meganz
diff --git a/‎src/syncinternals/syncinternals.cpp‎
Lines changed: 38 additions & 3 deletions b/‎src/syncinternals/syncinternals.cpp‎
Lines changed: 38 additions & 3 deletions
@@ -791,6 +791,7 @@ enum class MacAdvanceResult
 {
     Pending, // Chunk queued or in progress
     Ready, // Local MAC is computed (check state->localMac)
+    Obsolete, // Local file changed; discard state and rescan
     Failed // Error occurred
 };
 
@@ -832,6 +833,19 @@ MacAdvanceResult advanceMacComputation(MegaClient& mc,
         return MacAdvanceResult::Pending;
     }
 
+    // Empty file: compute local MAC directly without reading or queueing chunks
+    if (state->totalSize == 0)
+    {
+        SymmCipher cipher;
+        cipher.setkey(state->transferkey.data());
+
+        const int64_t localMac = state->partialMacs.macsmac(&cipher);
+
+        LOG_debug << logPrefix << "Local MAC computed for empty file: " << localMac;
+        state->setComplete(localMac);
+        return MacAdvanceResult::Ready;
+    }
+
     // Ready for next chunk - read and queue
     m_off_t readStart = state->currentPosition;
     m_off_t tentativeEnd = std::min(readStart + MacComputationState::BUFFER_SIZE, state->totalSize);
@@ -875,8 +889,7 @@ MacAdvanceResult advanceMacComputation(MegaClient& mc,
         LOG_debug << logPrefix << "File size changed: expected " << state->totalSize << ", got "
                   << fa->size;
         fa->fclose();
-        state->setFailed();
-        return MacAdvanceResult::Failed;
+        return MacAdvanceResult::Obsolete;
     }
 
     // Read chunk into buffer
@@ -987,6 +1000,13 @@ FsCloudComparisonResult asyncMacComputation(MegaClient& mc,
                                             LocalNode& syncNode)
 {
     static const std::string logPre{"asyncMacComputation: "};
+    const auto restartAfterInvalidation = [&syncNode, &fsNodeFullPath]() -> FsCloudComparisonResult
+    {
+        LOG_debug << logPre << "MAC state invalidated, requesting rescan: " << fsNodeFullPath;
+        syncNode.resetMacComputationIfAny();
+        syncNode.setScanAgain(true, false, false, 0);
+        return {NODE_COMP_PENDING, INVALID_META_MAC, INVALID_META_MAC, FingerprintMismatch::Other};
+    };
 
     // Check throttling first - skip if a recent mtime-only op just completed
     if (syncNode.shouldThrottleMacComputation(MAC_THROTTLE_WINDOW))
@@ -1044,6 +1064,10 @@ FsCloudComparisonResult asyncMacComputation(MegaClient& mc,
                         INVALID_META_MAC,
                         FingerprintMismatch::Other};
             }
+            else if (result == MacAdvanceResult::Obsolete)
+            {
+                return restartAfterInvalidation();
+            }
             else
             {
                 // Pending - return and wait
@@ -1096,6 +1120,11 @@ FsCloudComparisonResult asyncMacComputation(MegaClient& mc,
     // Advance computation (will queue first chunk)
     auto result = advanceMacComputation(mc, macComp, logPre);
 
+    if (result == MacAdvanceResult::Obsolete)
+    {
+        return restartAfterInvalidation();
+    }
+
     if (result == MacAdvanceResult::Failed)
     {
         syncNode.resetMacComputationIfAny();
@@ -1233,7 +1262,7 @@ CloneMacStatus initCloneCandidateMacComputation(MegaClient& mc, SyncUpload_inCli
 
         // Start first chunk - pass local macComp to ensure object stays alive
         auto result = advanceMacComputation(mc, macComp, logPre);
-        if (result == MacAdvanceResult::Failed)
+        if (result == MacAdvanceResult::Failed || result == MacAdvanceResult::Obsolete)
         {
             LOG_debug << logPre << "Failed to start computation of MAC for "
                       << upload.getLocalname();
@@ -1335,6 +1364,12 @@ CloneMacStatus checkPendingCloneMac(MegaClient& mc, SyncUpload_inClient& upload)
         upload.macComputation.reset();
         return CloneMacStatus::Failed;
     }
+    else if (result == MacAdvanceResult::Obsolete)
+    {
+        LOG_debug << logPre << "Obsolete: " << upload.getLocalname();
+        upload.macComputation.reset();
+        return CloneMacStatus::Failed;
+    }
 
     // Pending
     return CloneMacStatus::Pending;