Custom marshalling of a slice of structs [duplicate] - go

Question

Does anyone know of a simple way to pretty-print JSON output in Go?
I'd like to pretty-print the result of json.Marshal, as well as formatting an existing string of JSON so it's easier to read.

Answer 1

MarshalIndent will allow you to output your JSON with indentation and spacing. For example:
{
"data": 1234
}
The indent argument specifies the series of characters to indent with. Thus, json.MarshalIndent(data, "", " ") will pretty-print using four spaces for indentation.

Answer 2

The accepted answer is great if you have an object you want to turn into JSON. The question also mentions pretty-printing just any JSON string, and that's what I was trying to do. I just wanted to pretty-log some JSON from a POST request (specifically a CSP violation report).
To use MarshalIndent, you would have to Unmarshal that into an object. If you need that, go for it, but I didn't. If you just need to pretty-print a byte array, plain Indent is your friend.
Here's what I ended up with:
import (
"bytes"
"encoding/json"
"log"
"net/http"
)
func HandleCSPViolationRequest(w http.ResponseWriter, req *http.Request) {
body := App.MustReadBody(req, w)
if body == nil {
return
}
var prettyJSON bytes.Buffer
error := json.Indent(&prettyJSON, body, "", "\t")
if error != nil {
log.Println("JSON parse error: ", error)
App.BadRequest(w)
return
}
log.Println("CSP Violation:", string(prettyJSON.Bytes()))
}

Answer 3

For better memory usage, I guess this is better:
var out io.Writer
enc := json.NewEncoder(out)
enc.SetIndent("", " ")
if err := enc.Encode(data); err != nil {
panic(err)
}

Answer 4

I was frustrated by the lack of a fast, high quality way to marshal JSON to a colorized string in Go so I wrote my own Marshaller called ColorJSON.
With it, you can easily produce output like this using very little code:
package main
import (
"fmt"
"encoding/json"
"github.com/TylerBrock/colorjson"
)
func main() {
str := `{
"str": "foo",
"num": 100,
"bool": false,
"null": null,
"array": ["foo", "bar", "baz"],
"obj": { "a": 1, "b": 2 }
}`
var obj map[string]interface{}
json.Unmarshal([]byte(str), &obj)
// Make a custom formatter with indent set
f := colorjson.NewFormatter()
f.Indent = 4
// Marshall the Colorized JSON
s, _ := f.Marshal(obj)
fmt.Println(string(s))
}
I'm writing the documentation for it now but I was excited to share my solution.

Answer 5

Edit Looking back, this is non-idiomatic Go. Small helper functions like this add an extra step of complexity. In general, the Go philosophy prefers to include the 3 simple lines over 1 tricky line.
As #robyoder mentioned, json.Indent is the way to go. Thought I'd add this small prettyprint function:
package main
import (
"bytes"
"encoding/json"
"fmt"
)
//dont do this, see above edit
func prettyprint(b []byte) ([]byte, error) {
var out bytes.Buffer
err := json.Indent(&out, b, "", " ")
return out.Bytes(), err
}
func main() {
b := []byte(`{"hello": "123"}`)
b, _ = prettyprint(b)
fmt.Printf("%s", b)
}
https://go-sandbox.com/#/R4LWpkkHIN or http://play.golang.org/p/R4LWpkkHIN

Answer 6

Here's what I use. If it fails to pretty print the JSON it just returns the original string. Useful for printing HTTP responses that should contain JSON.
import (
"encoding/json"
"bytes"
)
func jsonPrettyPrint(in string) string {
var out bytes.Buffer
err := json.Indent(&out, []byte(in), "", "\t")
if err != nil {
return in
}
return out.String()
}

Answer 7

package cube
import (
"encoding/json"
"fmt"
"github.com/magiconair/properties/assert"
"k8s.io/api/rbac/v1beta1"
v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
"testing"
)
func TestRole(t *testing.T) {
clusterRoleBind := &v1beta1.ClusterRoleBinding{
ObjectMeta: v1.ObjectMeta{
Name: "serviceaccounts-cluster-admin",
},
RoleRef: v1beta1.RoleRef{
APIGroup: "rbac.authorization.k8s.io",
Kind: "ClusterRole",
Name: "cluster-admin",
},
Subjects: []v1beta1.Subject{{
Kind: "Group",
APIGroup: "rbac.authorization.k8s.io",
Name: "system:serviceaccounts",
},
},
}
b, err := json.MarshalIndent(clusterRoleBind, "", " ")
assert.Equal(t, nil, err)
fmt.Println(string(b))
}

Answer 8

Here is my solution:
import (
"bytes"
"encoding/json"
)
const (
empty = ""
tab = "\t"
)
func PrettyJson(data interface{}) (string, error) {
buffer := new(bytes.Buffer)
encoder := json.NewEncoder(buffer)
encoder.SetIndent(empty, tab)
err := encoder.Encode(data)
if err != nil {
return empty, err
}
return buffer.String(), nil
}

Answer 9

//You can do it with json.MarshalIndent(data, "", " ")
package main
import(
"fmt"
"encoding/json" //Import package
)
//Create struct
type Users struct {
ID int
NAME string
}
//Asign struct
var user []Users
func main() {
//Append data to variable user
user = append(user, Users{1, "Saturn Rings"})
//Use json package the blank spaces are for the indent
data, _ := json.MarshalIndent(user, "", " ")
//Print json formatted
fmt.Println(string(data))
}

Answer 10

Another example with http.ResponseWriter.
import (
"encoding/json"
"net/http"
)
func main() {
var w http.ResponseWriter
type About struct {
ProgName string
Version string
}
goObj := About{ProgName: "demo", Version: "0.0.0"}
beautifulJsonByte, err := json.MarshalIndent(goObj, "", " ")
if err != nil {
panic(err)
}
_, _ = w.Write(beautifulJsonByte)
}
output
{
"ProgName": "demo",
"Version": "0.0.0"
}

Answer 11

If you want to create a commandline utility to pretty print JSON
package main
import ("fmt"
"encoding/json"
"os"
"bufio"
"bytes"
)
func main(){
var out bytes.Buffer
reader := bufio.NewReader(os.Stdin)
text, _ := reader.ReadString('\n')
err := json.Indent(&out, []byte(text), "", " ")
if err != nil {
fmt.Println(err)
}
fmt.Println(string(out.Bytes()))
}
echo "{\"boo\":\"moo\"}" | go run main.go
will produce the following output :
{
"boo": "moo"
}
feel free to build a binary
go build main.go
and drop it in /usr/local/bin

Answer 12

A simple off the shelf pretty printer in Go. One can compile it to a binary through:
go build -o jsonformat jsonformat.go
It reads from standard input, writes to standard output and allow to set indentation:
package main
import (
"bytes"
"encoding/json"
"flag"
"fmt"
"io/ioutil"
"os"
)
func main() {
indent := flag.String("indent", " ", "indentation string/character for formatter")
flag.Parse()
src, err := ioutil.ReadAll(os.Stdin)
if err != nil {
fmt.Fprintf(os.Stderr, "problem reading: %s", err)
os.Exit(1)
}
dst := &bytes.Buffer{}
if err := json.Indent(dst, src, "", *indent); err != nil {
fmt.Fprintf(os.Stderr, "problem formatting: %s", err)
os.Exit(1)
}
if _, err = dst.WriteTo(os.Stdout); err != nil {
fmt.Fprintf(os.Stderr, "problem writing: %s", err)
os.Exit(1)
}
}
It allows to run a bash commands like:
cat myfile | jsonformat | grep "key"

Answer 13

i am sort of new to go, but this is what i gathered up so far:
package srf
import (
"bytes"
"encoding/json"
"os"
)
func WriteDataToFileAsJSON(data interface{}, filedir string) (int, error) {
//write data as buffer to json encoder
buffer := new(bytes.Buffer)
encoder := json.NewEncoder(buffer)
encoder.SetIndent("", "\t")
err := encoder.Encode(data)
if err != nil {
return 0, err
}
file, err := os.OpenFile(filedir, os.O_RDWR|os.O_CREATE, 0755)
if err != nil {
return 0, err
}
n, err := file.Write(buffer.Bytes())
if err != nil {
return 0, err
}
return n, nil
}
This is the execution of the function, and just standard
b, _ := json.MarshalIndent(SomeType, "", "\t")
Code:
package main
import (
"encoding/json"
"fmt"
"io/ioutil"
"log"
minerals "./minerals"
srf "./srf"
)
func main() {
//array of Test struct
var SomeType [10]minerals.Test
//Create 10 units of some random data to write
for a := 0; a < 10; a++ {
SomeType[a] = minerals.Test{
Name: "Rand",
Id: 123,
A: "desc",
Num: 999,
Link: "somelink",
People: []string{"John Doe", "Aby Daby"},
}
}
//writes aditional data to existing file, or creates a new file
n, err := srf.WriteDataToFileAsJSON(SomeType, "test2.json")
if err != nil {
log.Fatal(err)
}
fmt.Println("srf printed ", n, " bytes to ", "test2.json")
//overrides previous file
b, _ := json.MarshalIndent(SomeType, "", "\t")
ioutil.WriteFile("test.json", b, 0644)
}

Answer 14

Use json.MarshalIndent with string
This easyPrint function accepts argument data (any type of data) to print it into the intended (pretty) JSON format.
import (
"encoding/json"
"log"
)
func easyPrint(data interface{}) {
manifestJson, _ := json.MarshalIndent(data, "", " ")
log.Println(string(manifestJson))
}
With name argument.
TODO: make argument name optional.
func easyPrint(data interface{}, name string) {
manifestJson, _ := json.MarshalIndent(data, "", " ")
log.Println(name + " ->", string(manifestJson))
}