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jsonpath.go
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jsonpath.go
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/*
* Copyright 2020 The NATS Authors
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cmd
import (
"encoding/json"
"fmt"
"strconv"
"strings"
)
// Extracts a value from a JSON path - keys can be "name" or "person.name" or "persons[0].name"
func GetField(data []byte, jp string) ([]byte, error) {
m := make(map[string]interface{})
if err := json.Unmarshal(data, &m); err != nil {
return nil, fmt.Errorf("error parsing json: %v", err)
}
var tokens []string
for _, v := range strings.Split(jp, ".") {
ob := strings.Index(v, "[")
if ob != -1 {
cb := strings.Index(v, "]")
if cb == -1 {
return nil, fmt.Errorf("bad path - unterminated index expression: %q in %q", v, jp)
}
n := v[:ob]
i := v[ob+1 : cb]
tokens = append(tokens, n, i)
} else {
tokens = append(tokens, v)
}
}
var d interface{}
d = m
for _, t := range tokens {
switch v := d.(type) {
case map[string]interface{}:
d = v[t]
case []interface{}:
idx, err := strconv.Atoi(t)
if err != nil {
return nil, fmt.Errorf("error parsing index: %q in %q", t, jp)
}
if idx > len(v) {
return nil, fmt.Errorf("index is out of bounds: %d in %q", idx, jp)
}
d = v[idx]
default:
return nil, fmt.Errorf("unable to extract %q in %q from %v", t, jp, v)
}
}
return json.Marshal(d)
}