[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

3 files changed, 22 insertions, 0 deletions

diff --git a/internal/processing/account/account.go b/internal/processing/account/account.go
index 868308efe..aca46394a 100644
--- a/internal/processing/account/account.go
+++ b/internal/processing/account/account.go
@@ -51,6 +51,8 @@ type Processor interface {
 	Get(ctx context.Context, requestingAccount *gtsmodel.Account, targetAccountID string) (*apimodel.Account, gtserror.WithCode)
 	// GetLocalByUsername processes the given request for account information targeting a local account by username.
 	GetLocalByUsername(ctx context.Context, requestingAccount *gtsmodel.Account, username string) (*apimodel.Account, gtserror.WithCode)
+	// GetCustomCSSForUsername returns custom css for the given local username.
+	GetCustomCSSForUsername(ctx context.Context, username string) (string, gtserror.WithCode)
 	// Update processes the update of an account with the given form
 	Update(ctx context.Context, account *gtsmodel.Account, form *apimodel.UpdateCredentialsRequest) (*apimodel.Account, gtserror.WithCode)
 	// StatusesGet fetches a number of statuses (in time descending order) from the given account, filtered by visibility for
diff --git a/internal/processing/account/get.go b/internal/processing/account/get.go
index c558b52ed..7d373bc8c 100644
--- a/internal/processing/account/get.go
+++ b/internal/processing/account/get.go
@@ -55,6 +55,18 @@ func (p *processor) GetLocalByUsername(ctx context.Context, requestingAccount *g
 	return p.getAccountFor(ctx, requestingAccount, targetAccount)
 }
 
+func (p *processor) GetCustomCSSForUsername(ctx context.Context, username string) (string, gtserror.WithCode) {
+	customCSS, err := p.db.GetAccountCustomCSSByUsername(ctx, username)
+	if err != nil {
+		if err == db.ErrNoEntries {
+			return "", gtserror.NewErrorNotFound(errors.New("account not found"))
+		}
+		return "", gtserror.NewErrorInternalError(fmt.Errorf("db error: %s", err))
+	}
+
+	return customCSS, nil
+}
+
 func (p *processor) getAccountFor(ctx context.Context, requestingAccount *gtsmodel.Account, targetAccount *gtsmodel.Account) (*apimodel.Account, gtserror.WithCode) {
 	var blocked bool
 	var err error
diff --git a/internal/processing/account/update.go b/internal/processing/account/update.go
index 3b844a160..47c4a2b4b 100644
--- a/internal/processing/account/update.go
+++ b/internal/processing/account/update.go
@@ -124,6 +124,14 @@ func (p *processor) Update(ctx context.Context, account *gtsmodel.Account, form
 		}
 	}
 
+	if form.CustomCSS != nil {
+		customCSS := *form.CustomCSS
+		if err := validate.CustomCSS(customCSS); err != nil {
+			return nil, gtserror.NewErrorBadRequest(err, err.Error())
+		}
+		account.CustomCSS = text.SanitizePlaintext(customCSS)
+	}
+
 	updatedAccount, err := p.db.UpdateAccount(ctx, account)
 	if err != nil {
 		return nil, gtserror.NewErrorInternalError(fmt.Errorf("could not update account %s: %s", account.ID, err))