Move common connection code to a new net module

src/imap/client.rs

@@ -8,14 +8,12 @@ use anyhow::{Context as _, Result};
 use async_imap::Client as ImapClient;
 use async_imap::Session as ImapSession;
 
-use tokio::io::BufWriter;
-use tokio::net::{self, TcpStream};
-use tokio::time::timeout;
-use tokio_io_timeout::TimeoutStream;
+use tokio::net;
 
 use super::capabilities::Capabilities;
 use super::session::Session;
 use crate::login_param::build_tls;
+use crate::net::connect_buffered;
 use crate::socks::Socks5Config;
 
 use super::session::SessionStream;
@@ -94,15 +92,7 @@ impl Client {
     }
 
     pub async fn connect_secure(hostname: &str, port: u16, strict_tls: bool) -> Result<Self> {
-        let tcp_stream = timeout(IMAP_TIMEOUT, TcpStream::connect((hostname, port))).await??;
-        tcp_stream.set_nodelay(true)?;
-
-        let mut timeout_stream = TimeoutStream::new(tcp_stream);
-        timeout_stream.set_write_timeout(Some(IMAP_TIMEOUT));
-        timeout_stream.set_read_timeout(Some(IMAP_TIMEOUT));
-        let timeout_stream = Box::pin(timeout_stream);
-
-        let buffered_stream = BufWriter::new(timeout_stream);
+        let buffered_stream = connect_buffered((hostname, port), IMAP_TIMEOUT).await?;
 
         let tls = build_tls(strict_tls);
         let tls_stream: Box<dyn SessionStream> =
@@ -121,15 +111,7 @@ impl Client {
     }
 
     pub async fn connect_insecure(addr: impl net::ToSocketAddrs) -> Result<Self> {
-        let tcp_stream = timeout(IMAP_TIMEOUT, TcpStream::connect(addr)).await??;
-        tcp_stream.set_nodelay(true)?;
-
-        let mut timeout_stream = TimeoutStream::new(tcp_stream);
-        timeout_stream.set_write_timeout(Some(IMAP_TIMEOUT));
-        timeout_stream.set_read_timeout(Some(IMAP_TIMEOUT));
-        let timeout_stream = Box::pin(timeout_stream);
-
-        let buffered_stream = BufWriter::new(timeout_stream);
+        let buffered_stream = connect_buffered(addr, IMAP_TIMEOUT).await?;
 
         let stream: Box<dyn SessionStream> = Box::new(buffered_stream);
 

src/lib.rs

@@ -100,6 +100,7 @@ mod dehtml;
 mod authres;
 mod color;
 pub mod html;
+mod net;
 pub mod plaintext;
 mod ratelimit;
 pub mod summary;

src/net.rs

@@ -0,0 +1,36 @@
+use std::pin::Pin;
+///! # Common network utilities.
+use std::time::Duration;
+
+use anyhow::{Context as _, Result};
+use tokio::io::BufWriter;
+use tokio::net::{TcpStream, ToSocketAddrs};
+use tokio::time::timeout;
+use tokio_io_timeout::TimeoutStream;
+
+/// Returns a TCP connection with read/write timeouts set and
+/// Nagle's algorithm disabled (TCP_NODELAY set) in favor of userspace buffering.
+///
+/// Doing our own buffering ensures that calling `.flush()` on the socket results
+/// in immediate sending of the packet, which is important to reduce latency of
+/// interactive protocols such as IMAP.
+pub(crate) async fn connect_buffered(
+    addr: impl ToSocketAddrs,
+    timeout_val: Duration,
+) -> Result<BufWriter<Pin<Box<TimeoutStream<TcpStream>>>>> {
+    let tcp_stream = timeout(timeout_val, TcpStream::connect(addr))
+        .await
+        .context("connection timeout")?
+        .context("connection failure")?;
+    tcp_stream
+        .set_nodelay(true)
+        .context("cannot set TCP_NODELAY")?;
+
+    let mut timeout_stream = TimeoutStream::new(tcp_stream);
+    timeout_stream.set_write_timeout(Some(timeout_val));
+    timeout_stream.set_read_timeout(Some(timeout_val));
+    let pinned_stream = Box::pin(timeout_stream);
+
+    let buffered_stream = BufWriter::new(pinned_stream);
+    Ok(buffered_stream)
+}

src/socks.rs

@@ -4,14 +4,14 @@ use std::fmt;
 use std::pin::Pin;
 use std::time::Duration;
 
-use anyhow::{Context as _, Result};
+use anyhow::Result;
 pub use async_smtp::ServerAddress;
 use tokio::io::BufWriter;
 use tokio::net::{self, TcpStream};
-use tokio::time::timeout;
 use tokio_io_timeout::TimeoutStream;
 
 use crate::context::Context;
+use crate::net::connect_buffered;
 use fast_socks5::client::{Config, Socks5Stream};
 use fast_socks5::AuthenticationMethod;
 
@@ -60,16 +60,7 @@ impl Socks5Config {
         target_addr: impl net::ToSocketAddrs,
         timeout_val: Duration,
     ) -> Result<Socks5Stream<BufWriter<Pin<Box<TimeoutStream<TcpStream>>>>>> {
-        let tcp_stream = timeout(timeout_val, TcpStream::connect(target_addr))
-            .await
-            .context("connection timeout")?
-            .context("connection failure")?;
-
-        let mut timeout_stream = TimeoutStream::new(tcp_stream);
-        timeout_stream.set_write_timeout(Some(timeout_val));
-        timeout_stream.set_read_timeout(Some(timeout_val));
-        let pinned_stream = Box::pin(timeout_stream);
-        let buffered_stream = BufWriter::new(pinned_stream);
+        let buffered_stream = connect_buffered(target_addr, timeout_val).await?;
 
         let authentication_method = if let Some((username, password)) = self.user_password.as_ref()
         {