Possibly fix race condition in rate limiting

contrib/smash

@@ -0,0 +1,26 @@
+#! /bin/sh
+
+BASEURL=http://localhost:8080
+
+case "$1" in
+  a)
+    URL=$BASEURL/answer
+    ;;
+  b)
+    URL=$BASEURL/puzzles.json
+    ;;
+  *)
+    echo "Usage: $0 a|b" 1>&2
+    exit 1
+    ;;
+esac
+
+while true; do
+  curl \
+    -X POST \
+    -F "cat=base" \
+    -F "points=1" \
+    -F "id=test" \
+    -F "answer=moo" \
+    $URL
+done

src/instance.go

@@ -11,6 +11,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -21,12 +22,13 @@ type Instance struct {
 	ThemeDir        string
 	AttemptInterval time.Duration
 
-	categories  map[string]*Mothball
-	update      chan bool
-	jPuzzleList []byte
-	jPointsLog  []byte
-	nextAttempt map[string]time.Time
-	mux         *http.ServeMux
+	categories       map[string]*Mothball
+	update           chan bool
+	jPuzzleList      []byte
+	jPointsLog       []byte
+	nextAttempt      map[string]time.Time
+	nextAttemptMutex *sync.RWMutex
+	mux             *http.ServeMux
 }
 
 func (ctx *Instance) Initialize() error {
@@ -42,6 +44,7 @@ func (ctx *Instance) Initialize() error {
 	ctx.categories = map[string]*Mothball{}
 	ctx.update = make(chan bool, 10)
 	ctx.nextAttempt = map[string]time.Time{}
+	ctx.nextAttemptMutex = new(sync.RWMutex)
 	ctx.mux = http.NewServeMux()
 
 	ctx.BindHandlers()
@@ -129,8 +132,15 @@ func (ctx *Instance) ThemePath(parts ...string) string {
 
 func (ctx *Instance) TooFast(teamId string) bool {
 	now := time.Now()
+	
+	ctx.nextAttemptMutex.RLock()
 	next, _ := ctx.nextAttempt[teamId]
+	ctx.nextAttemptMutex.RUnlock()
+	
+	ctx.nextAttemptMutex.Lock()
 	ctx.nextAttempt[teamId] = now.Add(ctx.AttemptInterval)
+	ctx.nextAttemptMutex.Unlock()
+	
 	return now.Before(next)
 }
 
@@ -212,7 +222,10 @@ func (ctx *Instance) OpenCategoryFile(category string, parts ...string) (io.Read
 }
 
 func (ctx *Instance) ValidTeamId(teamId string) bool {
+	ctx.nextAttemptMutex.RLock()
 	_, ok := ctx.nextAttempt[teamId]
+	ctx.nextAttemptMutex.RUnlock()
+
 	return ok
 }
 

src/maintenance.go

@@ -186,19 +186,28 @@ func (ctx *Instance) readTeams() {
 	now := time.Now()
 	added := 0
 	for k, _ := range newList {
-		if _, ok := ctx.nextAttempt[k]; !ok {
+		ctx.nextAttemptMutex.RLock()
+		_, ok := ctx.nextAttempt[k]
+		ctx.nextAttemptMutex.RUnlock()
+
+		if !ok {
+			ctx.nextAttemptMutex.Lock()
 			ctx.nextAttempt[k] = now
+			ctx.nextAttemptMutex.Unlock()
+
 			added += 1
 		}
 	}
 
 	// For any removed team IDs, remove them
 	removed := 0
+	ctx.nextAttemptMutex.Lock() // XXX: This could be less of a cludgel
 	for k, _ := range ctx.nextAttempt {
 		if _, ok := newList[k]; !ok {
 			delete(ctx.nextAttempt, k)
 		}
 	}
+	ctx.nextAttemptMutex.Unlock()
 
 	if (added > 0) || (removed > 0) {
 		log.Printf("Team IDs updated: %d added, %d removed", added, removed)