# Module Netftp_client

    module Netftp_client: sig .. end

FTP client

Currently implements:

- Core FTP (RFC 959), except compressed transfer modes, and except page files
- Negotiation of FTP extensions (RFC 2389)
- Common FTP extensions (RFC 3659)
- IPv6 (RFC 2428)
- Internationalization (RFC 2640)
- Directory walking (NVFS) and direct access (TVFS)
- TLS (it is required, though, that a TLS provider is initialized, see `Tls` for more information)
- GSSAPI (RFC 2228)

The client is written in asynchronous style (using `Uq_engines`).

The interface of this module was changed in Ocamlnet-3.3. Before this release, the module was marked as "experimental". This is no longer the case, as the interface has been updated, and the missing features have been added (e.g. `STOR` support).

    exception FTP_error of exn

Something went wrong, often on socket level

    exception FTP_protocol_violation of string

The server violates the FTP specification

    exception FTP_timeout of string

A timeout on the control or data connection (this is a fatal error)

    exception GSSAPI_error of string

An error on GSSAPI level

    type cmd_state = [ `Auth_data
           | `Init
           | `Not_connected
           | `Pass_acct_seq
           | `Perm_failure
           | `Preliminary
           | `Proto_error
           | `Rename_seq
           | `Restart_seq
           | `Success
           | `Temp_failure
           | `User_acct_seq
           | `User_pass_seq ]

The command state:

- ``Not_connected`: Not connected.
- ``Init`: Just connected, no greeting message arrived yet
- ``Success`: Got the greeting message/last command was successful
- ``Proto_error`: currently unused
- ``Temp_failure`: Last command was not successful, and the code was between 400 and 499
- ``Perm_failure`: Last command was not successful, and the code was between 500 and 599
- ``Rename_seq`: Used instead of ``Success` after the RNFR command
- ``Restart_seq`: Used instead of ``Success` after the REST command
- ``User_pass_seq`: Used instead of ``Success` after the USER command when a password must be typed in
- ``User_acct_seq`: Used instead of ``Success` after the USER command when an account ID must be typed in
- ``Pass_acct_seq`: Used instead of ``Success` after the PASS command when an account iD must be typed in
- ``Preliminary`: a reply with code 100 to 199. There will be another final reply for the command
- ``Auth_data`: an ADAT reply inidicating that another round of authentication is necessary.

    type port = [ `Active of string * int * Unix.file_descr
           | `Ext_active of string * int * Unix.file_descr
           | `Ext_passive of int
           | `Passive of string * int
           | `Unspecified ]

The port of the data connection: ``Active` means that the server initiates the data connection to the listening client, and in the case of ``Passive` the client initiates the data connection to the listening server. The string argument is the IP address as dotted quad, the int argument is the port number, and the descriptor is the listening master socket.

    type form_code = [ `ASA | `Non_print | `Telnet ]

The `form_code` has a meaning when FTP is used to print files:

- ``Non_print`: This is not the case.
- ``Telnet`: Telnet control codes are used for vertical movement
- ``ASA`: ASA (Fortran) control codes are used for vertical movement

    type representation = [ `ASCII of form_code option
           | `EBCDIC of form_code option
           | `Image ]

The representation of the transferred file:

- ``ASCII`: An ASCII variant is used, i.e. the server sends files in ASCII encoding with CR/LF as end-of-line marker. Supported by all servers.
- ``EBCDIC`: An EBCDIC variant is used, i.e. the server sends files in EBCDIC encoding with NEL as end-of-line marker
- ``Image`: The file is transferred in its original binary representation. Supported by all servers.

"Local" representations are not supported.

This FTP client does not recode the files such that they match the selected representation. When files are downloaded, they are stored as they are received. When files are uploaded, they are sent as they are. The user of this client must do recodings when necessary (the class `Netftp_data_endpoint.data_converter` may be useful for this).

If no representation is selected, FTP servers assume ``ASCII None` as default.

    type structure = [ `File_structure | `Record_structure ]

The client supports two structures:

- ``File_structure`: Files are simply contiguous streams of bytes
- ``Record_structure`: Files are sequences of records. FTP does not make a difference between variable and fixed length records. It is not forbidden that the records are themselves structured into lines, in fact it can happen that end-of-line markers are contained in binary records. Operating systems that support record-structured files often store text files in this format, i.e. every line is stored in its own record, without end-of-line marker. If record structure is selected by a STRU command, it is recommended to use the classes `Netftp_data_endpoint.out_record_channel` and `Netftp_data_endpoint.in_record_channel` for the local representation of the files, otherwise the records may be incorrectly mapped to the local conventions.

Page-structured files (i.e. indexed files) are not supported.

If no structure is selected, FTP servers will assume file structure as default.

    type transmission_mode = [ `Block_mode | `Stream_mode ]

The transmission mode selects how the data are encoded in the data connection.

- ``Stream_mode`: This is the simple format that is responsible for all the failed FTP downloads. It is supported by all FTP servers, actually, you cannot assume a better transmission mode from an unknown FTP server. It is unreliable because it cannot distinguish between a transmission failure and the regular end-of-file condition.
- ``Block_mode`: This is an improved format using frames to protect the transmitted data. Unfortunately, almost no FTP server supports it.

Both modes are compatible with both structures, i.e. you can transfer a record-structured file in stream mode and a flat file in block mode. However, in practice this is not the case. Servers that only know flat files are likely to only support stream mode, and servers implementing record structure imply that block transfers base on the record format. So the advice is to use stream mode for flat files, and block mode for record files.

    type ftp_auth = [ `GSSAPI | `None | `TLS ]

    type ftp_data_prot = [ `C | `E | `P | `S ]

Meaning:

- ``C`: no protection (clear)
- ``S`: integrity protection
- ``E`: encryption without integrity protection
- ``P`: integrity protection and encryption (= privacy)

    type support_level = [ `If_possible | `None | `Required ]

    type ftp_state = {

`` | `cmd_state : `cmd_state`;` | `(*` | the command state | `*)`
`` | `ftp_connected : `bool`;` | `(*` | whether connected with the server | `*)`
`` | `ftp_data_conn : `bool`;` | `(*` | whether there is a clean data conn | `*)`
`` | `ftp_user : `string option`;` | `(*` | successfully sent user identifier | `*)`
`` | `ftp_password : `string option`;` | `(*` | successfully sent password | `*)`
`` | `ftp_account : `string option`;` | `(*` | successfully sent account identifier | `*)`
`` | `ftp_logged_in : `bool`;` | `(*` | whether the user is logged in | `*)`
`` | `ftp_host : `string`;` | `(*` | Host name | `*)`
`` | `ftp_port : `port`;` | `(*` | the selected port | `*)`
`` | `ftp_repr : `representation`;` | `(*` | the selected representation | `*)`
`` | `ftp_structure : `structure`;` | `(*` | the selected structure | `*)`
`` | `ftp_trans : `transmission_mode`;` | `(*` | the selected trans mode | `*)`
`` | `ftp_dir : `string list`;` | `(*` | The current directory, expressed as list of CWD changes minus CDUP changes. This is only reasonable if CWD does not include slashes. The list is in reverse order, i.e. deepest directory first. | `*)`

``

`ftp_features : `(string * string option) list option`;`

`(*`

The list of features returned by the last FEAT command. `None` means that no FEAT command was yet tried. `Some []` means that there are no features (either FEAT returned an empty list, or the FEAT command is not implemented by the server). Otherwise the list enumerates pairs `(label,param)` where `label` is the case-sensitive feature label and `param` the optional parameter. There is no defined order for the list of features.

`*)`

`` | `ftp_options : `(string * string option) list`;` | `(*` | Remembers the OPTS commands sent to the server. The list enumerates pairs `(command,optionparam)`, where `command` is the uppercase command name the option refers to. Only the last negotiated `optionparam` for the command is remembered. | `*)`
`` | `ftp_auth : `ftp_auth`;` | `(*` | Authentication/privacy mode (AUTH command) | `*)`
`` | `ftp_auth_data : `string option`;` | `(*` | The data from the last ADAT reply, already base64-decoded | `*)`
`` | `ftp_data_prot : `ftp_data_prot`;` | `(*` | Security protocol for data connections (PROT command) | `*)`
`` | `ftp_data_pbsz : `int`;` | `(*` | protection buffer size (PBSZ command) | `*)`
`` | `ftp_prot : `Netftp_data_endpoint.ftp_protector option`;` | `(*` | a security layer (RFC 2228) | `*)`

}
The ftp_state reflects the knowledge of the client about what has been agreed upon with the server.

    type cmd = [ `ACCT of string
           | `ADAT of string
           | `ALLO of int * int option
           | `APPE of
               string * (ftp_state -> Netftp_data_endpoint.local_sender)
           | `AUTH of string
           | `CDUP
           | `CWD of string
           | `Connect of string * int
           | `DELE of string
           | `Disconnect
           | `Dummy
           | `EPRT
           | `EPSV of [ `AF of Unix.socket_domain | `ALL ] option
           | `FEAT
           | `HELP of string option
           | `LANG of string option
           | `LIST of
               string option *
               (ftp_state -> Netftp_data_endpoint.local_receiver)
           | `MDTM of string
           | `MKD of string
           | `MLSD of
               string option *
               (ftp_state -> Netftp_data_endpoint.local_receiver)
           | `MLST of string option
           | `MODE of transmission_mode
           | `NLST of
               string option *
               (ftp_state -> Netftp_data_endpoint.local_receiver)
           | `NOOP
           | `OPTS of string * string option
           | `PASS of string
           | `PASV
           | `PBSZ of int
           | `PORT
           | `PROT of ftp_data_prot
           | `PWD
           | `QUIT
           | `REIN
           | `REST of string
           | `RETR of
               string * (ftp_state -> Netftp_data_endpoint.local_receiver)
           | `RMD of string
           | `RNFR of string
           | `RNTO of string
           | `SITE of string
           | `SIZE of string
           | `SMNT of string
           | `STAT of string option
           | `STOR of
               string * (ftp_state -> Netftp_data_endpoint.local_sender)
           | `STOU of ftp_state -> Netftp_data_endpoint.local_sender
           | `STRU of structure
           | `SYST
           | `Start_TLS of (module Netsys_crypto_types.TLS_CONFIG)
           | `Start_protection of Netftp_data_endpoint.ftp_protector
           | `TYPE of representation
           | `USER of string ]

An FTP command. Not all commands are implemented by all servers.

``Start_TLS` is a pseudo command - at this point the TLS handshake starts.

    type reply = int * string

Reply code plus text

    class type ftp_client_pi = object .. end

The client protocol interpreter...

    type ftp_method = ftp_client_pi -> unit Uq_engines.engine

An `ftp_method` is a small procedure doing some task

    exception FTP_method_temp_failure of int * string

    exception FTP_method_perm_failure of int * string

    exception FTP_method_unexpected_reply of int * string

These exceptions may be raised during execution by the FTP method. The int is the unexpected FTP control code and the string the corresponding text. A temporary failure has a code between 400 and 499, and a permanent failure has a code between 500 and 599.

    val connect_method : host:string -> ?port:int -> unit -> ftp_method

This method connects to the `host`

    val login_method : user:string ->
           get_password:(unit -> string) ->
           get_account:(unit -> string) -> unit -> ftp_method

This FTP method logs the `user` in. `get_password` is called when the FTP server asks for the password (may be skipped). `get_account` is called when the server asks for the account ID (may be skipped).

    val quit_method : unit -> ftp_method

Quits and disconnects

    val tls_method : config:(module Netsys_crypto_types.TLS_CONFIG) ->
           required:bool -> unit -> ftp_method

This FTP method negotiates the use of TLS. If `required`, it is an error if TLS is not supported. Otherwise, it is ok to omit the TLS protection.

    val gssapi_method : config:Netsys_gssapi.client_config ->
           required:bool -> (module Netsys_gssapi.GSSAPI) -> ftp_method

This method negotiates the use of GSSAPI authentication and security. You need to pass the GSSAPI provider (e.g. `Netgss.System`).

The `config` can often simply be created with `Netsys_gssapi.create_client_config()`, as normally reasonably defaults are assumed by the GSSAPI provider. See `Netsys_gssapi.create_client_config` for options.

If `required`, it is an error if the server doesn't support GSSAPI authentication. Otherwise, this method is a no-op in this case.

Note that you cannot combine `gssapi_method` with `tls_method`. Although the `gssapi_method` authenticates the user, you still need to log in, although without password (basically, GSSAPI just gives you permissions to be somebody, but you still need to select who you want to be).

    val walk_method : [ `Dir of string | `File of string | `Stay ] -> ftp_method

This FTP method walks to the target directory:

- ``File name`: The `name` is interpreted as slash-separated path. It is always interpreted relative to the home directory of the user (i.e. the directory after login), even if it begins with a slash. The FTP command walks to the directory containing `name`.
- ``Dir name`: The FTP command walks to the directory `name` (same syntax as for ``File`).
- ``Stay`: The FTP command does nothing (stays in the current directory).

    type filename = [ `NVFS of string | `TVFS of string | `Verbatim of string ]

There are several methods how to specify filenames:

- ``NVFS name`: The "Network Virtual File System" is the normal way of accessing FTP files. The client walks into the directory containing the file using `CWD` and `CDUP` commands, and calls the file operation from this directory. For simplicity, this client interprets slashes in `name` as path component separators. The FTP server will never see these slashes.
- ``TVFS name`: The optional "Trivial Network File System" avoids the `CWD` and `CDUP` commands. The tagged `name` is normalized (double slashed removed etc.), and is passed to the server as-is. Before using the faster TVFS one should check whether it is supported (feature "TVFS"). Note that even for TVFS there are no special files "." and ".."!
- ``Verbatim name`: The string `name` is passed to the server without transforming it in any way.

    val get_method : file:filename ->
           representation:representation ->
           store:(ftp_state -> Netftp_data_endpoint.local_receiver) ->
           unit -> ftp_method

This FTP method walks to the right directory and gets `file` from the server. The file is stored in the `local_receiver` that can be obtained by calling the `store` function. The selected `representation` remains unchanged.

    val put_method : ?meth:[ `APPE | `STOR ] ->
           file:filename ->
           representation:representation ->
           store:(ftp_state -> Netftp_data_endpoint.local_sender) ->
           unit -> ftp_method

This FTP method walks to the right directory and puts `file` to the server. The file is taken from the `local_sender` that can be obtained by calling the `store` function. The selected `representation` remains unchanged.

`meth` selects the method to use (default ``STOR`).

    val invoke_method : command:cmd -> unit -> ftp_method

This FTP method simply invokes `command`.

    val set_structure_method : structure -> ftp_method

Requests a certain structure for future file transfers

    val set_mode_method : transmission_mode -> ftp_method

Requests a certain mode for future file transfers

    val rename_method : file_from:filename ->
           file_to:filename -> unit -> ftp_method

Renames the `file_from` into `file_to`.

Both file names must be of the same type, either ``NVFS` or ``Verbatim`. If ``NVFS`, both names must be in the same directory.

    val mkdir_method : filename -> ftp_method

Creates the named directory

    val rmdir_method : filename -> ftp_method

Deletes the named directory

    val delete_method : filename -> ftp_method

Deletes the named file

    val list_method : dir:filename ->
           representation:representation ->
           store:(ftp_state -> Netftp_data_endpoint.local_receiver) ->
           unit -> ftp_method

Lists the contents of the directory `dir` using the LIST command. The `representation` must not be ``Image`.

    val nlst_method : dir:filename ->
           representation:representation ->
           store:(ftp_state -> Netftp_data_endpoint.local_receiver) ->
           unit -> ftp_method

Lists the contents of the directory `dir` using the NLST command The `representation` must not be ``Image`.

    val parse_nlst_document : string -> string list

Returns the filenames contained in the output of ``NLST`

    val mdtm_method : file:filename ->
           process_result:(float -> unit) -> unit -> ftp_method

Determines the date and time of the last modification of `file`. On success, `process_result` is called.

    val size_method : file:filename ->
           representation:representation ->
           process_result:(int64 -> unit) -> unit -> ftp_method

Determines the size of `file`. On success, `process_result` is called. The size depends on `representation`.

    val feat_method : ?process_result:((string * string option) list -> unit) ->
           unit -> ftp_method

Get the list of feature tokens (see also `Netftp_client.ftp_state.ftp_features`)

    type entry = string * (string * string) list

A file entry `(name, facts)`. The facts are given as pairs `(factname,value)` where `factname` is always lowercase. For parsers for common facts see below.

    val mlst_method : file:filename ->
           process_result:(entry list -> unit) ->
           unit -> ftp_method

Get the file entry for `file`.

    val mlsd_method : dir:filename ->
           store:(ftp_state -> Netftp_data_endpoint.local_receiver) ->
           unit -> ftp_method

Gets the entries for this directory.

    val parse_mlsd_document : string -> entry list

Returns the entries contained in the output of ``MLSD`

    type entry_type = [ `Cdir | `Dir | `File | `Other | `Pdir ]

Types:

- ``File`: entry refers to file
- ``Cdir`: entry refers to the directory being listed
- ``Pdir`: entry is a parent of the directory being listed
- ``Dir`: entry refers to directory
- ``Other`: entry is neither file nor directory

    type entry_perm = [ `Append
           | `Create
           | `Delete
           | `Delete_member
           | `Enter
           | `List
           | `Mkdir
           | `Read
           | `Rename
           | `Write ]

Permissions:

- ``Append`: append to file possible
- ``Create`: file can be created in this dir
- ``Delete`: file or dir can be deleted
- ``Enter`: dir can be entered
- ``Rename`: file or dir can be renamed
- ``List`: dir can be listed
- ``Mkdir`: subdir can be created in this dir
- ``Delete_member`: a file or dir can be deleted in this directory
- ``Read`: a file can be retrieved
- ``Write`: a file can be stored

The following functions extract commonly used facts from entries. They may raise `Not_found`.

    val get_name : entry -> string

    val get_size : entry -> int64

    val get_modify : entry -> float

    val get_create : entry -> float

    val get_type : entry -> entry_type

    val get_unique : entry -> string

    val get_perm : entry -> entry_perm list

    val get_lang : entry -> string

    val get_media_type : entry -> string

    val get_charset : entry -> string

    val get_unix_mode : entry -> int

    val get_unix_uid : entry -> string

    val get_unix_gid : entry -> string

    class ftp_client : ?event_system:Unixqueue.event_system -> unit -> object .. end

The ftp client is a user session that may even span several connections.

## Examples and Discussion

To download a single flat file from a server:

       let buffer = Buffer.create 1000 in
       let ch = new Netchannels.output_buffer buffer in
       let client = new ftp_client() in
       client # exec (connect_method ~host:"127.0.0.1" ());
       client # exec (login_method ~user:"foo"
                                    ~get_password:(fun () -> "password")
                                    ~get_account:(fun () -> "foo") ());
       client # exec (get_method ~file:(`NVFS "path/to/file")
                                 ~representation:`Image
                                 ~store:(fun _ -> `File_structure ch) ());

The file is stored in `buffer`. By using a different netchannel, it can be stored whereever wanted.

To download a record-structured text file, use a `store` like:

        let ch = (as above) in
        let rec_ch = new Netftp_data_endpoint.write_out_record_channel
                           ~repr:(`ASCII_unix `Enc_iso88591)
                           ch
        ...
        ... ~store:(fun _ -> `Record_structure rec_ch)

Here, the end-of-record is transcoded to newline. Note that the ASCII variant (``Enc_iso88591`) is ignored by `write_out_record_channel`. Open: How to select record structure using an FTP method.

Character conversions: To convert an EBCDIC file to ASCII, use something like

        let ch = (as above) in
        let converter = new Netftp_data_endpoint.data_converter
                             ~fromrepr:(`EBCDIC `Enc_cp1047)
                             ~torepr:(`ASCII_unix `Enc_iso88591) in
        let ch_ebcdic = new Netchannels.output_filter converter ch in
        ...
        ... ~representation:(`EBCDIC None)
        ... ~store:(fun _ -> `File_structure ch_ebcdic)

The class `data_converter` also performs the transformation of the end-of-line convention, unlike the similar class `Netconversion.conversion_pipe`.

# Debugging

    module Debug: sig .. end