class resolve_to_url_obj_channel :When this resolver gets an ID to read from, it calls the function?close:Netchannels.in_obj_channel -> unit -> url_of_id:(Pxp_types.resolver_id -> Neturl.url) -> base_url_of_id:(Pxp_types.resolver_id -> Neturl.url) -> channel_of_url:(Pxp_types.resolver_id -> Neturl.url -> accepted_id) -> unit ->resolver
url_of_id to get the corresponding URL (such IDs are normally
system IDs, but it is also possible to other kinds of IDs to URLs).
This URL may be a relative URL; however, a URL scheme must be used
which contains a path. The resolver converts the URL to an absolute
URL if necessary.
To do so, the resolver calls base_url_of_id to get the URL the relative
URL must be interpreted relative to. Usually, this function returns
the rid_system_base as URL. This URL must be absolute.
The third function, channel_of_url, is fed with the absolute URL
as input. This function opens the resource to read from, and returns
the accepted_id like resolve_to_any_obj_channel does. The resolver ID
passed to channel_of_url contains the string representation of the
absolute URL as system ID.
Both functions, url_of_id and channel_of_url, can raise
Not_competent to indicate that the object is not able to read from
the specified resource. However, there is a difference: A Not_competent
from url_of_id is left as is, but a Not_competent from channel_of_url
is converted to Not_resolvable. So only url_of_id decides which URLs
are accepted by the resolver and which not, and in the latter case,
other resolver can be tried. If channel_of_url raises Not_competent,
however, the whole resolution procedure will stop, and no other resolver
will be tried.
When the resolver is closed, the function passed by the close
argument is called. By default, the channel is closed
(i.e. the default is: close:(fun ch -> ch # close_in())).
