Read all data from TCP stream in Rust

One way to do this, is:

1. Set a read timeout on the TcpStream using set_read_timeout. This avoids a hanging client in case the server has stopped sending but left the connection open.
2. Read from the stream in a loop, using a BufReader, and aggregate the read bytes.
3. Break out of the loop in case the read timed out or the server closed the connection.

Here's some example code:

use std::{
    io::{self, BufReader, LineWriter, Read, Write},
    net::TcpStream,
    time::Duration,
};

fn main() -> io::Result<()> {
    println!("Start of program");

    // This is just to get data via TCP, we could of course parse the HTTP header for
    // the message length
    let server_host = "www.neverssl.com";
    let server_port = "80";

    let stream = TcpStream::connect(server_host.to_string() + ":" + server_port)?;

    let mut reader = BufReader::new(&stream);
    let mut writer = LineWriter::new(&stream);

    // Don't block indefinitely on `reader.read` when there's no data to read
    let max_read_time = Duration::from_millis(200);
    stream.set_read_timeout(Some(max_read_time))?;

    writer.write_all(format!("GET / HTTP/1.1\r\nhost: {server_host}\r\n\r\n").as_bytes())?;

    let mut total_bytes_read = vec![];
    let bytes_to_read_per_attempt = 1024;
    let mut read_attempt_nr = 0;
    loop {
        read_attempt_nr += 1;
        println!("Read attempt nr {read_attempt_nr}");
        let mut cur_buffer = vec![0; bytes_to_read_per_attempt];

        // If the reader has no data but the server hasn't closed the connection,
        // by default `reader.read()` would block until the server closes the connection.
        // Hence, we need `stream.set_read_timeout`.
        let nr_of_bytes_read = match reader.read(&mut cur_buffer) {
            Ok(nr_of_bytes_read) => nr_of_bytes_read,
            Err(err) => {
                if err.kind() == io::ErrorKind::WouldBlock || err.kind() == io::ErrorKind::TimedOut
                {
                    println!("Read attempt timed out");
                    break;
                } else {
                    return Err(err);
                }
            }
        };

        // Reading zero bytes indicates that the server closed the connection
        if nr_of_bytes_read == 0 {
            println!("Read zero bytes → Connection seems closed");
            break;
        }

        // Remove the excess null bytes at the end of cur_buffer
        cur_buffer.truncate(nr_of_bytes_read);
        total_bytes_read.append(&mut cur_buffer);

        println!("Read {nr_of_bytes_read} bytes in attempt nr {read_attempt_nr}");
    }
    let response = String::from_utf8_lossy(&total_bytes_read).to_string();
    let nr_of_bytes_received = total_bytes_read.len();

    println!("Server response : {response}");
    println!("{nr_of_bytes_received} bytes received");

    Ok(println!("End of program"))
}

This client assumes that if it hasn't received data from the server for 200 milliseconds (while the connection is still open), that the server's message is complete.

posted 12 months ago

CC BY-SA 4.0

12mo ago

Matthias Braun‭

93 reputation 4 1 14 11