Backup Process Fix - Wait for save query Response

Issue Fixed

The backup process now properly waits for the save query command to return with the file list before starting the file copy process.

Problem

Previously, the backup service would:

1. Send "save hold"
2. Wait 2 seconds
3. Send "save query"
4. Immediately start copying files without waiting for the response

This was incorrect because save query is asynchronous and needs time to return the file list.

Solution Implemented

The updated BackupHostedService now follows the correct flow:

Correct Backup Sequence

1. Send "save hold"
   
2. Wait 3 seconds (for save hold to complete)
   
3. Send "save query"
   
4.  WAIT for response (up to 10 seconds)
   - Poll log every 500ms
   - Look for "Files are now ready to be copied" OR "Data saved"
   
5.  Confirm files are ready
   
6. Parse file list from response
   
7. Copy files (ONLY after confirmation)
   
8. Send "save resume"

Key Changes

1. Response Waiting Loop

// Wait for "Files are now ready to be copied" message with timeout
var maxWaitTime = TimeSpan.FromSeconds(10);
var waitInterval = TimeSpan.FromMilliseconds(500);
var elapsedTime = TimeSpan.Zero;
bool filesReady = false;

while (elapsedTime < maxWaitTime && !cancellationToken.IsCancellationRequested)
{
    await Task.Delay(waitInterval, cancellationToken);
    elapsedTime += waitInterval;

    var currentLog = _runnerService.GetLog();
    
    // Check if we got the "Files are now ready to be copied" message
    if (currentLog.Contains("Files are now ready to be copied", StringComparison.OrdinalIgnoreCase) ||
        currentLog.Contains("Data saved", StringComparison.OrdinalIgnoreCase))
    {
        filesReady = true;
        _logger.LogInformation("Received confirmation that files are ready to be copied");
        break;
    }
}

2. Timeout Protection

if (!filesReady)
{
    _logger.LogError("Timeout waiting for 'save query' response. Files may not be ready.");
    await ResumeWorldSaving();
    return;  // Abort backup
}

3. File Copy ONLY After Confirmation

// Step 3: Parse file list from server response - ONLY proceed if we have the list
var filesToBackup = ParseFileList();

if (filesToBackup.Count == 0)
{
    _logger.LogWarning("No files identified for backup from save query response");
    await ResumeWorldSaving();
    return;  // Abort backup
}

_logger.LogInformation("Identified {Count} files to backup", filesToBackup.Count);

// Step 4: Create backup directory...
// Step 5: Copy files - ONLY after save query has returned the file list

Backup Flow Diagram

 Start Backup                        

             
             

 Send "save hold"                    
 Server pauses world saving          

             
              Wait 3 seconds

 Send "save query"                   
 Request file list                   

             
             
    
     Wait for Response    Poll every 500ms
     (max 10 seconds)         (up to 10 seconds)
    
             
             
   
    Files Ready        
   
                
    Yes           No (timeout)
                
                
  
Parse Files    Log Error      
List           Resume Saving  
   Abort Backup   
               
      

 Files > 0  

         
 Yes       No
         
         

 Create Backup Dir  
 Copy Files         
 Resume Saving      
 Cleanup Old        

Safety Features

1. Timeout Protection: 10-second maximum wait for response
2. Cancellation Support: Respects cancellation tokens
3. Validation: Checks for file list before copying
4. Always Resume: Guarantees "save resume" is called
5. Error Logging: Detailed logging at each step

Log Output Example

Successful Backup

[BackupHostedService] Starting backup process...
[BackupHostedService] Sending 'save hold' command...
[BackupHostedService] Waiting for save hold to complete...
[BackupHostedService] Sending 'save query' command and waiting for response...
[BackupHostedService] Received confirmation that files are ready to be copied
[BackupHostedService] Identified 42 files to backup
[BackupHostedService] Created backup directory: C:\Backups\Minecraft\backup_2025-01-15_14-30-00
[BackupHostedService] Starting file copy from: C:\BedrockServer\worlds\Bedrock level
[BackupHostedService] Backup completed. Copied 42 files, 0 failed to C:\Backups\Minecraft\backup_2025-01-15_14-30-00
[BackupHostedService] Sending 'save resume' command...
[BackupHostedService] World saving resumed
[BackupHostedService] Cleaned up 3 old backup(s)

Timeout Scenario

[BackupHostedService] Starting backup process...
[BackupHostedService] Sending 'save hold' command...
[BackupHostedService] Waiting for save hold to complete...
[BackupHostedService] Sending 'save query' command and waiting for response...
[BackupHostedService] Timeout waiting for 'save query' response. Files may not be ready.
[BackupHostedService] Sending 'save resume' command...
[BackupHostedService] World saving resumed

Benefits

1. Data Integrity: Files are only copied when confirmed ready
2. Reliability: Handles server delays and timeouts
3. Safety: Never copies files before they're ready
4. Traceability: Clear logging of each step
5. Robustness: Proper error handling and recovery

Testing

To verify the fix works:

1. Start the API with backup configured
2. Trigger a manual backup via UI
3. Check logs for:
   • "Waiting for response" message
   • "Received confirmation" message
   • File count before copying
4. Verify backup folder contains all files

References

• Minecraft Bedrock Commands: Official backup procedure
  • save hold - Prepare for backup
  • save query - Get file list (asynchronous!)
  • save resume - Resume normal operation

Status

Build: Successful
Fix: Implemented
Ready for: Testing and Production