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

Updates #1235

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

words/tails.txt

@@ -18,7 +18,6 @@ lion
 tapir
 anteater
 monkey
-lemur
 snake
 scorpion
 jerboa
@@ -35,7 +34,6 @@ moose
 alligator
 salamander
 tadpole
-giraffe
 astrapia
 pug
 greyhound
@@ -75,7 +73,6 @@ warbler
 penguin
 snowfinch
 broadbill
-finch
 thrush
 bishop
 swallow
@@ -91,7 +88,6 @@ vulture
 rat
 takaya
 skunk
-turtle
 tuxedo
 turkey
 elephant
@@ -109,7 +105,6 @@ bandicoot
 beagle
 beago
 collie
-beaver
 tiger
 liger
 rhino
@@ -117,14 +112,11 @@ bobcat
 corgi
 dachshund
 giraffe
-elephant
-rhino
 bonobo
 cetacean
 bear
 hyena
 burmese
-lynx
 caracal
 goat
 chameleon
@@ -157,7 +149,6 @@ pig
 prairiedog
 puma
 hippo
-marmoset
 quokka
 quoll
 bunny
@@ -176,7 +167,6 @@ vaquita
 wallaby
 walrus
 weasel
-corgi
 wolf
 zebra
 zonkey
@@ -186,7 +176,6 @@ zebu
 cuttlefish
 unicorn
 meerkat
-lynx
 jackalope
 heron
 fawn
@@ -199,7 +188,6 @@ werewolf
 tahr
 fossa
 xerus
-raccoon
 centaur
 raptor
 long

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
+}

words/words_test.go

@@ -0,0 +1,39 @@
+// 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
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestWords(t *testing.T) {
+	test := func(t *testing.T, words []string) {
+		t.Helper()
+		if len(words) == 0 {
+			t.Error("no words")
+		}
+		seen := map[string]bool{}
+		for _, w := range words {
+			if seen[w] {
+				t.Errorf("dup word %q", w)
+			}
+			seen[w] = true
+			if w == "" || strings.IndexFunc(w, nonASCIILower) != -1 {
+				t.Errorf("malformed word %q", w)
+			}
+		}
+	}
+	t.Run("tails", func(t *testing.T) { test(t, Tails()) })
+	t.Run("scales", func(t *testing.T) { test(t, Scales()) })
+	t.Logf("%v tails * %v scales = %v beautiful combinations", len(Tails()), len(Scales()), len(Tails())*len(Scales()))
+}
+
+func nonASCIILower(r rune) bool {
+	if 'a' <= r && r <= 'z' {
+		return false
+	}
+	return true
+}