Webserver

A lightweight HTTP/1.1 web server written in C++ as part of the 42 school webserver project.
This project implements a subset of Nginx-like behavior, including static file serving, CGI execution, configuration parsing, and proper HTTP error handling.

---

Table of Contents

• Overview
• Features
• Project Structure
• Architecture
  • Request Flow
  • Configuration System
  • HTTP Handling
  • CGI Execution
• Configuration File
• Error Handling
• Build & Run
• Testing
• Authors

---

Overview

This webserver is designed to:

• Parse and validate HTTP/1.1 requests
• Serve static files from configured roots
• Execute CGI scripts (e.g. Python, PHP, .sh)
• Handle multiple clients using non-blocking I/O
• Load and validate Nginx-style configuration files

The implementation focuses on clarity, correctness, and strict separation of responsibilities between modules.

---

Features

• HTTP methods: GET, POST, DELETE
• Static file serving
• Directory index support
• Custom error pages
• CGI execution via fork() + execve()
• Request body handling
• Chunked and non-chunked requests
• Multiple server blocks
• Location-based configuration
• Precise configuration error reporting (line/column)

---

Project Structure

├── include # Header files
├── src # Source files
│ ├── CGI.cpp
│ ├── ConfigTokenizer.cpp
│ ├── ConfigParser.cpp
│ ├── ConfigBuilder.cpp
│ ├── HttpRequestParser.cpp
│ ├── HttpResponse.cpp
│ ├── HttpResponseHandler.cpp
│ ├── Server.cpp
│ └── Webserver.cpp
├── sites # Static files and CGI scripts
├── tester # Test utilities
└── README.md

---

Architecture

Request Flow

             ┌────────────────────┐
             │     Client         │
             └─────────┬──────────┘
                       │  HTTP request
                       ▼
         ┌───────────────────────────────────┐
         │       A: Network & I/O Manager    │
         │---------------------------------- │
         │ - Accepts connections             │
         │ - poll/select/epoll monitors FDs  │
         │ - Non-blocking read/write         │
         └───────────┬───────────────────────┘
                     │ raw bytes
                     ▼
        ┌─────────────────────────────────────┐
        │   B: HTTP Request/Response Handler  │
        │-------------------------------------│
        │ - Parse HTTP request                │
        │ - Apply HTTP rules                  │
        │ - Determines action (static/CGI/etc)│
        └──────────┬───────────────┬──────────┘
                   │               │
       asks for config rules   needs CGI process
                   │               │
                   ▼               ▼
 ┌──────────────────────────────────────────────┐
 │        C: Configuration & CGI Manager        │
 │----------------------------------------------│
 │ - server.conf parser                         │
 │ - location/root/index/error_pages            │
 │ - CGI execution (execve)                     │
 │ - file path resolution                       │
 └──────────────────┬───────────────────────────┘
                    │ response data (file/CGI output)
                    ▼
        ┌─────────────────────────────────────┐
        │    B builds full HTTP response      │
        └──────────────────┬──────────────────┘
                           │ final bytes
                           ▼
         ┌────────────────────────────────────┐
         │    A: Sends response to client     │
         └────────────────────────────────────┘

Each step operates on well-defined data structures to avoid tight coupling.

---

Configuration System

The configuration system is split into three independent stages: ConfigTokenizer → ConfigParser → ConfigBuilder (Lexing) (Syntax) (Runtime objects)

1. ConfigTokenizer

• Converts raw configuration text into typed tokens
• Skips whitespace and comments
• Tracks line and column numbers
• Performs no syntax or semantic validation

2. ConfigParser

• Validates grammar and block structure
• Parses server and location blocks
• Ensures correct use of braces and semicolons
• Reports syntax errors with precise locations

3. ConfigBuilder

• Builds runtime configuration objects
• Applies default values
• Handles inheritance from server to location
• Produces final ServerConfig and LocationConfig structures

At runtime, the webserver only interacts with these built configuration objects.

---

HTTP Handling

• HTTP requests are parsed into an HttpRequest object
• Start line, headers, and body are validated
• Unsupported methods or malformed requests result in appropriate HTTP error codes

The server follows strict HTTP/1.1 rules unless explicitly specified otherwise.

---

CGI Execution

CGI execution is handled by a dedicated CGI class.

Responsibilities:

• Determine whether a request qualifies as CGI
• Prepare CGI environment variables
• Redirect stdin/stdout using pipes
• Execute the CGI interpreter via execve()
• Capture and return script output

Supported methods for CGI:

• GET
• POST

The implementation follows the CGI/1.1 specification closely.

---

Configuration File

The configuration syntax is inspired by Nginx:

server {
    listen 8080;
    server_name localhost;

    root ./sites/static;

    location /cgi {
        root ./sites/cgi;
        cgi_pass /usr/bin/python3;
        cgi_ext .py;
    }
}

Error Handling

The server provides custom error pages and standard HTTP responses for common client and server errors:

• Redirection errors (3xx): 301
• Client errors (4xx): 400, 403, 404, 405, 408, 413, 414, 431

• Server errors (5xx): 500 Not all HTTP status codes are implemented due to the project scope. Additional codes can be added easily if needed.

Build & Run

make
./webserv congiguration/config.conf
./webserv

The server will start listening according to the spesified configuration file. If not specified, the server will start listening according to the default config file(congiguration/simple.conf).

Testing

• Manual testing with curl
• Browser-based testing
• Custom CGI scripts

Someideas of testing cases:

• Invalid requests
• Unsupported methods
• Large request bodies
• Invalid configuration files

Authors

• Server: Lucio
• HTTP & response handling: Yuxin Wu
• Configuration & CGI: Lin Liu