[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

8 files changed, 316 insertions, 69 deletions

diff --git a/internal/api/nodeinfo.go b/internal/api/nodeinfo.go
index 29942aba4..2f0c234fd 100644
--- a/internal/api/nodeinfo.go
+++ b/internal/api/nodeinfo.go
@@ -20,6 +20,7 @@ package api
 import (
 	"github.com/gin-gonic/gin"
 	"github.com/superseriousbusiness/gotosocial/internal/api/nodeinfo"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/middleware"
 	"github.com/superseriousbusiness/gotosocial/internal/processing"
 	"github.com/superseriousbusiness/gotosocial/internal/router"
@@ -43,6 +44,16 @@ func (w *NodeInfo) Route(r *router.Router, m ...gin.HandlerFunc) {
 		}),
 	)
 
+	// If instance is configured to serve instance stats
+	// faithfully at nodeinfo, we should allow robots to
+	// crawl nodeinfo endpoints in a limited capacity.
+	// In all other cases, disallow everything.
+	if config.GetInstanceStatsMode() == config.InstanceStatsModeServe {
+		nodeInfoGroup.Use(middleware.RobotsHeaders("allowSome"))
+	} else {
+		nodeInfoGroup.Use(middleware.RobotsHeaders(""))
+	}
+
 	w.nodeInfo.Route(nodeInfoGroup.Handle)
 }
 
diff --git a/internal/api/robots.go b/internal/api/robots.go
new file mode 100644
index 000000000..3ed8282f5
--- /dev/null
+++ b/internal/api/robots.go
@@ -0,0 +1,52 @@
+// 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 api
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/api/robots"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
+	"github.com/superseriousbusiness/gotosocial/internal/router"
+)
+
+type Robots struct {
+	robots *robots.Module
+}
+
+func (rb *Robots) Route(r *router.Router, m ...gin.HandlerFunc) {
+	// Create a group so we can attach middlewares.
+	robotsGroup := r.AttachGroup("robots.txt")
+
+	// Use passed-in middlewares.
+	robotsGroup.Use(m...)
+
+	// Allow caching for 24 hrs.
+	// https://www.rfc-editor.org/rfc/rfc9309.html#section-2.4
+	robotsGroup.Use(
+		middleware.CacheControl(middleware.CacheControlConfig{
+			Directives: []string{"public", "max-age=86400"},
+			Vary:       []string{"Accept-Encoding"},
+		}),
+	)
+
+	rb.robots.Route(robotsGroup.Handle)
+}
+
+func NewRobots() *Robots {
+	return &Robots{}
+}
diff --git a/internal/api/robots/robots.go b/internal/api/robots/robots.go
new file mode 100644
index 000000000..98db4682d
--- /dev/null
+++ b/internal/api/robots/robots.go
@@ -0,0 +1,57 @@
+// 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 robots
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+)
+
+type Module struct{}
+
+func New() *Module {
+	return &Module{}
+}
+
+func (m *Module) Route(attachHandler func(method string, path string, f ...gin.HandlerFunc) gin.IRoutes) {
+	// Serve different robots.txt file depending on instance
+	// stats mode: Don't disallow scraping nodeinfo if admin
+	// has opted in to serving accurate stats there. In all
+	// other cases, disallow scraping nodeinfo.
+	var handler gin.HandlerFunc
+	if config.GetInstanceStatsMode() == config.InstanceStatsModeServe {
+		handler = m.robotsGETHandler
+	} else {
+		handler = m.robotsGETHandlerDisallowNodeInfo
+	}
+
+	// Attach handler at empty path as this
+	// is already grouped under /robots.txt.
+	attachHandler(http.MethodGet, "", handler)
+}
+
+func (m *Module) robotsGETHandler(c *gin.Context) {
+	c.String(http.StatusOK, apiutil.RobotsTxt)
+}
+
+func (m *Module) robotsGETHandlerDisallowNodeInfo(c *gin.Context) {
+	c.String(http.StatusOK, apiutil.RobotsTxtDisallowNodeInfo)
+}
diff --git a/internal/api/util/robots.go b/internal/api/util/robots.go
new file mode 100644
index 000000000..49fb04561
--- /dev/null
+++ b/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/
+`
+)
diff --git a/internal/api/wellknown/hostmeta/hostmeta.go b/internal/api/wellknown/hostmeta/hostmeta.go
index cb439fcd3..43c6b161e 100644
--- a/internal/api/wellknown/hostmeta/hostmeta.go
+++ b/internal/api/wellknown/hostmeta/hostmeta.go
@@ -21,6 +21,7 @@ import (
 	"net/http"
 
 	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
 	"github.com/superseriousbusiness/gotosocial/internal/processing"
 )
 
@@ -40,5 +41,6 @@ func New(processor *processing.Processor) *Module {
 }
 
 func (m *Module) Route(attachHandler func(method string, path string, f ...gin.HandlerFunc) gin.IRoutes) {
-	attachHandler(http.MethodGet, HostMetaPath, m.HostMetaGETHandler)
+	// Attach handler, injecting robots http header middleware to disallow all.
+	attachHandler(http.MethodGet, HostMetaPath, middleware.RobotsHeaders(""), m.HostMetaGETHandler)
 }
diff --git a/internal/api/wellknown/nodeinfo/nodeinfo.go b/internal/api/wellknown/nodeinfo/nodeinfo.go
index 9012006f4..270dde2b1 100644
--- a/internal/api/wellknown/nodeinfo/nodeinfo.go
+++ b/internal/api/wellknown/nodeinfo/nodeinfo.go
@@ -21,6 +21,10 @@ import (
 	"net/http"
 
 	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
 	"github.com/superseriousbusiness/gotosocial/internal/processing"
 )
 
@@ -42,5 +46,57 @@ func New(processor *processing.Processor) *Module {
 }
 
 func (m *Module) Route(attachHandler func(method string, path string, f ...gin.HandlerFunc) gin.IRoutes) {
-	attachHandler(http.MethodGet, NodeInfoWellKnownPath, m.NodeInfoWellKnownGETHandler)
+	// If instance is configured to serve instance stats
+	// faithfully at nodeinfo, we should allow robots to
+	// crawl nodeinfo endpoints in a limited capacity.
+	// In all other cases, disallow everything.
+	var robots gin.HandlerFunc
+	if config.GetInstanceStatsMode() == config.InstanceStatsModeServe {
+		robots = middleware.RobotsHeaders("allowSome")
+	} else {
+		robots = middleware.RobotsHeaders("")
+	}
+
+	// Attach handler, injecting robots http header middleware.
+	attachHandler(http.MethodGet, NodeInfoWellKnownPath, robots, m.NodeInfoWellKnownGETHandler)
+}
+
+// NodeInfoWellKnownGETHandler swagger:operation GET /.well-known/nodeinfo nodeInfoWellKnownGet
+//
+// Returns a well-known response which redirects callers to `/nodeinfo/2.0`.
+//
+// eg. `{"links":[{"rel":"http://nodeinfo.diaspora.software/ns/schema/2.0","href":"http://example.org/nodeinfo/2.0"}]}`
+// See: https://nodeinfo.diaspora.software/protocol.html
+//
+//	---
+//	tags:
+//	- .well-known
+//
+//	produces:
+//	- application/json
+//
+//	responses:
+//		'200':
+//			schema:
+//				"$ref": "#/definitions/wellKnownResponse"
+func (m *Module) NodeInfoWellKnownGETHandler(c *gin.Context) {
+	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	resp, errWithCode := m.processor.Fedi().NodeInfoRelGet(c.Request.Context())
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	// Encode JSON HTTP response.
+	apiutil.EncodeJSONResponse(
+		c.Writer,
+		c.Request,
+		http.StatusOK,
+		apiutil.AppJSON,
+		resp,
+	)
 }
diff --git a/internal/api/wellknown/nodeinfo/nodeinfoget.go b/internal/api/wellknown/nodeinfo/nodeinfoget.go
deleted file mode 100644
index c458f131e..000000000
--- a/internal/api/wellknown/nodeinfo/nodeinfoget.go
+++ /dev/null
@@ -1,66 +0,0 @@
-// 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 nodeinfo
-
-import (
-	"net/http"
-
-	"github.com/gin-gonic/gin"
-	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
-	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
-)
-
-// NodeInfoWellKnownGETHandler swagger:operation GET /.well-known/nodeinfo nodeInfoWellKnownGet
-//
-// Returns a well-known response which redirects callers to `/nodeinfo/2.0`.
-//
-// eg. `{"links":[{"rel":"http://nodeinfo.diaspora.software/ns/schema/2.0","href":"http://example.org/nodeinfo/2.0"}]}`
-// See: https://nodeinfo.diaspora.software/protocol.html
-//
-//	---
-//	tags:
-//	- .well-known
-//
-//	produces:
-//	- application/json
-//
-//	responses:
-//		'200':
-//			schema:
-//				"$ref": "#/definitions/wellKnownResponse"
-func (m *Module) NodeInfoWellKnownGETHandler(c *gin.Context) {
-	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
-		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
-		return
-	}
-
-	resp, errWithCode := m.processor.Fedi().NodeInfoRelGet(c.Request.Context())
-	if errWithCode != nil {
-		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
-		return
-	}
-
-	// Encode JSON HTTP response.
-	apiutil.EncodeJSONResponse(
-		c.Writer,
-		c.Request,
-		http.StatusOK,
-		apiutil.AppJSON,
-		resp,
-	)
-}
diff --git a/internal/api/wellknown/webfinger/webfinger.go b/internal/api/wellknown/webfinger/webfinger.go
index a50013b32..c70afab9d 100644
--- a/internal/api/wellknown/webfinger/webfinger.go
+++ b/internal/api/wellknown/webfinger/webfinger.go
@@ -21,6 +21,7 @@ import (
 	"net/http"
 
 	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
 	"github.com/superseriousbusiness/gotosocial/internal/processing"
 )
 
@@ -41,5 +42,6 @@ func New(processor *processing.Processor) *Module {
 }
 
 func (m *Module) Route(attachHandler func(method string, path string, f ...gin.HandlerFunc) gin.IRoutes) {
-	attachHandler(http.MethodGet, WebfingerBasePath, m.WebfingerGETRequest)
+	// Attach handler, injecting robots http header middleware to disallow all.
+	attachHandler(http.MethodGet, WebfingerBasePath, middleware.RobotsHeaders(""), m.WebfingerGETRequest)
 }