🌐 Multithreaded Proxy Webserver in C

A high-performance, multithreaded HTTP proxy server written in C. This project demonstrates advanced systems programming concepts including socket programming, POSIX threads, synchronization primitives, and automated response caching.

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🚀 Features

• Multithreaded Architecture: Uses a "thread-per-request" model to handle hundreds of concurrent client connections efficiently.
• HTTP/1.1 Compliant: Forwards method, path, and headers to remote servers, maintaining protocol integrity.
• Intelligent Caching: Implements a thread-safe LRU (Least Recently Used) caching mechanism to reduce latency for frequently accessed resources.
• Graceful Shutdown: Robust signal handling for SIGINT (Ctrl+C) ensuring all sockets are closed and memory is freed correctly.
• Dynamic Configuration: Easy-to-use command line interface to specify ports and enable/disable features.

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🛠 Project Structure

.
├── src/
│   ├── main.c          # Entry point and server loop
│   ├── proxy.c         # Caching and request parsing logic
│   └── server.c        # Socket handling and thread management
├── include/
│   └── proxy.h         # Global definitions and function prototypes
├── Makefile            # Build configuration
├── CMakeLists.txt      # Modern CMake build configuration
└── test.sh             # Automated testing script

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📦 Getting Started

Prerequisites

Ensure you have a POSIX-compliant environment (Linux, macOS, or WSL) and theFollowing tools installed:

• gcc or clang
• make or cmake
• curl (for testing)

Build Instructions

Using Make (Recommended)

# Clean previous builds
make clean

# Compile the project
make

Using CMake

mkdir build && cd build
cmake ..
make

Running the Server

Start the proxy server by specifying a port:

# Run with caching enabled on port 8080
./proxy_server -p 8080 -c

# Run without caching on port 9000
./proxy_server -p 9000

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🔍 Testing & Usage

Command Line Flags

• -p <port>: Required. Port on which the proxy will listen.
• -c: Optional. Enable response caching.
• -h/--help: Display help message.

Automated Testing

You can run the included test script to verify the build and basic functionality:

chmod +x test.sh
./test.sh

Manual Testing with Curl

To route your requests through the proxy:

curl -x http://localhost:8080 http://example.com

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🧠 Technical Deep Dive

1. The Threading Model

The server uses a master loop that accepts new connections. For every connection, a new detached POSIX thread is created. This allows the server to remain responsive while waiting for remote server responses.

2. Caching Strategy

The cache is implemented as an array of entries protected by a pthread_mutex. When a request is made, the proxy generates a key based on Host + Path.

• Cache Hit: Returns the response immediately from memory.
• Cache Miss: Fetches from the remote server, serves the client, and updates the cache.
• Eviction: When the cache is full, the entry with the oldest timestamp is evicted to make room for new data.

3. Memory Safety

The project uses strtok_r for thread-safe string parsing and ensures all dynamically allocated memory (requests, responses, thread arguments) is properly freed, even in error paths.

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📜 License

This project is licensed under the MIT License - see the LICENSE file for details.

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Created with ❤️ by Aditya (Aditya41150)