[feature] Use X-Robots-Tag headers to instruct scrapers/crawlers (#3737)

* [feature] Use `X-Robots-Tag` headers to instruct scrapers/crawlers

* use switch for RobotsHeaders

internal/api/util/robots.go

@@ -0,0 +1,133 @@
+// 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 util
+
+// See:
+//
+//   - https://developers.google.com/search/docs/crawling-indexing/robots-meta-tag#robotsmeta
+//   - https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Robots-Tag
+//   - https://www.rfc-editor.org/rfc/rfc9309.html
+const (
+	RobotsDirectivesDisallow  = "noindex, nofollow"
+	RobotsDirectivesAllowSome = "nofollow, noarchive, nositelinkssearchbox, max-image-preview:standard"
+	RobotsTxt                 = `# GoToSocial robots.txt -- to edit, see internal/api/util/robots.go
+# More info @ https://developers.google.com/search/docs/crawling-indexing/robots/intro
+
+# AI scrapers and the like.
+# https://github.com/ai-robots-txt/ai.robots.txt/
+User-agent: AI2Bot
+User-agent: Ai2Bot-Dolma
+User-agent: Amazonbot
+User-agent: anthropic-ai
+User-agent: Applebot
+User-agent: Applebot-Extended
+User-agent: Bytespider
+User-agent: CCBot
+User-agent: ChatGPT-User
+User-agent: ClaudeBot
+User-agent: Claude-Web
+User-agent: cohere-ai
+User-agent: cohere-training-data-crawler
+User-agent: Diffbot
+User-agent: DuckAssistBot
+User-agent: FacebookBot
+User-agent: FriendlyCrawler
+User-agent: Google-Extended
+User-agent: GoogleOther
+User-agent: GoogleOther-Image
+User-agent: GoogleOther-Video
+User-agent: GPTBot
+User-agent: iaskspider/2.0
+User-agent: ICC-Crawler
+User-agent: ImagesiftBot
+User-agent: img2dataset
+User-agent: ISSCyberRiskCrawler
+User-agent: Kangaroo Bot
+User-agent: Meta-ExternalAgent
+User-agent: Meta-ExternalFetcher
+User-agent: OAI-SearchBot
+User-agent: omgili
+User-agent: omgilibot
+User-agent: PanguBot
+User-agent: PerplexityBot
+User-agent: PetalBot
+User-agent: Scrapy
+User-agent: Sidetrade indexer bot
+User-agent: Timpibot
+User-agent: VelenPublicWebCrawler
+User-agent: Webzio-Extended
+User-agent: YouBot
+Disallow: /
+
+# Marketing/SEO "intelligence" data scrapers
+User-agent: AwarioRssBot
+User-agent: AwarioSmartBot
+User-agent: DataForSeoBot
+User-agent: magpie-crawler
+User-agent: Meltwater
+User-agent: peer39_crawler
+User-agent: peer39_crawler/1.0
+User-agent: PiplBot
+User-agent: scoop.it
+User-agent: Seekr
+Disallow: /
+
+# Well-known.dev crawler. Indexes stuff under /.well-known.
+# https://well-known.dev/about/
+User-agent: WellKnownBot
+Disallow: /
+
+# Rules for everything else.
+User-agent: *
+Crawl-delay: 500
+
+# API endpoints.
+Disallow: /api/
+
+# Auth/Sign in endpoints.
+Disallow: /auth/
+Disallow: /oauth/
+Disallow: /check_your_email
+Disallow: /wait_for_approval
+Disallow: /account_disabled
+Disallow: /signup
+
+# Fileserver/media.
+Disallow: /fileserver/
+
+# Fedi S2S API endpoints.
+Disallow: /users/
+Disallow: /emoji/
+
+# Settings panels.
+Disallow: /admin
+Disallow: /user
+Disallow: /settings/
+
+# Domain blocklist.
+Disallow: /about/suspended
+
+# Webfinger endpoint.
+Disallow: /.well-known/webfinger
+`
+	RobotsTxtDisallowNodeInfo = RobotsTxt + `
+# Disallow nodeinfo
+Disallow: /.well-known/nodeinfo
+Disallow: /nodeinfo/
+`
+)