Repository: nushell/nushell
File: crates/nu-command/src/network/port.rs (Rust)

Code before:
use nu_engine::command_prelude::*;
use nu_protocol::shell_error::io::IoError;

use std::net::{Ipv4Addr, SocketAddr, SocketAddrV4, TcpListener};

#[derive(Clone)]
pub struct Port;

impl Command for Port {
    fn name(&self) -> &str {
        "port"
    }

    fn signature(&self) -> Signature {
        Signature::build("port")
            .input_output_types(vec![(Type::Nothing, Type::Int)])
            .optional(
                "start",
                SyntaxShape::Int,
                "The start port to scan (inclusive).",
            )
            .optional("end", SyntaxShape::Int, "The end port to scan (inclusive).")
            .category(Category::Network)
    }

    fn description(&self) -> &str {
        "Get a free port from system."
    }

    fn search_terms(&self) -> Vec<&str> {
        vec!["network", "http"]
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        _input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        get_free_port(engine_state, stack, call)
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "get a free port between 3121 and 4000",
                example: "port 3121 4000",
                result: Some(Value::test_int(3121)),
            },
            Example {
                description: "get a free port from system",
                example: "port",
                result: None,
            },
        ]
    }
}

fn get_free_port(
    engine_state: &EngineState,
    stack: &mut Stack,
    call: &Call,
) -> Result<PipelineData, ShellError> {
    let from_io_error = IoError::factory(call.head, None);

    let start_port: Option<Spanned<usize>> = call.opt(engine_state, stack, 0)?;
    let end_port: Option<Spanned<usize>> = call.opt(engine_state, stack, 1)?;

    let listener = if start_port.is_none() && end_port.is_none() {
        // get free port from system.
        TcpListener::bind("127.0.0.1:0").map_err(&from_io_error)?
    } else {
        let (start_port, start_span) = match start_port {
            Some(p) => (p.item, Some(p.span)),
            None => (1024, None),
        };

        let start_port = match u16::try_from(start_port) {
            Ok(p) => p,
            Err(e) => {
                return Err(ShellError::CantConvert {
                    to_type: "u16".into(),
                    from_type: "usize".into(),
                    span: start_span.unwrap_or(call.head),
                    help: Some(format!("{e} (min: {}, max: {})", u16::MIN, u16::MAX)),
                });
            }
        };

        let (end_port, end_span) = match end_port {
            Some(p) => (p.item, Some(p.span)),
            None => (65535, None),
        };

        let end_port = match u16::try_from(end_port) {
            Ok(p) => p,
            Err(e) => {
                return Err(ShellError::CantConvert {
                    to_type: "u16".into(),
                    from_type: "usize".into(),
                    span: end_span.unwrap_or(call.head),
                    help: Some(format!("{e} (min: {}, max: {})", u16::MIN, u16::MAX)),
                });
            }
        };

        let range_span = match (start_span, end_span) {
            (Some(start), Some(end)) => Span::new(start.start, end.end),
            (Some(start), None) => start,
            (None, Some(end)) => end,
            (None, None) => call.head,
        };

        // check input range valid.
        if start_port > end_port {
            return Err(ShellError::InvalidRange {
                left_flank: start_port.to_string(),
                right_flank: end_port.to_string(),
                span: range_span,
            });
        }

        'search: {
            let mut last_err = None;
            for port in start_port..=end_port {
                let addr = SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::LOCALHOST, port));
                match TcpListener::bind(addr) {
                    Ok(listener) => break 'search Ok(listener),
                    Err(err) => last_err = Some(err),
                }
            }

            Err(IoError::new_with_additional_context(
                last_err.expect("range not empty, validated before"),
                range_span,
                None,
                "Every port has been tried, but no valid one was found",
            ))
        }?
    };

    let free_port = listener.local_addr().map_err(&from_io_error)?.port();
    Ok(Value::int(free_port as i64, call.head).into_pipeline_data())
}


Review comment (suggestion):
Those two `map`s can be collapsed into one.

`ntohs` being unsafe is overly cautious as an FFI call. It being effectively `u16::from_be` and an operation purely on pass-by-value.

Code after:
                        NO_ERROR => unreachable!("handled as Ok variant"),
                        ERROR_INSUFFICIENT_BUFFER => "The buffer for TcpTable is not large enough",
                        ERROR_INVALID_PARAMETER => "SizePointer was null or not writable",
                        ERROR_NOT_SUPPORTED => "GetTcpTable2 is not supported on this OS",
                        _ => "Unexpected error code from GetTcpTable2",
                    },
                )
            })
            .map_err(|(err, msg)| {
                ShellError::Io(IoError::new_with_additional_context(
                    std::io::Error::from_raw_os_error(err.0 as i32),
                    call_span,
                    None,
                    msg,
                ))
            })?;

        let used_ports: HashSet<u16> = table
            .table
            .iter()
            .map(|row| row.dwLocalPort as u16)
            .map(|raw| {
                // Convert from network byte order to host byte order.
                // SAFETY: `raw` is the exact value returned by the API for a port.
                unsafe { ntohs(raw) }
            })
            .collect();

        for port in range.item {
            if !used_ports.contains(&port) {
                return Ok(port);
            }
        }

        Err(IoError::new_with_additional_context(
            std::io::Error::from(std::io::ErrorKind::AddrInUse),
            call_span,
            None,
            "All ports in the range were taken",
        )
        .into())
    }
}

#[cfg(windows)]
use windows::search_port_in_range;