Add worker tagging (#862)

This allows workers to have tags assigned to them, which can then be filtered to control which targets they are allowed to serve.

sdk/strutil/strutil.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"sort"
 	"strings"
+	"unicode"
 
 	"github.com/hashicorp/errwrap"
 	glob "github.com/ryanuber/go-glob"
@@ -446,6 +447,16 @@ func Difference(a, b []string, lowercase bool) []string {
 	return items
 }
 
+// Printable returns true if all characters in the string are printable
+// according to Unicode
+func Printable(s string) bool {
+	return strings.IndexFunc(s, func(c rune) bool {
+		return !unicode.IsPrint(c)
+	}) == -1
+}
+
+// StringListToInterfaceList simply takes a []string and turns it into a
+// []interface{} to satisfy the input requirements for other library functions
 func StringListToInterfaceList(in []string) []interface{} {
 	ret := make([]interface{}, len(in))
 	for i, v := range in {

sdk/strutil/strutil_test.go

@@ -3,8 +3,11 @@ package strutil
 import (
 	"encoding/base64"
 	"encoding/json"
+	"fmt"
 	"reflect"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestStrUtil_StrListDelete(t *testing.T) {
@@ -598,3 +601,35 @@ func TestStrUtil_EqualStringMaps(t *testing.T) {
 		}
 	}
 }
+
+func TestPrintable(t *testing.T) {
+	cases := []struct {
+		input string
+		err   bool
+	}{
+		{
+			input: "/valid",
+		},
+		{
+			input: "foobarvalid",
+		},
+		{
+			input: "/invalid\u000A",
+			err:   true,
+		},
+		{
+			input: "/invalid\u000D",
+			err:   true,
+		},
+		{
+			input: "/invalid\u0000",
+			err:   true,
+		},
+	}
+
+	for i, tc := range cases {
+		t.Run(fmt.Sprint(i), func(t *testing.T) {
+			require.True(t, Printable(tc.input) != tc.err)
+		})
+	}
+}