ft-ping

A high-fidelity re-implementation of the classic ICMP network utility in C, focusing on low-level network programming.

Key Features • Architecture • Logic Flow • System Flow Diagram • Prerequisites • Installation • 1. Clone the Repository

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

The tool verifies the reachability of a remote host and measures the round-trip time (RTT) for packets sent to a destination. It handles packet construction, checksum calculation (RFC 1071), signal management, and precise statistical analysis of network latency.

Key Features

• ICMP Echo Logic: Implements the core ICMP echo request/reply mechanism to determine host availability.
• DNS Resolution: Resolves hostnames to IPv4 addresses using getaddrinfo, accepting both IP addresses and domain names as targets.
• Dual Socket Support: Intelligently 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).
• Precision RTT Statistics: Calculates minimum, maximum, average, and mean deviation (mdev) of round-trip times using gettimeofday.
• Robust Checksumming: A manual implementation of the 16-bit one's complement sum algorithm ensures ICMP header integrity.
• Graceful Shutdown: Intercepts SIGINT (Ctrl+C) to terminate the process cleanly and display a comprehensive statistical summary.

Architecture

Logic Flow

1. Initialization: Parse command-line arguments.
2. Resolution: Resolve the target hostname into an IPv4 address and sockaddr_in structure.
3. Socket Creation: Initialize an ICMP socket. Attempt to use SOCK_RAW with root privileges, falling back to SOCK_DGRAM if necessary. Drop root privileges immediately after socket binding for enhanced security.
4. Main Loop:
   • Construct and timestamp an ICMP echo request packet.
   • Calculate the packet's checksum.
   • Transmit the packet using sendto.
5. Reception:
   • Wait for an incoming packet using select with a timeout.
   • Receive the packet and parse the IP/ICMP headers.
   • Validate the packet's process ID and sequence number.
   • Calculate and display the RTT.
6. Termination: Upon receiving SIGINT, calculate the final statistics (including variance and standard deviation) and print a summary before exiting.

System Flow Diagram

graph TD
    A[Start] --> B[Parse Command-Line Arguments]
    B --> C[DNS Resolution via getaddrinfo]
    C --> D[Initialize Socket: RAW/DGRAM]
    D --> E[Set Signal Handler: 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]

Loading

Prerequisites

• Operating System: Linux (developed and tested on Debian/Ubuntu)
• Compiler: GCC (C99 standard or later)
• Build Tools: make
• Libraries: libc6-dev
• Permissions: Root privileges (sudo) or cap_net_raw capabilities are required for SOCK_RAW functionality.

Installation and Building

1. Clone the Repository

git clone https://github.com/jdecorte-be/ft-ping.git
cd ft-ping

2. Build the Executable

Use the provided Makefile to compile the source code.

make

The compiled binary ft_ping will be created in the root directory.

3. Set Capabilities (Optional)

To run ft_ping without sudo, you can grant the executable the required network capabilities:

sudo setcap cap_net_raw+ep ./ft_ping

Docker Environment (Optional)

To build and run the project in an isolated Docker container:

docker-compose up --build

Usage

The command syntax is designed to be similar to the standard ping utility.

Basic Usage

# Using sudo
sudo ./ft_ping google.com

# Or with capabilities set
./ft_ping 8.8.8.8

Options

Flag	Description	Example
-v	Verbose mode. Prints detailed packet information.	./ft_ping -v google.com
-h	Help. Displays the usage message and options.	./ft_ping -h

Troubleshooting

Issue	Probable Cause	Resolution
Lacking privilege for icmp socket	Missing root privileges or capabilities.	Run with sudo or set capabilities using setcap cap_net_raw+ep ft_ping.
unknown host	DNS resolution failed or no network access.	Check your internet connection and DNS settings (e.g., /etc/resolv.conf).
Checksum mismatch in received packet	Packet corruption or a logic error.	Ensure the network is stable. If persistent, it may indicate a bug.
Packet reception timeout	Host is down, or a firewall is blocking ICMP.	Verify the destination host is online and check firewall rules on both ends.

Roadmap

• IPv6 Support: Add support for ICMPv6 and AF_INET6.
• Custom Payload Size: Implement a -s flag to specify the data payload size.
• Custom Interval: Implement a -i flag to change the interval between packets.
• Flood Mode: Add a -f flag for high-frequency sending (superuser only).
• Time To Live (TTL): Implement a -t flag to set the packet's TTL value.
• Packet Count: Add a -c flag to stop after sending a specific number of packets.

License

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