plugin/metadata: metadata is just label=value (#1914)

This revert 17d807f0 and re-adds the metadata plugin as a plugin that
just sets a label to a value function.

Add package documentation on how to use the metadata package. Make it
clear that any caching is up to the Func implemented.

There are now - no in tree users. We could add the request metadata by
default under names that copy request.Request, i.e

request/ip - remote IP
request/port - remote port

Variables.go has been deleted.

Signed-off-by: Miek Gieben <miek@miek.nl>

2 files changed, 0 insertions, 187 deletions

diff --git a/plugin/pkg/variables/variables.go b/plugin/pkg/variables/variables.go
deleted file mode 100644
index 8e1cdbe77..000000000
--- a/plugin/pkg/variables/variables.go
+++ /dev/null
@@ -1,104 +0,0 @@
-package variables
-
-import (
-	"encoding/binary"
-	"fmt"
-	"net"
-	"strconv"
-
-	"github.com/coredns/coredns/request"
-)
-
-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(state request.Request, varName string) ([]byte, error) {
-	switch varName {
-	case queryName:
-		return []byte(state.QName()), nil
-
-	case queryType:
-		return uint16ToWire(state.QType()), nil
-
-	case clientIP:
-		return ipToWire(state.Family(), state.IP())
-
-	case clientPort:
-		return portToWire(state.Port())
-
-	case protocol:
-		return []byte(state.Proto()), nil
-
-	case serverIP:
-		ip, _, err := net.SplitHostPort(state.W.LocalAddr().String())
-		if err != nil {
-			ip = state.W.RemoteAddr().String()
-		}
-		return ipToWire(state.Family(), ip)
-
-	case serverPort:
-		_, port, err := net.SplitHostPort(state.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
-}
diff --git a/plugin/pkg/variables/variables_test.go b/plugin/pkg/variables/variables_test.go
deleted file mode 100644
index e0ff64c19..000000000
--- a/plugin/pkg/variables/variables_test.go
+++ /dev/null
@@ -1,83 +0,0 @@
-package variables
-
-import (
-	"bytes"
-	"testing"
-
-	"github.com/coredns/coredns/plugin/test"
-	"github.com/coredns/coredns/request"
-
-	"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
-		state := request.Request{W: &test.ResponseWriter{}, Req: m}
-
-		value, err := GetValue(state, tc.varName)
-
-		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)
-		}
-	}
-}