Building a Rust Port Scanner

A weekend experiment: a TCP connect scanner in Rust, and what it taught me about sockets, timeouts, and concurrency.

Design

100%

Diagram source

flowchart TD
    A[CLI args\ntarget + ports] --> B[Resolve host]
    B --> C[Spawn worker pool\nN = 512 tasks]
    C --> D[TcpStream::connect_timeout]
    D -- Ok --> E[Port OPEN]
    D -- Err --> F[closed / filtered]
    E --> G[Merge results\nsorted output]
    F --> G

Class view of the core

100%

Diagram source

classDiagram
    class Scanner {
        -String target
        -Vec_u16 ports
        -usize concurrency
        +scan() Vec_PortStatus
    }
    class PortStatus {
        <<enumeration>>
        Open
        Closed
        Filtered
    }
    class RateLimiter {
        -Duration interval
        +acquire() Future
    }
    Scanner "1" --> "many" PortStatus : produces
    Scanner o-- RateLimiter : throttles via

Data model

100%

Diagram source

erDiagram
    SCAN ||--o{ RESULT : yields
    SCAN {
        string target
        u16 port_range
        int workers
    }
    RESULT {
        u16 port
        string status
        float rtt_ms
    }

First benchmark

Scanning scanme.nmap.org ports 1–1024:

Workers	Time (s)
1	41.2
64	2.9
512	0.8

Lesson: the bottleneck was never the socket API — it was my initial sequential loop. Concurrency is the design decision here.