fix gzip not sending response code for no content responses (404, 301/302 redirects etc)

[aldas]

This is fix for #2480

Response code is not written from buffered writer to the actual writer when handler sent no-content response - ala 404 or redirect

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

	e.Use(middleware.Gzip())

	e.GET("/404", func(ctx echo.Context) error {
		return ctx.NoContent(http.StatusNotFound)
	})

	e.GET("/redirect", func(ctx echo.Context) error {
		return ctx.Redirect(http.StatusTemporaryRedirect, "/login")
	})

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

Example output after fix:

x@x:~/$ curl -v --compressed "http://localhost:8080/404"
*   Trying 127.0.0.1:8080...
* Connected to localhost (127.0.0.1) port 8080 (#0)
> GET /404 HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.88.1
> Accept: */*
> Accept-Encoding: deflate, gzip, br, zstd
> 
< HTTP/1.1 404 Not Found
< Vary: Accept-Encoding
< Date: Sun, 16 Jul 2023 17:20:11 GMT
< Content-Length: 0
< 
* Connection #0 to host localhost left intact

x@x:~/$ curl -v --compressed "http://localhost:8080/redirect"
*   Trying 127.0.0.1:8080...
* Connected to localhost (127.0.0.1) port 8080 (#0)
> GET /redirect HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.88.1
> Accept: */*
> Accept-Encoding: deflate, gzip, br, zstd
> 
< HTTP/1.1 307 Temporary Redirect
< Location: /login
< Vary: Accept-Encoding
< Date: Sun, 16 Jul 2023 17:20:16 GMT
< Content-Length: 0
< 
* Connection #0 to host localhost left intact

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (60af056) 92.81% compared to head (ad61e72) 92.82%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2481   +/-   ##
=======================================
  Coverage   92.81%   92.82%           
=======================================
  Files          39       39           
  Lines        4618     4624    +6     
=======================================
+ Hits         4286     4292    +6     
  Misses        241      241           
  Partials       91       91           

Impacted Files	Coverage Δ
middleware/compress.go	86.99% <100.00%> (+0.66%)	⬆️

☔ View full report in Codecov by Sentry.
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[ganigeorgiev]

@aldas If not abandoned or there are no other plans, is it possible to sync the latest master fixes with the v5_alpha branch?

[aldas]

v5 is not fully abandoned but you really should not use v5 today. For example we have briefly discussed switching back to Context being struct which is not in v5 yet.

At the moment and I am stalling on v5 because I want slog to land in Go standard library (Go 1.21 I think).

Are there specific features that you need from v5 that v4 does not have? I could check if those are backportable for you.

---

TLDR: I will promise you to find time to merge things from master to v5_alpha next week (I am using weeks starting on monday :) ). But you really should not use that branch for production-worthy things.

[ganigeorgiev]

Thank you @aldas for the quick response.

There is no specific feature from v5 that v4 doesn't have and we need, but I'm using v5_alpha deliberately in one of my open source projects (github.com/pocketbase) with the thinking that this way it should minimize the breaking changes and eventual manual migration steps that will be required by my users because we expose the echo router directly (basically last year I assumed that v5 would have been released before the stable version of my project and that's why we use v5_alpha). In hindsight, maybe it wasn't a good idea to rely on alpha branch in the first place, but things are already public anyway, so I will wait a little longer to see in what direction the echo development will take before making changes to my project.