From 45d0de234b4dbfd58d25b36bf7e82ae7a54d07b5 Mon Sep 17 00:00:00 2001
From: Howl <the@howl.moe>
Date: Wed, 6 Jul 2016 19:24:11 +0200
Subject: [PATCH] Fix race condition in specificRateLimiter

---
 app/rate_limiter.go | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/app/rate_limiter.go b/app/rate_limiter.go
index e162c92..b211501 100644
--- a/app/rate_limiter.go
+++ b/app/rate_limiter.go
@@ -1,6 +1,7 @@
 package app
 
 import (
+	"fmt"
 	"strconv"
 	"sync"
 	"time"
@@ -51,15 +52,30 @@ func (s *specificRateLimiter) Request(u string, perMinute int) {
 	if !exists {
 		c = makePrefilledChan(perMinute)
 		s.Mutex.Lock()
-		s.Map[u] = c
-		s.Mutex.Unlock()
-		<-c
-		go s.filler(u, perMinute)
+		// Now that we have exclusive read and write-access, we want to
+		// make sure we don't overwrite an existing channel. Otherwise,
+		// race conditions and panic happen.
+		if cNew, exists := s.Map[u]; exists {
+			c = cNew
+			s.Mutex.Unlock()
+		} else {
+			s.Map[u] = c
+			s.Mutex.Unlock()
+			<-c
+			go s.filler(u, perMinute)
+		}
 	}
 	<-c
 }
 
 func (s *specificRateLimiter) filler(el string, perMinute int) {
+	defer func() {
+		r := recover()
+		if r != nil {
+			fmt.Println(r)
+		}
+	}()
+
 	s.Mutex.RLock()
 	c := s.Map[el]
 	s.Mutex.RUnlock()