How to unmarshal/parse a request using Go correctly? - go

Question

How to parse a curl request response in Golang correctly? I have tried the following where I send a request to an api and its response is:
{
"Certificates": [
{
"Name": "some-name.here",
.......
}
],
"DataRange": "Certificates 1 - 1",
"TotalCount": 1
}
Now I want to use the Name in the Certificates in a string variable. i.e match. Before even I get to the looping through of the response, I get the error: json: cannot unmarshal object into Go value of type []program.Item. This error is coming from json.Unmarshal function where I pass my []bytes and the struct to use the bytes. Am I doing this correctly?
type Item struct {
Certificates []CertificatesInfo
}
type CertificatesInfo struct {
Name string
}
func main() {
url := .....
req, err := http.NewRequest("GET", url, nil)
resp, err := http.DefaultClient.Do(req)
if err != nil {
// handle err
continue
}
defer resp.Body.Close()
bodyBytes, err := io.ReadAll(resp.Body)
if err != nil {
continue
}
var ItemInfo []Item
if err := json.Unmarshal(bodyBytes, &ItemInfo); err != nil {
return nil, fmt.Errorf("failed to parse %v", err)
}
for _, infos := range ItemInfo {
for _, names := range infos.Certificates {
infraId:= names.Name
match:= display_name
}
}
}

Answer 1

There's a mismatch between your sample JSON response data (a single object containing a list of certificates), and your code, which is expecting a list of objects, each of which contain a list of certificates).
Assuming that your JSON example is correct, this bit:
var ItemInfo []Item
if err := json.Unmarshal(bodyBytes, &ItemInfo); err != nil {
. . .
should probably be
var itemInfo Item
if err := json.Unmarshal(bodyBytes, &ItemInfo); err != nil {
. . .
Works on my machine:
https://go.dev/play/p/8FqIif1zzsQ
package main
import (
"encoding/json"
"fmt"
)
func main() {
resp := Item{}
err := json.Unmarshal([]byte(data), &resp)
if err != nil {
fmt.Print(err)
panic(err)
}
fmt.Printf("resp.DataRange: %s\n", resp.DataRange)
fmt.Printf("resp.TotalCount: %d\n", resp.TotalCount)
fmt.Printf("len(resp.Certificates: %d\n", len(resp.Certificates))
for i, c := range resp.Certificates {
fmt.Printf("resp.Certificates[%d].Name: %s\n", i, c.Name)
}
}
type Item struct {
Certificates []CertificatesInfo
DataRange string
TotalCount int
}
type CertificatesInfo struct {
Name string
}
const data = `
{
"Certificates": [
{ "Name": "alpha" },
{ "Name": "bravo" },
{ "Name": "charlie" }
],
"DataRange": "Certificates 1 - 1",
"TotalCount": 3
}
`