From 0a5c83ece140ab81a8111756cb6a80a4687036ca Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Tue, 7 Jan 2020 19:11:34 +0000
Subject: [PATCH] lib/encoder: add string rendering and parsing for encodings

---
 lib/encoder/encoder.go      | 110 ++++++++++++++++++++++++++++++++++++
 lib/encoder/encoder_test.go |  56 ++++++++++++++++++
 2 files changed, 166 insertions(+)

diff --git a/lib/encoder/encoder.go b/lib/encoder/encoder.go
index 8d84ac2eb..ecb2f8c8d 100644
--- a/lib/encoder/encoder.go
+++ b/lib/encoder/encoder.go
@@ -16,6 +16,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"sort"
 	"strconv"
 	"strings"
 	"unicode/utf8"
@@ -32,6 +33,7 @@ const (
 )
 
 // NB keep the tests in fstests/fstests/fstests.go FsEncoding up to date with this
+// NB keep the aliases up to date below also
 
 // Possible flags for the MultiEncoder
 const (
@@ -99,6 +101,114 @@ type Encoder interface {
 // character classes
 type MultiEncoder uint
 
+// Aliases maps encodings to names and vice versa
+var (
+	encodingToName = map[MultiEncoder]string{}
+	nameToEncoding = map[string]MultiEncoder{}
+)
+
+// alias adds an alias for MultiEncoder.String() and MultiEncoder.Set()
+func alias(name string, mask MultiEncoder) {
+	nameToEncoding[name] = mask
+	// don't overwrite existing reverse translations
+	if _, ok := encodingToName[mask]; !ok {
+		encodingToName[mask] = name
+	}
+}
+
+func init() {
+	alias("None", EncodeZero)
+	alias("Slash", EncodeSlash)
+	alias("LtGt", EncodeLtGt)
+	alias("DoubleQuote", EncodeDoubleQuote)
+	alias("SingleQuote", EncodeSingleQuote)
+	alias("BackQuote", EncodeBackQuote)
+	alias("Dollar", EncodeDollar)
+	alias("Colon", EncodeColon)
+	alias("Question", EncodeQuestion)
+	alias("Asterisk", EncodeAsterisk)
+	alias("Pipe", EncodePipe)
+	alias("Hash", EncodeHash)
+	alias("Percent", EncodePercent)
+	alias("BackSlash", EncodeBackSlash)
+	alias("CrLf", EncodeCrLf)
+	alias("Del", EncodeDel)
+	alias("Ctl", EncodeCtl)
+	alias("LeftSpace", EncodeLeftSpace)
+	alias("LeftPeriod", EncodeLeftPeriod)
+	alias("LeftTilde", EncodeLeftTilde)
+	alias("LeftCrLfHtVt", EncodeLeftCrLfHtVt)
+	alias("RightSpace", EncodeRightSpace)
+	alias("RightPeriod", EncodeRightPeriod)
+	alias("RightCrLfHtVt", EncodeRightCrLfHtVt)
+	alias("InvalidUtf8", EncodeInvalidUtf8)
+	alias("Dot", EncodeDot)
+}
+
+// validStrings returns all the valid MultiEncoder strings
+func validStrings() string {
+	var out []string
+	for k := range nameToEncoding {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return strings.Join(out, ", ")
+}
+
+// String converts the MultiEncoder into text
+func (mask MultiEncoder) String() string {
+	// See if there is an exact translation - if so return that
+	if name, ok := encodingToName[mask]; ok {
+		return name
+	}
+	var out []string
+	// Otherwise decompose bit by bit
+	for bit := MultiEncoder(1); bit != 0; bit *= 2 {
+		if (mask & bit) != 0 {
+			if name, ok := encodingToName[bit]; ok {
+				out = append(out, name)
+			} else {
+				out = append(out, fmt.Sprintf("0x%X", uint(bit)))
+			}
+		}
+	}
+	return strings.Join(out, ",")
+}
+
+// Set converts a string into a MultiEncoder
+func (mask *MultiEncoder) Set(in string) error {
+	var out MultiEncoder
+	parts := strings.Split(in, ",")
+	for _, part := range parts {
+		part = strings.TrimSpace(part)
+		if bits, ok := nameToEncoding[part]; ok {
+			out |= bits
+		} else {
+			i, err := strconv.ParseInt(part, 0, 64)
+			if err != nil {
+				return fmt.Errorf("bad encoding %q: possible values are: %s", part, validStrings())
+			}
+			out |= MultiEncoder(i)
+		}
+	}
+	*mask = out
+	return nil
+}
+
+// Type returns a textual type of the MultiEncoder to satsify the pflag.Value interface
+func (mask MultiEncoder) Type() string {
+	return "Encoding"
+}
+
+// Scan implements the fmt.Scanner interface
+func (mask *MultiEncoder) Scan(s fmt.ScanState, ch rune) error {
+	token, err := s.Token(true, nil)
+	if err != nil {
+		return err
+	}
+	return mask.Set(string(token))
+}
+
 // Encode takes a raw name and substitutes any reserved characters and
 // patterns in it
 func (mask MultiEncoder) Encode(in string) string {
diff --git a/lib/encoder/encoder_test.go b/lib/encoder/encoder_test.go
index 487398ab9..b041aaca4 100644
--- a/lib/encoder/encoder_test.go
+++ b/lib/encoder/encoder_test.go
@@ -1,12 +1,68 @@
 package encoder
 
 import (
+	"fmt"
 	"regexp"
 	"strconv"
 	"strings"
 	"testing"
+
+	"github.com/spf13/pflag"
+	"github.com/stretchr/testify/assert"
 )
 
+// Check it satisfies the interfaces
+var (
+	_ pflag.Value = (*MultiEncoder)(nil)
+	_ fmt.Scanner = (*MultiEncoder)(nil)
+)
+
+func TestEncodeString(t *testing.T) {
+	for _, test := range []struct {
+		mask uint
+		want string
+	}{
+		{0, "None"},
+		{EncodeZero, "None"},
+		{EncodeDoubleQuote, "DoubleQuote"},
+		{EncodeDot, "Dot"},
+		{EncodeWin, "LtGt,DoubleQuote,Colon,Question,Asterisk,Pipe"},
+		{EncodeHashPercent, "Hash,Percent"},
+		{EncodeSlash | EncodeDollar | EncodeColon, "Slash,Dollar,Colon"},
+		{EncodeSlash | (1 << 31), "Slash,0x80000000"},
+	} {
+		got := MultiEncoder(test.mask).String()
+		assert.Equal(t, test.want, got)
+	}
+
+}
+
+func TestEncodeSet(t *testing.T) {
+	for _, test := range []struct {
+		in      string
+		want    uint
+		wantErr bool
+	}{
+		{"", 0, true},
+		{"None", 0, false},
+		{"None", EncodeZero, false},
+		{"DoubleQuote", EncodeDoubleQuote, false},
+		{"Dot", EncodeDot, false},
+		{"LtGt,DoubleQuote,Colon,Question,Asterisk,Pipe", EncodeWin, false},
+		{"Hash,Percent", EncodeHashPercent, false},
+		{"Slash,Dollar,Colon", EncodeSlash | EncodeDollar | EncodeColon, false},
+		{"Slash,0x80000000", EncodeSlash | (1 << 31), false},
+		{"Blerp", 0, true},
+		{"0xFGFFF", 0, true},
+	} {
+		var got MultiEncoder
+		err := got.Set(test.in)
+		assert.Equal(t, test.wantErr, err != nil, err)
+		assert.Equal(t, MultiEncoder(test.want), got, test.in)
+	}
+
+}
+
 type testCase struct {
 	mask uint
 	in   string