| 1 | // STRING_REVERSE codec (method 3) -- variable-length payload: |
| 2 | // |
| 3 | // [0:4] u32 str_offset (from payload start, always 8) |
| 4 | // [4:8] u32 str_length (excluding NUL) |
| 5 | // [8:N+1] string data + NUL |
| 6 | |
| 7 | package protocol |
| 8 | |
| 9 | const StringReverseHdrSize = 8 |
| 10 | |
| 11 | // StringReverseView is the decoded result of a STRING_REVERSE payload. |
| 12 | type StringReverseView struct { |
| 13 | Str string |
| 14 | StrLen uint32 |
| 15 | } |
| 16 | |
| 17 | // StringReverseEncode writes a STRING_REVERSE payload into buf. |
| 18 | // Returns total bytes written, or 0 if buf is too small. |
| 19 | func StringReverseEncode(s string, buf []byte) int { |
| 20 | total := StringReverseHdrSize + len(s) + 1 |
| 21 | if len(buf) < total { |
| 22 | return 0 |
| 23 | } |
| 24 | strLen, ok := checkedU32Int(len(s)) |
| 25 | if !ok { |
| 26 | return 0 |
| 27 | } |
| 28 | ne.PutUint32(buf[0:4], uint32(StringReverseHdrSize)) // str_offset |
| 29 | ne.PutUint32(buf[4:8], strLen) // str_length |
| 30 | if len(s) > 0 { |
| 31 | copy(buf[8:8+len(s)], s) |
| 32 | } |
| 33 | buf[8+len(s)] = 0 // NUL terminator |
| 34 | return total |
| 35 | } |
| 36 | |
| 37 | // StringReverseDecode decodes a STRING_REVERSE payload from buf. |
| 38 | func StringReverseDecode(buf []byte) (StringReverseView, error) { |
| 39 | if len(buf) < StringReverseHdrSize { |
| 40 | return StringReverseView{}, ErrTruncated |
| 41 | } |
| 42 | strOffset, err := checkedWireU32Int(buf, 0) |
| 43 | if err != nil { |
| 44 | return StringReverseView{}, err |
| 45 | } |
| 46 | strLength, err := checkedWireU32Int(buf, 4) |
| 47 | if err != nil { |
| 48 | return StringReverseView{}, err |
| 49 | } |
| 50 | strLength32 := ne.Uint32(buf[4:8]) |
| 51 | strEnd, ok := checkedAddInt(strOffset, strLength) |
| 52 | if !ok { |
| 53 | return StringReverseView{}, ErrOutOfBounds |
| 54 | } |
| 55 | strNulEnd, ok := checkedAddInt(strEnd, 1) |
| 56 | if !ok || strNulEnd > len(buf) { |
| 57 | return StringReverseView{}, ErrOutOfBounds |
| 58 | } |
| 59 | if buf[strEnd] != 0 { |
| 60 | return StringReverseView{}, ErrMissingNul |
| 61 | } |
| 62 | return StringReverseView{ |
| 63 | Str: string(buf[strOffset:strEnd]), |
| 64 | StrLen: strLength32, |
| 65 | }, nil |
| 66 | } |
| 67 | |
| 68 | // DispatchStringReverse decodes request, calls handler, encodes response. |
| 69 | func DispatchStringReverse(req []byte, resp []byte, handler func(string) (string, bool)) (int, bool) { |
| 70 | view, err := StringReverseDecode(req) |
| 71 | if err != nil { |
| 72 | return 0, false |
| 73 | } |
| 74 | result, ok := handler(view.Str) |
| 75 | if !ok { |
| 76 | return 0, false |
| 77 | } |
| 78 | n := StringReverseEncode(result, resp) |
| 79 | return n, n > 0 |
| 80 | } |