stream/mts/meta: added Keys() func and appropriate testing

A meta.Keys(d []byte) []string, error func has been added that will extract the keys of a metadata string. A test has also been added
to test that this function performs as expected.

stream/mts/meta/meta.go

@@ -164,6 +164,19 @@ func (m *Data) Encode() []byte {
 	return m.enc
 }
 
+// Keys returns all keys in a slice of metadata d.
+func Keys(d []byte) ([]string, error) {
+	tmp, err := GetAll(d)
+	if err != nil {
+		return nil, err
+	}
+	keys := make([]string, len(tmp))
+	for i, entry := range tmp {
+		keys[i] = entry[0]
+	}
+	return keys, nil
+}
+
 // Get returns the value for the given key in d.
 func Get(key string, d []byte) (string, error) {
 	err := checkMeta(d)

stream/mts/meta/meta_test.go

@@ -188,3 +188,17 @@ func TestGetAll(t *testing.T) {
 		t.Errorf("Did not get expected out. \nGot : %v, \nWant: %v\n", got, want)
 	}
 }
+
+// TestKeys checks that we can successfully get keys from some metadata using
+// the meta.Keys method.
+func TestKeys(t *testing.T) {
+	tstMeta := append([]byte{0x00, 0x10, 0x00, 0x12}, "loc=a,b,c\tts=12345"...)
+	want := []string{"loc", "ts"}
+	got, err := Keys(tstMeta)
+	if err != nil {
+		t.Errorf("Unexpected error: %v\n", err)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("Did not get expected out. \nGot : %v, \nWant: %v\n", got, want)
+	}
+}