dumb-arbitrarty-json-getter.go

package main

import (
  "encoding/json"
  "errors"
  "fmt"
  "reflect"
  "strconv"
)

func get(o interface{}, path []string) (interface{}, error) {
  if len(path) <= 0 {
    return o, nil
  }

  t := reflect.TypeOf(o)
  p, rest := path[0], path[1:]

  switch t.Kind() {
  case reflect.Map:
    r, ok := o.(map[string]interface{})[p]
    if !ok || r == nil {
      return nil, errors.New("key " + p + " does not exist")
    }
    return get(r, rest)

  case reflect.Slice:
    r := o.([]interface{})
    l, err := strconv.Atoi(p)
    if err != nil {
      return nil, err
    }
    if l >= len(r) {
      return nil, errors.New("index " + p + " is out of bounds")
    }
    return get(r[l], rest)
  }

  return nil, errors.New("unknown error")
}

func main() {
  var o map[string]interface{}

  err := json.Unmarshal([]byte(`{
    "foo": "bar",
    "baz": [1, "haha", {
      "lol": 3
    }]
  }`), &o)

  if err != nil {
    panic(err)
  }

  result, err := get(o, []string{"baz", "3", "lol"})
  if err != nil {
    panic(err)
  }

  fmt.Println(result)
}