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.

2 files changed, 11 insertions, 16 deletions

diff --git a/models/user/avatar.go b/models/user/avatar.go
index e6ca49efd0..9af2a9acc2 100644
--- a/models/user/avatar.go
+++ b/models/user/avatar.go
@@ -58,7 +58,7 @@ func GenerateRandomAvatar(ctx context.Context, u *User) error {
 }
 
 // AvatarLinkWithSize returns a link to the user's avatar with size. size <= 0 means default size
-func (u *User) AvatarLinkWithSize(size int) string {
+func (u *User) AvatarLinkWithSize(ctx context.Context, size int) string {
 	if u.ID == -1 {
 		// ghost user
 		return avatars.DefaultAvatarLink()
@@ -67,7 +67,7 @@ func (u *User) AvatarLinkWithSize(size int) string {
 	useLocalAvatar := false
 	autoGenerateAvatar := false
 
-	disableGravatar := system_model.GetSettingBool(system_model.KeyPictureDisableGravatar)
+	disableGravatar := system_model.GetSettingBool(ctx, system_model.KeyPictureDisableGravatar)
 
 	switch {
 	case u.UseCustomAvatar:
@@ -79,7 +79,7 @@ func (u *User) AvatarLinkWithSize(size int) string {
 
 	if useLocalAvatar {
 		if u.Avatar == "" && autoGenerateAvatar {
-			if err := GenerateRandomAvatar(db.DefaultContext, u); err != nil {
+			if err := GenerateRandomAvatar(ctx, u); err != nil {
 				log.Error("GenerateRandomAvatar: %v", err)
 			}
 		}
@@ -88,12 +88,12 @@ func (u *User) AvatarLinkWithSize(size int) string {
 		}
 		return avatars.GenerateUserAvatarImageLink(u.Avatar, size)
 	}
-	return avatars.GenerateEmailAvatarFastLink(u.AvatarEmail, size)
+	return avatars.GenerateEmailAvatarFastLink(ctx, u.AvatarEmail, size)
 }
 
 // AvatarLink returns the full avatar link with http host
-func (u *User) AvatarLink() string {
-	link := u.AvatarLinkWithSize(0)
+func (u *User) AvatarLink(ctx context.Context) string {
+	link := u.AvatarLinkWithSize(ctx, 0)
 	if !strings.HasPrefix(link, "//") && !strings.Contains(link, "://") {
 		return setting.AppURL + strings.TrimPrefix(link, setting.AppSubURL+"/")
 	}
diff --git a/models/user/user.go b/models/user/user.go
index 0917bea754..0a43de7435 100644
--- a/models/user/user.go
+++ b/models/user/user.go
@@ -1114,11 +1114,11 @@ type UserCommit struct { //revive:disable-line:exported
 }
 
 // ValidateCommitWithEmail check if author's e-mail of commit is corresponding to a user.
-func ValidateCommitWithEmail(c *git.Commit) *User {
+func ValidateCommitWithEmail(ctx context.Context, c *git.Commit) *User {
 	if c.Author == nil {
 		return nil
 	}
-	u, err := GetUserByEmail(c.Author.Email)
+	u, err := GetUserByEmail(ctx, c.Author.Email)
 	if err != nil {
 		return nil
 	}
@@ -1126,7 +1126,7 @@ func ValidateCommitWithEmail(c *git.Commit) *User {
 }
 
 // ValidateCommitsWithEmails checks if authors' e-mails of commits are corresponding to users.
-func ValidateCommitsWithEmails(oldCommits []*git.Commit) []*UserCommit {
+func ValidateCommitsWithEmails(ctx context.Context, oldCommits []*git.Commit) []*UserCommit {
 	var (
 		emails     = make(map[string]*User)
 		newCommits = make([]*UserCommit, 0, len(oldCommits))
@@ -1135,7 +1135,7 @@ func ValidateCommitsWithEmails(oldCommits []*git.Commit) []*UserCommit {
 		var u *User
 		if c.Author != nil {
 			if v, ok := emails[c.Author.Email]; !ok {
-				u, _ = GetUserByEmail(c.Author.Email)
+				u, _ = GetUserByEmail(ctx, c.Author.Email)
 				emails[c.Author.Email] = u
 			} else {
 				u = v
@@ -1151,12 +1151,7 @@ func ValidateCommitsWithEmails(oldCommits []*git.Commit) []*UserCommit {
 }
 
 // GetUserByEmail returns the user object by given e-mail if exists.
-func GetUserByEmail(email string) (*User, error) {
-	return GetUserByEmailContext(db.DefaultContext, email)
-}
-
-// GetUserByEmailContext returns the user object by given e-mail if exists with db context
-func GetUserByEmailContext(ctx context.Context, email string) (*User, error) {
+func GetUserByEmail(ctx context.Context, email string) (*User, error) {
 	if len(email) == 0 {
 		return nil, ErrUserNotExist{0, email, 0}
 	}