encoding/json: streamline, unexport valid Number checking

Followup to CL 12250.

For #10281.

Change-Id: If25d9cac92f10327bb355f2d11b00c625b464661
Reviewed-on: https://go-review.googlesource.com/17199Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/encoding/json/decode.go

@@ -60,7 +60,7 @@ import (
 // If the JSON array is smaller than the Go array,
 // the additional Go array elements are set to zero values.
 //
-// To unmarshal a JSON object into a string-keyed map, Unmarshal first 
+// To unmarshal a JSON object into a string-keyed map, Unmarshal first
 // establishes a map to use, If the map is nil, Unmarshal allocates a new map.
 // Otherwise Unmarshal reuses the existing map, keeping existing entries.
 // Unmarshal then stores key-value pairs from the JSON object into the map.
@@ -184,122 +184,64 @@ func (n Number) Int64() (int64, error) {
 	return strconv.ParseInt(string(n), 10, 64)
 }
 
-// IsValid returns if the number is a valid JSON number literal.
-func (n Number) IsValid() bool {
+// isValidNumber reports whether s is a valid JSON number literal.
+func isValidNumber(s string) bool {
 	// This function implements the JSON numbers grammar.
 	// See https://tools.ietf.org/html/rfc7159#section-6
 	// and http://json.org/number.gif
 
-	l := len(n)
-	if l == 0 {
+	if s == "" {
 		return false
 	}
 
-	i := 0
-	c := n[i]
-	i++
-
 	// Optional -
-	if c == '-' {
-		if i == l {
+	if s[0] == '-' {
+		s = s[1:]
+		if s == "" {
 			return false
 		}
-
-		c = n[i]
-		i++
 	}
 
-	// 1-9
-	if c >= '1' && c <= '9' {
-		// Eat digits.
-		for ; i < l; i++ {
-			c = n[i]
-			if c < '0' || c > '9' {
-				break
-			}
-		}
-		i++
-	} else if c != '0' {
-		// If it's not 0 or 1-9 it's invalid.
+	// Digits
+	switch {
+	default:
 		return false
-	} else {
-		if i == l {
-			// Just 0
-			return true
-		}
 
-		// Skip the 0
-		c = n[i]
-		i++
-	}
-
-	// . followed by 1 or more digits.
-	if c == '.' {
-		if i == l {
-			// Just 1. is invalid.
-			return false
-		}
+	case s[0] == '0':
+		s = s[1:]
 
-		// . needs to be followed by at least one digit.
-		c = n[i]
-		i++
-		if c < '0' || c > '9' {
-			return false
+	case '1' <= s[0] && s[0] <= '9':
+		s = s[1:]
+		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
+			s = s[1:]
 		}
+	}
 
-		// Eat digits.
-		for ; i < l; i++ {
-			c = n[i]
-			if c < '0' || c > '9' {
-				break
-			}
+	// . followed by 1 or more digits.
+	if len(s) >= 2 && s[0] == '.' && '0' <= s[1] && s[1] <= '9' {
+		s = s[2:]
+		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
+			s = s[1:]
 		}
-		i++
 	}
 
 	// e or E followed by an optional - or + and
 	// 1 or more digits.
-	if c == 'e' || c == 'E' {
-		if i == l {
-			// Just 1e is invalid.
-			return false
-		}
-
-		c = n[i]
-		i++
-
-		// Optional - or +
-		if c == '-' || c == '+' {
-			if i == l {
-				// Just 1e+ is invalid.
+	if len(s) >= 2 && (s[0] == 'e' || s[0] == 'E') {
+		s = s[1:]
+		if s[0] == '+' || s[0] == '-' {
+			s = s[1:]
+			if s == "" {
 				return false
 			}
-
-			c = n[i]
-			i++
 		}
-
-		// Need to have a digit.
-		if c < '0' || c > '9' {
-			return false
-		}
-
-		// Eat digits.
-		for ; i < l; i++ {
-			c = n[i]
-			if c < '0' || c > '9' {
-				break
-			}
+		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
+			s = s[1:]
 		}
-		i++
 	}
 
 	// Make sure we are at the end.
-	if i <= l {
-		return false
-	}
-
-	return true
+	return s == ""
 }
 
 // decodeState represents the state while decoding a JSON value.
@@ -909,7 +851,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 		default:
 			if v.Kind() == reflect.String && v.Type() == numberType {
 				v.SetString(s)
-				if !Number(s).IsValid() {
+				if !isValidNumber(s) {
 					d.error(fmt.Errorf("json: invalid number literal, trying to unmarshal %q into Number", item))
 				}
 				break

src/encoding/json/encode.go

@@ -534,8 +534,9 @@ func stringEncoder(e *encodeState, v reflect.Value, quoted bool) {
 		// we keep compatibility so check validity after this.
 		if numStr == "" {
 			numStr = "0" // Number's zero-val
-		} else if !Number(numStr).IsValid() {
-			e.error(fmt.Errorf("json: invalid number literal, trying to marshal %s", v.String()))
+		}
+		if !isValidNumber(numStr) {
+			e.error(fmt.Errorf("json: invalid number literal %q", numStr))
 		}
 		e.WriteString(numStr)
 		return

src/encoding/json/number_test.go

@@ -63,17 +63,17 @@ func TestNumberIsValid(t *testing.T) {
 	}
 
 	for _, test := range validTests {
-		if !Number(test).IsValid() {
+		if !isValidNumber(test) {
 			t.Errorf("%s should be valid", test)
 		}
 
 		var f float64
 		if err := Unmarshal([]byte(test), &f); err != nil {
-			t.Errorf("%s should be invalid: %v", test, err)
+			t.Errorf("%s should be valid but Unmarshal failed: %v", test, err)
 		}
 
 		if !jsonNumberRegexp.MatchString(test) {
-			t.Errorf("%s should be invalid", test)
+			t.Errorf("%s should be valid but regexp does not match", test)
 		}
 	}
 
@@ -102,32 +102,32 @@ func TestNumberIsValid(t *testing.T) {
 	}
 
 	for _, test := range invalidTests {
-		if Number(test).IsValid() {
+		if isValidNumber(test) {
 			t.Errorf("%s should be invalid", test)
 		}
 
 		var f float64
 		if err := Unmarshal([]byte(test), &f); err == nil {
-			t.Errorf("%s should be valid: %v", test, f)
+			t.Errorf("%s should be invalid but unmarshal wrote %v", test, f)
 		}
 
 		if jsonNumberRegexp.MatchString(test) {
-			t.Errorf("%s should be valid", test)
+			t.Errorf("%s should be invalid but matches regexp", test)
 		}
 	}
 }
 
 func BenchmarkNumberIsValid(b *testing.B) {
-	n := Number("-61657.61667E+61673")
+	s := "-61657.61667E+61673"
 	for i := 0; i < b.N; i++ {
-		n.IsValid()
+		isValidNumber(s)
 	}
 }
 
 func BenchmarkNumberIsValidRegexp(b *testing.B) {
 	var jsonNumberRegexp = regexp.MustCompile(`^-?(?:0|[1-9]\d*)(?:\.\d+)?(?:[eE][+-]?\d+)?$`)
-	n := "-61657.61667E+61673"
+	s := "-61657.61667E+61673"
 	for i := 0; i < b.N; i++ {
-		jsonNumberRegexp.MatchString(n)
+		jsonNumberRegexp.MatchString(s)
 	}
 }