377 lines
7.8 KiB
Go
377 lines
7.8 KiB
Go
package jsn
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import (
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"fmt"
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"strconv"
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"strings"
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"unsafe"
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)
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// Validate function validates JSON
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func Validate(s string) error {
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s = skipWS(s)
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tail, err := validateValue(s)
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if err != nil {
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return fmt.Errorf("cannot parse JSON: %s; unparsed tail: %q", err, startEndString(tail))
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}
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tail = skipWS(tail)
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if len(tail) > 0 {
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return fmt.Errorf("unexpected tail: %q", startEndString(tail))
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}
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return nil
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}
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// ValidateBytes validates JSON b.
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func ValidateBytes(b []byte) error {
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return Validate(b2s(b))
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}
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func validateValue(s string) (string, error) {
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if len(s) == 0 {
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return s, fmt.Errorf("cannot parse empty string")
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}
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if s[0] == '{' {
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tail, err := validateObject(s[1:])
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if err != nil {
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return tail, fmt.Errorf("cannot parse object: %s", err)
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}
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return tail, nil
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}
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if s[0] == '[' {
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tail, err := validateArray(s[1:])
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if err != nil {
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return tail, fmt.Errorf("cannot parse array: %s", err)
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}
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return tail, nil
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}
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if s[0] == '"' {
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sv, tail, err := validateString(s[1:])
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if err != nil {
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return tail, fmt.Errorf("cannot parse string: %s", err)
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}
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// Scan the string for control chars.
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for i := 0; i < len(sv); i++ {
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if sv[i] < 0x20 {
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return tail, fmt.Errorf("string cannot contain control char 0x%02X", sv[i])
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}
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}
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return tail, nil
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}
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if s[0] == 't' {
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if len(s) < len("true") || s[:len("true")] != "true" {
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return s, fmt.Errorf("unexpected value found: %q", s)
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}
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return s[len("true"):], nil
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}
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if s[0] == 'f' {
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if len(s) < len("false") || s[:len("false")] != "false" {
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return s, fmt.Errorf("unexpected value found: %q", s)
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}
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return s[len("false"):], nil
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}
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if s[0] == 'n' {
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if len(s) < len("null") || s[:len("null")] != "null" {
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return s, fmt.Errorf("unexpected value found: %q", s)
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}
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return s[len("null"):], nil
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}
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tail, err := validateNumber(s)
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if err != nil {
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return tail, fmt.Errorf("cannot parse number: %s", err)
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}
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return tail, nil
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}
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func validateArray(s string) (string, error) {
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s = skipWS(s)
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if len(s) == 0 {
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return s, fmt.Errorf("missing ']'")
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}
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if s[0] == ']' {
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return s[1:], nil
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}
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for {
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var err error
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s = skipWS(s)
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s, err = validateValue(s)
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if err != nil {
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return s, fmt.Errorf("cannot parse array value: %s", err)
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}
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s = skipWS(s)
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if len(s) == 0 {
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return s, fmt.Errorf("unexpected end of array")
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}
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if s[0] == ',' {
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s = s[1:]
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continue
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}
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if s[0] == ']' {
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s = s[1:]
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return s, nil
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}
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return s, fmt.Errorf("missing ',' after array value")
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}
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}
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func validateObject(s string) (string, error) {
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s = skipWS(s)
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if len(s) == 0 {
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return s, fmt.Errorf("missing '}'")
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}
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if s[0] == '}' {
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return s[1:], nil
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}
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for {
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var err error
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// Parse key.
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s = skipWS(s)
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if len(s) == 0 || s[0] != '"' {
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return s, fmt.Errorf(`cannot find opening '"" for object key`)
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}
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var key string
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key, s, err = validateKey(s[1:])
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if err != nil {
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return s, fmt.Errorf("cannot parse object key: %s", err)
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}
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// Scan the key for control chars.
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for i := 0; i < len(key); i++ {
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if key[i] < 0x20 {
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return s, fmt.Errorf("object key cannot contain control char 0x%02X", key[i])
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}
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}
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s = skipWS(s)
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if len(s) == 0 || s[0] != ':' {
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return s, fmt.Errorf("missing ':' after object key")
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}
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s = s[1:]
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// Parse value
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s = skipWS(s)
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s, err = validateValue(s)
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if err != nil {
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return s, fmt.Errorf("cannot parse object value: %s", err)
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}
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s = skipWS(s)
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if len(s) == 0 {
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return s, fmt.Errorf("unexpected end of object")
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}
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if s[0] == ',' {
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s = s[1:]
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continue
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}
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if s[0] == '}' {
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return s[1:], nil
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}
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return s, fmt.Errorf("missing ',' after object value")
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}
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}
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// validateKey is similar to validateString, but is optimized
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// for typical object keys, which are quite small and have no escape sequences.
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func validateKey(s string) (string, string, error) {
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for i := 0; i < len(s); i++ {
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if s[i] == '"' {
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// Fast path - the key doesn't contain escape sequences.
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return s[:i], s[i+1:], nil
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}
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if s[i] == '\\' {
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// Slow path - the key contains escape sequences.
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return validateString(s)
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}
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}
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return "", s, fmt.Errorf(`missing closing '"'`)
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}
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func validateString(s string) (string, string, error) {
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// Try fast path - a string without escape sequences.
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if n := strings.IndexByte(s, '"'); n >= 0 && strings.IndexByte(s[:n], '\\') < 0 {
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return s[:n], s[n+1:], nil
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}
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// Slow path - escape sequences are present.
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rs, tail, err := parseRawString(s)
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if err != nil {
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return rs, tail, err
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}
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for {
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n := strings.IndexByte(rs, '\\')
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if n < 0 {
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return rs, tail, nil
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}
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n++
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if n >= len(rs) {
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return rs, tail, fmt.Errorf("BUG: parseRawString returned invalid string with trailing backslash: %q", rs)
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}
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ch := rs[n]
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rs = rs[n+1:]
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switch ch {
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case '"', '\\', '/', 'b', 'f', 'n', 'r', 't':
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// Valid escape sequences - see http://json.org/
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break
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case 'u':
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if len(rs) < 4 {
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return rs, tail, fmt.Errorf(`too short escape sequence: \u%s`, rs)
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}
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xs := rs[:4]
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_, err := strconv.ParseUint(xs, 16, 16)
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if err != nil {
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return rs, tail, fmt.Errorf(`invalid escape sequence \u%s: %s`, xs, err)
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}
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rs = rs[4:]
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default:
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return rs, tail, fmt.Errorf(`unknown escape sequence \%c`, ch)
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}
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}
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}
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func validateNumber(s string) (string, error) {
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if len(s) == 0 {
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return s, fmt.Errorf("zero-length number")
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}
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if s[0] == '-' {
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s = s[1:]
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if len(s) == 0 {
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return s, fmt.Errorf("missing number after minus")
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}
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}
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i := 0
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for i < len(s) {
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if s[i] < '0' || s[i] > '9' {
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break
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}
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i++
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}
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if i <= 0 {
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return s, fmt.Errorf("expecting 0..9 digit, got %c", s[0])
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}
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if s[0] == '0' && i != 1 {
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return s, fmt.Errorf("unexpected number starting from 0")
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}
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if i >= len(s) {
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return "", nil
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}
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if s[i] == '.' {
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// Validate fractional part
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s = s[i+1:]
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if len(s) == 0 {
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return s, fmt.Errorf("missing fractional part")
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}
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i = 0
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for i < len(s) {
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if s[i] < '0' || s[i] > '9' {
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break
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}
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i++
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}
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if i == 0 {
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return s, fmt.Errorf("expecting 0..9 digit in fractional part, got %c", s[0])
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}
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if i >= len(s) {
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return "", nil
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}
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}
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if s[i] == 'e' || s[i] == 'E' {
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// Validate exponent part
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s = s[i+1:]
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if len(s) == 0 {
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return s, fmt.Errorf("missing exponent part")
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}
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if s[0] == '-' || s[0] == '+' {
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s = s[1:]
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if len(s) == 0 {
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return s, fmt.Errorf("missing exponent part")
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}
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}
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i = 0
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for i < len(s) {
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if s[i] < '0' || s[i] > '9' {
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break
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}
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i++
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}
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if i == 0 {
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return s, fmt.Errorf("expecting 0..9 digit in exponent part, got %c", s[0])
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}
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if i >= len(s) {
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return "", nil
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}
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}
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return s[i:], nil
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}
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func skipWS(s string) string {
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if len(s) == 0 || s[0] > 0x20 {
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// Fast path.
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return s
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}
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return skipWSSlow(s)
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}
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func skipWSSlow(s string) string {
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if len(s) == 0 || s[0] != 0x20 && s[0] != 0x0A && s[0] != 0x09 && s[0] != 0x0D {
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return s
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}
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for i := 1; i < len(s); i++ {
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if s[i] != 0x20 && s[i] != 0x0A && s[i] != 0x09 && s[i] != 0x0D {
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return s[i:]
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}
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}
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return ""
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}
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func b2s(b []byte) string {
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return *(*string)(unsafe.Pointer(&b))
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}
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const maxStartEndStringLen = 80
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func startEndString(s string) string {
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if len(s) <= maxStartEndStringLen {
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return s
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}
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start := s[:40]
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end := s[len(s)-40:]
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return start + "..." + end
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}
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func parseRawString(s string) (string, string, error) {
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n := strings.IndexByte(s, '"')
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if n < 0 {
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return s, "", fmt.Errorf(`missing closing '"'`)
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}
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if n == 0 || s[n-1] != '\\' {
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// Fast path. No escaped ".
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return s[:n], s[n+1:], nil
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}
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// Slow path - possible escaped " found.
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ss := s
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for {
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i := n - 1
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for i > 0 && s[i-1] == '\\' {
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i--
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}
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if uint(n-i)%2 == 0 {
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return ss[:len(ss)-len(s)+n], s[n+1:], nil
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}
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s = s[n+1:]
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n = strings.IndexByte(s, '"')
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if n < 0 {
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return ss, "", fmt.Errorf(`missing closing '"'`)
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}
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if n == 0 || s[n-1] != '\\' {
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return ss[:len(ss)-len(s)+n], s[n+1:], nil
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}
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}
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}
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