From 3f8b581af7c0c8146c5b111f92ba6a024310c525 Mon Sep 17 00:00:00 2001
From: Ran Vaknin <rvaknin@amazon.com>
Date: Wed, 6 Sep 2023 12:52:16 -0700
Subject: [PATCH] fix(s3-presigned-post): ensure unique conditions in policy
 (#5184)

* fix(s3-presigned-post): ensure unique conditions in policy
---
 .../src/createPresignedPost.ts                | 27 ++++++++++++++-----
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/packages/s3-presigned-post/src/createPresignedPost.ts b/packages/s3-presigned-post/src/createPresignedPost.ts
index bedf4e7f3187..a4abaac439b1 100644
--- a/packages/s3-presigned-post/src/createPresignedPost.ts
+++ b/packages/s3-presigned-post/src/createPresignedPost.ts
@@ -66,13 +66,26 @@ export const createPresignedPost = async (
 
   // Prepare policies.
   const expiration = new Date(now.valueOf() + Expires * 1000);
-  const conditions: PolicyEntry[] = [
-    ...Conditions,
-    ...Object.entries(fields).map(([k, v]) => ({ [k]: v })),
-    Key.endsWith("${filename}")
-      ? ["starts-with", "$key", Key.substring(0, Key.lastIndexOf("${filename}"))]
-      : { key: Key },
-  ];
+
+  const conditionsSet = new Set<string>();
+
+  for (const condition of Conditions) {
+    const stringifiedCondition = JSON.stringify(condition);
+    conditionsSet.add(stringifiedCondition);
+  }
+
+  for (const [k,v] of Object.entries(fields)) {
+    conditionsSet.add(JSON.stringify({ [k]: v }))
+  }  
+  
+  if (Key.endsWith("${filename}")) {
+    conditionsSet.add(JSON.stringify(["starts-with", "$key", Key.substring(0, Key.lastIndexOf("${filename}"))]));
+  } else {
+    conditionsSet.add(JSON.stringify({ key: Key }));
+  }
+
+  const conditions = Array.from(conditionsSet).map((item) => JSON.parse(item));
+
   const encodedPolicy = base64Encoder(
     utf8Decoder(
       JSON.stringify({