From a00e225d74dfa03aba2293530416f69c55373bed Mon Sep 17 00:00:00 2001
From: Evgeny <evgeny@poberezkin.com>
Date: Sat, 12 Sep 2026 08:30:13 +0100
Subject: [PATCH] xftp: hash of the shared part of file description (#1865)

Co-authored-by: Evgeny @ SimpleX Chat <259188159+evgeny-simplex@users.noreply.github.com>
---
 src/Simplex/FileTransfer/Description.hs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/Simplex/FileTransfer/Description.hs b/src/Simplex/FileTransfer/Description.hs
index cd2df9d33..4cbb08014 100644
--- a/src/Simplex/FileTransfer/Description.hs
+++ b/src/Simplex/FileTransfer/Description.hs
@@ -29,6 +29,7 @@ module Simplex.FileTransfer.Description
     YAMLFileDescription (..), -- for tests
     YAMLServerReplicas (..), -- for tests
     validateFileDescription,
+    sharedDescriptionHash,
     groupReplicasByServer,
     fdSeparator,
     kb,
@@ -72,6 +73,7 @@ import Simplex.FileTransfer.Protocol
 import Simplex.Messaging.Agent.QueryString
 import Simplex.Messaging.Agent.Store.DB (Binary (..), FromField (..), ToField (..))
 import qualified Simplex.Messaging.Crypto as C
+import Simplex.Messaging.Encoding (Encoding (..))
 import Simplex.Messaging.Encoding.String
 import Simplex.Messaging.Parsers (defaultJSON, parseAll)
 import Simplex.Messaging.Protocol (XFTPServer)
@@ -227,6 +229,13 @@ validateFileDescription fd@FileDescription {size, chunks}
     chunkNos = map (\FileChunk {chunkNo} -> chunkNo) chunks
     chunksSize = foldl' (\(s :: Int64) FileChunk {chunkSize} -> s + fromIntegral (unFileSize chunkSize)) 0
 
+sharedDescriptionHash :: FileDescription p -> ByteString
+sharedDescriptionHash FileDescription {size, digest, key, nonce, chunkSize, chunks} =
+  C.sha512Hash $ smpEncode (unFileSize size, unFileDigest digest, C.unSbKey key, nonce, unFileSize chunkSize) <> foldMap chunkFields chunks
+  where
+    chunkFields FileChunk {chunkNo, chunkSize = cSize, digest = cDigest} =
+      smpEncode (fromIntegral chunkNo :: Int64, unFileSize cSize, unFileDigest cDigest)
+
 encodeFileDescription :: FileDescription p -> YAMLFileDescription
 encodeFileDescription FileDescription {party, size, digest, key, nonce, chunkSize, chunks, redirect} =
   YAMLFileDescription