Fix duplicate sub-path for avatars (#31365)

Fix #31361, and add tests

And this PR introduces an undocumented & debug-purpose-only config
option: `USE_SUB_URL_PATH`. It does nothing for end users, it only helps
the development of sub-path related problems.

And also fix #31366

Co-authored-by: @ExplodingDragon

models/repo/avatar_test.go

@@ -0,0 +1,28 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRepoAvatarLink(t *testing.T) {
+	defer test.MockVariableValue(&setting.AppURL, "https://localhost/")()
+	defer test.MockVariableValue(&setting.AppSubURL, "")()
+
+	repo := &Repository{ID: 1, Avatar: "avatar.png"}
+	link := repo.AvatarLink(db.DefaultContext)
+	assert.Equal(t, "https://localhost/repo-avatars/avatar.png", link)
+
+	setting.AppURL = "https://localhost/sub-path/"
+	setting.AppSubURL = "/sub-path"
+	link = repo.AvatarLink(db.DefaultContext)
+	assert.Equal(t, "https://localhost/sub-path/repo-avatars/avatar.png", link)
+}

models/user/avatar.go

@@ -89,9 +89,11 @@ func (u *User) AvatarLinkWithSize(ctx context.Context, size int) string {
 	return avatars.GenerateEmailAvatarFastLink(ctx, u.AvatarEmail, size)
 }
 
-// AvatarLink returns the full avatar url with http host. TODO: refactor it to a relative URL, but it is still used in API response at the moment
+// AvatarLink returns the full avatar url with http host.
+// TODO: refactor it to a relative URL, but it is still used in API response at the moment
 func (u *User) AvatarLink(ctx context.Context) string {
-	return httplib.MakeAbsoluteURL(ctx, u.AvatarLinkWithSize(ctx, 0))
+	relLink := u.AvatarLinkWithSize(ctx, 0) // it can't be empty
+	return httplib.MakeAbsoluteURL(ctx, relLink)
 }
 
 // IsUploadAvatarChanged returns true if the current user's avatar would be changed with the provided data

models/user/avatar_test.go

@@ -0,0 +1,28 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package user
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUserAvatarLink(t *testing.T) {
+	defer test.MockVariableValue(&setting.AppURL, "https://localhost/")()
+	defer test.MockVariableValue(&setting.AppSubURL, "")()
+
+	u := &User{ID: 1, Avatar: "avatar.png"}
+	link := u.AvatarLink(db.DefaultContext)
+	assert.Equal(t, "https://localhost/avatars/avatar.png", link)
+
+	setting.AppURL = "https://localhost/sub-path/"
+	setting.AppSubURL = "/sub-path"
+	link = u.AvatarLink(db.DefaultContext)
+	assert.Equal(t, "https://localhost/sub-path/avatars/avatar.png", link)
+}