Interactive Brokers TWS API in Rust

main.rs

// MIT licensed.

use std::net::TcpStream;
use std::io::{Read, Write};
use std::sync::mpsc::channel;
use std::thread;

fn main() {
    let mut stream = TcpStream::connect("127.0.0.1:7496").expect("connect");
    stream.set_nodelay(true).expect("nodelay"); // Because we're wannabe HFT traders.
    println!("Connected");

    send_greeting(&mut stream);
    println!("Greeting sent");

    let greeting_response = read_message(&mut stream);
    println!("Greeting response: {:?}", greeting_response);

    send_start_api(&mut stream, 123456);

    let mut writer = stream.try_clone().expect("Clone");
    let mut reader = stream;

    let (writer_tx, writer_rx) = channel::<Vec<String>>();

    let reader_handle = thread::Builder::new().name("Reader".into()).spawn(move || {
        loop {
            let message = read_message(&mut reader);
            message_received(&message);
        }
    }).expect("Spawn");

    let writer_handle = thread::Builder::new().name("Writer".into()).spawn(move || {
        loop {
            let fields = writer_rx.recv().expect("Writer queue receive");
            let message = make_message(&fields);
            println!("Sending {:?} aka {:?} aka {:?}", 
                fields, String::from_utf8_lossy(&message), message);
            writer.write_all(&message).expect("Write all");
        }
    }).expect("Spawn");

    // Post-handshake delay or TWS bugs out.
    thread::sleep(std::time::Duration::from_millis(500));

    let request_market_data: Vec<String> = vec![
        (OutgoingRequestType::ReqMktData as u32).to_string(),
        "11".to_string(),     // Version
        "999".to_string(),    // Request id aka Ticker id
        "".to_string(),       // Contract id
        "BTC".to_string(),    // Symbol
        "CRYPTO".to_string(), // Security type
        "".to_string(),       // LastTradeDateOrContractMonth
        "".to_string(),       // strike
        "".to_string(),       // right
        "".to_string(),       // multiplier
        "PAXOS".to_string(),  // exchange
        "".to_string(),       // primaryExchange
        "USD".to_string(),    // currency
        "".to_string(),       // localSymbol
        "".to_string(),       // tradingClass
        "0".to_string(),      // Delta neutral contract? 0=false, 1=true
        "".to_string(),       // genericTickList
        "0".to_string(),      // is a snapshot?
        "0".to_string(),      // regulatorySnapshot - costs 1c ea.
        "".to_string(),       // mktDataOptions - unsupported.
    ];
    writer_tx.send(request_market_data).expect("Writer queue send");

    writer_handle.join().unwrap();
    reader_handle.join().unwrap();
}

fn add_length_prefix(bytes: &[u8]) -> Vec<u8> {
    let len = bytes.len() as u32;
    let mut data: Vec<u8> = Vec::new();
    data.push(((len >> 24) & 0xff) as u8);
    data.push(((len >> 16) & 0xff) as u8);
    data.push(((len >> 8) & 0xff) as u8);
    data.push((len & 0xff) as u8);
    data.extend(bytes);
    data
}

fn concat(a: &[u8], b: &[u8]) -> Vec<u8> {
    let mut both = a.to_owned();
    both.extend(b);
    both
}

const MIN_SERVER_VER_BOND_ISSUERID: u32 = 176; // From server_versions.py.
const DESIRED_VERSION: u32 = MIN_SERVER_VER_BOND_ISSUERID;

fn send_greeting(stream: &mut TcpStream) {
    let prefix = "API\0";
    let version = format!("v{}..{}", DESIRED_VERSION, DESIRED_VERSION);
    let version_msg = add_length_prefix(version.as_bytes());
    let both = concat(prefix.as_bytes(), &version_msg);
    stream.write_all(&both).expect("Greeting");
}

fn read_length(reader: &mut TcpStream) -> u32 {
    let mut len_buf: [u8; 4] = [0; 4];
    reader.read_exact(&mut len_buf).expect("Read length");
    let length: u32 = ((len_buf[0] as u32) << 24)
        | ((len_buf[1] as u32) << 16)
        | ((len_buf[2] as u32) << 8)
        | len_buf[3] as u32;
    length
}

fn split_message(message: &[u8]) -> Vec<String> {
    // Split into an array of buffers:
    let mut components = Vec::<Vec<u8>>::new();
    let mut current_component = Vec::<u8>::new();
    for byte in message {
        if *byte == 0 {
            if !current_component.is_empty() {
                components.push(current_component.clone());
                current_component.clear();
            }
        } else {
            current_component.push(*byte);
        }
    }
    if !current_component.is_empty() {
        components.push(current_component);
    }
    
    // Convert the buffers into strings:
    components
        .into_iter()
        .map(|v| String::from_utf8_lossy(&v).to_string())
        .collect()
}

fn read_message(reader: &mut TcpStream) -> Vec<String> {
    let length = read_length(reader);
    let mut buffer: Vec<u8> = vec![0; length as usize];
    reader.read_exact(&mut buffer).expect("Read message");
    split_message(&buffer)
}

enum OutgoingRequestType {
    ReqMktData                 = 1,
    StartApi                   = 71,
}

// Join and delimit the fields, prefixing the length.
fn make_message(fields: &[String]) -> Vec<u8> {
    let mut delimited_fields = Vec::<u8>::new();
    for field in fields {
        delimited_fields.extend(field.as_bytes());
        delimited_fields.push(0); // Even goes after the last field.
    }
    add_length_prefix(&delimited_fields)
}

fn send_start_api(stream: &mut TcpStream, client_id: u32) {
    let fields: Vec<String> = vec![
        (OutgoingRequestType::StartApi as u32).to_string(),
        "2".to_string(), // Version of the Start API message.
        client_id.to_string(),
        "".to_string(), // Optional capabilities.
    ];
    let message = make_message(&fields);
    stream.write_all(&message).expect("Start api");
}

enum IncomingRequestType {
    TickPrice = 1,
    ErrMsg    = 4,
}

fn message_received(fields: &[String]) {
    if fields.is_empty() { return }
    let Ok(t) = fields[0].parse::<u32>() else { return };
    if t == IncomingRequestType::ErrMsg as u32 {
        let _request_id = fields.get(2);
        let _code = fields.get(3);
        let Some(text) = fields.get(4) else { return };
        println!("Message: {}", text);
    } else if t == IncomingRequestType::TickPrice as u32 {
        let Some(tick_type) = fields.get(3) else { return };
        if tick_type != "4" { return } // 4 = 'Last' from ticktype.py.
        let Some(price) = fields.get(4) else { return };
        println!("Price: {}", price);
    } else {
        println!("Received: {:?}", fields); 
    }
}

Courtesy of https://www.splinter.com.au/2023/08/28/interactive-brokers-tws-api-rust-crypto-ticker/