Remove default charset from 'application/json' Content-Type header

[doortts]

Using application/json; charset=UTF-8 in response header is a common misuse. I think it is better to remove ; charset=UTF-8 from default json response Content-Type header to prevent the misconception.

See: #2567

[aldas]

You can not just remove/replace echo.MIMEApplicationJSONCharsetUTF8 as it is part of Echos public API and we are quite strict on API changes.

• it would be nice if there would be link to JSON spec and remark about charset in doccomment

other than that I think this is probably ok

[doortts]

@aldas Thank you for the comment.

• I recovered echo.MIMEApplicationJSONCharsetUTF8 and added 'Deprecated: ' comment. Just let let me know if this is not what you intended. https://github.com/labstack/echo/pull/2568/files?diff=unified#diff-aba8ba313c6b989153f1f96e641a8e0e75313485d2e13d64378e70858d5a4669R173
• I added a reference link what you mentioned to the issue documentation.
  • Related RFC note link
  • Related RFC 8.1 Chapter Link

[aldas]

done, Thanks @doortts

[washington-guedes]

There are clients outside of what was called "compliant recipient" that got broken, like flutter v2.1 in my case. Is it possible to have a middleware that forces the header Content-Type back to MIMEApplicationJSONCharsetUTF8? @aldas @doortts @nono

[aldas]

There are clients outside of what was called "compliant recipient" that got broken, like flutter v2.1 in my case. Is it possible to have a middleware that forces the header Content-Type back to MIMEApplicationJSONCharsetUTF8? @aldas @doortts @nono

Try

	e.GET("/", func(c echo.Context) error {
		c.Response().Header().Set(echo.HeaderContentType, echo.MIMEApplicationJSONCharsetUTF8)
		return c.JSON(http.StatusOK, "HI")
	})

This is how header is written for c.JSON - only when there is no content type header we set it as application/json

echo/context.go

Lines 243 to 248 in 88c379f

	func (c *context) writeContentType(value string) {
	header := c.Response().Header()
	if header.Get(HeaderContentType) == "" {
	header.Set(HeaderContentType, value)
	}
	}

Example

func main() {
	e := echo.New()

	e.GET("/", func(c echo.Context) error {
		c.Response().Header().Set(echo.HeaderContentType, echo.MIMEApplicationJSONCharsetUTF8)
		return c.JSON(http.StatusOK, "HI")
	})

	if err := e.Start(":8080"); err != nil && !errors.Is(err, http.ErrServerClosed) {
		log.Fatal(err)
	}
}

Output:

x@x:~/$ curl -v http://localhost:8080
* processing: http://localhost:8080
*   Trying [::1]:8080...
* Connected to localhost (::1) port 8080
> GET / HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/8.2.1
> Accept: */*
> 
< HTTP/1.1 200 OK
< Content-Type: application/json; charset=UTF-8
< Date: Tue, 07 May 2024 18:44:09 GMT
< Content-Length: 5
< 
"HI"
* Connection #0 to host localhost left intact

[aldas]

or you could create custom json serializer than sets that header before writing the json

package main

import (
	"encoding/json"
	"errors"
	"github.com/labstack/echo/v4"
	"log"
	"net/http"
)

type utf8JSONSerializer struct {
	echo.DefaultJSONSerializer
}

func (d utf8JSONSerializer) Serialize(c echo.Context, i interface{}, indent string) error {
	c.Response().Header().Set(echo.HeaderContentType, echo.MIMEApplicationJSONCharsetUTF8)
	return d.DefaultJSONSerializer.Serialize(c, i, indent)
}

func main() {
	e := echo.New()
	e.JSONSerializer = new(utf8JSONSerializer)

	e.GET("/", func(c echo.Context) error {
		return c.JSON(http.StatusOK, "HI")
	})

	if err := e.Start(":8080"); err != nil && !errors.Is(err, http.ErrServerClosed) {
		log.Fatal(err)
	}
}