From 8b575f77713e60205e7b38d6f87b102ff00c7461 Mon Sep 17 00:00:00 2001
From: Knut Ahlers <knut@ahlers.me>
Date: Thu, 1 Apr 2021 12:28:51 +0200
Subject: [PATCH] Fix: Concurrent access to map panic

Signed-off-by: Knut Ahlers <knut@ahlers.me>
---
 twitch.go         |  4 ++--
 twitchAPICache.go | 28 ++++++++++++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/twitch.go b/twitch.go
index f9eb942..79cf064 100644
--- a/twitch.go
+++ b/twitch.go
@@ -15,12 +15,12 @@ import (
 var twitch = newTwitchClient()
 
 type twitchClient struct {
-	apiCache twitchAPICache
+	apiCache *twitchAPICache
 }
 
 func newTwitchClient() *twitchClient {
 	return &twitchClient{
-		apiCache: make(twitchAPICache),
+		apiCache: newTwitchAPICache(),
 	}
 }
 
diff --git a/twitchAPICache.go b/twitchAPICache.go
index 894ad12..6812bf4 100644
--- a/twitchAPICache.go
+++ b/twitchAPICache.go
@@ -4,19 +4,32 @@ import (
 	"crypto/sha256"
 	"fmt"
 	"strings"
+	"sync"
 	"time"
 )
 
 type (
-	twitchAPICache      map[string]twitchAPICacheEntry
+	twitchAPICache struct {
+		data map[string]twitchAPICacheEntry
+		lock sync.RWMutex
+	}
 	twitchAPICacheEntry struct {
 		Data       interface{}
 		ValidUntil time.Time
 	}
 )
 
-func (t twitchAPICache) Get(key []string) interface{} {
-	e := t[t.deriveKey(key)]
+func newTwitchAPICache() *twitchAPICache {
+	return &twitchAPICache{
+		data: make(map[string]twitchAPICacheEntry),
+	}
+}
+
+func (t *twitchAPICache) Get(key []string) interface{} {
+	t.lock.RLock()
+	defer t.lock.RUnlock()
+
+	e := t.data[t.deriveKey(key)]
 	if e.ValidUntil.Before(time.Now()) {
 		return nil
 	}
@@ -24,14 +37,17 @@ func (t twitchAPICache) Get(key []string) interface{} {
 	return e.Data
 }
 
-func (t twitchAPICache) Set(key []string, valid time.Duration, data interface{}) {
-	t[t.deriveKey(key)] = twitchAPICacheEntry{
+func (t *twitchAPICache) Set(key []string, valid time.Duration, data interface{}) {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	t.data[t.deriveKey(key)] = twitchAPICacheEntry{
 		Data:       data,
 		ValidUntil: time.Now().Add(valid),
 	}
 }
 
-func (twitchAPICache) deriveKey(key []string) string {
+func (*twitchAPICache) deriveKey(key []string) string {
 	sha := sha256.New()
 
 	fmt.Fprintf(sha, "%s", strings.Join(key, ":"))