Golang unmarshall JSON from api.nal.usda.gov/ndb

Hello I try to unmarshal the JSON response from api.nal.usda.gov/ndb into struct, but it always returns empty:

{        []}

Example JSON:

{
    "list": {
        "q": "butter",
        "sr": "28",
        "ds": "any",
        "start": 0,
        "end": 50,
        "total": 4003,
        "group": "",
        "sort": "r",
        "item": [
            {
                "offset": 0,
                "group": "Branded Food Products Database",
                "name": "BLUE BUNNY, PEANUT BUTTER PANIC, ICE CREAM, POWERFUL PEANUT BUTTER ICE CREAM CHARGED WITH PEANUT BUTTER AND FUDGE SAUCES AND OVERLOADED WITH PEANUT BUTTER CUPS, UPC: 070640034086",
                "ndbno": "45011419",
                "ds": "BL"
            },
            {
                "offset": 1,
                "group": "Branded Food Products Database",
                "name": "BLUE BUNNY, ICE CREAM, PEANUT BUTTER PARTY, PEANUT BUTTER ICE CREAM, PEANUT BUTTER AND FUDGE SWIRLS, PEANUT BUTTER CUPS, UPC: 070640012411",
                "ndbno": "45110466",
                "ds": "BL"
            }
        ]
    }
}

I checked the JSON response with https://jsonformatter.curiousconcept.com/, and it´s fine. I hope you can tell me why, since I am quite new to Golang.

My Structs:

type List struct {
	Q     string `json:"q,omitempty"`
	Sr    string `json:"sr,omitempty"`
	Ds    string `json:"ds,omitempty"`
	Start string `json:"start,omitempty"`
	End   string `json:"end,omitempty"`
	Total string `json:"total,omitempty"`
	Group string `json:"group,omitempty"`
	Sort  string `json:"sort,omitempty"`
	Item  []Item `json:"item,omitempty"`
}

type Item struct {
	Offset string `json:"offset,omitempty"`
	Group  string `json:"group,omitempty"` //food group to which the food belongs
	Name   string `json:"name,omitempty"`  //the food’s name
	Ndbno  string `json:"nbno,omitempty"`  //the food’s NDB Number
	Ds     string `json:"ds,omitempty"`    //Data source: BL=Branded Food Products or SR=Standard Release
}

Code:

func (sr *SearchRequest) fetch() {

    url := "https://api.nal.usda.gov/ndb/search/?" +
        "format=" + sr.format +
        "&q=" + sr.q +
        "&sort=" + sr.sort +
        "&max=" + strconv.FormatInt(sr.max, 10) +
        "&offset=" + strconv.FormatInt(sr.offset, 10) +
        "&api_key=" + sr.c.ApiKey

    r, err := http.Get(url)
    if err != nil {
        panic(err.Error())
    }
    defer r.Body.Close()

    b, err := ioutil.ReadAll(r.Body)
    if err != nil {
        panic(err.Error())
    }

    l := new(List)
    err = json.Unmarshal(b, &l)
    if err != nil {
        fmt.Println(err)
    }

    fmt.Println(l)

}

The Go types do not match the structure of the JSON. There's one more level of objects in the JSON. Try this:

var v struct {
	List List
}
err := json.Unmarshal([]byte(data), &v)

Some of the string fields correspond to numbers in the JSON. Declare these fields with a numerical type (int, float64, ...).

playground example

IMHO your struct doesn't match to JSON you provided. Try:

package main
import (
"encoding/json"
"fmt"
)
type MyItem struct {
Q     string `json:"q,omitempty"`
Sr    string `json:"sr,omitempty"`
Ds    string `json:"ds,omitempty"`
Start int `json:"start,omitempty"`
End   int `json:"end,omitempty"`
Total int `json:"total,omitempty"`
Group string `json:"group,omitempty"`
Sort  string `json:"sort,omitempty"`
Item  []Item `json:"item,omitempty"`
}
type MyList struct {
List MyItem `json:"list"`
}
type Item struct {
Offset int `json:"offset,omitempty"`
Group  string `json:"group,omitempty"` //food group to which the food belongs
Name   string `json:"name,omitempty"`  //the food’s name
Ndbno  string `json:"nbno,omitempty"`  //the food’s NDB Number
Ds     string `json:"ds,omitempty"`    //Data source: BL=Branded Food Products or SR=Standard Release
}
var jsonStr = `{
"list": {
"q": "butter",
"sr": "28",
"ds": "any",
"start": 0,
"end": 50,
"total": 4003,
"group": "",
"sort": "r",
"item": [
{
"offset": 0,
"group": "Branded Food Products Database",
"name": "BLUE BUNNY, PEANUT BUTTER PANIC, ICE CREAM, POWERFUL PEANUT BUTTER ICE CREAM CHARGED WITH PEANUT BUTTER AND FUDGE SAUCES AND OVERLOADED WITH PEANUT BUTTER CUPS, UPC: 070640034086",
"ndbno": "45011419",
"ds": "BL"
},
{
"offset": 1,
"group": "Branded Food Products Database",
"name": "BLUE BUNNY, ICE CREAM, PEANUT BUTTER PARTY, PEANUT BUTTER ICE CREAM, PEANUT BUTTER AND FUDGE SWIRLS, PEANUT BUTTER CUPS, UPC: 070640012411",
"ndbno": "45110466",
"ds": "BL"
}]
}
}`
func main() {
b := jsonStr
l := new(MyList)
err := json.Unmarshal([]byte(b), &l)
if err != nil {
fmt.Println(err)
}
fmt.Println(l)
}

EDIT: It is hard to read result of println or printf with %+v so here is the result with spew.Dump(l) (go get -u github.com/davecgh/go-spew/spew):

List: (main.MyItem) {
Q: (string) (len=6) "butter",
Sr: (string) (len=2) "28",
Ds: (string) (len=3) "any",
Start: (int) 0,
End: (int) 50,
Total: (int) 4003,
Group: (string) "",
Sort: (string) (len=1) "r",
Item: ([]main.Item) (len=2 cap=4) {
(main.Item) {
Offset: (int) 0,
Group: (string) (len=30) "Branded Food Products Database",
Name: (string) (len=178) "BLUE BUNNY, PEANUT BUTTER PANIC, ICE CREAM, POWERFUL PEANUT BUTTER ICE CREAM CHARGED WITH PEANUT BUTTER AND FUDGE SAUCES AND OVERLOADED WITH PEANUT BUTTER CUPS, UPC: 070640034086",
Ndbno: (string) "",
Ds: (string) (len=2) "BL"
},
(main.Item) {
Offset: (int) 1,
Group: (string) (len=30) "Branded Food Products Database",
Name: (string) (len=138) "BLUE BUNNY, ICE CREAM, PEANUT BUTTER PARTY, PEANUT BUTTER ICE CREAM, PEANUT BUTTER AND FUDGE SWIRLS, PEANUT BUTTER CUPS, UPC: 070640012411",
Ndbno: (string) "",
Ds: (string) (len=2) "BL"
}
}
}
})