From 7736d3085cce0eb1e6370db1ae8919c919f16fa8 Mon Sep 17 00:00:00 2001
From: Reyzis2021 <reyzarium@gmail.com>
Date: Mon, 4 Nov 2024 15:06:10 +0300
Subject: [PATCH] SHORTY-81 Fix case with loops in URL redirection are not
 avoided

---
 .../zufar/urlshortener/shorten/controller/UrlController.kt | 7 +++++++
 .../zufar/urlshortener/shorten/repository/UrlRepository.kt | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/src/main/kotlin/com/zufar/urlshortener/shorten/controller/UrlController.kt b/src/main/kotlin/com/zufar/urlshortener/shorten/controller/UrlController.kt
index b149550..f807386 100644
--- a/src/main/kotlin/com/zufar/urlshortener/shorten/controller/UrlController.kt
+++ b/src/main/kotlin/com/zufar/urlshortener/shorten/controller/UrlController.kt
@@ -1,6 +1,7 @@
 package com.zufar.urlshortener.shorten.controller
 
 import com.zufar.urlshortener.common.exception.ErrorResponse
+import com.zufar.urlshortener.common.exception.InvalidRequestException
 import com.zufar.urlshortener.shorten.dto.*
 import com.zufar.urlshortener.shorten.repository.UrlRepository
 import com.zufar.urlshortener.shorten.service.*
@@ -164,6 +165,12 @@ class UrlController(
             httpServletRequest.getHeader("User-Agent")
         )
 
+        val existingMapping = urlRepository.findByShortUrl(originalUrl)
+        if (existingMapping.isPresent) {
+            log.warn("Loop detected: originalUrl='{}' points to another short URL.", originalUrl)
+            throw InvalidRequestException("URL cannot point to a loop back address")
+        }
+
         val urlHash = StringEncoder.encode(originalUrl)
         val urlMapping = urlRepository.findByUrlHash(urlHash)
         val shortUrl: String
diff --git a/src/main/kotlin/com/zufar/urlshortener/shorten/repository/UrlRepository.kt b/src/main/kotlin/com/zufar/urlshortener/shorten/repository/UrlRepository.kt
index 6f3af2e..8160b8b 100644
--- a/src/main/kotlin/com/zufar/urlshortener/shorten/repository/UrlRepository.kt
+++ b/src/main/kotlin/com/zufar/urlshortener/shorten/repository/UrlRepository.kt
@@ -11,4 +11,6 @@ interface UrlRepository : MongoRepository<UrlMapping, String> {
     fun findByUrlHash(urlHash: String): Optional<UrlMapping>
 
     fun findAllByUserId(userId: String, pageable: Pageable): Page<UrlMapping>
+
+    fun findByShortUrl(shortUrl: String): Optional<UrlMapping>
 }
\ No newline at end of file