adding first iteration of chunked file support

README_CHUNKED_UPLOAD.md

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+# Chunked Upload Implementation
+
+This document describes the chunked upload implementation added to the SimpleLogUpload Android application to solve issues with large file uploads on mobile networks.
+
+## Overview
+
+The chunked upload system splits large files into smaller pieces (chunks), uploads them individually, and then reassembles them on the server. This approach provides several benefits:
+
+1. Better reliability on unstable networks (especially 5G/mobile)
+2. Ability to resume interrupted uploads
+3. More accurate progress reporting
+4. Adaptability to different network conditions
+
+## Components
+
+### 1. ChunkedUploadManager
+
+The core component that handles:
+- Splitting files into chunks
+- Managing parallel uploads
+- Tracking upload progress
+- Handling network changes
+- Implementing retry logic
+- Verifying chunk status with server
+- Automatically retrying missing chunks
+
+```java
+ChunkedUploadManager uploadManager = new ChunkedUploadManager(
+        context, file, maxDownloads, expiryHours);
+```
+
+### 2. UploadStrategySelector
+
+Determines whether to use chunked uploads based on:
+- File size
+- Network type (WiFi vs. Mobile)
+- Configurable thresholds
+
+```java
+boolean useChunked = UploadStrategySelector.shouldUseChunkedUpload(context, file);
+```
+
+### 3. Modified UploadController
+
+The existing UploadController now:
+- Selects between standard and chunked uploads
+- Handles both upload methods with a unified API
+- Provides progress updates
+
+## API Requirements
+
+The server implements four endpoints:
+
+1. `/upload/start` - Initializes a chunked upload session
+   - Accepts: filename, filesize, chunk_size, total_chunks, max_downloads, expiry_hours
+   - Returns: upload_id
+
+2. `/upload/chunk` - Handles individual chunk uploads
+   - Accepts: upload_id, chunk_index, total_chunks, chunk (binary)
+   - Returns: success/failure
+
+3. `/upload/verify` - Verifies which chunks have been received
+   - Accepts: upload_id
+   - Returns: received_chunks, missing_chunks, total_chunks
+
+4. `/upload/complete` - Finalizes an upload by reassembling chunks
+   - Accepts: upload_id, filename, total_chunks
+   - Returns: upload code (same as standard upload)
+
+## Configuration
+
+The chunked upload system is configured with the following parameters:
+
+- WiFi chunk size: 10MB
+- Mobile chunk size: 2MB
+- WiFi threshold: 50MB (files larger than this use chunked upload)
+- Mobile threshold: 10MB
+- WiFi parallel uploads: 3
+- Mobile parallel uploads: 1
+
+These values can be adjusted in the `ChunkedUploadManager` and `UploadStrategySelector` classes.
+
+## Enhanced Reliability Features
+
+### Chunk Verification
+
+The system implements robust verification to ensure all chunks are properly uploaded:
+
+1. Client-side tracking of all uploaded chunks by index
+2. Server endpoint to verify which chunks have been received
+3. Automatic reupload of any missing chunks
+4. Verification that files actually exist on disk before finalizing
+
+### Network Handling
+
+The implementation includes robust network handling:
+
+- Detects network type (WiFi/Mobile/5G/LTE)
+- Adjusts chunk size and parallel uploads accordingly
+- Monitors network state changes
+- Pauses uploads on network loss
+- Resumes uploads when network is restored
+- Adapts to network type changes during upload
+
+### Progressive Retry
+
+Implements intelligent retry logic:
+
+- Specific retry of only failed chunks
+- Server-client synchronization of chunk status
+- Automatic recovery from partial upload failures
+- Verification before finalization to catch missing chunks
+
+## Testing
+
+To test this implementation:
+
+1. Ensure the server has the required endpoints implemented
+2. Test with large files (100MB+) on both WiFi and mobile networks
+3. Test with network transitions (WiFi -> Mobile)
+4. Test interrupting uploads and resuming them
+5. Compare performance with the previous implementation
+
+## Troubleshooting
+
+- Check logs for entries from `ChunkedUploadManager` and `UploadController`
+- Look for network-related logs to identify connection issues
+- Check server logs for chunk verification and missing chunk information
+- Verify server-side chunk handling is working correctly
+
+## Implementation Status
+
+- ✅ Basic chunked upload system
+- ✅ Network type detection and adaptivity
+- ✅ Chunk verification and automatic retry
+- ✅ Resume capability for interrupted uploads
+- ✅ Parallel chunk uploading
+- ✅ Network state monitoring
+- ✅ Progressive backoff and retry strategy
+- ✅ Enhanced progress tracking
+