# Module Nethttpd_plex

    module Nethttpd_plex: sig .. end

# Netplex support

The important function is `nethttpd_factory`, see below. The other functions are only needed for special effects.

An example is explained here: Example - A Simple Web Server

    type config_log_error = Nethttpd_types.request_info -> string -> unit

    type config_log_access = Nethttpd_types.full_info -> unit

    type config_error_response = Nethttpd_types.error_response_params -> string

Three type abbreviations for logging functions

    val std_log_error : Netplex_types.container -> config_log_error

Returns a function that logs errors using the `log_subch` method of the passed container

    val std_log_access : ?debug:bool -> Netplex_types.container -> config_log_access

Returns a function that logs accesses using the `log_subch` method of the passed container

If `debug` is set, additional debug log messages are printed that dump the whole access (incl. header and all available information)

    val std_error_response : config_error_response

A sample error response function

    val restrict_file_service_config : Netplex_types.config_file -> Netplex_types.address -> unit

Restricts the subsections and paremeters in the `service` configuration section of type "file" to the allowed ones.

    val read_file_service_config : Netplex_types.config_file ->
           Netplex_types.address -> string -> Nethttpd_services.file_service

`read_file_service_config cfg addr uri_path`: Reads the `service` configuration section of type "file" from config file `cfg` at address `addr`. `uri_path` is the default value put into the `file_uri` component of the returned record if no "uri" configuration parameter exists. (In other words, this is the path of the enclosing "uri" section, or "/" if there is only a "host" section.) All other parameters are only taken from the configuration section.

See below at `nethttpd_factory` how a file service needs to be configured.

    val restrict_dynamic_service_config : Netplex_types.config_file -> Netplex_types.address -> unit

Restricts the subsections and paremeters in the `service` configuration section of type "dynamic" to the allowed ones.

    val read_dynamic_service_config : (string *
            (Netplex_types.config_file ->
             Netplex_types.address ->
             string -> (#Netcgi.cgi_activation as 'a) Nethttpd_services.dynamic_service))
           list ->
           Netplex_types.config_file ->
           Netplex_types.address -> string -> 'a Nethttpd_services.dynamic_service

`read_dynamic_service_config handlers cfg addr uri_path`: Reads the `service` configuration section of type "dynamic" from config file `cfg` at address `addr`. The alist `handlers` defines the available handlers. Every handler `h` is called like `h cfg addr uri_path`. `uri_path` is like in `read_file_service_config`, i.e. the path of the enclosing "uri" section, or "/" by default.

The `h` function has to return the dynamic service to use, which is also returned by `read_dynamic_service_config`.

See below at `nethttpd_factory` how a dynamic service needs to be configured.

    type encap = [ `Engine | `Reactor ]

    val nethttpd_processor : ?hooks:Netplex_types.processor_hooks ->
           ?encap:encap ->
           (Netplex_types.container -> #Nethttpd_reactor.http_reactor_config) ->
           'a Nethttpd_types.http_service -> Netplex_types.processor

`netplex_processor mk_config http_service`: Creates a Netplex processor for Nethttpd.

`mk_config` determines the nethttpd config for a container. This is especially useful for setting the logging functions.

The resulting processor must be turned into a full Netplex service by `Netplex_sockserv.create_socket_service` which can then be added by calling the controller's method `add_service`.

`hooks`: One can pass a Netplex hook object to set the hooks of the processor.

`encap`: Selects the encapsulation, ``Reactor` or ``Engine`. The default is ``Reactor`. Each encapsulation has specific strengths and weaknesses:

- ``Reactor` is simpler code. Also, the request and response bodies need not to be buffered up, and are directly connected with the underlying socket (low memory requirement). The disadvantage is that a reactor processes TCP connections serially (important to know when there is only a single Unix process)
- ``Engine`: The request body needs to be completely buffered up. If pipelining is enabled, the response bodies are also buffered (FIXME). The advantage of this encapsulation is that the engine can process multiple TCP connections simultaneously, even in a single process/thread.

    type (#Netcgi.cgi_activation
           , [ `Dynamic_service of
                 (#Netcgi.cgi_activation as 'a) Nethttpd_services.dynamic_service
             | `File_service of Nethttpd_services.file_service ]) service_factory = (string * 'a Nethttpd_services.dynamic_service) list ->
           Netplex_types.config_file ->
           Netplex_types.address ->
           string ->
           [ `Dynamic_service of 'a Nethttpd_services.dynamic_service
           | `File_service of Nethttpd_services.file_service ]
           Nethttpd_types.http_service

The service factory function is called when a `service` configuration section of a certain type needs to be read. The function has args `handlers`, `cfg`, `addr`, and `uri_path`. It needs to return the `http_service`.

Such a function is usually `read_file_service_config`, or `read_dynamic_service_config`, or a derivative, whose return value is turned into a `http_service`. This can be done with `Nethttpd_services.file_service` and `Nethttpd_services.dynamic_service`.

    val default_services : (string *
            (#Netcgi.cgi_activation as 'a,
             [ `Dynamic_service of 'a Nethttpd_services.dynamic_service
             | `File_service of Nethttpd_services.file_service ])
            service_factory)
           list

The default services

    type httpd_factory = {

`` | `httpd_factory : `'a. (Netplex_types.container -> Nethttpd_reactor.http_reactor_config) -> 'a Nethttpd_types.http_service -> Netplex_types.processor`;`

}
The type of the `nethttpd_processor` function

    val nethttpd_factory : ?name:string ->
           ?hooks:Netplex_types.processor_hooks ->
           ?encap:encap ->
           ?config_cgi:Netcgi.config ->
           ?handlers:(string *
                      (#Netcgi.cgi_activation as 'a) Nethttpd_services.dynamic_service)
                     list ->
           ?services:(string *
                      ('a,
                       [ `Dynamic_service of 'a Nethttpd_services.dynamic_service
                       | `File_service of Nethttpd_services.file_service ])
                      service_factory)
                     list ->
           ?log_error:(Netplex_types.container -> config_log_error) ->
           ?log_access:(?debug:bool ->
                        Netplex_types.container -> config_log_access) ->
           ?error_response:config_error_response ->
           ?processor_factory:httpd_factory ->
           ?tls:(module Netsys_crypto_types.TLS_PROVIDER) ->
           unit -> Netplex_types.processor_factory

Factory for a web server component.

Configuration file. See below.

The `services` optional argument can be used to change the service types understood. If not passed, it defaults to `default_services`. The default includes "file" and "dynamic".

Arguments.

- `name`: The processor name. Defaults to "nethttpd". This name can be referenced by the "type" parameters in the `processor` section of the config file.
- `hooks`: One can pass a Netplex hook object to set the hooks of the processor. (This argument is ignored if a `processor_factory` is passed to this function.)
- `encap`: See `Nethttpd_plex.nethttpd_processor`. (This argument is ignored if a `processor_factory` is passed to this function.)
- `config_cgi`: The CGI configuration to use
- `handlers`: a list of handler function. These functions can be referenced from a `service` section in the config file where `type="dynamic"` (see example above). Defaults to the empty list.
- `services`: A list of service handlers that can be used by `service` sections in the config files. Defaults to `Nethttpd_plex.default_services` which defines "file" and "dynamic".
- `log_error`: The error logger. Defaults to `Nethttpd_plex.std_log_error`.
- `log_access`: The access logger. Defaults to `Nethttpd_plex.std_log_access`.
- `error_response`: a handler which is invoked to generate error responses. Defaults to `Nethttpd_plex.std_error_response`.
- `processor_factory`: the function creating the processor. Default is `nethttpd_processor`.
- `tls`: the TLS provider to use. By default, `Netsys_crypto.current_tls_opt` is used.

## Configuration files

The configuration file understood by `nethttpd_factory` looks like:

        processor {
          type = "nethttpd";          (* or what is passed as "name" arg *)
          timeout = 300.0;
          timeout_next_request = 15.0;
          access_log = "enabled";
          suppress_broken_pipe = true;
          host {
            pref_name = "myhost";     (* optional *)
            pref_port = 80;           (* optional *)
            names = "myhost:80 yourhost:81";  (* use *:0 for any name *)
            uri {
              path = "/the/path";
              method {
                allow = "GET POST";
                (* or: deny = "..." *)
                service {
                  type = "...";
                  ...
                }
              }
            }
            uri {
              ...
            }
          }
          host {
            ...
          }
        }

The `access_log` parameter can be set to `off`, `enabled`, or `debug`. The default is `off`. Access messages go to the "access" subchannel of the component logger. If `enabled`, one line is printed with the most important data. If `debug` is set, all access data are printed.

If `suppress_broken_pipe` the error "Broken pipe" is not logged in the error log. This error occurs frequently, and may be regarded as a normal condition.

The sections `host`, `uri` and `method` can be nested to any depth. However, on every nesting level only one of these section types must be used. For example, if a `host` section already contains `uri` subsections, it is not allowed to add `method` subsections. Furthermore, the outermost section must be `host`.

The `service` section may be one of (at least if the `services` parameter is not overridden):

        service {
          type = "file";
          docroot = "/a/path/in/the/filesystem";
          uri = "/the/uri/prefix/corresponding/to/docroot";
          media_types_file = "/etc/mime.types";
          media_type {
            type = "application/foo";
            suffix = "foo"
          }
          default_media_type = "text/plain";
          enable_gzip = true;   (* see doc in nethttpd_services.mli *)
          index_files = "index.html";
          enable_listings = true;
          hide_from_listings = "README";   (* list of PCRE regexps *)
        }

Note that `uri` is taken from the surrounding `uri` section (or assumed to be "/" if there is none) if omitted.

        service {
          type = "dynamic";
          handler = "name_of_handler";
        }

Binds the passed handler here.

Any of `host`, `uri`, and `method` sections may contain one or several `access` sections (which are AND-connected):

        access {
          type = "host";
          allow = "host1 host2 ...";
          (* or deny = "host1 host2 ..."; *)
        }

Other access control methods are not yet available.

## Configuring TLS

First of all, there needs to be a TLS provider. See `Tls` for more information how to get one.

If the TLS provider is initialized, you can have a `tls` subsection inside `processor`, like:

    processor {
      ...
      tls {
        x509 {
          trust {
            crt_file = "ca.pem";
          }
          key {
            crt_file = "server.crt";
            key_file = "server.key";
          }
        }
      }
    }

All of the files, `ca.pem`, `server.crt` and `server.key` need to be PEM-encoded. You can have several `key` sub-sections when you want to do name-based virtual hosting. Note, however, that this relies on the SNI extension of the TLS protocol, and not all clients support this extension.

Further parameters inside `tls`:

- `algorithms`: This is a string describing the cipher suites and protocol options that are in effect. This string is provider-specific. (GnuTLS calls this string the "priority string".) Example:

      tls {
         ...
         algorithms = "SECURE-128 !ARCFOUR-128";
      }

- `dh_params`: This sub-section may set DH parameters. Example:

      tls {
        ...
        dh_params {
          pkcs3_file = "/path/to/pkcs3_file";
        }
      }

- `peer_auth`: This string parameter may enable client certificates. Set it to "required" to enforce such a certificate.

      tls {
        ...
        peer_auth = "required";
      }