json2: unescape characters (#6836)

vlib/x/json2/decoder.v

@@ -223,8 +223,6 @@ fn (mut p Parser) decode_value() ?Any {
 fn (mut p Parser) decode_string() ?Any {
 	mut strwr := strings.new_builder(200)
 	for i := 0; i < p.tok.lit.len; i++ {
-		// s := p.tok.lit[i].str()
-		// println('$i $s')
 		if ((i-1 >= 0 && p.tok.lit[i-1] != `/`) || i == 0) && int(p.tok.lit[i]) in [9, 10, 0] {
 			return error('character must be escaped with a backslash.')
 		}
@@ -235,8 +233,33 @@ fn (mut p Parser) decode_string() ?Any {
 
 		if i+1 < p.tok.lit.len && p.tok.lit[i] == 92 {
 			peek := p.tok.lit[i+1]
-			if peek in [`b`, `f`, `n`, `r`, `t`, `u`, `\\`, `"`, `/`] {
-				if peek == `u` {
+			match peek{
+				`b` {
+					i++
+					strwr.write_b(`\b`)
+					continue
+				}
+				`f` {
+					i++
+					strwr.write_b(`\f`)
+					continue
+				}
+				`n` {
+					i++
+					strwr.write_b(`\n`)
+					continue
+				}
+				`r` {
+					i++
+					strwr.write_b(`\r`)
+					continue
+				}
+				`t` {
+					i++
+					strwr.write_b(`\t`)
+					continue
+				}
+				`u` {
 					if i+5 < p.tok.lit.len {
 						codepoint := p.tok.lit[i+2..i+6]
 						check_valid_hex(codepoint)?
@@ -248,12 +271,22 @@ fn (mut p Parser) decode_string() ?Any {
 						return error('incomplete unicode escape.')
 					}
 				}
-
+				`\\` {
 					i++
-				strwr.write_b(p.tok.lit[i])
+					strwr.write_b(`\\`)
 					continue
-			} else {
-				return error('invalid backslash escape.')
+				}
+				`"` {
+					i++
+					strwr.write_b(`\"`)
+					continue
+				}
+				`/` {
+					i++
+					strwr.write_b(`/`)
+					continue
+				}
+				else { return error('invalid backslash escape.') }
 			} 
 
 			if int(peek) == 85 {

vlib/x/json2/encoder.v

@@ -7,7 +7,11 @@ import strings
 
 fn write_value(v Any, i int, len int, mut wr strings.Builder) {
 	str := v.str()
-	wr.write(if v is string { '"$str"' } else { str })
+	if v is string { 
+		wr.write('"$str"') 
+	} else { 
+		wr.write(str)
+	}
 	if i >= len-1 { return }
 	wr.write_b(`,`)
 }

vlib/x/json2/json2_test.v

@@ -69,6 +69,28 @@ fn test_fast_raw_decode() {
 	assert str == '{"name":"Peter","age":"28","salary":"95000.5","title":"2"}'
 }
 
+fn test_character_unescape() {
+	// Need to test `\r`, `\b`, `\f` ??
+	message := '{
+		"newline":"new\\nline", 
+		"tab":"\\ttab", 
+		"backslash": "back\\\\slash", 
+		"quotes": "\\"quotes\\"", 
+		"slash":"\/dev\/null"
+	}'
+	mut obj := json2.raw_decode(message) or {
+		assert false
+		json2.Any{}
+	}
+	lines := obj.as_map()
+	eprintln("$lines")
+	assert lines['newline'].str() == 'new\nline'
+	assert lines['tab'].str() == '\ttab'
+	assert lines['backslash'].str() == 'back\\slash'
+	assert lines['quotes'].str() == '\"quotes\"'
+	assert lines['slash'].str() == '/dev/null'
+}
+
 /*
 struct User2 {
 	age  int