[feature] add rate limit middleware (#741)

* feat: add rate limit middleware

* chore: update vendor dir

* chore: update readme with new dependency

* chore: add rate limit infos to swagger.md file

* refactor: add ipv6 mask limiter option

Add IPv6 CIDR /64 mask

* refactor: increase rate limit to 1000

Address https://github.com/superseriousbusiness/gotosocial/pull/741#discussion_r945584800

Co-authored-by: tobi <31960611+tsmethurst@users.noreply.github.com>

internal/api/security/ratelimit.go

@@ -0,0 +1,70 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   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 security
+
+import (
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	limiter "github.com/ulule/limiter/v3"
+	mgin "github.com/ulule/limiter/v3/drivers/middleware/gin"
+	memory "github.com/ulule/limiter/v3/drivers/store/memory"
+)
+
+type RateLimitOptions struct {
+	Period time.Duration
+	Limit  int64
+}
+
+func (m *Module) LimitReachedHandler(c *gin.Context) {
+	code := http.StatusTooManyRequests
+	c.AbortWithStatusJSON(code, gin.H{"error": "rate limit reached"})
+}
+
+// returns a gin middleware that will automatically rate limit caller (by IP address)
+// and enrich the response header with the following headers:
+// - `x-ratelimit-limit` maximum number of requests allowed per time period (fixed)
+// - `x-ratelimit-remaining` number of remaining requests that can still be performed
+// - `x-ratelimit-reset` unix timestamp when the rate limit will reset
+// if `x-ratelimit-limit` is exceeded an HTTP 429 error is returned
+func (m *Module) RateLimit(rateOptions RateLimitOptions) func(c *gin.Context) {
+	rate := limiter.Rate{
+		Period: rateOptions.Period,
+		Limit:  rateOptions.Limit,
+	}
+
+	store := memory.NewStore()
+
+	limiterInstance := limiter.New(
+		store,
+		rate,
+		// apply /64 mask to IPv6 addresses
+		limiter.WithIPv6Mask(net.CIDRMask(64, 128)),
+	)
+
+	middleware := mgin.NewMiddleware(
+		limiterInstance,
+		// use custom rate limit reached error
+		mgin.WithLimitReachedHandler(m.LimitReachedHandler),
+	)
+
+	return middleware
+}