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>

1 files changed, 0 insertions, 83 deletions

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)
-		}
-	}
-}