Return nicer error if trying to pull from non-existent user (#18288)

* Return nicer error if trying to pull from non-existent user

Gitea serv will currently return an 500 if we try to pull from a repository where
the owner does not exist.

This PR checks for the UserNotExist Error when checking for the user and will
return a NotFound error instead.

Fix #18225

Author: zeripath

Diff for: routers/private/serv.go

@@ -111,8 +111,17 @@ func ServCommand(ctx *context.PrivateContext) {
 
 	owner, err := user_model.GetUserByName(results.OwnerName)
 	if err != nil {
+		if user_model.IsErrUserNotExist(err) {
+			// User is fetching/cloning a non-existent repository
+			log.Warn("Failed authentication attempt (cannot find repository: %s/%s) from %s", results.OwnerName, results.RepoName, ctx.RemoteAddr())
+			ctx.JSON(http.StatusNotFound, private.ErrServCommand{
+				Results: results,
+				Err:     fmt.Sprintf("Cannot find repository: %s/%s", results.OwnerName, results.RepoName),
+			})
+			return
+		}
 		log.Error("Unable to get repository owner: %s/%s Error: %v", results.OwnerName, results.RepoName, err)
-		ctx.JSON(http.StatusInternalServerError, private.ErrServCommand{
+		ctx.JSON(http.StatusForbidden, private.ErrServCommand{
 			Results: results,
 			Err:     fmt.Sprintf("Unable to get repository owner: %s/%s %v", results.OwnerName, results.RepoName, err),
 		})
@@ -135,7 +144,7 @@ func ServCommand(ctx *context.PrivateContext) {
 			for _, verb := range ctx.FormStrings("verb") {
 				if "git-upload-pack" == verb {
 					// User is fetching/cloning a non-existent repository
-					log.Error("Failed authentication attempt (cannot find repository: %s/%s) from %s", results.OwnerName, results.RepoName, ctx.RemoteAddr())
+					log.Warn("Failed authentication attempt (cannot find repository: %s/%s) from %s", results.OwnerName, results.RepoName, ctx.RemoteAddr())
 					ctx.JSON(http.StatusNotFound, private.ErrServCommand{
 						Results: results,
 						Err:     fmt.Sprintf("Cannot find repository: %s/%s", results.OwnerName, results.RepoName),
@@ -325,7 +334,7 @@ func ServCommand(ctx *context.PrivateContext) {
 			userMode := perm.UnitAccessMode(unitType)
 
 			if userMode < mode {
-				log.Error("Failed authentication attempt for %s with key %s (not authorized to %s %s/%s) from %s", user.Name, key.Name, modeString, ownerName, repoName, ctx.RemoteAddr())
+				log.Warn("Failed authentication attempt for %s with key %s (not authorized to %s %s/%s) from %s", user.Name, key.Name, modeString, ownerName, repoName, ctx.RemoteAddr())
 				ctx.JSON(http.StatusUnauthorized, private.ErrServCommand{
 					Results: results,
 					Err:     fmt.Sprintf("User: %d:%s with Key: %d:%s is not authorized to %s %s/%s.", user.ID, user.Name, key.ID, key.Name, modeString, ownerName, repoName),