[chore] The Big Middleware and API Refactor (tm) (#1250)

* interim commit: start refactoring middlewares into package under router

* another interim commit, this is becoming a big job

* another fucking massive interim commit

* refactor bookmarks to new style

* ambassador, wiz zeze commits you are spoiling uz

* she compiles, we're getting there

* we're just normal men; we're just innocent men

* apiutil

* whoopsie

* i'm glad noone reads commit msgs haha :blob_sweat:

* use that weirdo go-bytesize library for maxMultipartMemory

* fix media module paths

1 files changed, 77 insertions, 0 deletions

diff --git a/internal/middleware/ratelimit.go b/internal/middleware/ratelimit.go
new file mode 100644
index 000000000..ab947a124
--- /dev/null
+++ b/internal/middleware/ratelimit.go
@@ -0,0 +1,77 @@
+/*
+   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 middleware
+
+import (
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/ulule/limiter/v3"
+	limitergin "github.com/ulule/limiter/v3/drivers/middleware/gin"
+	"github.com/ulule/limiter/v3/drivers/store/memory"
+)
+
+const rateLimitPeriod = 5 * time.Minute
+
+// RateLimit 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, the request is aborted and an HTTP 429 TooManyRequests
+// status is returned.
+//
+// If the config AdvancedRateLimitRequests value is <= 0, then a noop handler will be returned,
+// which performs no rate limiting.
+func RateLimit() gin.HandlerFunc {
+	// only enable rate limit middleware if configured
+	// advanced-rate-limit-requests is greater than 0
+	rateLimitRequests := config.GetAdvancedRateLimitRequests()
+	if rateLimitRequests <= 0 {
+		// use noop middleware if ratelimiting is disabled
+		return func(c *gin.Context) {}
+	}
+
+	rate := limiter.Rate{
+		Period: rateLimitPeriod,
+		Limit:  int64(rateLimitRequests),
+	}
+
+	limiterInstance := limiter.New(
+		memory.NewStore(),
+		rate,
+		limiter.WithIPv6Mask(net.CIDRMask(64, 128)), // apply /64 mask to IPv6 addresses
+	)
+
+	limitReachedHandler := func(c *gin.Context) {
+		c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{"error": "rate limit reached"})
+	}
+
+	middleware := limitergin.NewMiddleware(
+		limiterInstance,
+		limitergin.WithLimitReachedHandler(limitReachedHandler), // use custom rate limit reached error
+	)
+
+	return middleware
+}