diff --git a/artiq/runtime.rs/Cargo.lock b/artiq/runtime.rs/Cargo.lock
index 6324f7558..6e5a7538d 100644
--- a/artiq/runtime.rs/Cargo.lock
+++ b/artiq/runtime.rs/Cargo.lock
@@ -2,7 +2,7 @@
 name = "runtime"
 version = "0.0.0"
 dependencies = [
- "fringe 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "fringe 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lwip 0.0.0",
  "std_artiq 0.0.0",
 ]
@@ -13,7 +13,7 @@ version = "0.0.0"
 
 [[package]]
 name = "fringe"
-version = "1.0.5"
+version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -44,5 +44,5 @@ dependencies = [
 ]
 
 [metadata]
-"checksum fringe 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "c5257685076edffc8f1a85a382135cdf27ba915ac74e47ae55aba19945c17955"
+"checksum fringe 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "987689dcfad85eee8d76b477865641ec483e63fb86d52966bfc350c4a647d78a"
 "checksum libc 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)" = "23e3757828fa702a20072c37ff47938e9dd331b92fac6e223d26d4b7a55f7ee2"
diff --git a/artiq/runtime.rs/Cargo.toml b/artiq/runtime.rs/Cargo.toml
index c9a0de84f..962e076cb 100644
--- a/artiq/runtime.rs/Cargo.toml
+++ b/artiq/runtime.rs/Cargo.toml
@@ -10,7 +10,7 @@ path = "src/lib.rs"
 
 [dependencies]
 std_artiq = { path = "libstd_artiq" }
-fringe = { version = "1.0.5", default-features = false, features = ["alloc"] }
+fringe = { version = "= 1.1.0", default-features = false, features = ["alloc"] }
 lwip = { path = "liblwip" }
 
 [profile.dev]
diff --git a/artiq/runtime.rs/liblwip/lib.rs b/artiq/runtime.rs/liblwip/lib.rs
index bfa332a1f..fb1903fa6 100644
--- a/artiq/runtime.rs/liblwip/lib.rs
+++ b/artiq/runtime.rs/liblwip/lib.rs
@@ -5,8 +5,10 @@ extern crate alloc;
 extern crate collections;
 extern crate libc;
 extern crate lwip_sys;
+extern crate std_artiq as std;
 
 use core::marker::PhantomData;
+use core::cell::RefCell;
 use alloc::boxed::Box;
 use collections::LinkedList;
 use libc::c_void;
@@ -31,6 +33,47 @@ pub enum Error {
     IllegalArgument,
 }
 
+impl Error {
+    fn as_str(&self) -> &str {
+        match *self {
+            Error::OutOfMemory => "out of memory error",
+            Error::Buffer => "buffer error",
+            Error::Timeout => "timeout",
+            Error::Routing => "routing error",
+            Error::InProgress => "operation in progress",
+            Error::IllegalValue => "illegal value",
+            Error::WouldBlock => "operation would block",
+            Error::AddressInUse => "address in use",
+            Error::AlreadyConnecting => "already connecting",
+            Error::AlreadyConnected => "already connected",
+            Error::NotConnected => "not connected",
+            Error::Interface => "low-level netif error",
+            Error::ConnectionAborted => "connection aborted",
+            Error::ConnectionReset => "connection reset",
+            Error::ConnectionClosed => "connection closed",
+            Error::IllegalArgument => "illegal argument",
+        }
+    }
+}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "{}", self.as_str())
+    }
+}
+
+impl std::error::Error for Error {
+    fn description(&self) -> &str {
+        self.as_str()
+    }
+}
+
+impl From<Error> for std::io::Error {
+    fn from(lower: Error) -> std::io::Error {
+        std::io::Error::new(std::io::ErrorKind::Other, lower)
+    }
+}
+
 pub type Result<T> = core::result::Result<T, Error>;
 
 fn result_from<T, F>(err: lwip_sys::err, f: F) -> Result<T>
@@ -165,6 +208,10 @@ impl<'payload> Pbuf<'payload> {
         Self::from_slice_with_type(slice, lwip_sys::PBUF_ROM)
     }
 
+    pub fn len(&self) -> usize {
+        unsafe { (*self.raw).len as usize }
+    }
+
     pub fn as_slice(&self) -> &'payload [u8] {
         unsafe {
             core::slice::from_raw_parts((*self.raw).payload as *const u8,
@@ -196,7 +243,7 @@ impl<'a> Drop for Pbuf<'a> {
 
 #[derive(Debug)]
 pub struct UdpSocketState {
-    recv_buffer: LinkedList<(SocketAddr, Pbuf<'static>)>
+    recv_buffer: LinkedList<(Pbuf<'static>, SocketAddr)>
 }
 
 impl UdpSocketState {
@@ -208,7 +255,7 @@ impl UdpSocketState {
 #[derive(Debug)]
 pub struct UdpSocket {
     raw:   *mut lwip_sys::udp_pcb,
-    state: Box<UdpSocketState>
+    state: Box<RefCell<UdpSocketState>>
 }
 
 impl UdpSocket {
@@ -217,9 +264,9 @@ impl UdpSocket {
                        pbuf: *mut lwip_sys::pbuf,
                        addr: *mut lwip_sys::ip_addr, port: u16) {
             unsafe {
-                let state = arg as *mut UdpSocketState;
+                let state = arg as *mut RefCell<UdpSocketState>;
                 let socket_addr = SocketAddr { ip: IpAddr::from_raw(addr), port: port };
-                (*state).recv_buffer.push_back((socket_addr, Pbuf::from_raw(pbuf)));
+                (*state).borrow_mut().recv_buffer.push_back((Pbuf::from_raw(pbuf), socket_addr));
             }
         }
 
@@ -227,54 +274,52 @@ impl UdpSocket {
             let raw = lwip_sys::udp_new();
             if raw.is_null() { return Err(Error::OutOfMemory) }
 
-            let mut state = Box::new(UdpSocketState { recv_buffer: LinkedList::new() });
-            let arg = &mut *state as *mut UdpSocketState as *mut _;
+            let mut state = Box::new(RefCell::new(UdpSocketState {
+                recv_buffer: LinkedList::new()
+            }));
+            let arg = &mut *state as *mut RefCell<UdpSocketState> as *mut _;
             lwip_sys::udp_recv(raw, recv, arg);
             Ok(UdpSocket { raw: raw, state: state })
         }
     }
 
-    pub fn state(&self) -> *const UdpSocketState {
+    pub fn state(&self) -> *const RefCell<UdpSocketState> {
         &*self.state
     }
 
-    pub fn bind(&mut self, addr: SocketAddr) -> Result<()> {
+    pub fn bind(&self, addr: SocketAddr) -> Result<()> {
         result_from(unsafe {
             lwip_sys::udp_bind(self.raw, &mut addr.ip.into_raw(), addr.port)
         }, || ())
     }
 
-    pub fn connect(&mut self, addr: SocketAddr) -> Result<()> {
+    pub fn connect(&self, addr: SocketAddr) -> Result<()> {
         result_from(unsafe {
             lwip_sys::udp_connect(self.raw, &mut addr.ip.into_raw(), addr.port)
         }, || ())
     }
 
-    pub fn disconnect(&mut self) -> Result<()> {
+    pub fn disconnect(&self) -> Result<()> {
         result_from(unsafe {
             lwip_sys::udp_disconnect(self.raw)
         }, || ())
     }
 
-    pub fn send<'a>(&'a mut self, pbuf: Pbuf<'a>) -> Result<()> {
+    pub fn send<'a>(&'a self, pbuf: Pbuf<'a>) -> Result<()> {
         result_from(unsafe {
             lwip_sys::udp_send(self.raw, pbuf.as_raw())
         }, || ())
     }
 
-    pub fn send_to<'a>(&'a mut self, addr: SocketAddr, pbuf: Pbuf<'a>) -> Result<()> {
+    pub fn send_to<'a>(&'a self, pbuf: Pbuf<'a>, addr: SocketAddr) -> Result<()> {
         result_from(unsafe {
             lwip_sys::udp_sendto(self.raw, pbuf.as_raw(),
                                  &mut addr.ip.into_raw(), addr.port)
         }, || ())
     }
 
-    pub fn try_recv(&mut self) -> Option<(SocketAddr, Pbuf<'static>)> {
-        self.state.recv_buffer.pop_front()
-    }
-
-    pub fn close(self) {
-        // just drop
+    pub fn try_recv(&self) -> Option<(Pbuf<'static>, SocketAddr)> {
+        self.state.borrow_mut().recv_buffer.pop_front()
     }
 }
 
@@ -298,7 +343,7 @@ impl TcpListenerState {
 #[derive(Debug)]
 pub struct TcpListener {
     raw:   *mut lwip_sys::tcp_pcb,
-    state: Box<TcpListenerState>
+    state: Box<RefCell<TcpListenerState>>
 }
 
 impl TcpListener {
@@ -307,8 +352,8 @@ impl TcpListener {
                          err: lwip_sys::err) -> lwip_sys::err {
             if err != lwip_sys::ERR_OK { return err }
             unsafe {
-                let state = arg as *mut TcpListenerState;
-                (*state).backlog.push_back(TcpStream::from_raw(newpcb));
+                let state = arg as *mut RefCell<TcpListenerState>;
+                (*state).borrow_mut().backlog.push_back(TcpStream::from_raw(newpcb));
             }
             lwip_sys::ERR_OK
         }
@@ -325,26 +370,22 @@ impl TcpListener {
                 return Err(Error::OutOfMemory)
             }
 
-            let mut state = Box::new(TcpListenerState {
+            let mut state = Box::new(RefCell::new(TcpListenerState {
                 backlog: LinkedList::new()
-            });
-            let arg = &mut *state as *mut TcpListenerState as *mut _;
+            }));
+            let arg = &mut *state as *mut RefCell<TcpListenerState> as *mut _;
             lwip_sys::tcp_arg(raw, arg);
             lwip_sys::tcp_accept(raw2, accept);
             Ok(TcpListener { raw: raw2, state: state })
         }
     }
 
-    pub fn state(&self) -> *const TcpListenerState {
+    pub fn state(&self) -> *const RefCell<TcpListenerState> {
         &*self.state
     }
 
-    pub fn try_accept(&mut self) -> Option<TcpStream> {
-        self.state.backlog.pop_front()
-    }
-
-    pub fn close(self) {
-        // just drop
+    pub fn try_accept(&self) -> Option<TcpStream> {
+        self.state.borrow_mut().backlog.pop_front()
     }
 }
 
@@ -383,7 +424,7 @@ impl TcpStreamState {
 #[derive(Debug)]
 pub struct TcpStream {
     raw:   *mut lwip_sys::tcp_pcb,
-    state: Box<TcpStreamState>
+    state: Box<RefCell<TcpStreamState>>
 }
 
 impl TcpStream {
@@ -392,11 +433,11 @@ impl TcpStream {
                        pbuf: *mut lwip_sys::pbuf, err: lwip_sys::err) -> lwip_sys::err {
             if err != lwip_sys::ERR_OK { return err }
             unsafe {
-                let state = arg as *mut TcpStreamState;
+                let state = arg as *mut RefCell<TcpStreamState>;
                 if pbuf.is_null() {
-                    (*state).recv_buffer.push_back(Err(Error::ConnectionClosed))
+                    (*state).borrow_mut().recv_buffer.push_back(Err(Error::ConnectionClosed))
                 } else {
-                    (*state).recv_buffer.push_back(Ok(Pbuf::from_raw(pbuf)))
+                    (*state).borrow_mut().recv_buffer.push_back(Ok(Pbuf::from_raw(pbuf)))
                 }
             }
             lwip_sys::ERR_OK
@@ -405,25 +446,25 @@ impl TcpStream {
         extern fn sent(arg: *mut c_void, raw: *mut lwip_sys::tcp_pcb,
                        _len: u16) -> lwip_sys::err {
             unsafe {
-                let state = arg as *mut TcpStreamState;
-                (*state).send_avail = lwip_sys::tcp_sndbuf_(raw) as usize;
+                let state = arg as *mut RefCell<TcpStreamState>;
+                (*state).borrow_mut().send_avail = lwip_sys::tcp_sndbuf_(raw) as usize;
             }
             lwip_sys::ERR_OK
         }
 
         extern fn err(arg: *mut c_void, err: lwip_sys::err) {
             unsafe {
-                let state = arg as *mut TcpStreamState;
-                (*state).recv_buffer.push_back(result_from(err, || unreachable!()))
+                let state = arg as *mut RefCell<TcpStreamState>;
+                (*state).borrow_mut().recv_buffer.push_back(result_from(err, || unreachable!()))
             }
         }
 
         unsafe {
-            let mut state = Box::new(TcpStreamState {
+            let mut state = Box::new(RefCell::new(TcpStreamState {
                 recv_buffer: LinkedList::new(),
                 send_avail:  lwip_sys::tcp_sndbuf_(raw) as usize
-            });
-            let arg = &mut *state as *mut TcpStreamState as *mut _;
+            }));
+            let arg = &mut *state as *mut RefCell<TcpStreamState> as *mut _;
             lwip_sys::tcp_arg(raw, arg);
             lwip_sys::tcp_recv(raw, recv);
             lwip_sys::tcp_sent(raw, sent);
@@ -432,34 +473,43 @@ impl TcpStream {
         }
     }
 
-    pub fn state(&self) -> *const TcpStreamState {
+    pub fn state(&self) -> *const RefCell<TcpStreamState> {
         &*self.state
     }
 
-    pub fn write(&mut self, data: &[u8]) -> Result<usize> {
+    pub fn write(&self, data: &[u8]) -> Result<usize> {
         let sndbuf = unsafe { lwip_sys::tcp_sndbuf_(self.raw) } as usize;
         let len = if data.len() < sndbuf { data.len() } else { sndbuf };
         let result = result_from(unsafe {
             lwip_sys::tcp_write(self.raw, data as *const [u8] as *const _, len as u16,
-                                lwip_sys::TCP_WRITE_FLAG_COPY)
+                                lwip_sys::TCP_WRITE_FLAG_COPY |
+                                lwip_sys::TCP_WRITE_FLAG_MORE)
         }, || len);
-        self.state.send_avail = unsafe { lwip_sys::tcp_sndbuf_(self.raw) } as usize;
+        self.state.borrow_mut().send_avail = unsafe { lwip_sys::tcp_sndbuf_(self.raw) } as usize;
         result
     }
 
-    pub fn try_read(&mut self) -> Result<Option<Pbuf<'static>>> {
-        match self.state.recv_buffer.front() {
+    pub fn flush(&self) -> Result<()> {
+        const EMPTY_DATA: [u8; 0] = [];
+        result_from(unsafe {
+            lwip_sys::tcp_write(self.raw, &EMPTY_DATA as *const [u8] as *const _, 0, 0)
+        }, || ())
+    }
+
+    pub fn try_read(&self) -> Result<Option<Pbuf<'static>>> {
+        let mut state = self.state.borrow_mut();
+        match state.recv_buffer.front() {
             None => return Ok(None),
             Some(&Err(err)) => return Err(err),
             Some(_) => ()
         }
-        match self.state.recv_buffer.pop_front() {
+        match state.recv_buffer.pop_front() {
             Some(Ok(pbuf)) => return Ok(Some(pbuf)),
             _ => unreachable!()
         }
     }
 
-    pub fn shutdown(&mut self, how: Shutdown) -> Result<()> {
+    pub fn shutdown(&self, how: Shutdown) -> Result<()> {
         let (shut_rx, shut_tx) = match how {
             Shutdown::Read  => (1, 0),
             Shutdown::Write => (0, 1),
diff --git a/artiq/runtime.rs/src/io.rs b/artiq/runtime.rs/src/io.rs
index 48dee82c4..fc7e802ae 100644
--- a/artiq/runtime.rs/src/io.rs
+++ b/artiq/runtime.rs/src/io.rs
@@ -1,8 +1,10 @@
 extern crate fringe;
 extern crate lwip;
 
+use std::cell::RefCell;
 use std::vec::Vec;
 use std::time::{Instant, Duration};
+use std::io::{Read, Write, Result, Error, ErrorKind};
 use self::fringe::OwnedStack;
 use self::fringe::generator::{Generator, Yielder};
 
@@ -37,7 +39,7 @@ impl Scheduler {
         Scheduler { threads: Vec::new(), index: 0 }
     }
 
-    pub unsafe fn spawn<F: FnOnce(Waiter) + Send>(&mut self, stack_size: usize, f: F) {
+    pub unsafe fn spawn<F: FnOnce(Waiter) + Send + 'static>(&mut self, stack_size: usize, f: F) {
         let stack = OwnedStack::new(stack_size);
         let thread = Thread {
             generator:   Generator::unsafe_new(stack, move |yielder, _| {
@@ -104,43 +106,34 @@ impl Scheduler {
 
 #[derive(Debug)]
 enum WaitEvent {
-    UdpReadable(*const lwip::UdpSocketState),
-    TcpAcceptable(*const lwip::TcpListenerState),
-    TcpWriteable(*const lwip::TcpStreamState),
-    TcpReadable(*const lwip::TcpStreamState),
+    UdpReadable(*const RefCell<lwip::UdpSocketState>),
+    TcpAcceptable(*const RefCell<lwip::TcpListenerState>),
+    TcpWriteable(*const RefCell<lwip::TcpStreamState>),
+    TcpReadable(*const RefCell<lwip::TcpStreamState>),
 }
 
 impl WaitEvent {
     fn completed(&self) -> bool {
         match *self {
             WaitEvent::UdpReadable(state) =>
-                unsafe { (*state).readable() },
+                unsafe { (*state).borrow().readable() },
             WaitEvent::TcpAcceptable(state) =>
-                unsafe { (*state).acceptable() },
+                unsafe { (*state).borrow().acceptable() },
             WaitEvent::TcpWriteable(state) =>
-                unsafe { (*state).writeable() },
+                unsafe { (*state).borrow().writeable() },
             WaitEvent::TcpReadable(state) =>
-                unsafe { (*state).readable() },
+                unsafe { (*state).borrow().readable() },
         }
     }
 }
 
 unsafe impl Send for WaitEvent {}
 
-#[derive(Debug, Clone, Copy, Eq, PartialEq)]
-pub enum Error {
-    Lwip(lwip::Error),
-    TimedOut,
-    Interrupted
-}
-
-pub type Result<T> = ::std::result::Result<T, Error>;
-
-#[derive(Debug)]
-pub struct Waiter<'a>(&'a mut Yielder<WaitResult, WaitRequest, OwnedStack>);
+#[derive(Debug, Clone, Copy)]
+pub struct Waiter<'a>(&'a Yielder<WaitResult, WaitRequest, OwnedStack>);
 
 impl<'a> Waiter<'a> {
-    pub fn sleep(&mut self, duration: Duration) -> Result<()> {
+    pub fn sleep(&self, duration: Duration) -> Result<()> {
         let request = WaitRequest {
             timeout: Some(Instant::now() + duration),
             event:   None
@@ -148,44 +141,174 @@ impl<'a> Waiter<'a> {
 
         match self.0.suspend(request) {
             WaitResult::TimedOut => Ok(()),
-            WaitResult::Interrupted => Err(Error::Interrupted),
+            WaitResult::Interrupted => Err(Error::new(ErrorKind::Interrupted, "")),
             _ => unreachable!()
         }
     }
 
-    fn suspend(&mut self, request: WaitRequest) -> Result<()> {
+    fn suspend(&self, request: WaitRequest) -> Result<()> {
         match self.0.suspend(request) {
             WaitResult::Completed => Ok(()),
-            WaitResult::TimedOut => Err(Error::TimedOut),
-            WaitResult::Interrupted => Err(Error::Interrupted)
+            WaitResult::TimedOut => Err(Error::new(ErrorKind::TimedOut, "")),
+            WaitResult::Interrupted => Err(Error::new(ErrorKind::Interrupted, ""))
         }
     }
 
-    pub fn udp_readable(&mut self, socket: &lwip::UdpSocket) -> Result<()> {
+    pub fn udp_readable(&self, socket: &lwip::UdpSocket) -> Result<()> {
         self.suspend(WaitRequest {
             timeout: None,
             event:   Some(WaitEvent::UdpReadable(socket.state()))
         })
     }
 
-    pub fn tcp_acceptable(&mut self, socket: &lwip::TcpListener) -> Result<()> {
+    pub fn tcp_acceptable(&self, socket: &lwip::TcpListener) -> Result<()> {
         self.suspend(WaitRequest {
             timeout: None,
             event:   Some(WaitEvent::TcpAcceptable(socket.state()))
         })
     }
 
-    pub fn tcp_writeable(&mut self, socket: &lwip::TcpStream) -> Result<()> {
+    pub fn tcp_writeable(&self, socket: &lwip::TcpStream) -> Result<()> {
         self.suspend(WaitRequest {
             timeout: None,
             event:   Some(WaitEvent::TcpWriteable(socket.state()))
         })
     }
 
-    pub fn tcp_readable(&mut self, socket: &lwip::TcpStream) -> Result<()> {
+    pub fn tcp_readable(&self, socket: &lwip::TcpStream) -> Result<()> {
         self.suspend(WaitRequest {
             timeout: None,
             event:   Some(WaitEvent::TcpReadable(socket.state()))
         })
     }
 }
+
+// Wrappers around lwip
+
+pub use self::lwip::{IpAddr, IP4_ANY, IP6_ANY, IP_ANY, SocketAddr};
+
+#[derive(Debug)]
+pub struct UdpSocket<'a> {
+    waiter: Waiter<'a>,
+    lower:  lwip::UdpSocket
+}
+
+impl<'a> UdpSocket<'a> {
+    pub fn new(waiter: Waiter<'a>) -> Result<UdpSocket> {
+        Ok(UdpSocket {
+            waiter: waiter,
+            lower:  try!(lwip::UdpSocket::new())
+        })
+    }
+
+    pub fn bind(&self, addr: SocketAddr) -> Result<()> {
+        Ok(try!(self.lower.bind(addr)))
+    }
+
+    pub fn connect(&self, addr: SocketAddr) -> Result<()> {
+        Ok(try!(self.lower.connect(addr)))
+    }
+
+    pub fn disconnect(&self) -> Result<()> {
+        Ok(try!(self.lower.disconnect()))
+    }
+
+    pub fn send_to(&self, buf: &[u8], addr: SocketAddr) -> Result<usize> {
+        try!(self.lower.send_to(lwip::Pbuf::from_slice(buf), addr));
+        Ok(buf.len())
+    }
+
+    pub fn recv_from(&self, buf: &mut [u8]) -> Result<(usize, SocketAddr)> {
+        try!(self.waiter.udp_readable(&self.lower));
+        let (pbuf, addr) = self.lower.try_recv().unwrap();
+        let len = ::std::cmp::min(buf.len(), pbuf.len());
+        (&mut buf[..len]).copy_from_slice(&pbuf.as_slice()[..len]);
+        Ok((len, addr))
+    }
+
+    pub fn send(&self, buf: &[u8]) -> Result<usize> {
+        try!(self.lower.send(lwip::Pbuf::from_slice(buf)));
+        Ok(buf.len())
+    }
+
+    pub fn recv(&self, buf: &mut [u8]) -> Result<usize> {
+        try!(self.waiter.udp_readable(&self.lower));
+        let (pbuf, _addr) = self.lower.try_recv().unwrap();
+        // lwip checks that addr matches the bind/connect call
+        let len = ::std::cmp::min(buf.len(), pbuf.len());
+        (&mut buf[..len]).copy_from_slice(&pbuf.as_slice()[..len]);
+        Ok(len)
+    }
+}
+
+#[derive(Debug)]
+pub struct TcpListener<'a> {
+    waiter: Waiter<'a>,
+    lower:  lwip::TcpListener
+}
+
+impl<'a> TcpListener<'a> {
+    pub fn bind(waiter: Waiter<'a>, addr: SocketAddr) -> Result<TcpListener> {
+        Ok(TcpListener {
+            waiter: waiter,
+            lower:  try!(lwip::TcpListener::bind(addr))
+        })
+    }
+
+    pub fn accept(&self) -> Result<(TcpStream, SocketAddr)> {
+        try!(self.waiter.tcp_acceptable(&self.lower));
+        loop {}
+        let stream_lower = self.lower.try_accept().unwrap();
+        let addr = SocketAddr::new(IP_ANY, 0); // FIXME: coax lwip into giving real addr here
+        Ok((TcpStream {
+            waiter: self.waiter,
+            lower:  stream_lower,
+            buffer: None
+        }, addr))
+    }
+}
+
+pub use self::lwip::Shutdown;
+
+#[derive(Debug)]
+pub struct TcpStream<'a> {
+    waiter: Waiter<'a>,
+    lower:  lwip::TcpStream,
+    buffer: Option<(lwip::Pbuf<'static>, usize)>
+}
+
+impl<'a> TcpStream<'a> {
+    pub fn shutdown(&self, how: Shutdown) -> Result<()> {
+        Ok(try!(self.lower.shutdown(how)))
+    }
+}
+
+impl<'a> Read for TcpStream<'a> {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
+        if self.buffer.is_none() {
+            try!(self.waiter.tcp_readable(&self.lower));
+            let pbuf = try!(self.lower.try_read()).unwrap();
+            self.buffer = Some((pbuf, 0))
+        }
+
+        let (pbuf, pos) = self.buffer.take().unwrap();
+        let slice = &pbuf.as_slice()[pos..];
+        let len = ::std::cmp::min(buf.len(), slice.len());
+        buf.copy_from_slice(&slice[..len]);
+        if len < slice.len() {
+            self.buffer = Some((pbuf, pos + len))
+        }
+        Ok(len)
+    }
+}
+
+impl<'a> Write for TcpStream<'a> {
+    fn write(&mut self, buf: &[u8]) -> Result<usize> {
+        try!(self.waiter.tcp_writeable(&self.lower));
+        Ok(try!(self.lower.write(buf)))
+    }
+
+    fn flush(&mut self) -> Result<()> {
+        Ok(try!(self.lower.flush()))
+    }
+}
diff --git a/artiq/runtime.rs/src/lib.rs b/artiq/runtime.rs/src/lib.rs
index 71407129c..04e987129 100644
--- a/artiq/runtime.rs/src/lib.rs
+++ b/artiq/runtime.rs/src/lib.rs
@@ -2,8 +2,6 @@
 
 #[macro_use]
 extern crate std_artiq as std;
-extern crate fringe;
-extern crate lwip;
 
 use std::prelude::v1::*;
 
@@ -14,21 +12,23 @@ extern {
     fn lwip_service();
 }
 
-fn timer(mut waiter: io::Waiter) {
+fn timer(waiter: io::Waiter) {
     loop {
         println!("tick");
         waiter.sleep(std::time::Duration::from_millis(1000)).unwrap();
     }
 }
 
-fn echo(mut waiter: io::Waiter) {
-    let mut socket = lwip::UdpSocket::new().unwrap();
-    socket.bind(lwip::SocketAddr::new(lwip::IP_ANY, 1234)).unwrap();
+fn echo(waiter: io::Waiter) {
+    let addr = io::SocketAddr::new(io::IP_ANY, 1234);
+    let listener = io::TcpListener::bind(waiter, addr).unwrap();
     loop {
-        waiter.udp_readable(&socket).unwrap();
-        let (addr, pbuf) = socket.try_recv().unwrap();
-        println!("{:?}", core::str::from_utf8(pbuf.as_slice()));
-        socket.send_to(addr, pbuf).unwrap();
+        let (mut stream, _addr) = listener.accept().unwrap();
+        loop {
+            let mut buf = [0];
+            stream.read(&mut buf).unwrap();
+            stream.write(&buf).unwrap();
+        }
     }
 }