words: add accessors and tests for a few of our favorite words

Updates #1235

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

words/words.go

@@ -0,0 +1,57 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package words contains accessors for some nice words.
+package words
+
+import (
+	"bytes"
+	_ "embed"
+	"strings"
+	"sync"
+)
+
+//go:embed tails.txt
+var tailsTxt []byte
+
+//go:embed scales.txt
+var scalesTxt []byte
+
+var (
+	once          sync.Once
+	tails, scales []string
+)
+
+// Tails returns words about tails.
+func Tails() []string {
+	once.Do(initWords)
+	return tails
+}
+
+// Scales returns words about scales.
+func Scales() []string {
+	once.Do(initWords)
+	return scales
+}
+
+func initWords() {
+	tails = parseWords(tailsTxt)
+	scales = parseWords(scalesTxt)
+}
+
+func parseWords(txt []byte) []string {
+	n := bytes.Count(txt, []byte{'\n'})
+	ret := make([]string, 0, n)
+	for len(txt) > 0 {
+		word := txt
+		i := bytes.IndexByte(txt, '\n')
+		if i != -1 {
+			word, txt = word[:i], txt[i+1:]
+		}
+		if word := strings.TrimSpace(string(word)); word != "" {
+			ret = append(ret, word)
+		}
+	}
+	return ret
+}