util: add parse fallback helpers (#20022)

util/def: add def.Bool and def.Duration default parse helpers

Replace multiple instances of def.Bool and def.Duration with a new util/def
package.

Updates #20018

Co-authored-by: Bobby <boby@codelabs.co.id>
Co-authored-by: Simon Law <sfllaw@tailscale.com>
Signed-off-by: Bobby <boby@codelabs.co.id>
Signed-off-by: Simon Law <sfllaw@tailscale.com>

util/def/def.go

@@ -0,0 +1,34 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package def parses strings with fallback default values.
+package def
+
+import (
+	"strconv"
+	"time"
+)
+
+// Bool parses s as a bool, returning def when s is empty or invalid.
+func Bool(s string, def bool) bool {
+	if s == "" {
+		return def
+	}
+	v, err := strconv.ParseBool(s)
+	if err != nil {
+		return def
+	}
+	return v
+}
+
+// Duration parses s as a time.Duration, returning def when s is empty or invalid.
+func Duration(s string, def time.Duration) time.Duration {
+	if s == "" {
+		return def
+	}
+	v, err := time.ParseDuration(s)
+	if err != nil {
+		return def
+	}
+	return v
+}

util/def/def_test.go

@@ -0,0 +1,121 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package def_test
+
+import (
+	"strconv"
+	"testing"
+	"time"
+
+	"tailscale.com/util/def"
+)
+
+func TestBool(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		def  bool
+		want bool
+	}{
+		{name: "empty_true", in: "", def: true, want: true},
+		{name: "empty_false", in: "", def: false, want: false},
+		{name: "valid_1", in: "1", def: false, want: true},
+		{name: "valid_t", in: "t", def: false, want: true},
+		{name: "valid_T", in: "T", def: false, want: true},
+		{name: "valid_TRUE", in: "TRUE", def: false, want: true},
+		{name: "valid_true", in: "true", def: false, want: true},
+		{name: "valid_True", in: "True", def: false, want: true},
+		{name: "valid_true_default_true", in: "true", def: true, want: true},
+		{name: "valid_0", in: "0", def: true, want: false},
+		{name: "valid_f", in: "f", def: true, want: false},
+		{name: "valid_F", in: "F", def: true, want: false},
+		{name: "valid_FALSE", in: "FALSE", def: true, want: false},
+		{name: "valid_false", in: "false", def: true, want: false},
+		{name: "valid_False", in: "False", def: true, want: false},
+		{name: "valid_false_default_false", in: "false", def: false, want: false},
+		{name: "invalid_true", in: "sure", def: true, want: true},
+		{name: "invalid_false", in: "sure", def: false, want: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := def.Bool(tt.in, tt.def); got != tt.want {
+				t.Errorf("Bool(%q, %v) = %v; want %v", tt.in, tt.def, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestDuration(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		def  time.Duration
+		want time.Duration
+	}{
+		{name: "empty_second", in: "", def: time.Second, want: time.Second},
+		{name: "empty_zero", in: "", def: 0, want: 0},
+		{name: "valid", in: "2m30s", def: time.Second, want: 2*time.Minute + 30*time.Second},
+		{name: "valid_zero", in: "0s", def: time.Second, want: 0},
+		{name: "invalid_second", in: "soon", def: time.Second, want: time.Second},
+		{name: "invalid_minute", in: "soon", def: time.Minute, want: time.Minute},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := def.Duration(tt.in, tt.def); got != tt.want {
+				t.Errorf("Duration(%q, %v) = %v; want %v", tt.in, tt.def, got, tt.want)
+			}
+		})
+	}
+}
+
+func FuzzBool(f *testing.F) {
+	for _, tc := range []struct {
+		in  string
+		def bool
+	}{
+		{in: "", def: true},
+		{in: "", def: false},
+		{in: "true", def: false},
+		{in: "false", def: true},
+		{in: "sure", def: true},
+		{in: "sure", def: false},
+	} {
+		f.Add(tc.in, tc.def)
+	}
+	f.Fuzz(func(t *testing.T, in string, fallback bool) {
+		got := def.Bool(in, fallback)
+		want, err := strconv.ParseBool(in)
+		if in == "" || err != nil {
+			want = fallback
+		}
+		if got != want {
+			t.Fatalf("Bool(%q, %v) = %v; want %v", in, fallback, got, want)
+		}
+	})
+}
+
+func FuzzDuration(f *testing.F) {
+	for _, tc := range []struct {
+		in  string
+		def time.Duration
+	}{
+		{in: "", def: time.Second},
+		{in: "", def: 0},
+		{in: "2m30s", def: time.Second},
+		{in: "soon", def: time.Second},
+	} {
+		f.Add(tc.in, int64(tc.def))
+	}
+	f.Fuzz(func(t *testing.T, in string, fallbackN int64) {
+		fallback := time.Duration(fallbackN)
+		got := def.Duration(in, fallback)
+		want, err := time.ParseDuration(in)
+		if in == "" || err != nil {
+			want = fallback
+		}
+		if got != want {
+			t.Fatalf("Duration(%q, %v) = %v; want %v", in, fallback, got, want)
+		}
+	})
+}