Go json manipulation

Hey there just started to transform my python code to Go, but have some issue on the json manipulations... here is my code so far

package test

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"strings"
	"time"
)

type Collection struct {
	Contract string
}

type Data struct {
	Activity Activity `json:"activity"`
}

type Activity struct {
	Activities Activities `json:"activities"`
	HasMore    bool       `json:"hasMore"`
}

type Activities []Sale

type Sale struct {
	From             string           `json:"from"`
	From_login       string           `json:"from_login"`
	To               string           `json:"to"`
	To_login         string           `json:"to_login"`
	Transaction_hash string           `json:"transaction_hash"`
	Timestamp        int              `json:"timestamp"`
	Types            string           `json:"type"`
	Price            float32          `json:"price"`
	Quantity         string           `json:"quantity"`
	Nft              Nft              `json:"nft"`
	Attributes       string           `json:"attributes"`
	Collection       CollectionStruct `json:"collection"`
}

type Nft struct {
	Name       string        `json:"name"`
	Thumbnail  string        `json:"thumbnail"`
	Asset_id   string        `json:"asset_id"`
	Collection NftCollection `json:"collection"`
}

type NftCollection struct {
	Avatar    string `json:"avatar"`
	Name      string `json:"name"`
	Certified bool   `json:"certified"`
}

type CollectionStruct struct {
	Avatar    string `json:"avatar"`
	Address   string `json:"address"`
	Name      string `json:"name"`
	Certified bool   `json:"certified"`
}

func (c Collection) GetSales(filter, types string) []Sale { // déclaration de ma méthode GetSales() liée à ma structure Collection
	client := &http.Client{Timeout: time.Duration(1) * time.Second}

	const url = "https://backend.api.io/query"

	// create a new request using http
	req, err := http.NewRequest("POST", url)
	if err != nil {
		panic(err)
	}

	// set header for the request
	req.Header.Set("Content-Type", "application/json")

	// send request
	res, err := client.Do(req)
	if err != nil {
		panic(err)
	}

	defer res.Body.Close()
	content, err_ := ioutil.ReadAll(res.Body)
	if err_ != nil {
		panic(err_)
	}

	var resultJson Data
	json.Unmarshal(content, &resultJson)
	fmt.Printf("%+v\n", resultJson)
	return resultJson.Activity.Activities.Sale

}

i don't understand why my Sale structure is empty :/ I created all of these structures in order to use Unmarshal so i can loop. I check the way the returned json is structured and copied it i'm sure i missed something but don't know what

EDIT: I think that i have something, actually the array is Activities and not Sale :

type Collection struct {
	Contract string
}

type Data struct {
	Activity Activity `json:"activity"`
}

type Activity struct {
	Activities Activities `json:"activities"`
	HasMore    bool       `json:"hasMore"`
}

type Activities []struct {
	Sale Sale //`json:"sale"`
}

type Sale struct {
	From             string           `json:"from"`
	From_login       string           `json:"from_login"`
	To               string           `json:"to"`
	To_login         string           `json:"to_login"`
	Transaction_hash string           `json:"transaction_hash"`
	Timestamp        int              `json:"timestamp"`
	Types            string           `json:"type"`
	Price            float32          `json:"price"`
	Quantity         string           `json:"quantity"`
	Nft              Nft              `json:"nft"`
	Attributes       string           `json:"attributes"`
	Collection       CollectionStruct `json:"collection"`
}

type Nft struct {
	Name       string        `json:"name"`
	Thumbnail  string        `json:"thumbnail"`
	Asset_id   string        `json:"asset_id"`
	Collection NftCollection `json:"collection"`
}

type NftCollection struct {
	Avatar    string `json:"avatar"`
	Name      string `json:"name"`
	Certified bool   `json:"certified"`
}

type CollectionStruct struct {
	Avatar    string `json:"avatar"`
	Address   string `json:"address"`
	Name      string `json:"name"`
	Certified bool   `json:"certified"`
}

But this time it returns me this : {Activity:{Activities:[] HasMore:false}} where Activities value should be an array of Nft struct

Your code as written won't compile (due to a couple of undefined variables), so it's hard to separate functional problems from syntactic problems.

However, one thing stands out: You're creating an HTTP request with req, err := http.NewRequest(...), but you're never executing the request with a client. See e.g. the documentation, which includes this example:

client := &http.Client{
CheckRedirect: redirectPolicyFunc,
}
resp, err := client.Get("http://example.com")
// ...
req, err := http.NewRequest("GET", "http://example.com", nil)
// ...
req.Header.Add("If-None-Match", `W/"wyzzy"`)
resp, err := client.Do(req)
// ...

If you use NewRequest to create a request, you must use client.Do(req) to execute it.

Adding to @larsks 's answer, there are more errors that I can see

1. ioutil.ReadAll already returns a byte array which you can directly use for un-marshalling. json.Unmarshal(content, &resultJson)

2. Many errors are ignored so execution won't stop if any error is encountered.

I suggest changing the function as follows:

func (c Collection) GetSales(filter, types string) []Sale {
const url = "https://api.com/"
req, err := http.NewRequest("POST", url, requestBody)
if err != nil {
panic(err)
}
res, err := http.DefaultClient.Do(req)
if err != nil {
panic(err)
}
defer res.Body.Close()
content, err := ioutil.ReadAll(res.Body)
if err != nil {
panic(err)
}
var resultJson Data
err = json.Unmarshal(content, &resultJson)
if err != nil {
panic(err)
}
fmt.Printf("%+v\n", resultJson)
return resultJson.Activity.Activities.Sales
}