package jsn import ( "bytes" "errors" "github.com/cespare/xxhash/v2" ) func Replace(w *bytes.Buffer, b []byte, from, to []Field) error { if len(from) != len(to) { return errors.New("'from' and 'to' must be of the same length") } h := xxhash.New() tmap := make(map[uint64]int, len(from)) for i, f := range from { if _, err := h.Write(f.Key); err != nil { return err } if _, err := h.Write(f.Value); err != nil { return err } tmap[h.Sum64()] = i h.Reset() } s, e, d := 0, 0, 0 state := expectKey ws, we := -1, len(b) for i := 0; i < len(b); i++ { // skip any left padding whitespace if ws == -1 && (b[i] == '{' || b[i] == '[') { ws = i } if state == expectObjClose || state == expectListClose { switch b[i] { case '{', '[': d++ case '}', ']': d-- } } switch { case state == expectKey && b[i] == '"': state = expectKeyClose s = i case state == expectKeyClose && b[i] == '"': state = expectColon if _, err := h.Write(b[(s + 1):i]); err != nil { return err } we = s case state == expectColon && b[i] == ':': state = expectValue case state == expectValue && b[i] == '"': state = expectString s = i case state == expectString && b[i] == '"': e = i case state == expectValue && b[i] == '[': state = expectListClose s = i d++ case state == expectListClose && d == 0 && b[i] == ']': e = i case state == expectValue && b[i] == '{': state = expectObjClose s = i d++ case state == expectObjClose && d == 0 && b[i] == '}': e = i case state == expectValue && (b[i] >= '0' && b[i] <= '9'): state = expectNumClose s = i case state == expectNumClose && ((b[i] < '0' || b[i] > '9') && (b[i] != '.' && b[i] != 'e' && b[i] != 'E' && b[i] != '+' && b[i] != '-')): e = i - 1 case state == expectValue && (b[i] == 'f' || b[i] == 'F' || b[i] == 't' || b[i] == 'T'): state = expectBoolClose s = i case state == expectBoolClose && (b[i] == 'e' || b[i] == 'E'): e = i case state == expectValue && b[i] == 'n': state = expectNull case state == expectNull && b[i] == 'l': e = i } if e != 0 { e++ if _, err := h.Write(b[s:e]); err != nil { return err } n, ok := tmap[h.Sum64()] h.Reset() if ok { if _, err := w.Write(b[ws:(we + 1)]); err != nil { return err } if len(to[n].Key) != 0 { var err error if _, err := w.Write(to[n].Key); err != nil { return err } if _, err := w.WriteString(`":`); err != nil { return err } if len(to[n].Value) != 0 { _, err = w.Write(to[n].Value) } else { _, err = w.WriteString("null") } if err != nil { return err } ws = e } else if b[e] == ',' { ws = e + 1 } else { ws = e } } if !ok && (b[s] == '[' || b[s] == '{') { // the i++ in the for loop will add 1 so we account for that (s - 1) i = s - 1 } state = expectKey we = len(b) e = 0 d = 0 } } if ws == -1 || (ws == 0 && we == len(b)) { w.Write(b) } else if ws < we { w.Write(b[ws:we]) } return nil }