From C to Rust

Modernizing Production Systems Without Starting Over

Introduction: Why Incremental Modernization Matters

Chapter 1: The Modernization Case

1. What Production C Systems Actually Look Like Today
2. Defect Patterns in Mature C Codebases
3. The Safety Promise: Memory, Concurrency and Types
4. Where Rust Gains Are Real and Measurable
5. The Hidden Costs of Migration
6. When Staying in C Is the Right Decision

Chapter 2: C and Rust Side by Side

1. Compilation, Linking and the Object Model
2. Primitive Types and Integer Semantics
3. Pointers Versus References: What Actually Changes
4. Structs, Unions, Enums and Data Layout
5. Ownership, Moves and Copy Semantics
6. Lifetimes and Borrowing for C Programmers
7. Stack, Heap and Allocation Patterns
8. RAII, Drop and Resource Management
9. Mutability, Aliasing and Interior Mutability
10. Error Handling: Return Codes Versus Result
11. Generics, Traits and Pattern Matching
12. Concurrency Primitives and Memory Ordering
13. The Role and Meaning of unsafe

Chapter 3: Assessing Your C Codebase

1. Inventorying Components and Dependencies
2. Mapping Ownership Assumptions and Lifetime Contracts
3. Locating Undefined Behavior and Memory Risks
4. Measuring Test Coverage and Reliability Baselines
5. Classifying Modules by Risk, Value and Complexity
6. Identifying Migration Candidates: The Decision Matrix
7. Building the Modernization Roadmap

Chapter 4: FFI Foundations: C and Rust Talking to Each Other

1. The ABI Contract: extern “C” and Symbol Visibility
2. Data Layout Compatibility with repr(C)
3. Passing Primitives, Pointers and Arrays
4. Strings Across the Boundary: CString and CStr
5. Structs, Unions, Enums and Opaque Handles
6. Function Pointers and Callbacks
7. Ownership Transfer at FFI Boundaries
8. Error Propagation Patterns
9. Panic Handling and Unwinding Across Languages
10. Thread Safety and Global State

Chapter 5: Build Systems and Tooling Integration

1. Cargo in a Make and CMake World
2. The cc Crate and Building C from Cargo
3. Bindgen: Generating Bindings Automatically
4. Build Scripts and pkg-config Integration
5. Cross-Compilation and Target Triples
6. Static Versus Dynamic Linking Strategies
7. Reproducible Builds and Dependency Management

Chapter 6: Migration Pattern 1: Wrapping C Libraries Safely

1. When Wrapping Is Better Than Rewriting
2. Designing Opaque Handle Interfaces
3. RAII Wrappers for Resource Handles
4. Lifetime-Aware APIs Around Raw Pointers
5. Validated Constructors and Error Types
6. Encapsulating unsafe: The Safety Boundary Pattern
7. Complete Example: Wrapping a C Configuration Parser

Chapter 7: Migration Pattern 2: Replacing Leaf Modules

1. Identifying Replaceable Leaf Components
2. Designing Drop-In Replacements via Stable ABIs
3. Migrating String Utilities and Formatters
4. Migrating Data Serialization Code
5. Migrating Protocol Parsers
6. Complete Example: Replacing a C Parser with Rust

Chapter 8: Migration Pattern 3: Strangler and Sidecar Approaches

1. The Strangler Pattern for Long-Lived Systems
2. Process Boundary Separation via IPC
3. Sidecar Services in Rust
4. Plugin Architectures with C-Compatible APIs
5. Gradual Traffic Migration and Feature Flags
6. Complete Example: Extracting a Subsystem Behind an API

Chapter 9: Creating Safe Abstractions Over Unsafe C APIs

1. Newtypes and Domain-Specific Types
2. Typestate Patterns for Stateful Resources
3. Smart Pointer Wrappers for Ownership Tracking
4. Synchronization Wrappers for Thread Safety
5. Invariants and Encapsulated unsafe Blocks
6. Writing Auditable Safety Comments
7. Complete Example: Safe Wrapper Around a C Memory Pool

Chapter 10: Testing Behavioral Equivalence During Migration

1. Characterization Tests for Legacy Systems
2. Differential Testing of C and Rust Implementations
3. Protocol Corpus and Golden Testing
4. Fuzzing Mixed-Language Systems
5. Concurrency and Stress Testing
6. ABI Compatibility and Regression Testing
7. Complete Example: Test Harness for Migrated Parser

Chapter 11: Performance Engineering and Verification

1. Establishing Reproducible C Baselines
2. Benchmarking Methodology and Pitfalls
3. Comparing Latency, Throughput and Memory Use
4. Allocation Behavior and Cache Performance
5. When Rust Is Slower (and Why)
6. Optimization Without Sacrificing Safety
7. Complete Example: Before/After Performance Comparison

Chapter 12: Security Modernization and unsafe Governance

1. Vulnerability Classes Rust Actually Prevents
2. What Rust Does Not Fix Automatically
3. Threat Modeling for Mixed-Language Systems
4. Supply Chain Security and Dependency Governance
5. Auditing and Reducing unsafe Code
6. Organizational Policies for unsafe Review
7. SBOM Generation and Reproducible Builds

Chapter 13: Concurrency Modernization

1. Thread Safety Patterns in Mature C Code
2. Send and Sync: What They Mean for C Interop
3. Migrating Lock-Based Components
4. Channels and Message Passing Patterns
5. Atomics and Memory Ordering Across Languages
6. Async Runtimes: When They Make Sense
7. Complete Example: Migrating a Threading Component

Chapter 14: Deployment, Operations and Organizational Adoption

1. Packaging Mixed-Language Applications
2. Observability Across Language Boundaries
3. Debugging Production Issues in C and Rust
4. Crash Reporting and Core Dump Analysis
5. Training C Engineers for Rust
6. Code Review Practices for Mixed Systems
7. Decision Frameworks: Migrate, Wrap, Rewrite, or Keep
8. Common Failed Migration Approaches and Anti-Patterns
9. Production Checklists

Chapter 15: Case Studies in Realistic Migration Scenarios

1. Case Study 1: Migrating a Binary Protocol Parser
2. Case Study 2: Wrapping a C Cryptographic Library
3. Case Study 3: Migrating a Multithreaded Event Daemon
4. Case Study 4: Embedded System Firmware Migration
5. Case Study 5: Command-Line Utility Rewrite

Conclusion: A Roadmap for Evolving C Systems

References