r3bl_terminal_async SharedWriter Indentation Bug #439
Description
Problem Description
I am integrating r3bl_terminal_async in a Rust application and using its SharedWriter as the output for the fern logger. Everything works in terms of asynchronous logging and prompt preservation, but the output exhibits a reproducible visual issue:
Issue Summary
When writing log messages through the SharedWriter (via log::info!, log::warn!, etc.), the first log line is correctly aligned at column 0, but every subsequent log line is automatically prefixed with exactly one extra space.
Example output:
banner
line 1
line 2
line 3This happens even though:
• none of my log messages contain leading spaces,
• my logger does not insert any leading whitespace,
• ANSI color codes have been completely removed,
• the logger was reduced to a minimal formatter writing raw strings,
• the underlying Write implementation also does not add spaces.
The issue persists regardless of logger configuration.
Minimal Reproduction Example
// src/main.rs
use anyhow::Result;
use anyhow::anyhow;
use r3bl_terminal_async::TerminalAsync;
use log::info;
use fern::Dispatch;
use log::LevelFilter;
use std::io::Write;
pub fn init_logger<W>(
writer: W,
level: LevelFilter,
) -> Result<(), fern::InitError>
where
W: Write + Send + 'static,
{
let boxed: Box<dyn Write + Send> = Box::new(writer);
Dispatch::new()
.level(level)
.format(|out, msg, _record| {
// Writes exactly: "<message>\n"
out.finish(format_args!("{}", msg))
})
.chain(boxed)
.apply()?;
Ok(())
}
#[tokio::main]
async fn main() -> Result<()> {
let maybe_terminal_async = TerminalAsync::try_new("> ")
.await
.map_err(|e| anyhow!(e.to_string()))?;
let Some(mut terminal_async) = maybe_terminal_async else {
println!("Not an interactive terminal.");
return Ok(());
};
let writer = terminal_async.clone_shared_writer();
init_logger(writer, LevelFilter::Info)?;
terminal_async.println("banner").await;
info!("line 1");
info!("line 2");
Ok(())
}Cargo.toml
[package]
name = "r3bl_test"
version = "0.1.0"
edition = "2024"
[dependencies]
anyhow = "1.0.100"
fern = "0.7.1"
log = "0.4.28"
r3bl_terminal_async = "0.6.0"
tokio = "1.48.0"Actual output
banner
line 1
line 2Expected output
banner
line 1
line 2Observations
• The indentation only appears when using the SharedWriter.
• Writing logs to stderr removes the indentation but breaks prompt redrawing (as expected).
• The extra leading space seems to be injected internally when SharedWriter handles multiple consecutive writes.
• The indentation appears consistently for every log message after the first one.
Conclusion
This is likely a rendering or buffer-handling quirk inside r3bl_terminal_async::SharedWriter, where the library inserts a padding space before lines printed after the first one in order to avoid overwriting the prompt or input buffer.
However, this padding occurs even with a completely empty formatter and no ANSI sequences, and results in misaligned multi-line log output.
I would appreciate guidance on:
• whether this is an intended behavior,
• whether there’s an API to disable this padding,
• or if this qualifies as a bug in the SharedWriter implementation.