# Sockets

`Sockets.Sockets` — Module

Support for sockets. Provides `IPAddr` and subtypes, `TCPSocket`, and `UDPSocket`.

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`Sockets.connect` — Method

    connect([host], port::Integer) -> TCPSocket

Connect to the host `host` on port `port`.

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`Sockets.connect` — Method

    connect(path::AbstractString) -> PipeEndpoint

Connect to the named pipe / UNIX domain socket at `path`.

Note

Path length on Unix is limited to somewhere between 92 and 108 bytes (cf. `man unix`).

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`Sockets.listen` — Method

    listen([addr, ]port::Integer; backlog::Integer=BACKLOG_DEFAULT) -> TCPServer

Listen on port on the address specified by `addr`. By default this listens on `localhost` only. To listen on all interfaces pass `IPv4(0)` or `IPv6(0)` as appropriate. `backlog` determines how many connections can be pending (not having called `accept`) before the server will begin to reject them. The default value of `backlog` is 511.

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`Sockets.listen` — Method

    listen(path::AbstractString) -> PipeServer

Create and listen on a named pipe / UNIX domain socket.

Note

Path length on Unix is limited to somewhere between 92 and 108 bytes (cf. `man unix`).

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`Sockets.getaddrinfo` — Function

    getaddrinfo(host::AbstractString, IPAddr) -> IPAddr

Gets the first IP address of the `host` of the specified `IPAddr` type. Uses the operating system's underlying getaddrinfo implementation, which may do a DNS lookup.

Examples

    julia> getaddrinfo("localhost", IPv6)
    ip"::1"

    julia> getaddrinfo("localhost", IPv4)
    ip"127.0.0.1"

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    getaddrinfo(host::AbstractString) -> IPAddr

Gets the first available IP address of `host`, which may be either an `IPv4` or `IPv6` address. Uses the operating system's underlying getaddrinfo implementation, which may do a DNS lookup.

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`Sockets.getipaddr` — Function

    getipaddr() -> IPAddr

Get an IP address of the local machine, preferring IPv4 over IPv6. Throws if no addresses are available.

    getipaddr(addr_type::Type{T}) where T<:IPAddr -> T

Get an IP address of the local machine of the specified type. Throws if no addresses of the specified type are available.

This function is a backwards-compatibility wrapper around `getipaddrs`. New applications should use `getipaddrs` instead.

Examples

    julia> getipaddr()
    ip"192.168.1.28"

    julia> getipaddr(IPv6)
    ip"fe80::9731:35af:e1c5:6e49"

See also `getipaddrs`.

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`Sockets.getipaddrs` — Function

    getipaddrs(addr_type::Type{T}=IPAddr; loopback::Bool=false) where T<:IPAddr -> Vector{T}

Get the IP addresses of the local machine.

Setting the optional `addr_type` parameter to `IPv4` or `IPv6` causes only addresses of that type to be returned.

The `loopback` keyword argument dictates whether loopback addresses (e.g. `ip"127.0.0.1"`, `ip"::1"`) are included.

Julia 1.2

This function is available as of Julia 1.2.

Examples

    julia> getipaddrs()
    5-element Vector{IPAddr}:
     ip"198.51.100.17"
     ip"203.0.113.2"
     ip"2001:db8:8:4:445e:5fff:fe5d:5500"
     ip"2001:db8:8:4:c164:402e:7e3c:3668"
     ip"fe80::445e:5fff:fe5d:5500"

    julia> getipaddrs(IPv6)
    3-element Vector{IPv6}:
     ip"2001:db8:8:4:445e:5fff:fe5d:5500"
     ip"2001:db8:8:4:c164:402e:7e3c:3668"
     ip"fe80::445e:5fff:fe5d:5500"

See also `islinklocaladdr`.

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`Sockets.islinklocaladdr` — Function

    islinklocaladdr(addr::IPAddr)

Tests if an IP address is a link-local address. Link-local addresses are not guaranteed to be unique beyond their network segment, therefore routers do not forward them. Link-local addresses are from the address blocks `169.254.0.0/16` or `fe80::/10`.

Examples

    filter(!islinklocaladdr, getipaddrs())

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`Sockets.getalladdrinfo` — Function

    getalladdrinfo(host::AbstractString) -> Vector{IPAddr}

Gets all of the IP addresses of the `host`. Uses the operating system's underlying `getaddrinfo` implementation, which may do a DNS lookup.

Examples

    julia> getalladdrinfo("google.com")
    2-element Vector{IPAddr}:
     ip"172.217.6.174"
     ip"2607:f8b0:4000:804::200e"

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`Sockets.DNSError` — Type

    DNSError

The type of exception thrown when an error occurs in DNS lookup. The `host` field indicates the host URL string. The `code` field indicates the error code based on libuv.

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`Sockets.getnameinfo` — Function

    getnameinfo(host::IPAddr) -> String

Performs a reverse-lookup for IP address to return a hostname and service using the operating system's underlying `getnameinfo` implementation.

Examples

    julia> getnameinfo(IPv4("8.8.8.8"))
    "google-public-dns-a.google.com"

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`Sockets.getsockname` — Function

    getsockname(sock::Union{TCPServer, TCPSocket}) -> (IPAddr, UInt16)

Get the IP address and port that the given socket is bound to.

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`Sockets.getpeername` — Function

    getpeername(sock::TCPSocket) -> (IPAddr, UInt16)

Get the IP address and port of the remote endpoint that the given socket is connected to. Valid only for connected TCP sockets.

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`Sockets.IPAddr` — Type

    IPAddr

Abstract supertype for IP addresses. `IPv4` and `IPv6` are subtypes of this.

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`Sockets.IPv4` — Type

    IPv4(host::Integer) -> IPv4

Return an IPv4 object from IP address `host` formatted as an `Integer`.

Examples

    julia> IPv4(3223256218)
    ip"192.30.252.154"

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    IPv4(str::AbstractString) -> IPv4

Parse an IPv4 address string into an `IPv4` object.

Examples

    julia> IPv4("127.0.0.1")
    ip"127.0.0.1"

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`Sockets.IPv6` — Type

    IPv6(host::Integer) -> IPv6

Return an IPv6 object from IP address `host` formatted as an `Integer`.

Examples

    julia> IPv6(3223256218)
    ip"::c01e:fc9a"

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    IPv6(str::AbstractString) -> IPv6

Parse an IPv6 address string into an `IPv6` object.

Examples

    julia> IPv6("::1")
    ip"::1"

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`Sockets.@ip_str` — Macro

    @ip_str str -> IPAddr

Parse `str` as an IP address.

Examples

    julia> ip"127.0.0.1"
    ip"127.0.0.1"

    julia> @ip_str "2001:db8:0:0:0:0:2:1"
    ip"2001:db8::2:1"

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`Sockets.TCPSocket` — Type

    TCPSocket(; delay=true)

Open a TCP socket using libuv. If `delay` is true, libuv delays creation of the socket's file descriptor till the first `bind` call. `TCPSocket` has various fields to denote the state of the socket as well as its send/receive buffers.

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`Sockets.UDPSocket` — Type

    UDPSocket()

Open a UDP socket using libuv. `UDPSocket` has various fields to denote the state of the socket.

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`Sockets.accept` — Function

    accept(server[, client])

Accepts a connection on the given server and returns a connection to the client. An uninitialized client stream may be provided, in which case it will be used instead of creating a new stream.

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`Sockets.listenany` — Function

    listenany([host::IPAddr,] port_hint; backlog::Integer=BACKLOG_DEFAULT) -> (UInt16, TCPServer)

Create a `TCPServer` on any port, using hint as a starting point. Returns a tuple of the actual port that the server was created on and the server itself. The backlog argument defines the maximum length to which the queue of pending connections for sockfd may grow.

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`Base.bind` — Function

    bind(socket::Union{TCPServer, UDPSocket, TCPSocket}, host::IPAddr, port::Integer; ipv6only=false, reuseaddr=false, kws...)

Bind `socket` to the given `host:port`. Note that `0.0.0.0` will listen on all devices.

- The `ipv6only` parameter disables dual stack mode. If `ipv6only=true`, only an IPv6 stack is created.
- If `reuseaddr=true`, multiple threads or processes can bind to the same address without error if they all set `reuseaddr=true`, but only the last to bind will receive any traffic.

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    bind(chnl::Channel, task::Task)

Associate the lifetime of `chnl` with a task. `Channel` `chnl` is automatically closed when the task terminates. Any uncaught exception in the task is propagated to all waiters on `chnl`.

The `chnl` object can be explicitly closed independent of task termination. Terminating tasks have no effect on already closed `Channel` objects.

When a channel is bound to multiple tasks, the first task to terminate will close the channel. When multiple channels are bound to the same task, termination of the task will close all of the bound channels.

Examples

    julia> c = Channel(0);

    julia> task = @async foreach(i->put!(c, i), 1:4);

    julia> bind(c,task);

    julia> for i in c
               @show i
           end;
    i = 1
    i = 2
    i = 3
    i = 4

    julia> isopen(c)
    false

    julia> c = Channel(0);

    julia> task = @async (put!(c, 1); error("foo"));

    julia> bind(c, task);

    julia> take!(c)
    1

    julia> put!(c, 1);
    ERROR: TaskFailedException
    Stacktrace:
    [...]
        nested task error: foo
    [...]

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`Sockets.send` — Function

    send(socket::UDPSocket, host::IPAddr, port::Integer, msg)

Send `msg` over `socket` to `host:port`.

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`Sockets.recv` — Function

    recv(socket::UDPSocket)

Read a UDP packet from the specified socket, and return the bytes received. This call blocks.

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`Sockets.recvfrom` — Function

    recvfrom(socket::UDPSocket) -> (host_port, data)

Read a UDP packet from the specified socket, returning a tuple of `(host_port, data)`, where `host_port` will be an InetAddr{IPv4} or InetAddr{IPv6}, as appropriate.

Julia 1.3

Prior to Julia version 1.3, the first returned value was an address (`IPAddr`). In version 1.3 it was changed to an `InetAddr`.

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`Sockets.setopt` — Function

    setopt(sock::UDPSocket; multicast_loop=nothing, multicast_ttl=nothing, enable_broadcast=nothing, ttl=nothing)

Set UDP socket options.

- `multicast_loop`: loopback for multicast packets (default: `true`).
- `multicast_ttl`: TTL for multicast packets (default: `nothing`).
- `enable_broadcast`: flag must be set to `true` if socket will be used for broadcast messages, or else the UDP system will return an access error (default: `false`).
- `ttl`: Time-to-live of packets sent on the socket (default: `nothing`).

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`Sockets.nagle` — Function

    nagle(socket::Union{TCPServer, TCPSocket}, enable::Bool)

Nagle's algorithm batches multiple small TCP packets into larger ones. This can improve throughput but worsen latency. Nagle's algorithm is enabled by default. This function sets whether Nagle's algorithm is active on a given TCP server or socket. The opposite option is called `TCP_NODELAY` in other languages.

Julia 1.3

This function requires Julia 1.3 or later.

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`Sockets.quickack` — Function

    quickack(socket::Union{TCPServer, TCPSocket}, enable::Bool)

On Linux systems, the TCP_QUICKACK is disabled or enabled on `socket`.

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This document was generated with Documenter.jl version 1.16.0 on Thursday 20 November 2025. Using Julia version 1.12.2.