How to handle index out of range in JSON ( Go) - json

Question

I'm developing a web service and part of that I read the Request.Body and try to unmarshal it.
if err := json.NewDecoder(body).Decode(r); err !=nil{
log.Error(err)
return err
}
The issue is that sometimes the client is sending an empty body and I get a panic runtime error: index out of range
goroutine 7 [running]:
How am I supposed to mitigate this?

Answer 1

I am decomposing your code:
NewDecoder: -
func NewDecoder(r io.Reader) *Decoder
NewDecoder returns a new decoder that reads from r. The decoder
introduces its own buffering and may read data from r beyond the JSON
values requested.
So NewDecoder only reads data from r. it's not care, is r empty...
Decode:-
func (dec *Decoder) Decode(v interface{}) error
Decode reads the next JSON-encoded value from its input and stores it
in the value pointed to by v.
See the documentation for Unmarshal for details about the conversion of JSON into a Go value.
To unmarshal JSON into an interface value, Unmarshal stores one of these in the interface value:
bool, for JSON booleans
float64, for JSON numbers
string, for JSON strings
[]interface{}, for JSON arrays
map[string]interface{}, for JSON objects
nil for JSON null
If a JSON value is not appropriate for a given target type, or if a
JSON number overflows the target type, Unmarshal skips that field and
completes the unmarshalling as best it can. If no more serious errors
are encountered, Unmarshal returns an UnmarshalTypeError describing
the earliest such error.
The JSON null value unmarshals into an interface, map, pointer, or
slice by setting that Go value to nil. Because null is often used in
JSON to mean “not present,” unmarshaling a JSON null into any other Go
type has no effect on the value and produces no error.
Reading above statement, it's clear that there is not chances, we get run time panic error. I was experimenting with a sample code to reproduce this ERROR. May error coming from inside the JSON package or your own code.

Answer 2

var dummy []byte
dummy = make([]byte, 10)
size, _ := body.Read(dummy)
if size > 0 {
if err := json.NewDecoder(body).Decode(r); err != nil {
log.Error(err)
return err
}
fmt.Fprintf(w, "%s", "Json cannot be empty")// where w is http.ResponseWriter