[feature] Allow users to set custom css for their profiles + threads (#808)

* add custom css account property + db func to fetch

* allow account to get/set custom css

* serve custom css for an account

* go fmt

* use monospace for customcss, add link

* add custom css to account cache

* fix broken field

* add custom css docs to user guide

* add `accounts-allow-custom-css` config flag

* add allow custom css to /api/v1/instance response

* only show/set custom css if allowed to do so

* only set/serve custom account css if enabled

* update swagger docs

* chain promise

* make bool a bit clearer

* use cache for GetAccountCustomCSSByUsername

4 files changed, 87 insertions, 13 deletions

diff --git a/internal/web/customcss.go b/internal/web/customcss.go
new file mode 100644
index 000000000..34e15844c
--- /dev/null
+++ b/internal/web/customcss.go
@@ -0,0 +1,60 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package web
+
+import (
+	"errors"
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/api"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+)
+
+func (m *Module) customCSSGETHandler(c *gin.Context) {
+	if !config.GetAccountsAllowCustomCSS() {
+		err := errors.New("accounts-allow-custom-css is not enabled on this instance")
+		api.ErrorHandler(c, gtserror.NewErrorNotFound(err), m.processor.InstanceGet)
+		return
+	}
+
+	if _, err := api.NegotiateAccept(c, api.TextCSS); err != nil {
+		api.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	// usernames on our instance will always be lowercase
+	username := strings.ToLower(c.Param(usernameKey))
+	if username == "" {
+		err := errors.New("no account username specified")
+		api.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	customCSS, errWithCode := m.processor.AccountGetCustomCSSForUsername(c.Request.Context(), username)
+	if errWithCode != nil {
+		api.ErrorHandler(c, errWithCode, m.processor.InstanceGet)
+		return
+	}
+
+	c.Header("Cache-Control", "no-cache")
+	c.Data(http.StatusOK, "text/css; charset=utf-8", []byte(customCSS))
+}
diff --git a/internal/web/profile.go b/internal/web/profile.go
index 0640c7df9..67407f8e4 100644
--- a/internal/web/profile.go
+++ b/internal/web/profile.go
@@ -99,6 +99,15 @@ func (m *Module) profileGETHandler(c *gin.Context) {
 		return
 	}
 
+	stylesheets := []string{
+		"/assets/Fork-Awesome/css/fork-awesome.min.css",
+		"/assets/dist/status.css",
+		"/assets/dist/profile.css",
+	}
+	if config.GetAccountsAllowCustomCSS() {
+		stylesheets = append(stylesheets, "/@"+account.Username+"/custom.css")
+	}
+
 	c.HTML(http.StatusOK, "profile.tmpl", gin.H{
 		"instance":         instance,
 		"account":          account,
@@ -106,11 +115,7 @@ func (m *Module) profileGETHandler(c *gin.Context) {
 		"statuses":         statusResp.Items,
 		"statuses_next":    statusResp.NextLink,
 		"show_back_to_top": showBackToTop,
-		"stylesheets": []string{
-			"/assets/Fork-Awesome/css/fork-awesome.min.css",
-			"/assets/dist/status.css",
-			"/assets/dist/profile.css",
-		},
+		"stylesheets":      stylesheets,
 		"javascript": []string{
 			"/assets/dist/frontend.js",
 		},
diff --git a/internal/web/thread.go b/internal/web/thread.go
index 824d3c33c..b7e1bef3d 100644
--- a/internal/web/thread.go
+++ b/internal/web/thread.go
@@ -104,15 +104,20 @@ func (m *Module) threadGETHandler(c *gin.Context) {
 		return
 	}
 
+	stylesheets := []string{
+		"/assets/Fork-Awesome/css/fork-awesome.min.css",
+		"/assets/dist/status.css",
+	}
+	if config.GetAccountsAllowCustomCSS() {
+		stylesheets = append(stylesheets, "/@"+username+"/custom.css")
+	}
+
 	c.HTML(http.StatusOK, "thread.tmpl", gin.H{
-		"instance": instance,
-		"status":   status,
-		"context":  context,
-		"ogMeta":   ogBase(instance).withStatus(status),
-		"stylesheets": []string{
-			"/assets/Fork-Awesome/css/fork-awesome.min.css",
-			"/assets/dist/status.css",
-		},
+		"instance":    instance,
+		"status":      status,
+		"context":     context,
+		"ogMeta":      ogBase(instance).withStatus(status),
+		"stylesheets": stylesheets,
 		"javascript": []string{
 			"/assets/dist/frontend.js",
 		},
diff --git a/internal/web/web.go b/internal/web/web.go
index 336525938..a74fc8e19 100644
--- a/internal/web/web.go
+++ b/internal/web/web.go
@@ -35,6 +35,7 @@ import (
 const (
 	confirmEmailPath = "/" + uris.ConfirmEmailPath
 	profilePath      = "/@:" + usernameKey
+	customCSSPath    = profilePath + "/custom.css"
 	statusPath       = profilePath + "/statuses/:" + statusIDKey
 	adminPanelPath   = "/admin"
 	userPanelpath    = "/user"
@@ -91,6 +92,9 @@ func (m *Module) Route(s router.Router) error {
 	// serve profile pages at /@username
 	s.AttachHandler(http.MethodGet, profilePath, m.profileGETHandler)
 
+	// serve custom css at /@username/custom.css
+	s.AttachHandler(http.MethodGet, customCSSPath, m.customCSSGETHandler)
+
 	// serve statuses
 	s.AttachHandler(http.MethodGet, statusPath, m.threadGETHandler)