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package json
import (
"fmt"
"unicode/utf8"
)
const hex = "0123456789abcdef"
var noEscapeTable = [256]bool{}
func init() {
for i := 0; i <= 0x7e; i++ {
noEscapeTable[i] = i >= 0x20 && i != '\\' && i != '"'
}
}
// AppendStrings encodes the input strings to json and
// appends the encoded string list to the input byte slice.
func (e Encoder) AppendStrings(dst []byte, vals []string) []byte {
if len(vals) == 0 {
return append(dst, '[', ']')
}
dst = append(dst, '[')
dst = e.AppendString(dst, vals[0])
if len(vals) > 1 {
for _, val := range vals[1:] {
dst = e.AppendString(append(dst, ','), val)
}
}
dst = append(dst, ']')
return dst
}
// AppendString encodes the input string to json and appends
// the encoded string to the input byte slice.
//
// The operation loops though each byte in the string looking
// for characters that need json or utf8 encoding. If the string
// does not need encoding, then the string is appended in its
// entirety to the byte slice.
// If we encounter a byte that does need encoding, switch up
// the operation and perform a byte-by-byte read-encode-append.
func (Encoder) AppendString(dst []byte, s string) []byte {
// Start with a double quote.
dst = append(dst, '"')
// Loop through each character in the string.
for i := 0; i < len(s); i++ {
// Check if the character needs encoding. Control characters, slashes,
// and the double quote need json encoding. Bytes above the ascii
// boundary needs utf8 encoding.
if !noEscapeTable[s[i]] {
// We encountered a character that needs to be encoded. Switch
// to complex version of the algorithm.
dst = appendStringComplex(dst, s, i)
return append(dst, '"')
}
}
// The string has no need for encoding and therefore is directly
// appended to the byte slice.
dst = append(dst, s...)
// End with a double quote
return append(dst, '"')
}
// AppendStringers encodes the provided Stringer list to json and
// appends the encoded Stringer list to the input byte slice.
func (e Encoder) AppendStringers(dst []byte, vals []fmt.Stringer) []byte {
if len(vals) == 0 {
return append(dst, '[', ']')
}
dst = append(dst, '[')
dst = e.AppendStringer(dst, vals[0])
if len(vals) > 1 {
for _, val := range vals[1:] {
dst = e.AppendStringer(append(dst, ','), val)
}
}
return append(dst, ']')
}
// AppendStringer encodes the input Stringer to json and appends the
// encoded Stringer value to the input byte slice.
func (e Encoder) AppendStringer(dst []byte, val fmt.Stringer) []byte {
if val == nil {
return e.AppendInterface(dst, nil)
}
return e.AppendString(dst, val.String())
}
//// appendStringComplex is used by appendString to take over an in
// progress JSON string encoding that encountered a character that needs
// to be encoded.
func appendStringComplex(dst []byte, s string, i int) []byte {
start := 0
for i < len(s) {
b := s[i]
if b >= utf8.RuneSelf {
r, size := utf8.DecodeRuneInString(s[i:])
if r == utf8.RuneError && size == 1 {
// In case of error, first append previous simple characters to
// the byte slice if any and append a replacement character code
// in place of the invalid sequence.
if start < i {
dst = append(dst, s[start:i]...)
}
dst = append(dst, `\ufffd`...)
i += size
start = i
continue
}
i += size
continue
}
if noEscapeTable[b] {
i++
continue
}
// We encountered a character that needs to be encoded.
// Let's append the previous simple characters to the byte slice
// and switch our operation to read and encode the remainder
// characters byte-by-byte.
if start < i {
dst = append(dst, s[start:i]...)
}
switch b {
case '"', '\\':
dst = append(dst, '\\', b)
case '\b':
dst = append(dst, '\\', 'b')
case '\f':
dst = append(dst, '\\', 'f')
case '\n':
dst = append(dst, '\\', 'n')
case '\r':
dst = append(dst, '\\', 'r')
case '\t':
dst = append(dst, '\\', 't')
default:
dst = append(dst, '\\', 'u', '0', '0', hex[b>>4], hex[b&0xF])
}
i++
start = i
}
if start < len(s) {
dst = append(dst, s[start:]...)
}
return dst
}
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