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?
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.
You'll just want to make sure the Request.Body isn't empty before trying to unmarshal it.
if body != "" || body != nil || len(body) > 0 {
if err := json.NewDecoder(body).Decode(r); err != nil {
log.Error(err)
return err
}
}
Or, if you want to prepare for anything, use the IsJSON function from this answer (golang playground) to check if the body is valid JSON before trying to decode it as JSON.
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