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Module Netcgi_common

module Netcgi_common: sig .. end
Functions to develop new connectors.

The following module is provided as a set of helper functions to define new connectors. As a normal user of Netcgi, you should not use this module.

The goal of this module is to factor out common routines to easily set up new connectors. Here is the normal flow of operations:

  • You start by reading the request environment properties as well as the input header. Often both are undistinguished and provided through some sort of meta-variables. The function Netcgi_common.update_props_inheader helps you to sort them and to normalize the input header fields. You also need to set up a Netchannels.out_obj_channel to the output stream of your connector. Then, Netcgi_common.cgi_environment can create an environment object for you. If stderr output is not appropriate (e.g. ot is not redirected to the server log), you need to override #log_error.
  • From the environment object and arguments, Netcgi_common.cgi creates a CGI object. Often, arguments are read from the environment #cgi_query_string (in case of GET) or from an input channel (in case of POST). Netcgi_common.cgi_with_args handles this for you: it requires a Netchannels.in_obj_channel from which the arguments are read (only used in the case of POST).
  • Netcgi_common.exn_handler_default provides a default error page for uncaught exceptions. It also allows the user to pass his own exception handler that has precedence on the default one.
To see this schema in use, we recommend you have a look to the implementation of the CGI connector because it is very simple.


type representation = [ `MIME of Netmime.mime_message | `Simple of Netmime.mime_body ] 
type store = [ `File of string | `Memory ] 
exception Oversized
exception Too_many_arguments
Hit the limit max_arguments
class type cgi_argument = object .. end
class type rw_cgi_argument = object .. end
class simple_arg : ?ro:bool -> string -> string -> rw_cgi_argument
class mime_arg : ?work_around_backslash_bug:bool -> ?name:string -> Netmime.mime_message -> rw_cgi_argument


The cookie implementation has been moved to Nethttp.Cookie. New code should directly call the functions defined there.
module Cookie: sig .. end


type config = {
   tmp_directory :string;
   tmp_prefix :string;
   permitted_http_methods :[ `DELETE | `GET | `HEAD | `POST | `PUT ] list;
   permitted_input_content_types :string list;
   input_content_length_limit :int;
   max_arguments :int;
   workarounds :[ `Backslash_bug
| `MSIE_Content_type_bug
| `Work_around_MSIE_Content_type_bug
| `Work_around_backslash_bug ] list
   default_exn_handler :bool;
type output_type = [ `Direct of string
| `Transactional of
config ->
Netchannels.out_obj_channel -> Netchannels.trans_out_obj_channel ]
val fix_MSIE_Content_type_bug : string -> string
fix_MSIE_Content_type_bug ct transforms the content-type string ct to fix the MSIE Content-Type bug.
val is_MSIE : string -> bool
is_MSIE user_agent tells whether the user_agent is Microsoft Internet Explorer. Useful to know when to apply Netcgi_common.fix_MSIE_Content_type_bug.
class cgi_environment : config:config -> properties:(string * string) list -> input_header:(string * string) list -> Netchannels.out_obj_channel -> object .. end
new cgi_environment ~config ~properties ~input_header out_obj generates a Netcgi.cgi_environment object, from the arguments.


type other_url_spec = [ `Env | `None | `This of string ] 
type query_string_spec = [ `Args of rw_cgi_argument list
| `Env
| `None
| `This of cgi_argument list ]
type cache_control = [ `Max_age of int | `No_cache | `Unspecified ] 
type request_method = [ `DELETE | `GET | `HEAD | `POST | `PUT of cgi_argument ] 
val string_of_request_method : request_method -> string
type arg_store_type = [ `Automatic
| `Automatic_max of float
| `Discard
| `File
| `File_max of float
| `Memory
| `Memory_max of float ]
type arg_store = cgi_environment ->
string -> Netmime.mime_header_ro -> arg_store_type
class cgi : cgi_environment -> output_type -> request_method -> cgi_argument list -> object .. end
cgi env op meth args constructs Netcgi.cgi objects.
val cgi_with_args : (cgi_environment ->
output_type ->
request_method -> cgi_argument list -> 'a) ->
cgi_environment ->
output_type ->
Netchannels.in_obj_channel -> arg_store -> 'a
cgi_with_args (new cgi) env out op ?put_arg in_chan constructs a Netcgi.cgi object. However, new cgi can be replaced by any function, so it is easy to use this to construct extensions of the cgi class (as needed by some connectors). The arguments of the cgi object are taken from the environment env (for HEAD, GET, DELETE) or from the in_chan (for POST, PUT) and processed according to arg_store.
Raises HTTP if the data does not conform the standards or it not allowed.


exception HTTP of Nethttp.http_status * string
Exception raised by various functions of this library to return to the user agent an appropriate error page with the specified http-status (this exception must be caught by the connector and a default answer sent).

The string is a description of the cause of the error.

This exception is for use by connectors only, users should deal with the exceptions in their code by generating a response with the usual #set_header and #out_channel of Netcgi.cgi.

val exn_handler_default : cgi_environment ->
exn_handler:(cgi_environment -> (unit -> unit) -> unit) ->
finally:(unit -> unit) -> (unit -> exn option) -> unit
exn_handler_default env ~exn_handler ~finally run_cgi will basically execute exn_handler env run_cgi. Provided that the environment config default_exn_handler is set to true (the default), any exception e not caught by the user provided exn_handler (or that is raised by it) will be passed to the default handler of OCamlNet which will rollback the current output, produce a page describing the exception e, and close the output channel of env. Note that the default handler treats HTTP exceptions specially -- for example, the response to HTTP(`Method_not_allowed,...) includes an "Allow" header (as mandated by HTTP/1.1);...

Note that, regardless of the value of default_exn_handler, the Exit exception is always caught and treated like an acceptable early termination (thus produces no error page).

Whether run_cgi terminates normally or by an exception, finally() is executed last.

Sometimes, you want that some "special" exceptions (for example exceptions internal to the connector) CANNOT to be caught by exn_handler. In this case, run_cgi() catches the exception, say e, and returns it as Some e. The exception e will "go through" exn_handler_default, it will not even be passed to the default handler. Therefore, you must take care that it is handled by the surrounding code or your connector may die without an error message. Of course, run_cgi must return None if no "special" exception is raised.

REMARK: Stricly speaking, exn_handler env run_cgi is obviously not possible because the return type of run_cgi is not unit but you can ignore that to understand what this function does.

val error_page : cgi_environment ->
Nethttp.http_status ->
(string * string list) list -> string -> string -> unit
error_page env status fields msg detail: Logs an error message and outputs an error page via env.

status is the status of the error page, e.g. `Internal_server_error. fields are put into the response header of the error page.

msg occurs in the log message and in the error page, and should be a concise description without linefeeds. detail is only printed to the error page, and may be longer than this, and may also include HTML markup.

Useful functions

The following functions are used in several connectors and are gouped here for convenience.

val update_props_inheader : string * string ->
(string * string) list * (string * string) list ->
(string * string) list * (string * string) list
update_props_inheader (name, value) (props, inheader) returns (props, inheader) to which the new parameter name-value has been added -- to props or inheader, depending on name. Unless you know what you are going, you must use this function to classify parameters as it also performs some standardisation.
val rm_htspace : (char -> bool) -> string -> int -> int -> string
rm_htspace is_space s low up returns the substring s.[low .. up - 1] stripped of possible heading and trailing spaces identified by the function is_space.
Raises Invalid_argument if low < 0 or up > String.length s
val rev_split : (char -> bool) -> string -> string list
split_rev is_delim s split s at each character is_delim and returns the list of substrings in reverse order. Several consecutive delimiters are treated as a single one. The substrings do not share s memory.
val is_prefix : string -> string -> bool
is_prefix pre s checks whether pre is a prefix of s.
type http_method = [ `DELETE | `GET | `HEAD | `POST | `PUT ] 
val string_of_http_method : http_method -> string
Returns the string value of the method
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