[feature/performance] Wrap incoming HTTP requests in timeout handler (#2353)

* deinterface router, start messing about with deadlines

* weeeee

* thanks linter (thinter)

* write Connection: close when timing out requests

* update wording

* don't replace req

* don't bother with fancy Cause functions (I'll use them one day...)

internal/router/timeout.go

@@ -0,0 +1,61 @@
+// 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 router
+
+import (
+	"context"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+const requestTimeout = 10 * time.Minute
+
+type timeoutHandler struct {
+	*gin.Engine
+}
+
+// ServeHTTP wraps the embedded Gin engine's ServeHTTP
+// function with an injected context which times out
+// non-upgraded inbound requests after 10 minutes.
+func (th timeoutHandler) ServeHTTP(
+	w http.ResponseWriter,
+	r *http.Request,
+) {
+	if upgr := r.Header.Get("Upgrade"); upgr != "" {
+		// Upgrade to wss (probably).
+		// Leave well enough alone.
+		th.Engine.ServeHTTP(w, r)
+		return
+	}
+
+	// Create timeout ctx.
+	toCtx, cancelCtx := context.WithTimeout(
+		r.Context(),
+		requestTimeout,
+	)
+	defer cancelCtx()
+
+	// Serve the request using a shallow copy
+	// with the new context, without replacing
+	// the underlying request, since the latter
+	// may be used later outside of the Gin
+	// engine for post-request cleanup tasks.
+	th.Engine.ServeHTTP(w, r.WithContext(toCtx))
+}