govis: support double quote escapes

This is supported by both OpenBSD and FreBSD so it seems possible that
we will run into \" sequences at some point. The handling is basically
identical to \\ sequences.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

pkg/govis/govis.go

@@ -41,6 +41,7 @@ const (
 	VisNoSlash                               // VIS_NOSLASH: Inhibit printing '\'.
 	VisHTTPStyle                             // VIS_HTTPSTYLE: HTTP-style escape %xx.
 	VisGlob                                  // VIS_GLOB: Encode glob(3) magics.
+	VisDoubleQuote                           // VIS_DQ: Encode double-quotes (").
 	visMask        VisFlag = (1 << iota) - 1 // Mask of all flags.
 
 	VisWhite VisFlag = (VisSpace | VisTab | VisNewline)

pkg/govis/unvis.go

@@ -225,9 +225,9 @@ func (p *unvisParser) escapeSequence() error {
 	}
 
 	switch ch {
-	case '\\':
+	case '\\', '"':
 		p.Step()
-		return p.output.WriteByte('\\')
+		return p.output.WriteByte(byte(ch))
 
 	case '0', '1', '2', '3', '4', '5', '6', '7':
 		return p.escapeDigits(8, false)

pkg/govis/unvis_test.go

@@ -65,12 +65,13 @@ func TestUnvisCStyleEscape(t *testing.T) {
 		expected string
 	}{
 		{"", ""},
-		{"\\n\\v\\t\\s", "\n\v\t "},
-		{"\\\\n\\tt", "\\n\tt"},
-		{"\\b", "\b"},
-		{"\\r\\b\\n", "\r\b\n"},
-		{"\\a\\a\\b", "\x07\x07\b"},
-		{"\\f\\s\\E", "\f \x1b"},
+		{`\n\v\t\s`, "\n\v\t "},
+		{`\\n\tt`, "\\n\tt"},
+		{`\b`, "\b"},
+		{`\r\b\n`, "\r\b\n"},
+		{`\a\a\b`, "\x07\x07\b"},
+		{`\f\s\E`, "\f \x1b"},
+		{`\"foo\"\\"bar`, `"foo"\"bar`},
 		// Hidden markers. They actually aren't generated by vis(3) but for
 		// some reason, they're supported...
 		{"test\\\ning", "testing"},

pkg/govis/vis.go

@@ -81,7 +81,8 @@ func vis(output *strings.Builder, ch byte, flag VisFlag) {
 		// We must *always* encode stuff characters not in ASCII.
 	case flag&VisGlob == VisGlob && isglob(ch):
 		// Glob characters are graphical but can be forced to be encoded.
-	case flag&VisNoSlash == 0 && ch == '\\':
+	case flag&VisNoSlash == 0 && ch == '\\',
+		flag&VisDoubleQuote == VisDoubleQuote && ch == '"':
 		// Prefix \ if applicable.
 		_ = output.WriteByte('\\')
 		fallthrough

pkg/govis/vis_test.go

@@ -104,6 +104,11 @@ func TestVisFlags(t *testing.T) {
 		{"62_\u00c6\u00c62\u00ae\u00b7m\u00db\u00c3r^\u00bfp\u00c6u'q\u00fbc2\u00f0u\u00b8\u00dd\u00e8v\u00ff\u00b0\u00dc\u00c2\u00f53\u00db-k\u00f2sd4\\p\u00da\u00a6\u00d3\u00eea<\u00e6s{\u00a0p\u00f0\u00ffj\u00e0\u00e8\u00b8\u00b8\u00bc\u00fcb", `62_\303\206\303\2062\302\256\302\267m\303\233\303\203r^\302\277p\303\206u'q\303\273c2\303\260u\302\270\303\235\303\250v\303\277\302\260\303\234\303\202\303\2653\303\233-k\303\262sd4\\p\303\232\302\246\303\223\303\256a<\303\246s{\302\240p\303\260\303\277j\303\240\303\250\302\270\302\270\302\274\303\274b`, VisGlob | VisOctal},
 		{"'3Ze\u050e|\u02del\u069du-Rpct4+Z5b={@_{b", `'3Ze\M-T\M^N|\M-K\M^^l\M-Z\M^]u-Rpct4+Z5b={@_{b`, VisGlob},
 		{"'3Ze\u050e|\u02del\u069du-Rpct4+Z5b={@_{b", `'3Ze\324\216|\313\236l\332\235u-Rpct4+Z5b={@_{b`, VisGlob | VisOctal},
+		// VisDoubleQuote
+		{`Foo="Bar's"`, `Foo="Bar's"`, 0},
+		{`Foo="Bar's"`, `Foo=\"Bar's\"`, VisDoubleQuote},
+		{`"“Unicode” ‘Quote’s’"`, `\"\M-b\M^@\M^\Unicode\M-b\M^@\M^] \M-b\M^@\M^XQuote\M-b\M^@\M^Ys\M-b\M^@\M^Y\"`, VisDoubleQuote},
+		{`"“Unicode” ‘Quote’s’"`, `\"\342\200\234Unicode\342\200\235 \342\200\230Quote\342\200\231s\342\200\231\"`, VisDoubleQuote | VisOctal},
 	} {
 		t.Run(fmt.Sprintf("Test%.2d", idx), func(t *testing.T) {
 			enc, err := Vis(test.input, test.flag)