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.

3 files changed, 11 insertions, 10 deletions

diff --git a/routers/api/v1/user/follower.go b/routers/api/v1/user/follower.go
index e9d4ae478b..bc03b22ea7 100644
--- a/routers/api/v1/user/follower.go
+++ b/routers/api/v1/user/follower.go
@@ -17,7 +17,7 @@ import (
 func responseAPIUsers(ctx *context.APIContext, users []*user_model.User) {
 	apiUsers := make([]*api.User, len(users))
 	for i := range users {
-		apiUsers[i] = convert.ToUser(users[i], ctx.Doer)
+		apiUsers[i] = convert.ToUser(ctx, users[i], ctx.Doer)
 	}
 	ctx.JSON(http.StatusOK, &apiUsers)
 }
diff --git a/routers/api/v1/user/key.go b/routers/api/v1/user/key.go
index 8aad69884f..f90c65817d 100644
--- a/routers/api/v1/user/key.go
+++ b/routers/api/v1/user/key.go
@@ -4,6 +4,7 @@
 package user
 
 import (
+	std_ctx "context"
 	"net/http"
 
 	asymkey_model "code.gitea.io/gitea/models/asymkey"
@@ -21,20 +22,20 @@ import (
 )
 
 // appendPrivateInformation appends the owner and key type information to api.PublicKey
-func appendPrivateInformation(apiKey *api.PublicKey, key *asymkey_model.PublicKey, defaultUser *user_model.User) (*api.PublicKey, error) {
+func appendPrivateInformation(ctx std_ctx.Context, apiKey *api.PublicKey, key *asymkey_model.PublicKey, defaultUser *user_model.User) (*api.PublicKey, error) {
 	if key.Type == asymkey_model.KeyTypeDeploy {
 		apiKey.KeyType = "deploy"
 	} else if key.Type == asymkey_model.KeyTypeUser {
 		apiKey.KeyType = "user"
 
 		if defaultUser.ID == key.OwnerID {
-			apiKey.Owner = convert.ToUser(defaultUser, defaultUser)
+			apiKey.Owner = convert.ToUser(ctx, defaultUser, defaultUser)
 		} else {
 			user, err := user_model.GetUserByID(db.DefaultContext, key.OwnerID)
 			if err != nil {
 				return apiKey, err
 			}
-			apiKey.Owner = convert.ToUser(user, user)
+			apiKey.Owner = convert.ToUser(ctx, user, user)
 		}
 	} else {
 		apiKey.KeyType = "unknown"
@@ -87,7 +88,7 @@ func listPublicKeys(ctx *context.APIContext, user *user_model.User) {
 	for i := range keys {
 		apiKeys[i] = convert.ToPublicKey(apiLink, keys[i])
 		if ctx.Doer.IsAdmin || ctx.Doer.ID == keys[i].OwnerID {
-			apiKeys[i], _ = appendPrivateInformation(apiKeys[i], keys[i], user)
+			apiKeys[i], _ = appendPrivateInformation(ctx, apiKeys[i], keys[i], user)
 		}
 	}
 
@@ -187,7 +188,7 @@ func GetPublicKey(ctx *context.APIContext) {
 	apiLink := composePublicKeysAPILink()
 	apiKey := convert.ToPublicKey(apiLink, key)
 	if ctx.Doer.IsAdmin || ctx.Doer.ID == key.OwnerID {
-		apiKey, _ = appendPrivateInformation(apiKey, key, ctx.Doer)
+		apiKey, _ = appendPrivateInformation(ctx, apiKey, key, ctx.Doer)
 	}
 	ctx.JSON(http.StatusOK, apiKey)
 }
@@ -208,7 +209,7 @@ func CreateUserPublicKey(ctx *context.APIContext, form api.CreateKeyOption, uid
 	apiLink := composePublicKeysAPILink()
 	apiKey := convert.ToPublicKey(apiLink, key)
 	if ctx.Doer.IsAdmin || ctx.Doer.ID == key.OwnerID {
-		apiKey, _ = appendPrivateInformation(apiKey, key, ctx.Doer)
+		apiKey, _ = appendPrivateInformation(ctx, apiKey, key, ctx.Doer)
 	}
 	ctx.JSON(http.StatusCreated, apiKey)
 }
diff --git a/routers/api/v1/user/user.go b/routers/api/v1/user/user.go
index 55f3df40b9..6fd4b3a95c 100644
--- a/routers/api/v1/user/user.go
+++ b/routers/api/v1/user/user.go
@@ -74,7 +74,7 @@ func Search(ctx *context.APIContext) {
 
 	ctx.JSON(http.StatusOK, map[string]interface{}{
 		"ok":   true,
-		"data": convert.ToUsers(ctx.Doer, users),
+		"data": convert.ToUsers(ctx, ctx.Doer, users),
 	})
 }
 
@@ -102,7 +102,7 @@ func GetInfo(ctx *context.APIContext) {
 		ctx.NotFound("GetUserByName", user_model.ErrUserNotExist{Name: ctx.Params(":username")})
 		return
 	}
-	ctx.JSON(http.StatusOK, convert.ToUser(ctx.ContextUser, ctx.Doer))
+	ctx.JSON(http.StatusOK, convert.ToUser(ctx, ctx.ContextUser, ctx.Doer))
 }
 
 // GetAuthenticatedUser get current user's information
@@ -116,7 +116,7 @@ func GetAuthenticatedUser(ctx *context.APIContext) {
 	//   "200":
 	//     "$ref": "#/responses/User"
 
-	ctx.JSON(http.StatusOK, convert.ToUser(ctx.Doer, ctx.Doer))
+	ctx.JSON(http.StatusOK, convert.ToUser(ctx, ctx.Doer, ctx.Doer))
 }
 
 // GetUserHeatmapData is the handler to get a users heatmap