Justniffer

Project Page

Overview

Justniffer is a network TCP packet sniffer and logging tool designed to capture, decode, and analyze TCP/IP traffic with a strong focus on HTTP. Its flexible logging engine allows it to adapt to virtually any TCP‑based protocol, making it useful for debugging, performance analysis, and custom traffic inspection.

Justniffer can decode HTTP requests and responses, extracting:

• Client and server IP addresses
• Requested URLs
• HTTP headers
• Message bodies
• TLS info
• Timing information (request time, response time, idle time, etc.)

For non‑HTTP traffic, Justniffer provides a powerful and customizable logging system that allows you to extract any relevant information from the TCP data stream.

Packet capture is performed using libpcap, ensuring compatibility with standard capture formats and tools such as tcpdump.

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Features

• HTTP request/response decoding
• Customizable log formats for any TCP‑based protocol
• Performance metrics: request time, response time, idle time, connection time

sequenceDiagram
    participant Client
    participant Server

    %% Connection setup
    Client->>Server: SYN (connect)
    Note right of Server: %connection.time
    Server-->>Client: SYN/ACK
    Client->>Server: ACK
    Note right of Server: ESTABLISHED

    %% Idle before request
    Note right of Server: %idle.time.0\n(after connection, before request)

    %% Request phase
    Client->>Server: Request (first packet)
    Server-->>Client: ACK

    Client->>Server: Request (data...)
    Note right of Server: %request.time
    Server-->>Client: ACK

    Client->>Server: Request (last packet)
    Server-->>Client: ACK

    %% Response phase
    Note right of Server: %response.time.begin

    Server-->>Client: Response (first packet)
    Client->>Server: ACK

    Server-->>Client: Response (data...)
    Note right of Server: %response.time.end
    Client->>Server: ACK

    Server-->>Client: Response (last packet)
    Client->>Server: ACK

    %% Idle after response
    Note right of Server: %idle.time.1\n(after response, before next request/close)

    %% Connection close
    Server-->>Client: CLOSE

• libpcap‑based capture (live or from .pcap files)
• Promiscuous mode support for passive monitoring
• Extensible via external scripts (bash, Python, Perl, ELF binaries) — Learn more
• Reconstructs TCP streams including reordering, retransmissions, fragmentation

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Quick Start

Install on Ubuntu

sudo apt install software-properties-common
sudo add-apt-repository ppa:oreste-notelli/ppa
sudo apt update
sudo apt install justniffer

Capture HTTP traffic in access‑log style

justniffer -i eth0

Add response time to each log entry

justniffer -i eth0 -a " %response.time"

Capture full HTTP requests and responses

justniffer -i eth0 -r

Use a custom log format

justniffer -i eth0 -l "%request.timestamp %source.ip %dest.ip %request.header.host %request.url"

Read from a PCAP file

justniffer -f file.cap

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Examples

Example 1 — Retrieve HTTP traffic in access‑log format

justniffer -i eth0

output:

192.168.2.2 - - [15/Apr/2009:17:19:57 +0200] "GET /sflogo.php?group_id=205860&type=2 HTTP/1.1" 200 0 "" "Mozilla/5.0 ..."
...

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Example 2 — Append additional fields (e.g., HTTP response time)

justniffer -i eth0 -a " %response.time"

output:

192.168.2.5 - - [22/Apr/2009:22:27:36 +0200] "GET /sflogo.php?group_id=205860&type=2 HTTP/1.1" ... 0.427993
...

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Example 3 — Capture all TCP traffic

(add -u or -x to encode unprintable characters)

justniffer -i eth0 -r

output:

GET /doc/maint-guide/ch-upload.en.html HTTP/1.1
Host: www.debian.org
...

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Example 4 — Define a completely custom log format

justniffer -i eth0 -l "%request.timestamp %source.ip %dest.ip %request.header.host %request.url"

output:

06/28/11 13:30:48 192.168.2.2 72.14.221.118 i1.ytimg.com /vi/TjSk6CVN5LY/default.jpg
...

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Example 5 — Read from a capture file

justniffer -f /file.cap

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Documentation

Full documentation, advanced examples, and usage guides:
👉 https://onotelli.github.io/justniffer/

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Contributing

Pull requests, bug reports, and feature suggestions are welcome.

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License

Justniffer is released under the GPLv3 license.