module Uq_resolver

: sig

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 [root:Uq_engines], here only redefined for systematic reasons

type 't engine_state = [

| `Working of int

| `Done of 't

| `Error of exn

| `Aborted

]

class type ['t] engine =

method state : 't engine_state

method abort : unit -> unit

method request_notification : (unit -> bool) -> unit

method event_system : Unixqueue.event_system

Exceptions

exception Host_not_found of string

This host cannot be resolved

The type of resolvers:

class type resolver =

method host_by_name : string -> Unixqueue.event_system -> Unix.host_entry engine

Look up the passed host name up. The implementation can be synchronous or asynchronous. In the first case, an engine is returned that is already in one of the states `Done he or `Error e where he is the host entry, or e is an exception like Host_not_found. In this case the passed event system is ignored. If the implementation is asynchronous, the caller must run the event system until the state of the engine transitions to `Done he or `Error e.

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 usually 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

val set_current_resolver : resolver -> unit

Set the pluggable resolver

end