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# erl_epmd (kernel v10.3)

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Erlang interface towards epmd

This module communicates with the EPMD daemon, see epmd. To implement your own epmd module please see ERTS User's Guide: How to Implement an Alternative Node Discovery for Erlang Distribution

# Summary

## Functions

address_please(Name, Host, AddressFamily)

Called by the distribution module to resolves the `Host` to an IP address of a remote node.

listen_port_please(Name, Host)

Called by the distribution module to get which port the local node should listen to when accepting new distribution requests.

names(Host)

Called by `net_adm:names/0`. `Host` defaults to the localhost. Returns the names and associated port numbers of the Erlang nodes that `epmd` registered at the specified host. Returns `{error, address}` if `epmd` is not operational.

port_please(Name, Host)

Equivalent to `port_please(Name, Host, infinity)`.

port_please(Name, Host, Timeout)

Requests the distribution port for the given node of an EPMD instance. Together with the port it returns a distribution protocol version which has been 5 since Erlang/OTP R6.

register_node(Name, Port)

Equivalent to `register_node(Name, Port, inet)`.

register_node(Name, Port, Driver)

Registers the node with `epmd` and tells epmd what port will be used for the current node. It returns a creation number. This number is incremented on each register to help differentiate a new node instance connecting to epmd with the same name.

start_link()

This function is invoked as this module is added as a child of the `erl_distribution` supervisor.

# Functions

# address_please(Name, Host, AddressFamily)

(since OTP 21.0)

    -spec address_please(Name, Host, AddressFamily) -> Success | {error, term()}
                            when
                                Name :: string(),
                                Host :: string() | inet:ip_address(),
                                AddressFamily :: inet | inet6,
                                Port :: non_neg_integer(),
                                Version :: non_neg_integer(),
                                Success :: {ok, inet:ip_address()} | {ok, inet:ip_address(), Port, Version}.

Called by the distribution module to resolves the `Host` to an IP address of a remote node.

As an optimization this function may also return the port and version of the remote node. If port and version are returned `port_please/3` will not be called.

# listen_port_please(Name, Host)

(since OTP 23.0)

    -spec listen_port_please(Name, Host) -> {ok, Port}
                                when
                                    Name :: atom() | string(),
                                    Host :: atom() | string() | inet:ip_address(),
                                    Port :: non_neg_integer().

Called by the distribution module to get which port the local node should listen to when accepting new distribution requests.

# names(Host)

(since OTP 21.0)

    -spec names(Host) -> {ok, [{Name, Port}]} | {error, Reason}
                   when
                       Host :: atom() | string() | inet:ip_address(),
                       Name :: string(),
                       Port :: non_neg_integer(),
                       Reason :: address | file:posix().

Called by `net_adm:names/0`. `Host` defaults to the localhost. Returns the names and associated port numbers of the Erlang nodes that `epmd` registered at the specified host. Returns `{error, address}` if `epmd` is not operational.

Example:

    (arne@dunn)1> erl_epmd:names(localhost).
    {ok,[{"arne",40262}]}

# port_please(Name, Host)

(since OTP 21.0)

    -spec port_please(Name, Host) -> {port, Port, Version} | noport | closed | {error, term()}
                         when
                             Name :: atom() | string(),
                             Host :: atom() | string() | inet:ip_address(),
                             Port :: non_neg_integer(),
                             Version :: non_neg_integer().

Equivalent to `port_please(Name, Host, infinity)`.

# port_please(Name, Host, Timeout)

(since OTP 21.0)

    -spec port_please(Name, Host, Timeout) -> {port, Port, Version} | noport | closed | {error, term()}
                         when
                             Name :: atom() | string(),
                             Host :: atom() | string() | inet:ip_address(),
                             Timeout :: non_neg_integer() | infinity,
                             Port :: non_neg_integer(),
                             Version :: non_neg_integer().

Requests the distribution port for the given node of an EPMD instance. Together with the port it returns a distribution protocol version which has been 5 since Erlang/OTP R6.

# register_node(Name, Port)

(since OTP 21.0)

    -spec register_node(Name, Port) -> Result
                           when
                               Name :: string(),
                               Port :: non_neg_integer(),
                               Creation :: non_neg_integer(),
                               Result :: {ok, Creation} | {error, already_registered} | term().

Equivalent to `register_node(Name, Port, inet)`.

# register_node(Name, Port, Driver)

(since OTP 21.0)

    -spec register_node(Name, Port, Driver) -> Result
                           when
                               Name :: string(),
                               Port :: non_neg_integer(),
                               Driver :: inet_tcp | inet6_tcp | inet | inet6,
                               Creation :: non_neg_integer() | -1,
                               Result :: {ok, Creation} | {error, already_registered} | term().

Registers the node with `epmd` and tells epmd what port will be used for the current node. It returns a creation number. This number is incremented on each register to help differentiate a new node instance connecting to epmd with the same name.

After the node has successfully registered with epmd it will automatically attempt reconnect to the daemon if the connection is broken.

# start_link()

(since OTP 21.0)

    -spec start_link() -> {ok, pid()} | ignore | {error, term()}.

This function is invoked as this module is added as a child of the `erl_distribution` supervisor.