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_test.go

@@ -0,0 +1,90 @@
+package api4
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func handlerForGzip(c *Context, w http.ResponseWriter, r *http.Request) {
+	// gziphandler default requires body size greater than 1400 bytes
+	var body [1400]byte
+	w.Write(body[:])
+}
+
+func testAPIHandlerGzipMode(t *testing.T, name string, h http.Handler, token string) {
+	t.Run("Handler: "+name+" No Accept-Encoding", func(t *testing.T) {
+		resp := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/api/v4/test", nil)
+		req.Header.Set(model.HEADER_AUTH, "Bearer "+token)
+		h.ServeHTTP(resp, req)
+		assert.Equal(t, http.StatusOK, resp.Code)
+		assert.Equal(t, "", resp.Header().Get("Content-Encoding"))
+	})
+
+	t.Run("Handler: "+name+" With Accept-Encoding", func(t *testing.T) {
+		resp := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/api/v4/test", nil)
+		req.Header.Set("Accept-Encoding", "gzip")
+		req.Header.Set(model.HEADER_AUTH, "Bearer "+token)
+
+		h.ServeHTTP(resp, req)
+		assert.Equal(t, http.StatusOK, resp.Code)
+		assert.Equal(t, "gzip", resp.Header().Get("Content-Encoding"))
+	})
+}
+
+func testAPIHandlerNoGzipMode(t *testing.T, name string, h http.Handler, token string) {
+	t.Run("Handler: "+name+" No Accept-Encoding", func(t *testing.T) {
+		resp := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/api/v4/test", nil)
+		req.Header.Set(model.HEADER_AUTH, "Bearer "+token)
+
+		h.ServeHTTP(resp, req)
+		assert.Equal(t, http.StatusOK, resp.Code)
+		assert.Equal(t, "", resp.Header().Get("Content-Encoding"))
+	})
+
+	t.Run("Handler: "+name+" With Accept-Encoding", func(t *testing.T) {
+		resp := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/api/v4/test", nil)
+		req.Header.Set("Accept-Encoding", "gzip")
+		req.Header.Set(model.HEADER_AUTH, "Bearer "+token)
+
+		h.ServeHTTP(resp, req)
+		assert.Equal(t, http.StatusOK, resp.Code)
+		assert.Equal(t, "", resp.Header().Get("Content-Encoding"))
+	})
+}
+
+func TestAPIHandlersWithGzip(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	api := Init(th.Server, th.Server.AppOptions, th.Server.Router)
+	session, _ := th.App.GetSession(th.Client.AuthToken)
+
+	t.Run("with WebserverMode == \"gzip\"", func(t *testing.T) {
+		th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.WebserverMode = "gzip" })
+
+		testAPIHandlerGzipMode(t, "ApiHandler", api.ApiHandler(handlerForGzip), "")
+		testAPIHandlerGzipMode(t, "ApiSessionRequired", api.ApiSessionRequired(handlerForGzip), session.Token)
+		testAPIHandlerGzipMode(t, "ApiSessionRequiredMfa", api.ApiSessionRequiredMfa(handlerForGzip), session.Token)
+		testAPIHandlerGzipMode(t, "ApiHandlerTrustRequester", api.ApiHandlerTrustRequester(handlerForGzip), "")
+		testAPIHandlerGzipMode(t, "ApiSessionRequiredTrustRequester", api.ApiSessionRequiredTrustRequester(handlerForGzip), session.Token)
+	})
+
+	t.Run("with WebserverMode == \"nogzip\"", func(t *testing.T) {
+		th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.WebserverMode = "nogzip" })
+
+		testAPIHandlerNoGzipMode(t, "ApiHandler", api.ApiHandler(handlerForGzip), "")
+		testAPIHandlerNoGzipMode(t, "ApiSessionRequired", api.ApiSessionRequired(handlerForGzip), session.Token)
+		testAPIHandlerNoGzipMode(t, "ApiSessionRequiredMfa", api.ApiSessionRequiredMfa(handlerForGzip), session.Token)
+		testAPIHandlerNoGzipMode(t, "ApiHandlerTrustRequester", api.ApiHandlerTrustRequester(handlerForGzip), "")
+		testAPIHandlerNoGzipMode(t, "ApiSessionRequiredTrustRequester", api.ApiSessionRequiredTrustRequester(handlerForGzip), session.Token)
+	})
+}