khenaidoo | ac63710 | 2019-01-14 15:44:34 -0500 | [diff] [blame^] | 1 | package json |
| 2 | |
| 3 | import "unicode/utf8" |
| 4 | |
| 5 | const hex = "0123456789abcdef" |
| 6 | |
| 7 | var noEscapeTable = [256]bool{} |
| 8 | |
| 9 | func init() { |
| 10 | for i := 0; i <= 0x7e; i++ { |
| 11 | noEscapeTable[i] = i >= 0x20 && i != '\\' && i != '"' |
| 12 | } |
| 13 | } |
| 14 | |
| 15 | // AppendStrings encodes the input strings to json and |
| 16 | // appends the encoded string list to the input byte slice. |
| 17 | func (e Encoder) AppendStrings(dst []byte, vals []string) []byte { |
| 18 | if len(vals) == 0 { |
| 19 | return append(dst, '[', ']') |
| 20 | } |
| 21 | dst = append(dst, '[') |
| 22 | dst = e.AppendString(dst, vals[0]) |
| 23 | if len(vals) > 1 { |
| 24 | for _, val := range vals[1:] { |
| 25 | dst = e.AppendString(append(dst, ','), val) |
| 26 | } |
| 27 | } |
| 28 | dst = append(dst, ']') |
| 29 | return dst |
| 30 | } |
| 31 | |
| 32 | // AppendString encodes the input string to json and appends |
| 33 | // the encoded string to the input byte slice. |
| 34 | // |
| 35 | // The operation loops though each byte in the string looking |
| 36 | // for characters that need json or utf8 encoding. If the string |
| 37 | // does not need encoding, then the string is appended in it's |
| 38 | // entirety to the byte slice. |
| 39 | // If we encounter a byte that does need encoding, switch up |
| 40 | // the operation and perform a byte-by-byte read-encode-append. |
| 41 | func (Encoder) AppendString(dst []byte, s string) []byte { |
| 42 | // Start with a double quote. |
| 43 | dst = append(dst, '"') |
| 44 | // Loop through each character in the string. |
| 45 | for i := 0; i < len(s); i++ { |
| 46 | // Check if the character needs encoding. Control characters, slashes, |
| 47 | // and the double quote need json encoding. Bytes above the ascii |
| 48 | // boundary needs utf8 encoding. |
| 49 | if !noEscapeTable[s[i]] { |
| 50 | // We encountered a character that needs to be encoded. Switch |
| 51 | // to complex version of the algorithm. |
| 52 | dst = appendStringComplex(dst, s, i) |
| 53 | return append(dst, '"') |
| 54 | } |
| 55 | } |
| 56 | // The string has no need for encoding an therefore is directly |
| 57 | // appended to the byte slice. |
| 58 | dst = append(dst, s...) |
| 59 | // End with a double quote |
| 60 | return append(dst, '"') |
| 61 | } |
| 62 | |
| 63 | // appendStringComplex is used by appendString to take over an in |
| 64 | // progress JSON string encoding that encountered a character that needs |
| 65 | // to be encoded. |
| 66 | func appendStringComplex(dst []byte, s string, i int) []byte { |
| 67 | start := 0 |
| 68 | for i < len(s) { |
| 69 | b := s[i] |
| 70 | if b >= utf8.RuneSelf { |
| 71 | r, size := utf8.DecodeRuneInString(s[i:]) |
| 72 | if r == utf8.RuneError && size == 1 { |
| 73 | // In case of error, first append previous simple characters to |
| 74 | // the byte slice if any and append a remplacement character code |
| 75 | // in place of the invalid sequence. |
| 76 | if start < i { |
| 77 | dst = append(dst, s[start:i]...) |
| 78 | } |
| 79 | dst = append(dst, `\ufffd`...) |
| 80 | i += size |
| 81 | start = i |
| 82 | continue |
| 83 | } |
| 84 | i += size |
| 85 | continue |
| 86 | } |
| 87 | if noEscapeTable[b] { |
| 88 | i++ |
| 89 | continue |
| 90 | } |
| 91 | // We encountered a character that needs to be encoded. |
| 92 | // Let's append the previous simple characters to the byte slice |
| 93 | // and switch our operation to read and encode the remainder |
| 94 | // characters byte-by-byte. |
| 95 | if start < i { |
| 96 | dst = append(dst, s[start:i]...) |
| 97 | } |
| 98 | switch b { |
| 99 | case '"', '\\': |
| 100 | dst = append(dst, '\\', b) |
| 101 | case '\b': |
| 102 | dst = append(dst, '\\', 'b') |
| 103 | case '\f': |
| 104 | dst = append(dst, '\\', 'f') |
| 105 | case '\n': |
| 106 | dst = append(dst, '\\', 'n') |
| 107 | case '\r': |
| 108 | dst = append(dst, '\\', 'r') |
| 109 | case '\t': |
| 110 | dst = append(dst, '\\', 't') |
| 111 | default: |
| 112 | dst = append(dst, '\\', 'u', '0', '0', hex[b>>4], hex[b&0xF]) |
| 113 | } |
| 114 | i++ |
| 115 | start = i |
| 116 | } |
| 117 | if start < len(s) { |
| 118 | dst = append(dst, s[start:]...) |
| 119 | } |
| 120 | return dst |
| 121 | } |