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rust.sync_dns_lookup

Stability High

Detects synchronous DNS lookups that block async runtimes.

Why It Matters

Sync DNS in async:

Blocks runtime — Entire thread pool stalled
Unpredictable latency — DNS can take seconds
Causes timeouts — Other tasks starved

Example

// ❌ Before (blocking DNS lookup)
async fn connect_to_host(host: &str) -> TcpStream {
    let addrs = std::net::ToSocketAddrs::to_socket_addrs(host)?; // Blocks!
    TcpStream::connect(addrs.next().unwrap()).await?
}

// ✅ After (async DNS resolution)
use tokio::net::lookup_host;

async fn connect_to_host(host: &str) -> TcpStream {
    let addrs = lookup_host(host).await?; // Non-blocking
    TcpStream::connect(addrs.next().unwrap()).await?
}

What Unfault Detects

std::net DNS resolution in async fns
gethostbyname in async context
Blocking resolvers in tokio code

Auto-Fix

Unfault can replace with tokio::net::lookup_host.