Vfrdtyky

The ideal way is not to use ioutil.ReadAll, but rather use a decoder on the reader directly. Here's a nice function that gets a url and decodes its response onto a target structure.

var myClient = &http.Client{Timeout: 10 * time.Second}



func getJson(url string, target interface{}) error {

    r, err := myClient.Get(url)

    if err != nil {

        return err

    }

    defer r.Body.Close()



    return json.NewDecoder(r.Body).Decode(target)

}

Example use:

type Foo struct {

    Bar string

}



func main() {

    foo1 := new(Foo) // or &Foo{}

    getJson("http://example.com", foo1)

    println(foo1.Bar)



    // alternately:



    foo2 := Foo{}

    getJson("http://example.com", &foo2)

    println(foo2.Bar)

}

You should not be using the default *http.Client structure in production as this answer originally demonstrated! (Which is what http.Get/etc call to). The reason is that the default client has no timeout set; if the remote server is unresponsive, you're going to have a bad day.

Your Problem were the slice declarations in your data structs (except for Track, they shouldn't be slices...). This was compounded by some rather goofy fieldnames in the fetched json file, which can be fixed via structtags, see godoc.

The code below parsed the json successfully. If you've further questions, let me know.

package main



import "fmt"

import "net/http"

import "io/ioutil"

import "encoding/json"



type Tracks struct {

    Toptracks Toptracks_info

}



type Toptracks_info struct {

    Track Track_info

    Attr  Attr_info `json: "@attr"`

}



type Track_info struct {

    Name       string

    Duration   string

    Listeners  string

    Mbid       string

    Url        string

    Streamable Streamable_info

    Artist     Artist_info   

    Attr       Track_attr_info `json: "@attr"`

}



type Attr_info struct {

    Country    string

    Page       string

    PerPage    string

    TotalPages string

    Total      string

}



type Streamable_info struct {

    Text      string `json: "#text"`

    Fulltrack string

}



type Artist_info struct {

    Name string

    Mbid string

    Url  string

}



type Track_attr_info struct {

    Rank string

}



func perror(err error) {

    if err != nil {

        panic(err)

    }

}



func get_content() {

    url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=Netherlands"



    res, err := http.Get(url)

    perror(err)

    defer res.Body.Close()



    decoder := json.NewDecoder(res.Body)

    var data Tracks

    err = decoder.Decode(&data)

    if err != nil {

        fmt.Printf("%Tn%sn%#vn",err, err, err)

        switch v := err.(type){

            case *json.SyntaxError:

                fmt.Println(string(body[v.Offset-40:v.Offset]))

        }

    }

    for i, track := range data.Toptracks.Track{

        fmt.Printf("%d: %s %sn", i, track.Artist.Name, track.Name)

    }

}



func main() {

    get_content()

}

You need upper case property names in your structs in order to be used by the json packages.

Upper case property names are exported properties. Lower case property names are not exported.

You also need to pass the your data object by reference (&data).

package main



import "os"

import "fmt"

import "net/http"

import "io/ioutil"

import "encoding/json"



type tracks struct {

    Toptracks toptracks_info

}



type toptracks_info struct {

    Track track_info

    Attr  attr_info

}



type track_info struct {

    Name       string

    Duration   string

    Listeners  string

    Mbid       string

    Url        string

    Streamable streamable_info

    Artist     artist_info

    Attr       track_attr_info

}



type attr_info struct {

    Country    string

    Page       string

    PerPage    string

    TotalPages string

    Total      string

}



type streamable_info struct {

    Text      string

    Fulltrack string

}



type artist_info struct {

    Name string

    Mbid string

    Url  string

}



type track_attr_info struct {

    Rank string

}



func get_content() {

    // json data

    url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=Netherlands"



    res, err := http.Get(url)



    if err != nil {

        panic(err.Error())

    }



    body, err := ioutil.ReadAll(res.Body)



    if err != nil {

        panic(err.Error())

    }



    var data tracks

    json.Unmarshal(body, &data)

    fmt.Printf("Results: %vn", data)

    os.Exit(0)

}



func main() {

    get_content()

}

The results from json.Unmarshal (into var data interface{}) do not directly match your Go type and variable declarations. For example,

package main



import (

    "encoding/json"

    "fmt"

    "io/ioutil"

    "net/http"

    "os"

)



type Tracks struct {

    Toptracks Toptracks_info

}



type Toptracks_info struct {

    Track Track_info

    Attr  Attr_info

}



type Track_info struct {

    Name       string

    Duration   string

    Listeners  string

    Mbid       string

    Url        string

    Streamable Streamable_info

    Artist     Artist_info

    Attr       Track_attr_info

}



type Attr_info struct {

    Country    string

    Page       string

    PerPage    string

    TotalPages string

    Total      string

}



type Streamable_info struct {

    Text      string

    Fulltrack string

}



type Artist_info struct {

    Name string

    Mbid string

    Url  string

}



type Track_attr_info struct {

    Rank string

}



func get_content() {

    // json data

    url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=Netherlands"

    url += "&limit=1" // limit data for testing

    res, err := http.Get(url)

    if err != nil {

        panic(err.Error())

    }

    body, err := ioutil.ReadAll(res.Body)

    if err != nil {

        panic(err.Error())

    }

    var data interface{} // TopTracks

    err = json.Unmarshal(body, &data)

    if err != nil {

        panic(err.Error())

    }

    fmt.Printf("Results: %vn", data)

    os.Exit(0)

}



func main() {

    get_content()

}

Output:

Results: map[toptracks:map[track:map[name:Get Lucky (feat. Pharrell Williams) listeners:1863 url:http://www.last.fm/music/Daft+Punk/_/Get+Lucky+(feat.+Pharrell+Williams) artist:map[name:Daft Punk mbid:056e4f3e-d505-4dad-8ec1-d04f521cbb56 url:http://www.last.fm/music/Daft+Punk] image:[map[#text:http://userserve-ak.last.fm/serve/34s/88137413.png size:small] map[#text:http://userserve-ak.last.fm/serve/64s/88137413.png size:medium] map[#text:http://userserve-ak.last.fm/serve/126/88137413.png size:large] map[#text:http://userserve-ak.last.fm/serve/300x300/88137413.png size:extralarge]] @attr:map[rank:1] duration:369 mbid: streamable:map[#text:1 fulltrack:0]] @attr:map[country:Netherlands page:1 perPage:1 totalPages:500 total:500]]]