ft_ping

Overview • Features • Architecture • Installation • Usage • Troubleshooting • Roadmap • License

Overview

ft_ping is a high-fidelity re-implementation of the classic ICMP network utility. Developed in C, this project serves as a deep dive into low-level network programming, specifically focusing on the Internet Control Message Protocol (ICMP) as defined in RFC 792.

The tool allows users to verify the reachability of a remote host and measure the round-trip time (RTT) for messages sent from the source host to a destination computer. It handles complex tasks such as packet construction, checksum calculation (RFC 1071), signal management, and precise statistical analysis of network latency.

Key Features

• ICMP Echo Request/Reply Logic: Implements the fundamental handshake of the ICMP protocol to determine host availability.
• Precision RTT Calculation: Computes minimum, maximum, average, and standard deviation (mdev) of round-trip times using gettimeofday and advanced mathematical variance formulas.
• DNS Resolution: Dynamically resolves hostnames to IPv4 addresses using getaddrinfo, ensuring compatibility with both IP strings and domain names.
• Dual Socket Support: Implements a smart fallback mechanism. It attempts to open a SOCK_RAW socket (requiring root privileges) and gracefully falls back to SOCK_DGRAM if run as a standard user (where supported by the OS).
• Signal Handling: Integrated SIGINT (Ctrl+C) interception to gracefully terminate the process and display a comprehensive statistical summary.
• Robust Checksumming: Manual implementation of the 16-bit one's complement sum algorithm required for ICMP header integrity.

Architecture

Logic Flow

1. Initialization: Parse CLI arguments using argp.
2. Resolution: Convert the target hostname into a sockaddr_in structure.
3. Privilege Management: Initialize the ICMP socket. If root, use SOCK_RAW. If not, attempt SOCK_DGRAM. Drop privileges immediately after socket creation for security.
4. Transmission Loop:
   • Construct an ICMP header.
   • Calculate the checksum.
   • Transmit the packet and record the timestamp.
5. Reception Logic:
   • Monitor the socket for incoming data using select with a timeout.
   • Parse the received IP/ICMP header.
   • Validate the process ID and sequence number.
   • Calculate the elapsed RTT.
6. Termination: Calculate final variance and standard deviation of the session and exit.

System Flow Diagram

graph TD
    A[Start] --> B[Parse Command Line Arguments]
    B --> C[DNS Resolution: getaddrinfo]
    C --> D[Initialize Socket: RAW/DGRAM]
    D --> E[Set Signals: SIGINT]
    E --> F[Send ICMP Echo Request]
    F --> G[Wait for Response: select/recvmsg]
    G --> H{Valid Reply?}
    H -- Yes --> I[Update Stats & Print Info]
    H -- No/Timeout --> J[Handle Error/Wait]
    I --> K{SIGINT Received?}
    J --> K
    K -- No --> L[Sleep 1s] --> F
    K -- Yes --> M[Calculate Final Stats]
    M --> N[Display Summary & Exit]

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Prerequisites

To build and run ft_ping, you need the following environment:

• OS: Linux (Debian/Ubuntu recommended)
• Compiler: GCC (support for C99 or later)
• Libraries: libc6-dev
• Permissions: Root privileges are required for SOCK_RAW usage, or cap_net_raw capabilities must be set on the executable.

Installation

1. Clone the Repository

git clone https://github.com/yourusername/ft_ping.git
cd ft_ping

2. Build the Executable

Use the provided Makefile to compile the source code.

make

Expected output:

Compiling: srcs/main.c
Compiling: srcs/ping.c
Linking: ft_ping
Build complete!

3. Docker Environment (Optional)

If you wish to test in a clean environment, use the provided Dockerfile:

docker-compose up --build

Usage Guide

Basic Command

sudo ./ft_ping google.com

Verbose Mode

To see detailed packet information (including ID and sequence tracking):

./ft_ping -v 8.8.8.8

Key Function Parameters

• int send_echo_icmp(t_ping *ping): Constructs the ICMP header. It sets icmp->type = ICMP_ECHO and maps the ping->pid to the icmp->un.echo.id to identify returned packets.
• int recv_echo_icmp(t_ping *ping): Utilizes recvmsg and CMSG_DATA to extract the TTL (Time To Live) from the packet's ancillary data when using raw sockets.
• int checksum(uint16_t *buf, int len): Performs a 16-bit sum of the header, handles odd-byte lengths, and returns the one's complement.

Troubleshooting

Issue	Cause	Resolution
Lacking privilege for icmp socket	Missing root or capabilities	Run with sudo or use setcap cap_net_raw+ep ft_ping
unknown host	DNS failure or No Network	Verify /etc/resolv.conf and active internet connection
checksum mismatch	Corrupted packet or logic error	Ensure the data buffer is zeroed before checksum calculation
packet too short	Malformed ICMP response	Check network MTU or if a firewall is stripping headers

Roadmap

• IPv6 Support: Integration of ICMP6 and AF_INET6 for modern network compatibility.
• Custom Payload: Allow users to specify the number of bytes in the data segment.
• Adaptive Interval: Implement a -i flag to change the transmission frequency from the default 1 second.
• Flood Mode: Add a high-frequency -f mode for stress testing (superuser only).

License

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