# Module Uq_resolver

    module Uq_resolver: sig .. end

Support for pluggable resolvers

A resolver maps several kinds of names to addresses, or vice versa. Currently, only DNS host lookups are supported (but this can be extended if needed).

The plugin mechanism allows one to change the name resovler Ocamlnet uses. Resolvers can be both synchronous or asynchronous. Note however, that the default resolver is synchronous and simply bases on `Unix.gethostbyname`.

Requirements of the resolver:

- IP addresses may be enclosed in square brackets, but also given without such brackets. If such an IP address is passed to the resolver, the string address is just converted to a `Unix.inet_addr`.

## Asynchronous Interface

The following types are the same as in `Uq_engines`, here only redefined for systematic reasons

    type 't engine_state = [ `Aborted | `Done of 't | `Error of exn | `Working of int ]

    class type ['t] engine = object .. end

Exceptions

    exception Host_not_found of string

This host cannot be resolved

The type of resolvers:

    class type resolver = object .. end

## Synchronous Interface

    val get_host_by_name : ?resolver:resolver -> string -> Unix.host_entry

Look up the host, and return the host entry or raise the exception `Host_not_found`.

If a `resolver` is passed, this resolver is used, otherwise the pluggable resolver is used.

    val sockaddr_of_socksymbol : ?resolver:resolver -> Netsockaddr.socksymbol -> Unix.sockaddr

Use the resolver to look up names in `Netsockaddr.socksymbol`, and convert the symbol to a `Unix.sockaddr` only containing IP addresses.

If a `resolver` is passed, this resolver is used, otherwise the pluggable resolver is used.

## Resolvers

    val default_resolver : unit -> resolver

The default resolver uses `Unix.gethostbyname` to look up names. Note that this means that no IPv6 addresses are returned.

    val gai_resolver : ?ipv4:bool -> ?ipv6:bool -> unit -> resolver

This resolver uses `Unix.getaddrinfo`. One can set whether IPv4 or IPv6 addresses may be returned (only one type is returned). The order of addresses cannot be set, but there is a global config file `/etc/gai.info`.

The `h_aliases` field of the result is not set.

By default, both `ipv4` and `ipv6` are enabled.

## Plugins

    val current_resolver : unit -> resolver

Returns the pluggable resolver. Unless overridden by `set_current_resolver`, the returned resolver depends on the result of `Netsys.is_ipv6_system`.

    val set_current_resolver : resolver -> unit

Set the pluggable resolver