168 lines
2.8 KiB
Go
168 lines
2.8 KiB
Go
package jsn
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import (
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"bytes"
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"github.com/cespare/xxhash/v2"
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)
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func Filter(w *bytes.Buffer, b []byte, keys []string) error {
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var err error
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kmap := make(map[uint64]struct{}, len(keys))
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for i := range keys {
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kmap[xxhash.Sum64String(keys[i])] = struct{}{}
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}
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// is an list
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isList := false
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// list item
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item := 0
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// field in an object
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field := 0
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s, e, d := 0, 0, 0
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var k []byte
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state := expectKey
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for i := 0; i < len(b); i++ {
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if state == expectObjClose || state == expectListClose {
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switch b[i] {
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case '{', '[':
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d++
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case '}', ']':
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d--
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}
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}
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if state == expectKey {
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switch b[i] {
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case '[':
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if !isList {
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err = w.WriteByte('[')
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}
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isList = true
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case '{':
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if item == 0 {
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err = w.WriteByte('{')
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} else {
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_, err = w.Write([]byte("},{"))
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}
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field = 0
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item++
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}
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if err != nil {
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return err
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}
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}
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switch {
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case state == expectKey && b[i] == '"':
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state = expectKeyClose
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s = i
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case state == expectKeyClose && b[i] == '"':
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state = expectColon
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k = b[(s + 1):i]
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case state == expectColon && b[i] == ':':
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state = expectValue
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case state == expectValue && b[i] == '"':
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state = expectString
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case state == expectString && b[i] == '"':
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e = i
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case state == expectValue && b[i] == '[':
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state = expectListClose
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d++
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case state == expectListClose && d == 0 && b[i] == ']':
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e = i
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case state == expectValue && b[i] == '{':
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state = expectObjClose
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d++
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case state == expectObjClose && d == 0 && b[i] == '}':
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e = i
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case state == expectValue && (b[i] >= '0' && b[i] <= '9'):
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state = expectNumClose
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case state == expectNumClose &&
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((b[i] < '0' || b[i] > '9') &&
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(b[i] != '.' && b[i] != 'e' && b[i] != 'E' && b[i] != '+' && b[i] != '-')):
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e = i - 1
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case state == expectValue &&
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(b[i] == 'f' || b[i] == 'F' || b[i] == 't' || b[i] == 'T'):
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state = expectBoolClose
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case state == expectBoolClose && (b[i] == 'e' || b[i] == 'E'):
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e = i
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case state == expectValue && b[i] == 'n':
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state = expectNull
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case state == expectNull && b[i] == 'l':
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e = i
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}
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if e != 0 {
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state = expectKey
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cb := b[s:(e + 1)]
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e = 0
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if _, ok := kmap[xxhash.Sum64(k)]; !ok {
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continue
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}
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if field != 0 {
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if err := w.WriteByte(','); err != nil {
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return err
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}
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}
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sk := 0
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for i := 0; i < len(cb); i++ {
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if cb[i] == '\n' || cb[i] == '\t' {
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if _, err := w.Write(cb[sk:i]); err != nil {
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return err
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}
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sk = i + 1
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}
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}
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if sk > 0 && sk < len(cb) {
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_, err = w.Write(cb[sk:len(cb)])
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} else {
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_, err = w.Write(cb)
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}
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if err != nil {
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return err
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}
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field++
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}
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}
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if item != 0 {
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if err := w.WriteByte('}'); err != nil {
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return err
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}
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}
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if isList {
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if err := w.WriteByte(']'); err != nil {
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return err
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}
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}
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return nil
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}
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