BufReader and Writer

help
#1

I've been coding for about 3 weeks in Rust and loving it. I've drafted a few questions here, but found the answer moments before clicking the Create Topic button. But this one has me stumped.

I have a pipe. I want to call pipe.read_line(), pipe.read_exact(), and pipe.write_all(). To call read_line(), I pass the pipe to a BufReader. But BufReader then owns the pipe so I see no way to later call pipe.write_all().

Here's my code:

use crate::server::Server;
use std::ffi::OsString;
use named_pipe::PipeClient;
use std::io::{Read, BufRead, BufReader, Write};
use anyhow::Context;
use crate::bytevec::ByteVec;

impl Server {
    pub fn main(pipe_name: &str) -> anyhow::Result<()> {
        let mut server = Server{};
        let pipe_name = OsString::from(pipe_name);
        let mut pipe = BufReader::new(PipeClient::connect(pipe_name)?);
        let mut line = String::new();
        let bytes_read = pipe.read_line(&mut line)?;
        if 0 == bytes_read {
            return Ok(());
        }
        let message_length: usize = line.trim().parse().context(
            "expected the message length")?;
        let mut buffer = ByteVec::new();
        buffer.0.resize(message_length, 0);
        pipe.read_exact(&mut buffer.0)?;
        let result = server.serve(buffer);
        pipe.write_all(&result.0)?;
        Ok(())
    }
}

The compiler complains. I understand the error 100%. I don't understand how to practically work around it.

error[E0599]: no method named `write_all` found for struct `std::io::BufReader<named_pipe::PipeClient>` in the current scope
  --> src\server\winmain.rs:24:14
   |
24 |         pipe.write_all(&result.0)?;
   |              ^^^^^^^^^ method not found in `std::io::BufReader<named_pipe::PipeClient>`

warning: unused import: `Write`
 --> src\server\winmain.rs:4:41
  |
4 | use std::io::{Read, BufRead, BufReader, Write};
  |                                         ^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

Thanks for your help!

#2

One way to accomplish it in this case is to get the PipeClient back out of the BufReader which can be done by changing the last line to either

pipe.into_inner().write_all(&result.0)?;

or

pipe.get_mut().write_all(&result.0)?;

The first one takes the pipe out of the BufReader and the second one just borrows the pipe from BufReader

#3

Well that's certainly annoying. One would think that the bufread/write would also implement the other trait and just pass it through. You will probably have to use get_mut or implement it a BufReaderWriter yourself.

#4

Thank you! That looks much more idiomatic than what I tried.

#5

Thanks! I did indeed implement my own BufReaderWriter, but I'll also give drewkett's suggestion a try.

#6

This would be nice for sockets, but it would cause bugs in cases like BufWriter<File>, when unflushed data in the BufWriter can affect the Read output. :frowning:

#7

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