EC
ErrorKind::WouldBlock
RustINFOCriticalI/O

Operation would block

Quick Answer

Register the socket with an event loop (tokio, mio) and retry when ready.

What this means

A non-blocking I/O operation cannot proceed immediately. Equivalent to EAGAIN/EWOULDBLOCK.

Why it happens
  1. 1Reading from a non-blocking socket with no data available
  2. 2Writing to a non-blocking socket with a full buffer

Fix

Use async I/O instead

Use async I/O instead
// With tokio:
use tokio::io::AsyncReadExt;
let mut stream = tokio::net::TcpStream::connect("host:80").await?;
let mut buf = [0u8; 1024];
stream.read(&mut buf).await?; // never returns WouldBlock

Why this works

Async runtimes handle WouldBlock internally via OS readiness notifications.

Code examples
Non-blocking setrust
stream.set_nonblocking(true)?;
Same error in other languages
EAGAIN / EWOULDBLOCKin Linux / POSIX→
Sources

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