std::io

Status: experimental

Stream-oriented I/O abstractions and process standard streams.

Buffering

Standard output is buffered so that the several writes a formatted line arrives as - the literal segments, a rendered value, the newline - cost one write(2). The buffer drains on the newline that ends a write, so a line is on its way out as soon as it is complete, whether standard output is a terminal, a pipe, or a file. A program that announces a line and then blocks is therefore visible to whatever is reading it:

println("{}", server.addr())
server.serve(routes)?

Text with no terminator accumulates: a prompt written with print needs an explicit flush before the read.

use std::io
print("name: ")
io::stdout().flush()

Byte-at-a-time and byte-range writes accumulate too - that is the high-throughput path, and it drains when the buffer fills, on an explicit flush, and at exit. Standard error is never buffered, and writing to it flushes standard output first, so the two streams keep their order.

API details and source

The implementation source contains the complete declarations and implementation notes. The table below lists canonical Gossamer call signatures; every item name links directly to its implementation file.

Item	Canonical signature or declaration	Description
BufReader	type BufReader	Buffered wrapper around any Reader.
BufWriter	type BufWriter	Buffered wrapper around any Writer.
Copy	fn Copy(dst: io::Writer, src: io::Reader) -> Result<i64, io::Error>	Copies all bytes from src to dst; returns the byte count.
Error	type Error	Errors raised by I/O operations.
ReadAll	fn ReadAll(reader: io::Reader) -> Result<String, io::Error>	Drains a reader to a String. Mirrors Go's io.ReadAll.
Reader	trait Reader	Pull-style byte source.
Writer	trait Writer	Push-style byte sink.
stderr	fn stderr() -> io::Writer	Returns a handle to the process's standard error stream.
stdin	fn stdin() -> io::Reader	Returns a handle to the process's standard input stream. Use read_line(&mut String) for interactive prompts.
stdout	fn stdout() -> io::Writer	Returns a handle to the process's standard output stream.