在render.Bind中清空空的http.Request.Body

Question

I am using github.com/pressly/chi to build this simple program where I try to decode some JSON from the http.Request.Body:

package main

import (
    "encoding/json"
    "fmt"
    "net/http"

    "github.com/pressly/chi"
    "github.com/pressly/chi/render"
)

type Test struct {
    Name string `json:"name"`
}

func (p *Test) Bind(r *http.Request) error {
    err := json.NewDecoder(r.Body).Decode(p)
    if err != nil {
        return err
    }
    return nil
}

func main() {
    r := chi.NewRouter()

    r.Post("/products", func(w http.ResponseWriter, r *http.Request) {
        var p Test
        // err := render.Bind(r, &p)
        err := json.NewDecoder(r.Body).Decode(&p)

        if err != nil {
            panic(err)
        }

        fmt.Println(p)
    })

    http.ListenAndServe(":8080", r)
}

When I don't use render.Bind() (from "github.com/pressly/chi/render"), it works as expected.

However, when I uncomment the line err := render.Bind(r, &p) and I comment the line err := json.NewDecoder(r.Body).Decode(&p), it panics with EOF :

2017/06/20 22:26:39 http: panic serving 127.0.0.1:39696: EOF

and thus the json.Decode() fails.

Am I doing something wrong or is the http.Request.Body is already read somewhere else before render.Bind() is called?

Answer 1

render.Bind's purpose is to perform decode and execute Bind(r) to do post decode operations.

For eg.:

type Test struct {
   Name string `json:"name"`
}

func (p *Test) Bind(r *http.Request) error {
   // At this point, Decode is already done by `chi`
   p.Name = p.Name + " after decode"
  return nil
}

If you have to do only JSON decode no other actions needs to be done after decode with respect to decoded values. Just use:

// Use Directly JSON decoder of std pkg
err := json.NewDecoder(r.Body).Decode(&p)

OR

// Use wrapper method from chi DecodeJSON
err := render.DecodeJSON(r.Body, &p)