadata small fixes

* Add client port validation to variables_test

* plugin/metadata: improve README

* plugin/metadata: rename methods

* plugin/metadata: Update Metadataer interface, update doc, cosmetic code changes

* plugin/metadata: move colllisions check to OnStartup(). Fix default variables metadataer.

* plugin/metadata: Fix comment for method setValue

* plugin/metadata: change variables order to fix linter warning

* plugin/metadata: rename Metadataer to Provider

plugin/pkg/variables/variables.go

@@ -0,0 +1,109 @@
+package variables
+
+import (
+	"encoding/binary"
+	"fmt"
+	"net"
+	"strconv"
+
+	"github.com/coredns/coredns/request"
+
+	"github.com/miekg/dns"
+)
+
+const (
+	queryName  = "qname"
+	queryType  = "qtype"
+	clientIP   = "client_ip"
+	clientPort = "client_port"
+	protocol   = "protocol"
+	serverIP   = "server_ip"
+	serverPort = "server_port"
+)
+
+// All is a list of available variables provided by GetMetadataValue
+var All = []string{queryName, queryType, clientIP, clientPort, protocol, serverIP, serverPort}
+
+// GetValue calculates and returns the data specified by the variable name.
+// Supported varNames are listed in allProvidedVars.
+func GetValue(varName string, w dns.ResponseWriter, r *dns.Msg) ([]byte, error) {
+	req := request.Request{W: w, Req: r}
+	switch varName {
+	case queryName:
+		//Query name is written as ascii string
+		return []byte(req.QName()), nil
+
+	case queryType:
+		return uint16ToWire(req.QType()), nil
+
+	case clientIP:
+		return ipToWire(req.Family(), req.IP())
+
+	case clientPort:
+		return portToWire(req.Port())
+
+	case protocol:
+		// Proto is written as ascii string
+		return []byte(req.Proto()), nil
+
+	case serverIP:
+		ip, _, err := net.SplitHostPort(w.LocalAddr().String())
+		if err != nil {
+			ip = w.RemoteAddr().String()
+		}
+		return ipToWire(family(w.RemoteAddr()), ip)
+
+	case serverPort:
+		_, port, err := net.SplitHostPort(w.LocalAddr().String())
+		if err != nil {
+			port = "0"
+		}
+		return portToWire(port)
+	}
+
+	return nil, fmt.Errorf("unable to extract data for variable %s", varName)
+}
+
+// uint16ToWire writes unit16 to wire/binary format
+func uint16ToWire(data uint16) []byte {
+	buf := make([]byte, 2)
+	binary.BigEndian.PutUint16(buf, uint16(data))
+	return buf
+}
+
+// ipToWire writes IP address to wire/binary format, 4 or 16 bytes depends on IPV4 or IPV6.
+func ipToWire(family int, ipAddr string) ([]byte, error) {
+
+	switch family {
+	case 1:
+		return net.ParseIP(ipAddr).To4(), nil
+	case 2:
+		return net.ParseIP(ipAddr).To16(), nil
+	}
+	return nil, fmt.Errorf("invalid IP address family (i.e. version) %d", family)
+}
+
+// portToWire writes port to wire/binary format, 2 bytes
+func portToWire(portStr string) ([]byte, error) {
+
+	port, err := strconv.ParseUint(portStr, 10, 16)
+	if err != nil {
+		return nil, err
+	}
+	return uint16ToWire(uint16(port)), nil
+}
+
+// Family returns the family of the transport, 1 for IPv4 and 2 for IPv6.
+func family(ip net.Addr) int {
+	var a net.IP
+	if i, ok := ip.(*net.UDPAddr); ok {
+		a = i.IP
+	}
+	if i, ok := ip.(*net.TCPAddr); ok {
+		a = i.IP
+	}
+	if a.To4() != nil {
+		return 1
+	}
+	return 2
+}

plugin/pkg/variables/variables_test.go

@@ -0,0 +1,80 @@
+package variables
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/test"
+	"github.com/miekg/dns"
+)
+
+func TestGetValue(t *testing.T) {
+	// test.ResponseWriter has the following values:
+	// 		The remote will always be 10.240.0.1 and port 40212.
+	// 		The local address is always 127.0.0.1 and port 53.
+	tests := []struct {
+		varName       string
+		expectedValue []byte
+		shouldErr     bool
+	}{
+		{
+			queryName,
+			[]byte("example.com."),
+			false,
+		},
+		{
+			queryType,
+			[]byte{0x00, 0x01},
+			false,
+		},
+		{
+			clientIP,
+			[]byte{10, 240, 0, 1},
+			false,
+		},
+		{
+			clientPort,
+			[]byte{0x9D, 0x14},
+			false,
+		},
+		{
+			protocol,
+			[]byte("udp"),
+			false,
+		},
+		{
+			serverIP,
+			[]byte{127, 0, 0, 1},
+			false,
+		},
+		{
+			serverPort,
+			[]byte{0, 53},
+			false,
+		},
+		{
+			"wrong_var",
+			[]byte{},
+			true,
+		},
+	}
+
+	for i, tc := range tests {
+		m := new(dns.Msg)
+		m.SetQuestion("example.com.", dns.TypeA)
+		m.Question[0].Qclass = dns.ClassINET
+
+		value, err := GetValue(tc.varName, &test.ResponseWriter{}, m)
+
+		if tc.shouldErr && err == nil {
+			t.Errorf("Test %d: Expected error, but didn't recieve", i)
+		}
+		if !tc.shouldErr && err != nil {
+			t.Errorf("Test %d: Expected no error, but got error: %v", i, err.Error())
+		}
+
+		if !bytes.Equal(tc.expectedValue, value) {
+			t.Errorf("Test %d: Expected %v but got %v", i, tc.expectedValue, value)
+		}
+	}
+}