Remove captcha IP-specificity

It's a notable deployment complication for little gain. Since captchas on Nyaa aren't on many pages, overflowing the stored captcha limit is also hard.

router/uploadHandler.go

@@ -46,7 +46,7 @@ func UploadHandler(w http.ResponseWriter, r *http.Request) {
 			}
 		}
 	} else if r.Method == "GET" {
-		uploadForm.CaptchaID = captcha.GetID(r.RemoteAddr)
+		uploadForm.CaptchaID = captcha.GetID()
 		htv := UploadTemplateVariables{uploadForm, NewSearchForm(), Navigation{}, r.URL, mux.CurrentRoute(r)}
 		err = uploadTemplate.ExecuteTemplate(w, "index.html", htv)
 	} else {

service/captcha/captcha.go

@@ -3,7 +3,6 @@ package captcha
 import (
 	"errors"
 	"net/http"
-	"sync"
 	"time"
 
 	"github.com/dchest/captcha"
@@ -13,23 +12,11 @@ const lifetime = time.Minute * 20
 
 var (
 	server            = captcha.Server(captcha.StdWidth, captcha.StdHeight)
-	captchas = captchaMap{
-		m: make(map[string]store, 64),
-	}
-
 	ErrInvalidCaptcha = errors.New("invalid captcha")
 )
 
 func init() {
 	captcha.SetCustomStore(captcha.NewMemoryStore(1<<10, lifetime))
-
-	go func() {
-		t := time.Tick(time.Minute)
-		for {
-			<-t
-			captchas.cleanUp()
-		}
-	}()
 }
 
 // Captcha is to be embedded into any form struct requiring a captcha
@@ -37,56 +24,9 @@ type Captcha struct {
 	CaptchaID, Solution string
 }
 
-// Captchas are IP-specific and need eventual cleanup
-type captchaMap struct {
-	sync.Mutex
-	m map[string]store
-}
-
-type store struct {
-	id      string
-	created time.Time
-}
-
-// Returns a captcha id by IP. If a captcha for this IP already exists, it is
-// reloaded and returned. Otherwise, a new captcha is created.
-func (n *captchaMap) get(ip string) string {
-	n.Lock()
-	defer n.Unlock()
-
-	old, ok := n.m[ip]
-
-	// No existing captcha, it expired or this IP already used the captcha
-	if !ok || !captcha.Reload(old.id) {
-		id := captcha.New()
-		n.m[ip] = store{
-			id:      id,
-			created: time.Now(),
-		}
-		return id
-	}
-
-	old.created = time.Now()
-	n.m[ip] = old
-	return old.id
-}
-
-// Remove expired ip -> captchaID mappings
-func (n *captchaMap) cleanUp() {
-	n.Lock()
-	defer n.Unlock()
-
-	till := time.Now().Add(-lifetime)
-	for ip, c := range n.m {
-		if c.created.Before(till) {
-			delete(n.m, ip)
-		}
-	}
-}
-
-// GetID returns a new or previous captcha id by IP
-func GetID(ip string) string {
-	return captchas.get(ip)
+// GetID returns a new captcha id
+func GetID() string {
+	return captcha.New()
 }
 
 // Extract a Captcha struct from an HTML form