Add missing `X-Total-Count` and fix some related bugs (#17968)

* Add missing `X-Total-Count` and fix some related bugs

Adds `X-Total-Count` header to APIs that return a list but doesn't have it yet.
Fixed bugs:
* not returned after reporting error (https://github.com/qwerty287/gitea/blob/39eb82446c6fe5da3d79124e1f701f3795625b69/routers/api/v1/user/star.go#L70)
* crash with index out of bounds, API issue/issueSubscriptions

I also found various endpoints that return lists but do not apply/support pagination yet:
```
/repos/{owner}/{repo}/issues/{index}/labels
/repos/{owner}/{repo}/issues/comments/{id}/reactions
/repos/{owner}/{repo}/branch_protections
/repos/{owner}/{repo}/contents
/repos/{owner}/{repo}/hooks/git
/repos/{owner}/{repo}/issue_templates
/repos/{owner}/{repo}/releases/{id}/assets
/repos/{owner}/{repo}/reviewers
/repos/{owner}/{repo}/teams
/user/emails
/users/{username}/heatmap
```
If this is not expected, an new issue should be opened.

Closes #13043

* fmt

* Update routers/api/v1/repo/issue_subscription.go

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

* Use FindAndCount

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>
Co-authored-by: 6543 <6543@obermui.de>

5 files changed, 33 insertions, 17 deletions

diff --git a/models/commit_status.go b/models/commit_status.go
index 93b6f93f96..cd7497eed8 100644
--- a/models/commit_status.go
+++ b/models/commit_status.go
@@ -231,11 +231,11 @@ type CommitStatusIndex struct {
 }
 
 // GetLatestCommitStatus returns all statuses with a unique context for a given commit.
-func GetLatestCommitStatus(repoID int64, sha string, listOptions db.ListOptions) ([]*CommitStatus, error) {
+func GetLatestCommitStatus(repoID int64, sha string, listOptions db.ListOptions) ([]*CommitStatus, int64, error) {
 	return getLatestCommitStatus(db.GetEngine(db.DefaultContext), repoID, sha, listOptions)
 }
 
-func getLatestCommitStatus(e db.Engine, repoID int64, sha string, listOptions db.ListOptions) ([]*CommitStatus, error) {
+func getLatestCommitStatus(e db.Engine, repoID int64, sha string, listOptions db.ListOptions) ([]*CommitStatus, int64, error) {
 	ids := make([]int64, 0, 10)
 	sess := e.Table(&CommitStatus{}).
 		Where("repo_id = ?", repoID).And("sha = ?", sha).
@@ -244,15 +244,15 @@ func getLatestCommitStatus(e db.Engine, repoID int64, sha string, listOptions db
 
 	sess = db.SetSessionPagination(sess, &listOptions)
 
-	err := sess.Find(&ids)
+	count, err := sess.FindAndCount(&ids)
 	if err != nil {
-		return nil, err
+		return nil, count, err
 	}
 	statuses := make([]*CommitStatus, 0, len(ids))
 	if len(ids) == 0 {
-		return statuses, nil
+		return statuses, count, nil
 	}
-	return statuses, e.In("id", ids).Find(&statuses)
+	return statuses, count, e.In("id", ids).Find(&statuses)
 }
 
 // FindRepoRecentCommitStatusContexts returns repository's recent commit status contexts
@@ -340,7 +340,7 @@ func ParseCommitsWithStatus(oldCommits []*asymkey_model.SignCommit, repo *repo_m
 		commit := &SignCommitWithStatuses{
 			SignCommit: c,
 		}
-		statuses, err := GetLatestCommitStatus(repo.ID, commit.ID.String(), db.ListOptions{})
+		statuses, _, err := GetLatestCommitStatus(repo.ID, commit.ID.String(), db.ListOptions{})
 		if err != nil {
 			log.Error("GetLatestCommitStatus: %v", err)
 		} else {
diff --git a/models/issue.go b/models/issue.go
index d2f06846c2..ea8eb4a9aa 100644
--- a/models/issue.go
+++ b/models/issue.go
@@ -238,7 +238,7 @@ func (issue *Issue) loadReactions(ctx context.Context) (err error) {
 		return nil
 	}
 	e := db.GetEngine(ctx)
-	reactions, err := findReactions(e, FindReactionsOptions{
+	reactions, _, err := findReactions(e, FindReactionsOptions{
 		IssueID: issue.ID,
 	})
 	if err != nil {
diff --git a/models/issue_comment.go b/models/issue_comment.go
index 754fa3439e..e54d41bf0d 100644
--- a/models/issue_comment.go
+++ b/models/issue_comment.go
@@ -593,7 +593,7 @@ func (c *Comment) loadReactions(e db.Engine, repo *repo_model.Repository) (err e
 	if c.Reactions != nil {
 		return nil
 	}
-	c.Reactions, err = findReactions(e, FindReactionsOptions{
+	c.Reactions, _, err = findReactions(e, FindReactionsOptions{
 		IssueID:   c.IssueID,
 		CommentID: c.ID,
 	})
diff --git a/models/issue_reaction.go b/models/issue_reaction.go
index 4072733a1c..2e0ab07db7 100644
--- a/models/issue_reaction.go
+++ b/models/issue_reaction.go
@@ -71,7 +71,7 @@ func (opts *FindReactionsOptions) toConds() builder.Cond {
 }
 
 // FindCommentReactions returns a ReactionList of all reactions from an comment
-func FindCommentReactions(comment *Comment) (ReactionList, error) {
+func FindCommentReactions(comment *Comment) (ReactionList, int64, error) {
 	return findReactions(db.GetEngine(db.DefaultContext), FindReactionsOptions{
 		IssueID:   comment.IssueID,
 		CommentID: comment.ID,
@@ -79,7 +79,7 @@ func FindCommentReactions(comment *Comment) (ReactionList, error) {
 }
 
 // FindIssueReactions returns a ReactionList of all reactions from an issue
-func FindIssueReactions(issue *Issue, listOptions db.ListOptions) (ReactionList, error) {
+func FindIssueReactions(issue *Issue, listOptions db.ListOptions) (ReactionList, int64, error) {
 	return findReactions(db.GetEngine(db.DefaultContext), FindReactionsOptions{
 		ListOptions: listOptions,
 		IssueID:     issue.ID,
@@ -87,20 +87,22 @@ func FindIssueReactions(issue *Issue, listOptions db.ListOptions) (ReactionList,
 	})
 }
 
-func findReactions(e db.Engine, opts FindReactionsOptions) ([]*Reaction, error) {
-	e = e.
+func findReactions(e db.Engine, opts FindReactionsOptions) ([]*Reaction, int64, error) {
+	sess := e.
 		Where(opts.toConds()).
 		In("reaction.`type`", setting.UI.Reactions).
 		Asc("reaction.issue_id", "reaction.comment_id", "reaction.created_unix", "reaction.id")
 	if opts.Page != 0 {
-		e = db.SetEnginePagination(e, &opts)
+		sess = db.SetSessionPagination(sess, &opts)
 
 		reactions := make([]*Reaction, 0, opts.PageSize)
-		return reactions, e.Find(&reactions)
+		count, err := sess.FindAndCount(&reactions)
+		return reactions, count, err
 	}
 
 	reactions := make([]*Reaction, 0, 10)
-	return reactions, e.Find(&reactions)
+	count, err := sess.FindAndCount(&reactions)
+	return reactions, count, err
 }
 
 func createReaction(e db.Engine, opts *ReactionOptions) (*Reaction, error) {
@@ -120,7 +122,7 @@ func createReaction(e db.Engine, opts *ReactionOptions) (*Reaction, error) {
 		findOpts.CommentID = opts.Comment.ID
 	}
 
-	existingR, err := findReactions(e, findOpts)
+	existingR, _, err := findReactions(e, findOpts)
 	if err != nil {
 		return nil, err
 	}
diff --git a/models/issue_watch.go b/models/issue_watch.go
index 181cd23433..92dc847415 100644
--- a/models/issue_watch.go
+++ b/models/issue_watch.go
@@ -126,6 +126,20 @@ func getIssueWatchers(e db.Engine, issueID int64, listOptions db.ListOptions) (I
 	return watches, sess.Find(&watches)
 }
 
+// CountIssueWatchers count watchers/unwatchers of a given issue
+func CountIssueWatchers(issueID int64) (int64, error) {
+	return countIssueWatchers(db.GetEngine(db.DefaultContext), issueID)
+}
+
+func countIssueWatchers(e db.Engine, issueID int64) (int64, error) {
+	return e.
+		Where("`issue_watch`.issue_id = ?", issueID).
+		And("`issue_watch`.is_watching = ?", true).
+		And("`user`.is_active = ?", true).
+		And("`user`.prohibit_login = ?", false).
+		Join("INNER", "`user`", "`user`.id = `issue_watch`.user_id").Count(new(IssueWatch))
+}
+
 func removeIssueWatchersByRepoID(e db.Engine, userID, repoID int64) error {
 	_, err := e.
 		Join("INNER", "issue", "`issue`.id = `issue_watch`.issue_id AND `issue`.repo_id = ?", repoID).