[feature] Add global instance CSS customization setting (#3352)

Allow instance admins to add custom CSS that will affect
every page of their instance.

This is done with a new CustomCSS instance setting that
works pretty much exactly like the Users CustomCSS property.
This custom CSS is then requested for every page load.
User styles/themes take precedence over this CSS.

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

20 files changed, 126 insertions, 25 deletions

diff --git a/internal/api/client/instance/instancepatch.go b/internal/api/client/instance/instancepatch.go
index 64263caf6..5085399eb 100644
--- a/internal/api/client/instance/instancepatch.go
+++ b/internal/api/client/instance/instancepatch.go
@@ -175,6 +175,7 @@ func validateInstanceUpdate(form *apimodel.InstanceSettingsUpdateRequest) error
 		form.ContactEmail == nil &&
 		form.ShortDescription == nil &&
 		form.Description == nil &&
+		form.CustomCSS == nil &&
 		form.Terms == nil &&
 		form.Avatar == nil &&
 		form.AvatarDescription == nil &&
diff --git a/internal/api/model/instance.go b/internal/api/model/instance.go
index 5232e8d66..d59424fa5 100644
--- a/internal/api/model/instance.go
+++ b/internal/api/model/instance.go
@@ -33,6 +33,8 @@ type InstanceSettingsUpdateRequest struct {
 	ShortDescription *string `form:"short_description" json:"short_description" xml:"short_description"`
 	// Longer description of the instance, max 5,000 chars. HTML formatting accepted.
 	Description *string `form:"description" json:"description" xml:"description"`
+	// Custom CSS for the instance.
+	CustomCSS *string `form:"custom_css" json:"custom_css,omitempty" xml:"custom_css"`
 	// Terms and conditions of the instance, max 5,000 chars. HTML formatting accepted.
 	Terms *string `form:"terms" json:"terms" xml:"terms"`
 	// Image to use as the instance thumbnail.
diff --git a/internal/api/model/instancev1.go b/internal/api/model/instancev1.go
index efa6d6faa..6dedd04cc 100644
--- a/internal/api/model/instancev1.go
+++ b/internal/api/model/instancev1.go
@@ -38,6 +38,8 @@ type InstanceV1 struct {
 	//
 	// This should be displayed on the 'about' page for an instance.
 	Description string `json:"description"`
+	// Custom CSS for the instance.
+	CustomCSS string `json:"custom_css,omitempty"`
 	// Raw (unparsed) version of description.
 	DescriptionText string `json:"description_text,omitempty"`
 	// A shorter description of the instance.
diff --git a/internal/api/model/instancev2.go b/internal/api/model/instancev2.go
index 8d6873497..982ed0c63 100644
--- a/internal/api/model/instancev2.go
+++ b/internal/api/model/instancev2.go
@@ -53,6 +53,8 @@ type InstanceV2 struct {
 	Description string `json:"description"`
 	// Raw (unparsed) version of description.
 	DescriptionText string `json:"description_text,omitempty"`
+	// Instance Custom Css
+	CustomCSS string `json:"custom_css,omitempty"`
 	// Basic anonymous usage data for this instance.
 	Usage InstanceV2Usage `json:"usage"`
 	// An image used to represent this instance.
diff --git a/internal/db/bundb/migrations/20240924222938_add_instance_custom_css.go b/internal/db/bundb/migrations/20240924222938_add_instance_custom_css.go
new file mode 100644
index 000000000..14231927a
--- /dev/null
+++ b/internal/db/bundb/migrations/20240924222938_add_instance_custom_css.go
@@ -0,0 +1,44 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// 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 migrations
+
+import (
+	"context"
+	"strings"
+
+	"github.com/uptrace/bun"
+)
+
+func init() {
+	up := func(ctx context.Context, db *bun.DB) error {
+		_, err := db.ExecContext(ctx, "ALTER TABLE ? ADD COLUMN ? TEXT", bun.Ident("instances"), bun.Ident("custom_css"))
+		if err != nil && !(strings.Contains(err.Error(), "already exists") || strings.Contains(err.Error(), "duplicate column name") || strings.Contains(err.Error(), "SQLSTATE 42701")) {
+			return err
+		}
+		return nil
+	}
+
+	down := func(ctx context.Context, db *bun.DB) error {
+		_, err := db.ExecContext(ctx, "ALTER TABLE ? DROP COLUMN ?", bun.Ident("instances"), bun.Ident("custom_css"))
+		return err
+	}
+
+	if err := Migrations.Register(up, down); err != nil {
+		panic(err)
+	}
+}
diff --git a/internal/gtsmodel/instance.go b/internal/gtsmodel/instance.go
index 027d8fba4..97c0268ce 100644
--- a/internal/gtsmodel/instance.go
+++ b/internal/gtsmodel/instance.go
@@ -34,6 +34,7 @@ type Instance struct {
 	ShortDescriptionText   string       `bun:""`                                                            // Raw text version of short description (before parsing).
 	Description            string       `bun:""`                                                            // Longer description of this instance.
 	DescriptionText        string       `bun:""`                                                            // Raw text version of long description (before parsing).
+	CustomCSS              string       `bun:",nullzero"`                                                   // Custom CSS for the instance.
 	Terms                  string       `bun:""`                                                            // Terms and conditions of this instance.
 	TermsText              string       `bun:""`                                                            // Raw text version of terms (before parsing).
 	ContactEmail           string       `bun:""`                                                            // Contact email address for this instance
diff --git a/internal/processing/instance.go b/internal/processing/instance.go
index a9be6db1d..fab71b1de 100644
--- a/internal/processing/instance.go
+++ b/internal/processing/instance.go
@@ -227,6 +227,17 @@ func (p *Processor) InstancePatch(ctx context.Context, form *apimodel.InstanceSe
 		columns = append(columns, []string{"description", "description_text"}...)
 	}
 
+	// validate & update site custom css if it's set on the form
+	if form.CustomCSS != nil {
+		customCSS := *form.CustomCSS
+		if err := validate.InstanceCustomCSS(customCSS); err != nil {
+			return nil, gtserror.NewErrorBadRequest(err, err.Error())
+		}
+
+		instance.CustomCSS = text.SanitizeToPlaintext(customCSS)
+		columns = append(columns, []string{"custom_css"}...)
+	}
+
 	// Validate & update site
 	// terms if set on the form.
 	if form.Terms != nil {
diff --git a/internal/typeutils/internaltofrontend.go b/internal/typeutils/internaltofrontend.go
index 750d4eec4..fda59610b 100644
--- a/internal/typeutils/internaltofrontend.go
+++ b/internal/typeutils/internaltofrontend.go
@@ -1534,6 +1534,7 @@ func (c *Converter) InstanceToAPIV1Instance(ctx context.Context, i *gtsmodel.Ins
 		Title:                i.Title,
 		Description:          i.Description,
 		DescriptionText:      i.DescriptionText,
+		CustomCSS:            i.CustomCSS,
 		ShortDescription:     i.ShortDescription,
 		ShortDescriptionText: i.ShortDescriptionText,
 		Email:                i.ContactEmail,
@@ -1674,6 +1675,7 @@ func (c *Converter) InstanceToAPIV2Instance(ctx context.Context, i *gtsmodel.Ins
 		SourceURL:       instanceSourceURL,
 		Description:     i.Description,
 		DescriptionText: i.DescriptionText,
+		CustomCSS:       i.CustomCSS,
 		Usage:           apimodel.InstanceV2Usage{}, // todo: not implemented
 		Languages:       config.GetInstanceLanguages().TagStrs(),
 		Rules:           c.InstanceRulesToAPIRules(i.Rules),
diff --git a/internal/validate/formvalidation.go b/internal/validate/formvalidation.go
index 207e8e05e..4de7636a5 100644
--- a/internal/validate/formvalidation.go
+++ b/internal/validate/formvalidation.go
@@ -189,6 +189,16 @@ func CustomCSS(customCSS string) error {
 	return nil
 }
 
+func InstanceCustomCSS(customCSS string) error {
+
+	maximumCustomCSSLength := config.GetAccountsCustomCSSLength()
+	if length := len([]rune(customCSS)); length > maximumCustomCSSLength {
+		return fmt.Errorf("custom_css must be less than %d characters, but submitted custom_css was %d characters", maximumCustomCSSLength, length)
+	}
+
+	return nil
+}
+
 // EmojiShortcode just runs the given shortcode through the regular expression
 // for emoji shortcodes, to figure out whether it's a valid shortcode, ie., 1-30 characters,
 // a-zA-Z, numbers, and underscores.
diff --git a/internal/web/about.go b/internal/web/about.go
index 2bc558962..843dda652 100644
--- a/internal/web/about.go
+++ b/internal/web/about.go
@@ -54,7 +54,7 @@ func (m *Module) aboutGETHandler(c *gin.Context) {
 		Template:    "about.tmpl",
 		Instance:    instance,
 		OGMeta:      apiutil.OGBase(instance),
-		Stylesheets: []string{cssAbout},
+		Stylesheets: []string{cssAbout, instanceCustomCSSPath},
 		Extra: map[string]any{
 			"showStrap":        true,
 			"blocklistExposed": config.GetInstanceExposeSuspendedWeb(),
diff --git a/internal/web/confirmemail.go b/internal/web/confirmemail.go
index e512761f4..21028c6c4 100644
--- a/internal/web/confirmemail.go
+++ b/internal/web/confirmemail.go
@@ -127,8 +127,9 @@ func (m *Module) confirmEmailPOSTHandler(c *gin.Context) {
 	// Serve page informing user that their
 	// email address is now confirmed.
 	page := apiutil.WebPage{
-		Template: "confirmed_email.tmpl",
-		Instance: instance,
+		Template:    "confirmed_email.tmpl",
+		Instance:    instance,
+		Stylesheets: []string{instanceCustomCSSPath},
 		Extra: map[string]any{
 			"email":    user.Email,
 			"username": user.Account.Username,
diff --git a/internal/web/customcss.go b/internal/web/customcss.go
index b4072f2a7..36ae9de55 100644
--- a/internal/web/customcss.go
+++ b/internal/web/customcss.go
@@ -55,3 +55,22 @@ func (m *Module) customCSSGETHandler(c *gin.Context) {
 	c.Header(cacheControlHeader, cacheControlNoCache)
 	c.Data(http.StatusOK, textCSSUTF8, []byte(customCSS))
 }
+
+func (m *Module) instanceCustomCSSGETHandler(c *gin.Context) {
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.TextCSS); err != nil {
+		apiutil.WebErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	instanceV1, errWithCode := m.processor.InstanceGetV1(c.Request.Context())
+	if errWithCode != nil {
+		apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	instanceCustomCSS := instanceV1.CustomCSS
+
+	c.Header(cacheControlHeader, cacheControlNoCache)
+	c.Data(http.StatusOK, textCSSUTF8, []byte(instanceCustomCSS))
+}
diff --git a/internal/web/domain-blocklist.go b/internal/web/domain-blocklist.go
index 5d631e0f7..7b6710049 100644
--- a/internal/web/domain-blocklist.go
+++ b/internal/web/domain-blocklist.go
@@ -67,7 +67,7 @@ func (m *Module) domainBlockListGETHandler(c *gin.Context) {
 		Template:    "domain-blocklist.tmpl",
 		Instance:    instance,
 		OGMeta:      apiutil.OGBase(instance),
-		Stylesheets: []string{cssFA},
+		Stylesheets: []string{cssFA, instanceCustomCSSPath},
 		Javascript:  []string{jsFrontend},
 		Extra:       map[string]any{"blocklist": domainBlocks},
 	}
diff --git a/internal/web/index.go b/internal/web/index.go
index 25960cf7f..dd9d80561 100644
--- a/internal/web/index.go
+++ b/internal/web/index.go
@@ -59,7 +59,7 @@ func (m *Module) indexHandler(c *gin.Context) {
 		Template:    "index.tmpl",
 		Instance:    instance,
 		OGMeta:      apiutil.OGBase(instance),
-		Stylesheets: []string{cssAbout, cssIndex},
+		Stylesheets: []string{cssAbout, cssIndex, instanceCustomCSSPath},
 		Extra:       map[string]any{"showStrap": true},
 	}
 
diff --git a/internal/web/profile.go b/internal/web/profile.go
index 60157fd19..741dc2a83 100644
--- a/internal/web/profile.go
+++ b/internal/web/profile.go
@@ -132,7 +132,7 @@ func (m *Module) profileGETHandler(c *gin.Context) {
 	}
 
 	// Prepare stylesheets for profile.
-	stylesheets := make([]string, 0, 6)
+	stylesheets := make([]string, 0, 7)
 
 	// Basic profile stylesheets.
 	stylesheets = append(
@@ -142,6 +142,7 @@ func (m *Module) profileGETHandler(c *gin.Context) {
 			cssStatus,
 			cssThread,
 			cssProfile,
+			instanceCustomCSSPath,
 		}...,
 	)
 
diff --git a/internal/web/settings-panel.go b/internal/web/settings-panel.go
index ec8166e95..41cd8666e 100644
--- a/internal/web/settings-panel.go
+++ b/internal/web/settings-panel.go
@@ -53,6 +53,7 @@ func (m *Module) SettingsPanelHandler(c *gin.Context) {
 			cssProfile, // Used for rendering stub/fake profiles.
 			cssStatus,  // Used for rendering stub/fake statuses.
 			cssSettings,
+			instanceCustomCSSPath,
 		},
 		Javascript: []string{jsSettings},
 	}
diff --git a/internal/web/signup.go b/internal/web/signup.go
index a943f3680..64b9f4e2d 100644
--- a/internal/web/signup.go
+++ b/internal/web/signup.go
@@ -126,9 +126,10 @@ func (m *Module) signupPOSTHandler(c *gin.Context) {
 	// Serve a page informing the
 	// user that they've signed up.
 	page := apiutil.WebPage{
-		Template: "signed-up.tmpl",
-		Instance: instance,
-		OGMeta:   apiutil.OGBase(instance),
+		Template:    "signed-up.tmpl",
+		Instance:    instance,
+		Stylesheets: []string{instanceCustomCSSPath},
+		OGMeta:      apiutil.OGBase(instance),
 		Extra: map[string]any{
 			"email":    user.UnconfirmedEmail,
 			"username": user.Account.Username,
diff --git a/internal/web/tag.go b/internal/web/tag.go
index 5c3cd31a6..423000f99 100644
--- a/internal/web/tag.go
+++ b/internal/web/tag.go
@@ -59,7 +59,7 @@ func (m *Module) tagGETHandler(c *gin.Context) {
 		Template:    "tag.tmpl",
 		Instance:    instance,
 		OGMeta:      apiutil.OGBase(instance),
-		Stylesheets: []string{cssFA, cssThread, cssTag},
+		Stylesheets: []string{cssFA, cssThread, cssTag, instanceCustomCSSPath},
 		Extra:       map[string]any{"tagName": tagName},
 	}
 
diff --git a/internal/web/thread.go b/internal/web/thread.go
index d3ba6ea5e..246c05b97 100644
--- a/internal/web/thread.go
+++ b/internal/web/thread.go
@@ -115,7 +115,7 @@ func (m *Module) threadGETHandler(c *gin.Context) {
 	}
 
 	// Prepare stylesheets for thread.
-	stylesheets := make([]string, 0, 5)
+	stylesheets := make([]string, 0, 6)
 
 	// Basic thread stylesheets.
 	stylesheets = append(
@@ -131,6 +131,7 @@ func (m *Module) threadGETHandler(c *gin.Context) {
 	if theme := targetAccount.Theme; theme != "" {
 		stylesheets = append(
 			stylesheets,
+			instanceCustomCSSPath,
 			themesPathPrefix+"/"+theme,
 		)
 	}
diff --git a/internal/web/web.go b/internal/web/web.go
index 185bf7120..35f8f21b0 100644
--- a/internal/web/web.go
+++ b/internal/web/web.go
@@ -36,20 +36,21 @@ import (
 )
 
 const (
-	confirmEmailPath   = "/" + uris.ConfirmEmailPath
-	profileGroupPath   = "/@:username"
-	statusPath         = "/statuses/:" + apiutil.WebStatusIDKey // leave out the '/@:username' prefix as this will be served within the profile group
-	tagsPath           = "/tags/:" + apiutil.TagNameKey
-	customCSSPath      = profileGroupPath + "/custom.css"
-	rssFeedPath        = profileGroupPath + "/feed.rss"
-	assetsPathPrefix   = "/assets"
-	distPathPrefix     = assetsPathPrefix + "/dist"
-	themesPathPrefix   = assetsPathPrefix + "/themes"
-	settingsPathPrefix = "/settings"
-	settingsPanelGlob  = settingsPathPrefix + "/*panel"
-	userPanelPath      = settingsPathPrefix + "/user"
-	adminPanelPath     = settingsPathPrefix + "/admin"
-	signupPath         = "/signup"
+	confirmEmailPath      = "/" + uris.ConfirmEmailPath
+	profileGroupPath      = "/@:username"
+	statusPath            = "/statuses/:" + apiutil.WebStatusIDKey // leave out the '/@:username' prefix as this will be served within the profile group
+	tagsPath              = "/tags/:" + apiutil.TagNameKey
+	customCSSPath         = profileGroupPath + "/custom.css"
+	instanceCustomCSSPath = "/custom.css"
+	rssFeedPath           = profileGroupPath + "/feed.rss"
+	assetsPathPrefix      = "/assets"
+	distPathPrefix        = assetsPathPrefix + "/dist"
+	themesPathPrefix      = assetsPathPrefix + "/themes"
+	settingsPathPrefix    = "/settings"
+	settingsPanelGlob     = settingsPathPrefix + "/*panel"
+	userPanelPath         = settingsPathPrefix + "/user"
+	adminPanelPath        = settingsPathPrefix + "/admin"
+	signupPath            = "/signup"
 
 	cacheControlHeader    = "Cache-Control"     // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
 	cacheControlNoCache   = "no-cache"          // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control#response_directives
@@ -114,6 +115,7 @@ func (m *Module) Route(r *router.Router, mi ...gin.HandlerFunc) {
 	r.AttachHandler(http.MethodGet, settingsPathPrefix, m.SettingsPanelHandler)
 	r.AttachHandler(http.MethodGet, settingsPanelGlob, m.SettingsPanelHandler)
 	r.AttachHandler(http.MethodGet, customCSSPath, m.customCSSGETHandler)
+	r.AttachHandler(http.MethodGet, instanceCustomCSSPath, m.instanceCustomCSSGETHandler)
 	r.AttachHandler(http.MethodGet, rssFeedPath, m.rssFeedGETHandler)
 	r.AttachHandler(http.MethodGet, confirmEmailPath, m.confirmEmailGETHandler)
 	r.AttachHandler(http.MethodPost, confirmEmailPath, m.confirmEmailPOSTHandler)