Golang json.Unmarshal is not working as expected - json

Question

Im trying to unmarshal json response from vcenter rest api. when the response body is simply printed it looks like the o/p below
{"value":[{"memory_size_MiB":16384,"vm":"vm-10236","name":"Normal_Windows_192.168.1.10","power_state":"POWERED_OFF","cpu_count":8},{"memory_size_MiB":8192,"vm":"vm-10238","name":"Normal_Windows_192.168.1.11","power_state":"POWERED_OFF","cpu_count":4}]}
i have exported both struct and struct fields however the fields like memory_size_MiB, power_state,cpu_count is not being unmarshalled. when the struct is printed it looks like below:-
{Value:[{Mem:0 Vm:vm-10236 Name:Normal_Windows_192.168.1.10 Powerstat: Cpu:0} {Mem:0 Vm:vm-10238 Name:Normal_Windows_192.168.1.11 Powerstat: Cpu:0} {Mem:0 Vm:vm-10582 Name:Normal_Windows_192.168.1.12 Powerstat: Cpu:0}]}%
Below is my main.go
package main
import (
...
)
type SessionData struct {
VmwareApiSessionId string `json:"value"`
}
//{"memory_size_MiB":16384,"vm":"vm-10236","name":"Normal_Windows_192.168.19.100","power_state":"POWERED_OFF","cpu_count":8}
type Vm struct {
Mem int `json: "memory_size_MiB"`
Vm string `json: "vm"`
Name string `json: "name"`
Powerstat string `json: "power_state"`
Cpu int `json: "cpu_count"`
}
//{Value:[{Mem:0 Vm:vm-10236 Name:Normal_Windows_192.168.1.10 Powerstat: Cpu:0} {Mem:0 Vm:vm-10238 Name:Normal_Windows_192.168.1.11 Powerstat: Cpu:0} {Mem:0 Vm:vm-10582 Name:Normal_Windows_192.168.1.12 Powerstat: Cpu:0}]}
type ColVmList struct {
Value []Vm `json: "value"`
}
func getVmList(sessid string,cli *http.Client) ColVmList {
vms := ColVmList{}
req,err:=http.NewRequest("GET","https://sandbox.vmware.local/rest/vcenter/vm",nil)
req.Header.Add("vmware-api-session-id",sessid)
resp,err := cli.Do(req)
if err != nil {
log.Fatal("Error %s", err)
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
fmt.Println(string(body))
err = json.Unmarshal([]byte(body),&vms)
if err != nil {
log.Fatal("error %s", err)
}
return vms
}
func main(){
//authpart
loginurl = "https://sandbox.vmware.local/rest/com/vmware/cis/session"
//login...
err = json.Unmarshal([]byte(string(body)),&sessVal)
if err != nil{
log.Fatal(err)
}
var allvmlist ColVmList
allvmlist = getVmList(sessVal.VmwareApiSessionId,&cli)
fmt.Printf("%v",allvmlist)
}

Answer 1

Your struct tags are not well formed. Remove the space between json: and the string "..." in the struct tags. i.e. it MUST be json:"..." not json: "...".
And the reason some fields are correctly unmarshaled even with not well-formed struct tags is because the fields' names match the json property names.
func main() {
data := []byte(`{"memory_size_MiB":16384}`)
var obj1 struct {
Mem int `json: "memory_size_MiB"`
}
if err := json.Unmarshal(data, &obj1); err != nil {
panic(err)
}
fmt.Println(obj1)
var obj2 struct {
Mem int `json:"memory_size_MiB"`
}
if err := json.Unmarshal(data, &obj2); err != nil {
panic(err)
}
fmt.Println(obj2)
}
https://go.dev/play/p/gUR5ed2n0D1