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