Add context cache as a request level cache (#22294)

To avoid duplicated load of the same data in an HTTP request, we can set
a context cache to do that. i.e. Some pages may load a user from a
database with the same id in different areas on the same page. But the
code is hidden in two different deep logic. How should we share the
user? As a result of this PR, now if both entry functions accept
`context.Context` as the first parameter and we just need to refactor
`GetUserByID` to reuse the user from the context cache. Then it will not
be loaded twice on an HTTP request.

But of course, sometimes we would like to reload an object from the
database, that's why `RemoveContextData` is also exposed.

The core context cache is here. It defines a new context
```go
type cacheContext struct {
	ctx  context.Context
	data map[any]map[any]any
        lock sync.RWMutex
}

var cacheContextKey = struct{}{}

func WithCacheContext(ctx context.Context) context.Context {
	return context.WithValue(ctx, cacheContextKey, &cacheContext{
		ctx:  ctx,
		data: make(map[any]map[any]any),
	})
}
```

Then you can use the below 4 methods to read/write/del the data within
the same context.

```go
func GetContextData(ctx context.Context, tp, key any) any
func SetContextData(ctx context.Context, tp, key, value any)
func RemoveContextData(ctx context.Context, tp, key any)
func GetWithContextCache[T any](ctx context.Context, cacheGroupKey string, cacheTargetID any, f func() (T, error)) (T, error)
```

Then let's take a look at how `system.GetString` implement it.

```go
func GetSetting(ctx context.Context, key string) (string, error) {
	return cache.GetWithContextCache(ctx, contextCacheKey, key, func() (string, error) {
		return cache.GetString(genSettingCacheKey(key), func() (string, error) {
			res, err := GetSettingNoCache(ctx, key)
			if err != nil {
				return "", err
			}
			return res.SettingValue, nil
		})
	})
}
```

First, it will check if context data include the setting object with the
key. If not, it will query from the global cache which may be memory or
a Redis cache. If not, it will get the object from the database. In the
end, if the object gets from the global cache or database, it will be
set into the context cache.

An object stored in the context cache will only be destroyed after the
context disappeared.

6 files changed, 15 insertions, 11 deletions

diff --git a/tests/integration/api_comment_test.go b/tests/integration/api_comment_test.go
index cc7712e54..70affc989 100644
--- a/tests/integration/api_comment_test.go
+++ b/tests/integration/api_comment_test.go
@@ -128,7 +128,7 @@ func TestAPIGetComment(t *testing.T) {
 	DecodeJSON(t, resp, &apiComment)
 
 	assert.NoError(t, comment.LoadPoster(db.DefaultContext))
-	expect := convert.ToComment(comment)
+	expect := convert.ToComment(db.DefaultContext, comment)
 
 	assert.Equal(t, expect.ID, apiComment.ID)
 	assert.Equal(t, expect.Poster.FullName, apiComment.Poster.FullName)
diff --git a/tests/integration/api_issue_reaction_test.go b/tests/integration/api_issue_reaction_test.go
index 76140d751..42793c66c 100644
--- a/tests/integration/api_issue_reaction_test.go
+++ b/tests/integration/api_issue_reaction_test.go
@@ -65,7 +65,7 @@ func TestAPIIssuesReactions(t *testing.T) {
 	DecodeJSON(t, resp, &apiReactions)
 	expectResponse := make(map[int]api.Reaction)
 	expectResponse[0] = api.Reaction{
-		User:     convert.ToUser(user2, user2),
+		User:     convert.ToUser(db.DefaultContext, user2, user2),
 		Reaction: "eyes",
 		Created:  time.Unix(1573248003, 0),
 	}
@@ -125,12 +125,12 @@ func TestAPICommentReactions(t *testing.T) {
 	DecodeJSON(t, resp, &apiReactions)
 	expectResponse := make(map[int]api.Reaction)
 	expectResponse[0] = api.Reaction{
-		User:     convert.ToUser(user2, user2),
+		User:     convert.ToUser(db.DefaultContext, user2, user2),
 		Reaction: "laugh",
 		Created:  time.Unix(1573248004, 0),
 	}
 	expectResponse[1] = api.Reaction{
-		User:     convert.ToUser(user1, user1),
+		User:     convert.ToUser(db.DefaultContext, user1, user1),
 		Reaction: "laugh",
 		Created:  time.Unix(1573248005, 0),
 	}
diff --git a/tests/integration/api_team_test.go b/tests/integration/api_team_test.go
index 27fe5e12e..792051313 100644
--- a/tests/integration/api_team_test.go
+++ b/tests/integration/api_team_test.go
@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/organization"
 	"code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unit"
@@ -210,7 +211,7 @@ func checkTeamResponse(t *testing.T, testName string, apiTeam *api.Team, name, d
 func checkTeamBean(t *testing.T, id int64, name, description string, includesAllRepositories bool, permission string, units []string, unitsMap map[string]string) {
 	team := unittest.AssertExistsAndLoadBean(t, &organization.Team{ID: id})
 	assert.NoError(t, team.GetUnits(), "GetUnits")
-	apiTeam, err := convert.ToTeam(team)
+	apiTeam, err := convert.ToTeam(db.DefaultContext, team)
 	assert.NoError(t, err)
 	checkTeamResponse(t, fmt.Sprintf("checkTeamBean/%s_%s", name, description), apiTeam, name, description, includesAllRepositories, permission, units, unitsMap)
 }
diff --git a/tests/integration/api_team_user_test.go b/tests/integration/api_team_user_test.go
index ec977fa57..468697a39 100644
--- a/tests/integration/api_team_user_test.go
+++ b/tests/integration/api_team_user_test.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
 	api "code.gitea.io/gitea/modules/structs"
@@ -34,7 +35,7 @@ func TestAPITeamUser(t *testing.T) {
 	user2.Created = user2.Created.In(time.Local)
 	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{Name: "user2"})
 
-	expectedUser := convert.ToUser(user, user)
+	expectedUser := convert.ToUser(db.DefaultContext, user, user)
 
 	// test time via unix timestamp
 	assert.EqualValues(t, expectedUser.LastLogin.Unix(), user2.LastLogin.Unix())
diff --git a/tests/integration/api_user_orgs_test.go b/tests/integration/api_user_orgs_test.go
index 831ca018b..8f914b487 100644
--- a/tests/integration/api_user_orgs_test.go
+++ b/tests/integration/api_user_orgs_test.go
@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
 	api "code.gitea.io/gitea/modules/structs"
@@ -35,7 +36,7 @@ func TestUserOrgs(t *testing.T) {
 			Name:        user17.Name,
 			UserName:    user17.Name,
 			FullName:    user17.FullName,
-			AvatarURL:   user17.AvatarLink(),
+			AvatarURL:   user17.AvatarLink(db.DefaultContext),
 			Description: "",
 			Website:     "",
 			Location:    "",
@@ -46,7 +47,7 @@ func TestUserOrgs(t *testing.T) {
 			Name:        user3.Name,
 			UserName:    user3.Name,
 			FullName:    user3.FullName,
-			AvatarURL:   user3.AvatarLink(),
+			AvatarURL:   user3.AvatarLink(db.DefaultContext),
 			Description: "",
 			Website:     "",
 			Location:    "",
@@ -105,7 +106,7 @@ func TestMyOrgs(t *testing.T) {
 			Name:        user17.Name,
 			UserName:    user17.Name,
 			FullName:    user17.FullName,
-			AvatarURL:   user17.AvatarLink(),
+			AvatarURL:   user17.AvatarLink(db.DefaultContext),
 			Description: "",
 			Website:     "",
 			Location:    "",
@@ -116,7 +117,7 @@ func TestMyOrgs(t *testing.T) {
 			Name:        user3.Name,
 			UserName:    user3.Name,
 			FullName:    user3.FullName,
-			AvatarURL:   user3.AvatarLink(),
+			AvatarURL:   user3.AvatarLink(db.DefaultContext),
 			Description: "",
 			Website:     "",
 			Location:    "",
diff --git a/tests/integration/user_avatar_test.go b/tests/integration/user_avatar_test.go
index 08ecb8b74..7aeba6a33 100644
--- a/tests/integration/user_avatar_test.go
+++ b/tests/integration/user_avatar_test.go
@@ -12,6 +12,7 @@ import (
 	"net/url"
 	"testing"
 
+	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/avatar"
@@ -73,7 +74,7 @@ func TestUserAvatar(t *testing.T) {
 
 		user2 = unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2}) // owner of the repo3, is an org
 
-		req = NewRequest(t, "GET", user2.AvatarLinkWithSize(0))
+		req = NewRequest(t, "GET", user2.AvatarLinkWithSize(db.DefaultContext, 0))
 		_ = session.MakeRequest(t, req, http.StatusOK)
 
 		// Can't test if the response matches because the image is re-generated on upload but checking that this at least doesn't give a 404 should be enough.