TCP Echo Server in Pure C

"Concurrency is not a luxury, it is a system requirement."

A precision-engineered, from-scratch implementation of a scable TCP echo server in pure C. Built with a focus on systems programming excellence, manual memory management, and high-performance I/O multiplexing via epoll.

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The Philosophy

Modern networking libraries often abstract away the visceral mechanics of the socket API and the kernel's event notification systems. tcp-server-c strips away the abstraction. It is designed to serve as a reference implementation for how high-concurrency systems manage state, memory, and I/O during the "C10k" challenge.

Key Engineering Pillars

• Linux Native Scability: Leverages epoll in Edge-Triggered mode for O(1) event notification.
• Strict Lint Compliance: Zero-warning policy with cppcheck, clang-tidy, and clang-format.
• Memory Integrity: Verified leak-free performance via valgrind and AddressSanitizer.
• Robust Error Handling: Defensive programming at the socket level to handle network instability and signal interruptions.

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Architectural Blueprint

The codebase is strictly modular, separating the concerns of the socket layer, the event loop, and the connection state machine.

graph TD
    Main[main.c: Entry Point] --> Signals[Signal Handling: Graceful Shutdown]
    Main --> Server[server.c: Core Loop]
    Server --> Epoll[epoll_handler.c: I/O Multiplexing]
    Server --> SocketOps[socket_ops.c: Sockets/Binding]
    Server --> Conn[connection.c: State Machine]
    Conn --> Data[Read/Write Buffers]
    Data --> Process[Echo Logic]

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Capabilities

Feature	Implementation	Engineering Note
Multiplexing	epoll	Scalable I/O handling for thousands of concurrent clients.
Edge Triggering	EPOLLET	Minimizes kernel-to-user-space context switches.
State Tracking	connection_t	Per-socket read/write buffering and metadata.
Non-blocking I/O	O_NONBLOCK	Prevents loop starvation during partial I/O operations.
Clean Shutdown	SIGINT/SIGTERM	Automated resource reclamation and socket closure.

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Technical Deep-Dives

The project includes an extensive educational curriculum documentation in docs/:

1. Socket Fundamentals: Understanding descriptors, binding, and the listen/accept handshake.
2. TCP Protocol Layer: The mechanics of sliding windows, buffering, and flow control.
3. Server Lifecycle: Managing the transition from initialization to steady state.
4. I/O Multiplexing: Why epoll succeeds where select and poll fail.
5. Memory & Buffering: Efficient buffer compaction and avoidance of fragments.
6. Error Handling: Recovering from broken pipes and transient failures.

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Core Tooling

Verified components of the development lifecycle:

• Linter: clang-tidy & cppcheck (Strict mode)
• Formatter: clang-format (LLVM style)
• Memory Check: valgrind & ASan
• Coverage: gcov & lcov

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Part of the implement-from-scratch series.