Incorrect response code with gzip

[thomascriley]

Issue Description

The status code is not written to the response writer when there is no content in the response. This is new as of 4.11.0 and possibly a result of #2267. Previously, writing of the header happened in the write header function. This was removed in favor of a delayed write.

echo/middleware/compress.go

Lines 139 to 146 in 60af056

	func (w *gzipResponseWriter) WriteHeader(code int) {
	w.Header().Del(echo.HeaderContentLength) // Issue #444
	w.wroteHeader = true
	// Delay writing of the header until we know if we'll actually compress the response
	w.code = code
	}

This delayed write only happens when a body is written. i.e. wroteBody == true

echo/middleware/compress.go

Lines 110 to 127 in 60af056

	if !grw.wroteBody {
	if res.Header().Get(echo.HeaderContentEncoding) == gzipScheme {
	res.Header().Del(echo.HeaderContentEncoding)
	}
	// We have to reset response to it's pristine state when
	// nothing is written to body or error is returned.
	// See issue #424, #407.
	res.Writer = rw
	w.Reset(io.Discard)
	} else if !grw.minLengthExceeded {
	// Write uncompressed response
	res.Writer = rw
	if grw.wroteHeader {
	grw.ResponseWriter.WriteHeader(grw.code)
	}
	grw.buffer.WriteTo(rw)
	w.Reset(io.Discard)
	}

Checklist

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

Expected behaviour

The status code should be written to the response writer even though a body is not written to the response when gzip middleware is used

Actual behaviour

The status code is lost within the gzip middleware when a body is not written, resulting in a 200 response

Steps to reproduce

1. Create a handler with the Gzip middleware
2. Within the handler, write a non-200 response without writing a body

Working code to debug

package main

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

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

	some := map[string]string{"error": "missing"}
	someBytes, err := json.Marshal(some)
	if err != nil {
		panic(err)
	}

	// status is 200 not 404
	e.GET("/get/default", func(ctx echo.Context) error {
		return ctx.NoContent(http.StatusNotFound)
	}, middleware.Gzip())

	// status is 200 not 307
	e.GET("/redirect", func(ctx echo.Context) error {
		return ctx.Redirect(http.StatusTemporaryRedirect, "/get/config/some")
	}, middleware.Gzip())

	// works
	e.GET("/get/config/some", func(ctx echo.Context) error {
		return ctx.JSON(http.StatusBadRequest, some)
	}, middleware.GzipWithConfig(middleware.GzipConfig{MinLength: len(someBytes) + 10}))

	// status is 200 not 404
	e.GET("/get/config/zero", func(ctx echo.Context) error {
		return ctx.NoContent(http.StatusNotFound)
	}, middleware.GzipWithConfig(middleware.GzipConfig{MinLength: 0}))

	log.Fatal(e.Start(":8080"))
}

Version/commit

4.11.0

[aldas]

@thomascriley should be fixed in v4.11.1 (https://github.com/labstack/echo/releases/tag/v4.11.1)