From b3008a51c7f68af2593bf26652f5fad4bdbd9475 Mon Sep 17 00:00:00 2001
From: Luke Granger-Brown <hg@lukegb.com>
Date: Mon, 1 Jan 2024 14:16:20 +0000
Subject: [PATCH] tumblrandom: use better random

---
 go/tumblrandom/tumblrandom.go | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/go/tumblrandom/tumblrandom.go b/go/tumblrandom/tumblrandom.go
index cc4163d1dc..f6ec2ae4e6 100644
--- a/go/tumblrandom/tumblrandom.go
+++ b/go/tumblrandom/tumblrandom.go
@@ -12,7 +12,7 @@ import (
 	"io"
 	"io/fs"
 	"log"
-	mathrand "math/rand"
+	"math/big"
 	"net"
 	"net/http"
 	"os"
@@ -289,7 +289,12 @@ func (a *app) random(rw http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	n := mathrand.Intn(len(u.Likes))
+	bigN, err := rand.Int(rand.Reader, big.NewInt(int64(len(u.Likes))))
+	if err != nil {
+		http.Error(rw, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	n := int(bigN.Int64())
 	l := u.Likes[n]
 	http.Redirect(rw, r, l.PostURL, http.StatusSeeOther)
 }