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LibUV in Lua

The luv project provides access to the multi-platform support library libuv to lua code. It was primariliy developed for the luvit project as the uv builtin module, but can be used in other lua environments.

TCP Echo Server Example

Here is a small example showing a TCP echo server:

local uv = require('uv')

local server = uv.new_tcp()
server:bind("", 1337)
server:listen(128, function (err)
  assert(not err, err)
  local client = uv.new_tcp()
  client:read_start(function (err, chunk)
    assert(not err, err)
    if chunk then
print("TCP server listening at port 1337")

Methods vs Functions

As a quick note, libuv is a C library and as such, there are no such things as methods. The luv bindings allow calling the libuv functions as either functions or methods. For example, calling server:bind(host, port) is equivalent to calling uv.tcp_bind(server, host, port). All wrapped uv types in lua have method shortcuts where is makes sense. Some are even renamed shorter like the tcp_ prefix that removed in method form. Under the hood it's the exact same C function.

Table Of Contents

The rest of the docs are organized by libuv type. There is some hierarchy as most types are considered handles and some are considered streams.

uv_loop_t — Event loop

The event loop is the central part of libuv’s functionality. It takes care of polling for i/o and scheduling callbacks to be run based on different sources of events.

In luv, there is an implicit uv loop for every lua state that loads the library. You can use this library in an multithreaded environment as long as each thread has it's own lua state with corresponsding own uv loop.


Closes all internal loop resources. This function must only be called once the loop has finished its execution or it will raise a UV_EBUSY error.[mode])

optional mode defaults to "default"

This function runs the event loop. It will act differently depending on the specified mode:

  • "default": Runs the event loop until there are no more active and referenced handles or requests. Always returns false.

  • "once": Poll for i/o once. Note that this function blocks if there are no pending callbacks. Returns false when done (no active handles or requests left), or true if more callbacks are expected (meaning you should run the event loop again sometime in the future).

  • "nowait": Poll for i/o once but don’t block if there are no pending callbacks. Returns false if done (no active handles or requests left), or true if more callbacks are expected (meaning you should run the event loop again sometime in the future).

Luvit will implicitly call after loading user code, but if you use the luv bindings directly, you need to call this after registering your initial set of event callbacks to start the event loop.


Returns true if there are active handles or request in the loop.


Stop the event loop, causing uv_run() to end as soon as possible. This will happen not sooner than the next loop iteration. If this function was called before blocking for i/o, the loop won’t block for i/o on this iteration.


Get backend file descriptor. Only kqueue, epoll and event ports are supported.

This can be used in conjunction with uv_run("nowait") to poll in one thread and run the event loop’s callbacks in another.

Note: Embedding a kqueue fd in another kqueue pollset doesn’t work on all platforms. It’s not an error to add the fd but it never generates events.


Get the poll timeout. The return value is in milliseconds, or -1 for no timeout.

Return the current timestamp in milliseconds. The timestamp is cached at the start of the event loop tick, see uv.update_time() for details and rationale.

The timestamp increases monotonically from some arbitrary point in time. Don’t make assumptions about the starting point, you will only get disappointed.

Note: Use uv.hrtime() if you need sub-millisecond granularity.


Update the event loop’s concept of “now”. Libuv caches the current time at the start of the event loop tick in order to reduce the number of time-related system calls.

You won’t normally need to call this function unless you have callbacks that block the event loop for longer periods of time, where “longer” is somewhat subjective but probably on the order of a millisecond or more.


Walk the list of handles: callback will be executed with the handle.

-- Example usage of uv.walk to close all handles that aren't already closing.
uv.walk(function (handle)
  if not handle:is_closing() then

uv_handle_t — Base handle

uv_handle_t is the base type for all libuv handle types.

Structures are aligned so that any libuv handle can be cast to uv_handle_t. All API functions defined here work with any handle type.


method form handle:is_active()

Returns true if the handle is active, false if it’s inactive. What “active” means depends on the type of handle:

  • A uv_async_t handle is always active and cannot be deactivated, except by closing it with uv_close().

  • A uv_pipe_t, uv_tcp_t, uv_udp_t, etc. handlebasically any handle that deals with i/ois active when it is doing something that involves i/o, like reading, writing, connecting, accepting new connections, etc.

  • A uv_check_t, uv_idle_t, uv_timer_t, etc. handle is active when it has been started with a call to uv.check_start(), uv.idle_start(), etc.

Rule of thumb: if a handle of type uv_foo_t has a uv.foo_start() function, then it’s active from the moment that function is called. Likewise, uv.foo_stop() deactivates the handle again.


method form handle:is_closing()

Returns true if the handle is closing or closed, false otherwise.

Note: This function should only be used between the initialization of the handle and the arrival of the close callback.

uv.close(handle, callback)

method form handle:close(callback)

Request handle to be closed. callback will be called asynchronously after this call. This MUST be called on each handle before memory is released.

Handles that wrap file descriptors are closed immediately but callback will still be deferred to the next iteration of the event loop. It gives you a chance to free up any resources associated with the handle.

In-progress requests, like uv_connect_t or uv_write_t, are cancelled and have their callbacks called asynchronously with status=UV_ECANCELED.


method form handle:ref()

Reference the given handle. References are idempotent, that is, if a handle is already referenced calling this function again will have no effect.

See Reference counting.


method form handle:unref()

Un-reference the given handle. References are idempotent, that is, if a handle is not referenced calling this function again will have no effect.

See Reference counting.


method form handle:has_ref()

Returns true if the handle referenced, false otherwise.

See Reference counting.

uv.send_buffer_size(handle, [size]) -> size

method form handle:send_buffer_size(size)

Gets or sets the size of the send buffer that the operating system uses for the socket.

If size is omitted, it will return the current send buffer size, otherwise it will use size to set the new send buffer size.

This function works for TCP, pipe and UDP handles on Unix and for TCP and UDP handles on Windows.

Note: Linux will set double the size and return double the size of the original set value.

uv.recv_buffer_size(handle, [size])

method form handle:recv_buffer_size(size)

Gets or sets the size of the receive buffer that the operating system uses for the socket.

If size is omitted, it will return the current receive buffer size, otherwise it will use size to set the new receive buffer size.

This function works for TCP, pipe and UDP handles on Unix and for TCP and UDP handles on Windows.

Note: Linux will set double the size and return double the size of the original set value.


method form handle:fileno()

Gets the platform dependent file descriptor equivalent.

The following handles are supported: TCP, pipes, TTY, UDP and poll. Passing any other handle type will fail with UV_EINVAL.

If a handle doesn’t have an attached file descriptor yet or the handle itself has been closed, this function will return UV_EBADF.

Warning: Be very careful when using this function. libuv assumes it’s in control of the file descriptor so any change to it may lead to malfunction.

Reference counting

The libuv event loop (if run in the default mode) will run until there are no active and referenced handles left. The user can force the loop to exit early by unreferencing handles which are active, for example by calling uv.unref() after calling uv.timer_start().

A handle can be referenced or unreferenced, the refcounting scheme doesn’t use a counter, so both operations are idempotent.

All handles are referenced when active by default, see uv.is_active() for a more detailed explanation on what being active involves.

uv_timer_t — Timer handle

Timer handles are used to schedule callbacks to be called in the future.

uv.new_timer() -> timer

Creates and initializes a new uv_timer_t. Returns the lua userdata wrapping it.

-- Creating a simple setTimeout wrapper
local function setTimeout(timeout, callback)
  local timer = uv.new_timer()
  timer:start(timeout, 0, function ()
  return timer

-- Creating a simple setInterval wrapper
local function setInterval(interval, callback)
  local timer = uv.new_timer()
  timer:start(interval, interval, function ()
  return timer

-- And clearInterval
local function clearInterval(timer)

uv.timer_start(timer, timeout, repeat, callback)

method form timer:start(timeout, repeat, callback)

Start the timer. timeout and repeat are in milliseconds.

If timeout is zero, the callback fires on the next event loop iteration. If repeat is non-zero, the callback fires first after timeout milliseconds and then repeatedly after repeat milliseconds.


method form timer:stop()

Stop the timer, the callback will not be called anymore.


method form timer:again()

Stop the timer, and if it is repeating restart it using the repeat value as the timeout. If the timer has never been started before it raises EINVAL.

uv.timer_set_repeat(timer, repeat)

method form timer:set_repeat(repeat)

Set the repeat value in milliseconds.

Note: If the repeat value is set from a timer callback it does not immediately take effect. If the timer was non-repeating before, it will have been stopped. If it was repeating, then the old repeat value will have been used to schedule the next timeout.

uv.timer_get_repeat(timer) -> repeat

method form timer:get_repeat() -> repeat

Get the timer repeat value.

uv_prepare_t — Prepare handle

Prepare handles will run the given callback once per loop iteration, right before polling for i/o.

local prepare = uv.new_prepare()
  print("Before I/O polling")

uv.new_prepare() -> prepare

Creates and initializes a new uv_prepare_t. Returns the lua userdata wrapping it.

uv.prepare_start(prepare, callback)

method form prepare:start(callback)

Start the handle with the given callback.


method form prepare:stop()

Stop the handle, the callback will no longer be called.

uv_check_t — Check handle

Check handles will run the given callback once per loop iteration, right after polling for i/o.

local check = uv.new_check()
  print("After I/O polling")

uv.new_check() -> check

Creates and initializes a new uv_check_t. Returns the lua userdata wrapping it.

uv.check_start(check, callback)

method form check:start(callback)

Start the handle with the given callback.


method form check:stop()

Stop the handle, the callback will no longer be called.

uv_idle_t — Idle handle

Idle handles will run the given callback once per loop iteration, right before the uv_prepare_t handles.

Note: The notable difference with prepare handles is that when there are active idle handles, the loop will perform a zero timeout poll instead of blocking for i/o.

Warning: Despite the name, idle handles will get their callbacks called on every loop iteration, not when the loop is actually “idle”.

local idle = uv.new_idle()
  print("Before I/O polling, no blocking")

uv.new_idle() -> idle

Creates and initializes a new uv_idle_t. Returns the lua userdata wrapping it.

uv.idle_start(idle, callback)

method form idle:start(callback)

Start the handle with the given callback.


method form idle:stop()

Stop the handle, the callback will no longer be called.

uv_async_t — Async handle

Async handles allow the user to “wakeup” the event loop and get a callback called from another thread.

local async
async = uv.new_async(function()
  print("async operation ran")


uv.new_async(callback) -> async

Creates and initializes a new uv_async_t. Returns the lua userdata wrapping it. A NULL callback is allowed.

Note: Unlike other handle initialization functions, it immediately starts the handle.


method form async:send()

Wakeup the event loop and call the async handle’s callback.

Note: It’s safe to call this function from any thread. The callback will be called on the loop thread.

Warning: libuv will coalesce calls to uv.async_send(async), that is, not every call to it will yield an execution of the callback, the only guarantee is that it will be called at least once. Thus, calling this function may not wakeup the event loop if it was already called previously within a short period of time.

uv_poll_t — Poll handle

Poll handles are used to watch file descriptors for readability and writability, similar to the purpose of poll(2).

The purpose of poll handles is to enable integrating external libraries that rely on the event loop to signal it about the socket status changes, like c-ares or libssh2. Using uv_poll_t for any other purpose is not recommended; uv_tcp_t, uv_udp_t, etc. provide an implementation that is faster and more scalable than what can be achieved with uv_poll_t, especially on Windows.

It is possible that poll handles occasionally signal that a file descriptor is readable or writable even when it isn’t. The user should therefore always be prepared to handle EAGAIN or equivalent when it attempts to read from or write to the fd.

It is not okay to have multiple active poll handles for the same socket, this can cause libuv to busyloop or otherwise malfunction.

The user should not close a file descriptor while it is being polled by an active poll handle. This can cause the handle to report an error, but it might also start polling another socket. However the fd can be safely closed immediately after a call to uv.poll_stop() or uv.close().

Note On windows only sockets can be polled with poll handles. On Unix any file descriptor that would be accepted by poll(2) can be used.

uv.new_poll(fd) -> poll

Initialize the handle using a file descriptor.

The file descriptor is set to non-blocking mode.

uv.new_socket_poll(fd) -> poll

Initialize the handle using a socket descriptor. On Unix this is identical to uv.poll_init(). On windows it takes a SOCKET handle.

The socket is set to non-blocking mode.

uv.poll_start(poll, events, callback)

method form poll:start()

Starts polling the file descriptor. events is "r", "w", or "rw" and translates to a bitmask made up of UV_READABLE and UV_WRITABLE. As soon as an event is detected the callback will be called with status set to 0, and the detected events set on the events field.

The user should not close the socket while the handle is active. If the user does that anyway, the callback may be called reporting an error status, but this is not guaranteed.

Note Calling `uv.poll_start()`` on a handle that is already active is fine. Doing so will update the events mask that is being watched for.


method form poll:stop()

Stop polling the file descriptor, the callback will no longer be called.

uv_signal_t — Signal handle

Signal handles implement Unix style signal handling on a per-event loop bases.

Reception of some signals is emulated on Windows:

  • SIGINT is normally delivered when the user presses CTRL+C. However, like on Unix, it is not generated when terminal raw mode is enabled.
  • SIGBREAK is delivered when the user pressed CTRL + BREAK.
  • SIGHUP is generated when the user closes the console window. On SIGHUP the program is given approximately 10 seconds to perform cleanup. After that Windows will unconditionally terminate it.
  • SIGWINCH is raised whenever libuv detects that the console has been resized. SIGWINCH is emulated by libuv when the program uses a uv_tty_t handle to write to the console. SIGWINCH may not always be delivered in a timely manner; libuv will only detect size changes when the cursor is being moved. When a readable uv_tty_t handle is used in raw mode, resizing the console buffer will also trigger a SIGWINCH signal.

Watchers for other signals can be successfully created, but these signals are never received. These signals are: SIGILL, SIGABRT, SIGFPE, SIGSEGV, SIGTERM and SIGKILL.

Calls to raise() or abort() to programmatically raise a signal are not detected by libuv; these will not trigger a signal watcher.

Note: On Linux SIGRT0 and SIGRT1 (signals 32 and 33) are used by the NPTL pthreads library to manage threads. Installing watchers for those signals will lead to unpredictable behavior and is strongly discouraged. Future versions of libuv may simply reject them.

-- Create a new signal handler
local sigint = uv.new_signal()
-- Define a handler function
uv.signal_start(sigint, "sigint", function(signal)
print("got " .. signal .. ", shutting down")

uv.new_signal() -> signal

Creates and initializes a new uv_signal_t. Returns the lua userdata wrapping it.

uv.signal_start(signal, signum, callback)

method form signal:start(signum, callback)

Start the handle with the given callback, watching for the given signal.


method form signal:stop()

Stop the handle, the callback will no longer be called.

uv_process_t — Process handle

Process handles will spawn a new process and allow the user to control it and establish communication channels with it using streams.


Disables inheritance for file descriptors / handles that this process inherited from its parent. The effect is that child processes spawned by this process don’t accidentally inherit these handles.

It is recommended to call this function as early in your program as possible, before the inherited file descriptors can be closed or duplicated.

Note This function works on a best-effort basis: there is no guarantee that libuv can discover all file descriptors that were inherited. In general it does a better job on Windows than it does on Unix.

uv.spawn(file, options, onexit) -> process, pid

Initializes the process handle and starts the process. If the process is successfully spawned, this function will return the handle and pid of the child process.

Possible reasons for failing to spawn would include (but not be limited to) the file to execute not existing, not having permissions to use the setuid or setgid specified, or not having enough memory to allocate for the new process.

local stdout = uv.new_pipe(false)
local stderr = uv.new_pipe(false)
local stdin = uv.new_pipe(false)

local handle, pid

local function onexit(code, signal)
  p("exit", {code=code,signal=signal})

local function onclose()

local function onread(err, chunk)
  assert(not err, err)
  if (chunk) then
    p("data", {data=chunk})

local function onshutdown()
  uv.close(handle, onclose)

handle, pid = uv.spawn("cat", {
  stdio = {stdin, stdout, stderr}
}, onexit)


uv.read_start(stdout, onread)
uv.read_start(stderr, onread)
uv.write(stdin, "Hello World")
uv.shutdown(stdin, onshutdown)
  • options.args - Command line arguments as a list of string. The first string should be the path to the program. On Windows this uses CreateProcess which concatenates the arguments into a string this can cause some strange errors. (See options.verbatim below for Windows.)
  • options.stdio - Set the file descriptors that will be made available to the child process. The convention is that the first entries are stdin, stdout, and stderr. (Note On Windows file descriptors after the third are available to the child process only if the child processes uses the MSVCRT runtime.)
  • options.env - Set environment variables for the new process.
  • options.cwd - Set current working directory for the subprocess.
  • options.uid - Set the child process' user id.
  • options.gid - Set the child process' group id.
  • options.verbatim - If true, do not wrap any arguments in quotes, or perform any other escaping, when converting the argument list into a command line string. This option is only meaningful on Windows systems. On Unix it is silently ignored.
  • options.detached - If true, spawn the child process in a detached state - this will make it a process group leader, and will effectively enable the child to keep running after the parent exits. Note that the child process will still keep the parent's event loop alive unless the parent process calls uv.unref() on the child's process handle.
  • options.hide - If true, hide the subprocess console window that would normally be created. This option is only meaningful on Windows systems. On Unix it is silently ignored.

The options.stdio entries can take many shapes.

  • If they are numbers, then the child process inherits that same zero-indexed fd from the parent process.
  • If uv_stream_h handles are passed in, those are used as a read-write pipe or inherited stream depending if the stream has a valid fd.
  • Including nil placeholders means to ignore that fd in the child.

When the child process exits, the onexit callback will be called with exit code and signal.

uv.process_kill(process, sigmun)

method form process:kill(sigmun)

Sends the specified signal to the given process handle.

uv.kill(pid, sigmun)

Sends the specified signal to the given PID.

uv_stream_t — Stream handle

Stream handles provide an abstraction of a duplex communication channel. uv_stream_t is an abstract type, libuv provides 3 stream implementations in the form of uv_tcp_t, uv_pipe_t and uv_tty_t.

uv.shutdown(stream, [callback]) -> req

(method form stream:shutdown([callback]) -> req)

Shutdown the outgoing (write) side of a duplex stream. It waits for pending write requests to complete. The callback is called after shutdown is complete.

uv.listen(stream, backlog, callback)

(method form stream:listen(backlog, callback))

Start listening for incoming connections. backlog indicates the number of connections the kernel might queue, same as listen(2). When a new incoming connection is received the callback is called.

uv.accept(stream, client_stream)

(method form stream:accept(client_stream))

This call is used in conjunction with uv.listen() to accept incoming connections. Call this function after receiving a callback to accept the connection.

When the connection callback is called it is guaranteed that this function will complete successfully the first time. If you attempt to use it more than once, it may fail. It is suggested to only call this function once per connection call.

server:listen(128, function (err)
  local client = uv.new_tcp()

uv.read_start(stream, callback)

(method form stream:read_start(callback))

Callback is of the form (err, data).

Read data from an incoming stream. The callback will be made several times until there is no more data to read or uv.read_stop() is called. When we’ve reached EOF, data will be nil.

stream:read_start(function (err, chunk)
  if err then
    -- handle read error
  elseif chunk then
    -- handle data
    -- handle disconnect


(method form stream:read_stop())

Stop reading data from the stream. The read callback will no longer be called.

uv.write(stream, data, [callback])

(method form stream:write(data, [callback]))

Write data to stream.

data can either be a lua string or a table of strings. If a table is passed in, the C backend will use writev to send all strings in a single system call.

The optional callback is for knowing when the write is complete.

uv.write2(stream, data, send_handle, callback)

(method form stream:write2(data, send_handle, callback))

Extended write function for sending handles over a pipe. The pipe must be initialized with ip option to true.

**Note: send_handle must be a TCP socket or pipe, which is a server or a connection (listening or connected state). Bound sockets or pipes will be assumed to be servers.

uv.try_write(stream, data)

(method form stream:try_write(data))

Same as uv.write(), but won’t queue a write request if it can’t be completed immediately.

Will return number of bytes written (can be less than the supplied buffer size).


(method form stream:is_readable())

Returns true if the stream is readable, false otherwise.


(method form stream:is_writable())

Returns true if the stream is writable, false otherwise.

uv.stream_set_blocking(stream, blocking)

(method form stream:set_blocking(blocking))

Enable or disable blocking mode for a stream.

When blocking mode is enabled all writes complete synchronously. The interface remains unchanged otherwise, e.g. completion or failure of the operation will still be reported through a callback which is made asynchronously.

Warning: Relying too much on this API is not recommended. It is likely to change significantly in the future. Currently this only works on Windows and only for uv_pipe_t handles. Also libuv currently makes no ordering guarantee when the blocking mode is changed after write requests have already been submitted. Therefore it is recommended to set the blocking mode immediately after opening or creating the stream.

uv_tcp_t — TCP handle

TCP handles are used to represent both TCP streams and servers.

uv_tcp_t is a ‘subclass’ of uv_stream_t(#uv_stream_t--stream-handle).

uv.new_tcp() -> tcp

Creates and initializes a new uv_tcp_t. Returns the lua userdata wrapping it.

uv.tcp_open(tcp, sock)

(method form tcp:open(sock))

Open an existing file descriptor or SOCKET as a TCP handle.

**Note: The user is responsible for setting the file descriptor in non-blocking mode.

uv.tcp_nodelay(tcp, enable)

(method form tcp:nodelay(enable))

Enable / disable Nagle’s algorithm.

uv.tcp_keepalive(tcp, enable, [delay])

(method form tcp:keepalive(enable, [delay]))

Enable / disable TCP keep-alive. delay is the initial delay in seconds, ignored when enable is false.

uv.tcp_simultaneous_accepts(tcp, enable)

(method form tcp:simultaneous_accepts(enable))

Enable / disable simultaneous asynchronous accept requests that are queued by the operating system when listening for new TCP connections.

This setting is used to tune a TCP server for the desired performance. Having simultaneous accepts can significantly improve the rate of accepting connections (which is why it is enabled by default) but may lead to uneven load distribution in multi-process setups.

uv.tcp_bind(tcp, address, port)

(method form tcp:bind(address, port))

Bind the handle to an address and port. address should be an IP address and not a domain name.

When the port is already taken, you can expect to see an UV_EADDRINUSE error from either uv.tcp_bind(), uv.listen() or uv.tcp_connect(). That is, a successful call to this function does not guarantee that the call to uv.listen() or uv.tcp_connect() will succeed as well.

Use a port of 0 to let the OS assign an ephemeral port. You can look it up later using uv.tcp_getsockname().


(method form tcp:getsockname())

Get the current address to which the handle is bound.


(method form tcp:getpeername())

Get the address of the peer connected to the handle.

uv.tcp_connect(tcp, address, port, callback) -> req

(method form tcp:connect(host, port, callback) -> req)

uv.tcp_write_queue_size(tcp) -> size

(method form tcp:write_queue_size() -> size)

Establish an IPv4 or IPv6 TCP connection.

The callback is made when the connection has been established or when a connection error happened.

local client = uv.new_tcp()
client:connect("", 8080, function (err)
  -- check error and carry on.

uv_pipe_t — Pipe handle

Pipe handles provide an abstraction over local domain sockets on Unix and named pipes on Windows.

local pipe = uv.new_pipe(false)


pipe:listen(128, function()
  local client = uv.new_pipe(false)

uv.new_pipe(ipc) -> pipe

Creates and initializes a new uv_pipe_t. Returns the lua userdata wrapping it. The ipc argument is a boolean to indicate if this pipe will be used for handle passing between processes.

uv.pipe_open(file) -> pipe

Open an existing file descriptor or uv_handle_t as a pipe.

Note: The file descriptor is set to non-blocking mode.

uv.pipe_bind(pipe, name)

(method form pipe:bind(name))

Bind the pipe to a file path (Unix) or a name (Windows).

Note: Paths on Unix get truncated to sizeof(sockaddr_un.sun_path) bytes, typically between 92 and 108 bytes.

uv.pipe_connect(pipe, name, callback)

(method form pipe:connect(name, callback))

Connect to the Unix domain socket or the named pipe.

Note: Paths on Unix get truncated to sizeof(sockaddr_un.sun_path) bytes, typically between 92 and 108 bytes.


(method form pipe:getsockname())

Returns the name of the Unix domain socket or the named pipe.

uv.pipe_pending_instances(pipe, count)

(method form pipe:pending_instances(count))

Set the number of pending pipe instance handles when the pipe server is waiting for connections.

Note: This setting applies to Windows only.


(method form pipe:pending_count())

Returns the pending pipe count for the named pipe.


(method form pipe:pending_type())

Used to receive handles over IPC pipes.

First - call [uv.pipe_pending_count][], if it’s > 0 then initialize a handle of the given type, returned by [uv.pipe_pending_type][] and call [uv.accept(pipe, handle)][].

uv_tty_t — TTY handle

TTY handles represent a stream for the console.

-- Simple echo program
local stdin = uv.new_tty(0, true)
local stdout = uv.new_tty(1, false)

stdin:read_start(function (err, data)
  assert(not err, err)
  if data then

uv.new_tty(fd, readable) -> tty

Initialize a new TTY stream with the given file descriptor. Usually the file descriptor will be:

  • 0 - stdin
  • 1 - stdout
  • 2 - stderr

readable, specifies if you plan on calling uv_read_start() with this stream. stdin is readable, stdout is not.

On Unix this function will try to open /dev/tty and use it if the passed file descriptor refers to a TTY. This lets libuv put the tty in non-blocking mode without affecting other processes that share the tty.

Note: If opening /dev/tty fails, libuv falls back to blocking writes for non-readable TTY streams.


(method form tty:set_mode(mode))

Set the TTY using the specified terminal mode.

Parameter mode is a C enum with the following values:

  • 0 - UV_TTY_MODE_NORMAL: Initial/normal terminal mode

  • 1 - UV_TTY_MODE_RAW: Raw input mode (On Windows, ENABLE_WINDOW_INPUT is also enabled)

  • 2 - UV_TTY_MODE_IO: Binary-safe I/O mode for IPC (Unix-only)


To be called when the program exits. Resets TTY settings to default values for the next process to take over.

This function is async signal-safe on Unix platforms but can fail with error code UV_EBUSY if you call it when execution is inside uv_tty_set_mode().

uv.tty_get_winsize() -> w, h

(method form tty:get_winsize() -> w, h)

Gets the current Window size.

uv_udp_t — UDP handle

UDP handles encapsulate UDP communication for both clients and servers.

uv.new_udp() -> udp

Initialize a new UDP handle. The actual socket is created lazily.

uv.udp_open(udp, fd)

(method form udp:open(fd))

Opens an existing file descriptor or Windows SOCKET as a UDP handle.

Unix only: The only requirement of the sock argument is that it follows the datagram contract (works in unconnected mode, supports sendmsg()/recvmsg(), etc). In other words, other datagram-type sockets like raw sockets or netlink sockets can also be passed to this function.

The file descriptor is set to non-blocking mode.

Note: The passed file descriptor or SOCKET is not checked for its type, but it’s required that it represents a valid datagram socket.

uv.udp_bind(udp, host, port)

(method form udp:bind(host, port))

Bind the UDP handle to an IP address and port.


(method form udp:getsockname())

Get the local IP and port of the UDP handle.

uv.udp_set_membership(udp, multicast_addr, interface_addr, membership)

(method form udp:set_membership(multicast_addr, interface_addr, membership))

Set membership for a multicast address.

multicast_addr is multicast address to set membership for.

interface_addr is interface address.

membership can be the string "leave" or "join".

uv.udp_set_multicast_loop(udp, on)

(method form udp:set_multicast_loop(on))

Set IP multicast loop flag. Makes multicast packets loop back to local sockets.

on is a boolean.

uv.udp_set_multicast_ttl(udp, tty)

(method form udp:set_multicast_ttl(tty))

Set the multicast ttl.

ttl is an integer 1 through 255.

uv.udp_set_multicast_interface(udp, interface_addr)

(method form udp:set_multicast_interface(interface_addr))

Set the multicast interface to send or receive data on.

uv.udp_set_broadcast(udp, on)

Set broadcast on or off.

(method form udp:set_broadcast(, on))

uv.udp_set_ttl(udp, ttl)

(method form udp:set_ttl(ttl))

Set the time to live.

ttl is an integer 1 through 255.

uv.udp_send(udp, data, host, port, callback)

(method form udp:send(data, host, port, callback))

Send data over the UDP socket. If the socket has not previously been bound with uv_udp_bind() it will be bound to (the “all interfaces” IPv4 address) and a random port number.

uv.udp_try_send(udp, data, host, port)

(method form udp:try_send(data, host, port))

Same as uv_udp_send(), but won’t queue a send request if it can’t be completed immediately.

uv.udp_recv_start(udp, callback)

(method form udp:recv_start(callback))

Prepare for receiving data. If the socket has not previously been bound with uv_udp_bind() it is bound to (the “all interfaces” IPv4 address) and a random port number.


(method form udp:recv_stop())

uv_fs_event_t — FS Event handle

TODO: port docs from using functions and methods from fs_event.c

uv_fs_poll_t — FS Poll handle

TODO: port docs from using functions and methods from fs_poll.c

Filesystem operations

TODO: port docs from using functions from fs.c

DNS utility functions

TODO: port docs from using functions from dns.c

Miscellaneous utilities

TODO: port docs from using functions from misc.c