Dont return 400 from .Bind() in POST / PUT with no body

[cousinbenson]

Issue Description

The default binder currently returns 400 if req.ContentLength == 0 during methods that aren't GET or DELETE. It is generally NOT regarded bad practice to make POST / PUT requests with an empty body. It should be up the resource to determine whether or not this should error and not the HTTP protocol.

#1214 was created with regards to this issue, but eventually went stale after no action was taken.

Some discussion on the topic can be found here:

• https://stackoverflow.com/questions/4191593/is-it-considered-bad-practice-to-perform-http-post-without-entity-body
• http://lists.w3.org/Archives/Public/ietf-http-wg/2010JulSep/0272.html

Checklist

• Dependencies installed
• No typos
• Searched existing issues and docs

Expected behaviour

c.Bind() should not return 400 for POST / PUT with empty bodies

Actual behaviour

c.Bind() returns 400 for POST / PUT with empty bodies

Steps to reproduce

call c.Bind() in a POST handler with an empty body

Working code to debug

package main

import (
	"net/http"
	"github.com/labstack/echo"
)

func main() {
	srv := echo.New()
	srv.POST("/test", testPostBody)
	srv.Start(":1234")
}

type Params struct {
	Foo string `param:"foo"`
	Bar string `query:"bar"`
}

func testPostBody(c echo.Context) error {
	var params Params
	if err := c.Bind(&params); err != nil {
		return echo.NewHTTPError(http.StatusBadRequest, err)
	}

	return c.String(200, "OK")
}

Version/commit

[beaufosheau]

I have a request that binds to an array of structs and it currently does not work with v4.1.11 (works fine in previous versions). Is it bad practice to bind to an array or is this just a minor bug? I am getting the error, "Binding element must be a struct."

g.POST("/CallDownloadRequest", func(c echo.Context) error {
	notes := c.QueryParam("notes")

	var calls []downloadCallRequest
	err := c.Bind(&calls)
	if err != nil {
		fmt.Println(err.Error())
		return c.String(http.StatusBadRequest, "Unable to parse the request")
	}

       // logic
}

Sorry if this is in the wrong place, just seemed related to your changes. I can make a PR if needed.

[vishr]

package main

import (
	"github.com/labstack/echo/v4"
)

type (
	Book struct {
		Name string `json:"name"`
	}
)

func main() {
	e := echo.New()
	e.POST("/", func(c echo.Context) error {
		var books []*Book
		if err := c.Bind(&books); err != nil {
			return err
		}
		return c.JSON(200, books)
	})

	e.Logger.Fatal(e.Start(":1323"))
}

curl -X POST \
  http://localhost:1323 \
  -H 'Content-Type: application/json' \
  -d '[{"name": "book1"}, {"name": "book2"}]'

Above works for me.

[beaufosheau]

Thanks for the quick response! It must be something with my local machine. I have tried your code and it works fine on my laptop and with Postman but curl returns the same error as before. This is all with rolling back to v4.1.10 as well, so definitely unrelated to this issue. Thanks for the help anyway!

package main

import "github.com/labstack/echo"

type (
	Book struct {
		Name string `json:"name"`
	}
)

func main() {
	e := echo.New()
	e.POST("/", func(c echo.Context) error {
		var books []*Book
		if err := c.Bind(&books); err != nil {
			return err
		}
		return c.JSON(200, books)
	})

	e.Logger.Fatal(e.Start(":1323"))
}

C:\<User>\go\src\books>curl -X POST   http://localhost:1323   -H 'Content-Type:application/json'   -d "[{\"name\" : \"book1\" }, {\"name\" : \"book2\" }]"
{"message":"binding element must be a struct"}