ChunkGuard: Fault-Tolerant Chunked File Download System

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Overview

ChunkGuard is a production-grade, fault-tolerant file download system designed to transfer large files reliably over unstable or high-latency network connections. The system partitions large payloads into independently verifiable chunks, executing concurrent transfers using HTTP Range requests while guaranteeing byte-level integrity via cryptographic SHA-256 hashing.

In the event of network disruption or data corruption, ChunkGuard pinpoints the specific affected chunk and re-downloads only that segment, eliminating the need to restart entire transfers.

Key Features

• Chunked Downloads: Partitions files into configurable byte ranges leveraging standard HTTP Range requests.
• Cryptographic Verification: Enforces dual-layer SHA-256 hash checks at both the per-chunk and whole-file levels.
• Selective Fault Recovery: Retries only corrupted or failed chunks rather than restarting the entire download.
• Concurrent Transfer Engine: Supports multi-worker async downloads to maximize network throughput.
• Resumable Transfers: Maintains persistent state on disk to allow smooth recovery across process restarts.
• Exponential Backoff: Implements dynamic retry schedules with randomized jitter to mitigate network spikes and server rate limits.
• Whole-File Integrity Gate: Verifies final payload checksum post-reassembly prior to finalization.

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Repository Structure

ChunkGuard/
├── README.md                          # Project documentation entry point
├── LICENSE                            # Apache 2.0 License
│
├── docs/
│   ├── PROJECT_OVERVIEW.md            # High-level system overview
│   ├── ARCHITECTURE.md                # Component design & architectural decisions
│   ├── TECHNICAL_SPECIFICATION.md     # Detailed protocols, data schemas, & algorithms
│   ├── API_REFERENCE.md               # Complete Python & CLI API specification
│   ├── DATA_FLOW.md                   # State machine diagrams & data path sequences
│   ├── ERROR_HANDLING.md              # Error taxonomy & recovery strategies
│   ├── SECURITY.md                    # Security analysis & threat model
│   ├── DEPLOYMENT_GUIDE.md            # Installation, configuration, & operations
│   ├── USER_GUIDE.md                  # Comprehensive end-user guide
│   ├── TESTING_STRATEGY.md            # Test plans, benchmarks, & coverage targets
│   ├── PERFORMANCE.md                 # Benchmarks, memory profile, & tuning
│   ├── CONTRIBUTING.md                # Developer contribution standards
│   ├── CHANGELOG.md                   # Version history
│   ├── GLOSSARY.md                    # Terminology index
│   └── FAQ.md                         # Frequently asked questions
│
├── src/                               # System implementation
│   ├── chunk_manager.py               # Chunk partitioning & boundary logic
│   ├── download_engine.py             # Asynchronous download orchestrator
│   ├── hash_verifier.py               # Streaming SHA-256 verification
│   ├── state_manager.py               # Atomic state file manager
│   ├── retry_handler.py               # Exponential backoff & retry policies
│   ├── file_assembler.py              # Chunk reassembly & final integrity check
│   ├── config.py                      # System configuration parser
│   ├── models.py                      # Data models & schemas
│   ├── exceptions.py                  # Custom exception definitions
│   ├── logger.py                      # Structured JSON logging engine
│   └── main.py                        # Command Line Interface (CLI) entry point
│
├── tests/                             # Test suite
│   ├── unit/                          # Unit test modules
│   ├── integration/                   # Integration test modules
│   └── fixtures/                      # Mock data & server fixtures
│
└── config/
    └── default_config.yaml            # Default system configuration template

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Quick Start

Installation

# Clone repository
git clone https://github.com/PxA-Labs/ChunkGuard.git
cd ChunkGuard

# Install dependencies
pip install -r requirements.txt

Usage Examples

# Execute a new chunked download
python -m src.main download \
  --url "https://example.com/distribution-image.iso" \
  --output "./downloads/distribution-image.iso"

# Resume an interrupted transfer
python -m src.main resume \
  --state-file "./downloads/.chunkguard/distribution-image.iso.state"

# Verify payload checksum against expected hash
python -m src.main verify \
  --file "./downloads/distribution-image.iso" \
  --expected-hash "sha256:abcdef1234567890..."

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Technical Documentation Index

Document	Targeted Audience	Description
Project Overview	Technical & Non-Technical	Business context, problem statement, and scope
Architecture	System Architects & Engineers	Structural design, component responsibilities, and trade-offs
Technical Specification	Software Engineers	In-depth protocols, schemas, and mathematical specifications
API Reference	Integration Developers	Full documentation of Python SDK and CLI commands
Data Flow	Core Maintainers	State transition models and execution sequence diagrams
Error Handling	Systems & Reliability Engineers	Comprehensive exception taxonomy and fault escalation rules
Security	Security Analysts & Auditors	Threat model, cryptographic assurances, and mitigations
Deployment Guide	DevOps & SREs	Operations, environment setup, and monitoring integration
User Guide	End Users & Automation Engineers	Detailed command syntax and workflow examples
Testing Strategy	QA & Test Engineers	Test suite structure, fault injection, and coverage goals
Performance	Performance Engineers	Benchmarks, memory profile, and tuning strategies
Contributing	Contributors	Development setup, code guidelines, and pull request procedures
Glossary	All Readers	Index of technical terms and acronyms
FAQ	All Readers	Answers to common technical and operational questions

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License

This project is licensed under the Apache License 2.0. See the LICENSE file for the complete terms.