Use gzip for API responses [MM-11426] (#10602)

* Use gzip for API responses [MM-11426]

- Update api4/handlers to use gziphandler wrapper if api configured to
use gzip
- Add test to ensure `Content-Encoding` header is set if `WebserverMode=="gzip"` and `Accept-Encoding="gzip"` present in http request

Authored-by: Tyler Ramer <tyaramer@gmail.com>

* WIP: refractor handlers_test

Clean up, include gzip tests for all functions in handlers

Authored-by: Tyler Ramer <tyaramer@gmail.com>

* fixup! WIP: refractor handlers_test

* fixup! fixup! WIP: refractor handlers_test

api4/handlers.go

@@ -6,6 +6,7 @@ package api4
 import (
 	"net/http"
 
+	"github.com/NYTimes/gziphandler"
 	"github.com/mattermost/mattermost-server/web"
 )
 
@@ -14,7 +15,7 @@ type Context = web.Context
 // ApiHandler provides a handler for API endpoints which do not require the user to be logged in order for access to be
 // granted.
 func (api *API) ApiHandler(h func(*Context, http.ResponseWriter, *http.Request)) http.Handler {
-	return &web.Handler{
+	handler := &web.Handler{
 		GetGlobalAppOptions: api.GetGlobalAppOptions,
 		HandleFunc:          h,
 		RequireSession:      false,
@@ -22,12 +23,16 @@ func (api *API) ApiHandler(h func(*Context, http.ResponseWriter, *http.Request))
 		RequireMfa:          false,
 		IsStatic:            false,
 	}
+	if *api.ConfigService.Config().ServiceSettings.WebserverMode == "gzip" {
+		return gziphandler.GzipHandler(handler)
+	}
+	return handler
 }
 
 // ApiSessionRequired provides a handler for API endpoints which require the user to be logged in in order for access to
 // be granted.
 func (api *API) ApiSessionRequired(h func(*Context, http.ResponseWriter, *http.Request)) http.Handler {
-	return &web.Handler{
+	handler := &web.Handler{
 		GetGlobalAppOptions: api.GetGlobalAppOptions,
 		HandleFunc:          h,
 		RequireSession:      true,
@@ -35,13 +40,18 @@ func (api *API) ApiSessionRequired(h func(*Context, http.ResponseWriter, *http.R
 		RequireMfa:          true,
 		IsStatic:            false,
 	}
+	if *api.ConfigService.Config().ServiceSettings.WebserverMode == "gzip" {
+		return gziphandler.GzipHandler(handler)
+	}
+	return handler
+
 }
 
 // ApiSessionRequiredMfa provides a handler for API endpoints which require a logged-in user session  but when accessed,
 // if MFA is enabled, the MFA process is not yet complete, and therefore the requirement to have completed the MFA
 // authentication must be waived.
 func (api *API) ApiSessionRequiredMfa(h func(*Context, http.ResponseWriter, *http.Request)) http.Handler {
-	return &web.Handler{
+	handler := &web.Handler{
 		GetGlobalAppOptions: api.GetGlobalAppOptions,
 		HandleFunc:          h,
 		RequireSession:      true,
@@ -49,13 +59,18 @@ func (api *API) ApiSessionRequiredMfa(h func(*Context, http.ResponseWriter, *htt
 		RequireMfa:          false,
 		IsStatic:            false,
 	}
+	if *api.ConfigService.Config().ServiceSettings.WebserverMode == "gzip" {
+		return gziphandler.GzipHandler(handler)
+	}
+	return handler
+
 }
 
 // ApiHandlerTrustRequester provides a handler for API endpoints which do not require the user to be logged in and are
 // allowed to be requested directly rather than via javascript/XMLHttpRequest, such as site branding images or the
 // websocket.
 func (api *API) ApiHandlerTrustRequester(h func(*Context, http.ResponseWriter, *http.Request)) http.Handler {
-	return &web.Handler{
+	handler := &web.Handler{
 		GetGlobalAppOptions: api.GetGlobalAppOptions,
 		HandleFunc:          h,
 		RequireSession:      false,
@@ -63,12 +78,17 @@ func (api *API) ApiHandlerTrustRequester(h func(*Context, http.ResponseWriter, *
 		RequireMfa:          false,
 		IsStatic:            false,
 	}
+	if *api.ConfigService.Config().ServiceSettings.WebserverMode == "gzip" {
+		return gziphandler.GzipHandler(handler)
+	}
+	return handler
+
 }
 
 // ApiSessionRequiredTrustRequester provides a handler for API endpoints which do require the user to be logged in and
 // are allowed to be requested directly rather than via javascript/XMLHttpRequest, such as emoji or file uploads.
 func (api *API) ApiSessionRequiredTrustRequester(h func(*Context, http.ResponseWriter, *http.Request)) http.Handler {
-	return &web.Handler{
+	handler := &web.Handler{
 		GetGlobalAppOptions: api.GetGlobalAppOptions,
 		HandleFunc:          h,
 		RequireSession:      true,
@@ -76,4 +96,9 @@ func (api *API) ApiSessionRequiredTrustRequester(h func(*Context, http.ResponseW
 		RequireMfa:          true,
 		IsStatic:            false,
 	}
+	if *api.ConfigService.Config().ServiceSettings.WebserverMode == "gzip" {
+		return gziphandler.GzipHandler(handler)
+	}
+	return handler
+
 }