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replace.go
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replace.go
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package jsn
import (
"bytes"
"errors"
"hash/maphash"
)
// Replace function replaces key-value pairs provided in the `from` argument with those in the `to` argument
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")
}
if len(from) == 0 || len(to) == 0 {
_, err := w.Write(b)
return err
}
h := maphash.Hash{}
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)
instr := false
slash := 0
for i := 0; i < len(b); i++ {
if instr && b[i] == '\\' {
slash++
continue
}
// skip any left padding whitespace
if ws == -1 && (b[i] == '{' || b[i] == '[') {
ws = i
}
if b[i] == '"' && (slash%2 == 0) {
instr = !instr
}
if state == expectObjClose || state == expectListClose {
if !instr {
switch b[i] {
case '{', '[':
d++
case '}', ']':
d--
}
}
}
switch {
case state == expectKey && b[i] == '"':
state = expectKeyClose
s = i
case state == expectKeyClose && (b[i] == '"' && (slash%2 == 0)):
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] == '"' && (slash%2 == 0)):
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
s = i
case state == expectNull && (b[i-1] == 'l' && b[i] == 'l'):
e = i
}
if e != 0 {
e++
if e <= s {
return errors.New("invalid json")
}
if _, err := h.Write(b[s:e]); err != nil {
return err
}
if (we + 1) <= ws {
return errors.New("invalid json")
}
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
}
slash = 0
}
if ws == -1 || (ws == 0 && we == len(b)) {
w.Write(b)
} else if ws < we {
w.Write(b[ws:we])
}
return nil
}