Write the body of a request in datastore

How can I write the body of a request in datastore?

In my func init() I declare my router using gorilla mux, so that if I do a post request to /add I will need to add some data to datastore, but I am just starting with datastore so I don't really know how to.

I have declared a struct item

type Item Struct {
  ID int64
  Type string `json:type`
}

The router will redirect to the function CItem

func CItem(w http.ResponseWriter, r *http.Request) { 
  var item Item
  data := json.NewDecoder(r.Body).Decode(&item)
  defer r.Body.Close()
  fmt.Fprintln(w, data)
}

But when I do a post request using paw for example I get:
invalid character 'y' in literal true (expecting 'r')

Or using curl:
curl -X POST -d "{\"type\": \"that\"}" http://localhost:8080/add

How can I fix this, and what do I need to do next to store my data in datastore a small example will be nice.

Here are some comments on your code so far and a quick example showing how to store the entity:

type Item Struct {
  ID int64
  Type string `json:"type"` // <-- quotes needed
}
func CItem(w http.ResponseWriter, r *http.Request) { 
   var item Item
   err := json.NewDecoder(r.Body).Decode(&item) // <-- decode returns an error, not data
   if err != nil {
        http.Error(w, err.Error(), 400)
        return
   }
   // defer r.Body.Close()  <-- no need to close request body
   fmt.Fprintln(w, item) // <-- print the decoded item
   c := appengine.NewContext(r)
   key, err := datastore.Put(c, datastore.NewIncompleteKey(c, "citem", nil), &item)
   if err != nil {
       http.Error(w, err.Error(), http.StatusInternalServerError)
       return
   }
   fmt.Fprintln(w, "key is", key)
}

So you'll have a class describing the request and another describing the NDB/DB entity. You'll have to manually map the data points from the request to the datastore object and then save it