Split "modules/context.go" to separate files (#24569)

The "modules/context.go" is too large to maintain.

This PR splits it to separate files, eg: context_request.go,
context_response.go, context_serve.go

This PR will help:

1. The future refactoring for Gitea's web context (eg: simplify the context)
2. Introduce proper "range request" support
3. Introduce context function

This PR only moves code, doesn't change any logic.

modules/context/context_cookie.go

@@ -0,0 +1,105 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package context
+
+import (
+	"encoding/hex"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/util"
+	"code.gitea.io/gitea/modules/web/middleware"
+
+	"github.com/minio/sha256-simd"
+	"golang.org/x/crypto/pbkdf2"
+)
+
+const CookieNameFlash = "gitea_flash"
+
+func removeSessionCookieHeader(w http.ResponseWriter) {
+	cookies := w.Header()["Set-Cookie"]
+	w.Header().Del("Set-Cookie")
+	for _, cookie := range cookies {
+		if strings.HasPrefix(cookie, setting.SessionConfig.CookieName+"=") {
+			continue
+		}
+		w.Header().Add("Set-Cookie", cookie)
+	}
+}
+
+// SetSiteCookie convenience function to set most cookies consistently
+// CSRF and a few others are the exception here
+func (ctx *Context) SetSiteCookie(name, value string, maxAge int) {
+	middleware.SetSiteCookie(ctx.Resp, name, value, maxAge)
+}
+
+// DeleteSiteCookie convenience function to delete most cookies consistently
+// CSRF and a few others are the exception here
+func (ctx *Context) DeleteSiteCookie(name string) {
+	middleware.SetSiteCookie(ctx.Resp, name, "", -1)
+}
+
+// GetSiteCookie returns given cookie value from request header.
+func (ctx *Context) GetSiteCookie(name string) string {
+	return middleware.GetSiteCookie(ctx.Req, name)
+}
+
+// GetSuperSecureCookie returns given cookie value from request header with secret string.
+func (ctx *Context) GetSuperSecureCookie(secret, name string) (string, bool) {
+	val := ctx.GetSiteCookie(name)
+	return ctx.CookieDecrypt(secret, val)
+}
+
+// CookieDecrypt returns given value from with secret string.
+func (ctx *Context) CookieDecrypt(secret, val string) (string, bool) {
+	if val == "" {
+		return "", false
+	}
+
+	text, err := hex.DecodeString(val)
+	if err != nil {
+		return "", false
+	}
+
+	key := pbkdf2.Key([]byte(secret), []byte(secret), 1000, 16, sha256.New)
+	text, err = util.AESGCMDecrypt(key, text)
+	return string(text), err == nil
+}
+
+// SetSuperSecureCookie sets given cookie value to response header with secret string.
+func (ctx *Context) SetSuperSecureCookie(secret, name, value string, maxAge int) {
+	text := ctx.CookieEncrypt(secret, value)
+	ctx.SetSiteCookie(name, text, maxAge)
+}
+
+// CookieEncrypt encrypts a given value using the provided secret
+func (ctx *Context) CookieEncrypt(secret, value string) string {
+	key := pbkdf2.Key([]byte(secret), []byte(secret), 1000, 16, sha256.New)
+	text, err := util.AESGCMEncrypt(key, []byte(value))
+	if err != nil {
+		panic("error encrypting cookie: " + err.Error())
+	}
+
+	return hex.EncodeToString(text)
+}
+
+// GetCookieInt returns cookie result in int type.
+func (ctx *Context) GetCookieInt(name string) int {
+	r, _ := strconv.Atoi(ctx.GetSiteCookie(name))
+	return r
+}
+
+// GetCookieInt64 returns cookie result in int64 type.
+func (ctx *Context) GetCookieInt64(name string) int64 {
+	r, _ := strconv.ParseInt(ctx.GetSiteCookie(name), 10, 64)
+	return r
+}
+
+// GetCookieFloat64 returns cookie result in float64 type.
+func (ctx *Context) GetCookieFloat64(name string) float64 {
+	v, _ := strconv.ParseFloat(ctx.GetSiteCookie(name), 64)
+	return v
+}