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NAME

       ftp - A File Transfer Protocol client.

DESCRIPTION

       This  module  implements  a  client  for  file  transfer according to a subset of the File
       Transfer Protocol (FTP), see RFC 959.

       The FTP client always tries to use passive FTP mode and only resort to active FTP mode  if
       this fails. This default behavior can be changed by start option mode.

       An  FTP  client  can  be started in two ways. One is using the service_start function, the
       other is to start it directly as a standalone process using function open.

       For a simple example of an FTP session, see FTP User's Guide.

       In addition to the ordinary functions for receiving and sending files (see recv/2, recv/3,
       send/2,  and  send/3)  there  are  functions  for  receiving remote files as binaries (see
       recv_bin/2) and for sending binaries to be stored as remote files (see send_bin/3).

       A set of functions is provvided for sending and receiving contiguous parts of a file to be
       stored   in   a   remote   file.  For  send,  see  send_chunk_start/2,  send_chunk/2,  and
       send_chunk_end/1. For receive, see recv_chunk_start/2 and recv_chunk/).

       The return values of the following functions depend much on the implementation of the  FTP
       server at the remote host. In particular, the results from ls and nlist varies. Often real
       errors are not reported as errors by ls, even if, for example, a file  or  directory  does
       not  exist.  nlist  is  usually  more  strict,  but some implementations have the peculiar
       behaviour of responding with an error if the request is a listing of  the  contents  of  a
       directory that exists but is empty.

FTP CLIENT SERVICE START/STOP

       The  FTP  client  can  be  started  and  stopped dynamically in runtime by calling the ftp
       application API ftp:start_service(ServiceConfig) and ftp:stop_service(Pid).

       The available configuration options are as follows:

         {host, Host}:

           Host = string() | ip_address()

         {port, Port}:

           Port = integer() > 0

           Default is 21.

         {mode, Mode}:

           Mode = active | passive

           Default is passive.

         {verbose, Verbose}:

           Verbose = boolean()

           Determines if the FTP communication is to be verbose or not.

           Default is false.

         {debug, Debug}:

           Debug = trace | debug | disable

           Debugging using the dbg toolkit.

           Default is disable.

         {ipfamily, IpFamily}:

           IpFamily = inet | inet6 | inet6fb4

           With inet6fb4 the client behaves as before, that is, tries to use IPv6,  and  only  if
           that does not work it uses IPv4).

           Default is inet (IPv4).

         {timeout, Timeout}:

           Timeout = non_neg_integer()

           Connection time-out.

           Default is 60000 (milliseconds).

         {dtimeout, DTimeout}:

           DTimeout = non_neg_integer() | infinity

           Data connect time-out. The time the client waits for the server to connect to the data
           socket.

           Default is infinity.

         {progress, Progress}:

           Progress = ignore | {CBModule, CBFunction, InitProgress}

           CBModule = atom(), CBFunction = atom()

           InitProgress = term()

           Default is ignore.

       Option progress is intended to be used by applications that want to create  some  type  of
       progress  report,  such  as  a  progress  bar in a GUI. Default for the progress option is
       ignore, that is, the option is not used.  When  the  progress  option  is  specified,  the
       following happens when ftp:send/[3,4] or ftp:recv/[3,4] are called:

         * Before  a file is transferred, the following call is made to indicate the start of the
           file transfer and how large the file is. The return value of the callback function  is
           to  be  a  new value for the UserProgressTerm that will be used as input the next time
           the callback function is called.

            CBModule:CBFunction(InitProgress, File, {file_size, FileSize})

         * Every time a chunk of bytes is transferred the following call is made:

            CBModule:CBFunction(UserProgressTerm, File, {transfer_size, TransferSize})

         * At the end of the file the following call is made to indicate the end of the transfer:

            CBModule:CBFunction(UserProgressTerm, File, {transfer_size, 0})

       The callback function is to be defined as follows:

        CBModule:CBFunction(UserProgressTerm, File, Size) -> UserProgressTerm

        CBModule = CBFunction = atom()

        UserProgressTerm = term()

        File = string()

        Size = {transfer_size, integer()} | {file_size, integer()} | {file_size, unknown}

       For remote files, ftp cannot determine the file size in a  platform  independent  way.  In
       this  case  the  size  becomes  unknown and it is left to the application to determine the
       size.

   Note:
       The callback is made by a middleman process, hence the file transfer is  not  affected  by
       the  code  in the progress callback function. If the callback crashes, this is detected by
       the FTP connection process, which then prints  an  info-report  and  goes  on  as  if  the
       progress option was set to ignore.

       The file transfer type is set to the default of the FTP server when the session is opened.
       This is usually ASCCI mode.

       The current local working directory (compare lpwd/1) is  set  to  the  value  reported  by
       file:get_cwd/1, the wanted local directory.

       The  return  value Pid is used as a reference to the newly created FTP client in all other
       functions, and they are to be called by the process that created the connection.  The  FTP
       client  process  monitors  the  process  that  created  it  and terminates if that process
       terminates.

DATA TYPES

       The following type definitions are used by more than one function in the FTP client API:

       pid() = identifier of an FTP connection

       string() = list of ASCII characters

       shortage_reason() = etnospc | epnospc

       restriction_reason() = epath | efnamena | elogin | enotbinary - all restrictions  are  not
       always relevant to all functions

       common_reason() = econn | eclosed | term() - some explanation of what went wrong

EXPORTS

       account(Pid, Account) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Account = string()
                 Reason = eacct | common_reason()

              Sets the account for an operation, if needed.

       append(Pid, LocalFile) ->
       append(Pid, LocalFile, RemoteFile) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 LocalFile = RemoteFile = string()
                 Reason = epath | elogin | etnospc | epnospc | efnamena | common_reason

              Transfers  the file LocalFile to the remote server. If RemoteFile is specified, the
              name of the remote file that  the  file  is  appended  to  is  set  to  RemoteFile,
              otherwise to LocalFile. If the file does not exists, it is created.

       append_bin(Pid, Bin, RemoteFile) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Bin = binary()
                 RemoteFile = string()
                 Reason = restriction_reason()| shortage_reason() | common_reason()

              Transfers  the  binary  Bin  to  the  remote  server  and  appends  it  to the file
              RemoteFile. If the file does not exist, it is created.

       append_chunk(Pid, Bin) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Bin = binary()
                 Reason = echunk | restriction_reason() | common_reason()

              Transfers the chunk Bin to  the  remote  server,  which  appends  it  to  the  file
              specified in the call to append_chunk_start/2.

              For  some  errors,  for  example,  file  system  full,  it  is  necessary  to  call
              append_chunk_end to get the proper reason.

       append_chunk_start(Pid, File) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 File = string()
                 Reason = restriction_reason() | common_reason()

              Starts the transfer of chunks for appending to the file File at the remote  server.
              If the file does not exist, it is created.

       append_chunk_end(Pid) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Reason = echunk | restriction_reason() | shortage_reason()

              Stops transfer of chunks for appending to the remote server. The file at the remote
              server, specified in the call to append_chunk_start/2, is closed by the server.

       cd(Pid, Dir) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Dir = string()
                 Reason = restriction_reason() | common_reason()

              Changes the working directory at the remote server to Dir.

       close(Pid) -> ok

              Types:

                 Pid = pid()

              Ends an FTP session, created using function open.

       delete(Pid, File) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 File = string()
                 Reason = restriction_reason() | common_reason()

              Deletes the file File at the remote server.

       formaterror(Tag) -> string()

              Types:

                 Tag = {error, atom()} | atom()

              Given an error return value {error, AtomReason}, this function returns  a  readable
              string describing the error.

       lcd(Pid, Dir) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Dir = string()
                 Reason = restriction_reason()

              Changes the working directory to Dir for the local client.

       lpwd(Pid) -> {ok, Dir}

              Types:

                 Pid = pid()

              Returns the current working directory at the local client.

       ls(Pid) ->
       ls(Pid, Pathname) -> {ok, Listing} | {error, Reason}

              Types:

                 Pid = pid()
                 Pathname = string()
                 Listing = string()
                 Reason = restriction_reason() | common_reason()

              Returns a list of files in long format.

              Pathname  can  be a directory, a group of files, or a file. The Pathname string can
              contain wildcards.

              ls/1 implies the current remote directory of the user.

              The format of Listing depends on the operating system. On  UNIX,  it  is  typically
              produced from the output of the ls -l shell command.

       mkdir(Pid, Dir) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Dir = string()
                 Reason = restriction_reason() | common_reason()

              Creates the directory Dir at the remote server.

       nlist(Pid) ->
       nlist(Pid, Pathname) -> {ok, Listing} | {error, Reason}

              Types:

                 Pid = pid()
                 Pathname = string()
                 Listing = string()
                 Reason = restriction_reason() | common_reason()

              Returns a list of files in short format.

              Pathname  can  be a directory, a group of files, or a file. The Pathname string can
              contain wildcards.

              nlist/1 implies the current remote directory of the user.

              The format of Listing is a stream of filenames where each filename is separated  by
              <CRLF>  or  <NL>.  Contrary  to  function  ls,  the purpose of nlist is to enable a
              program to process filename information automatically.

       open(Host) -> {ok, Pid} | {error, Reason}
       open(Host, Opts) -> {ok, Pid} | {error, Reason}

              Types:

                 Host = string() | ip_address()
                 Opts = options()
                 options() = [option()]
                 option() = start_option() | open_option()
                 start_option() = {verbose, verbose()} | {debug, debug()}
                 verbose() = boolean() (default is false)
                 debug() = disable | debug | trace (default is disable)
                 open_option() = {ipfamily, ipfamily()} | {port, port()} | {mode, mode()} | {tls,
                 tls_options()}  |  {timeout,  timeout()}  |  {dtimeout, dtimeout()} | {progress,
                 progress()  |  {sock_ctrl,  sock_opts()}  |   {sock_data_act,   sock_opts()}   |
                 {sock_data_pass, sock_opts()} }
                 ipfamily() = inet | inet6 | inet6fb4 (default is inet)
                 port() = integer() > 0 (default is 21)
                 mode() = active | passive (default is passive)
                 tls_options() = [ssl:tls_option()]
                 sock_opts()  =  [gen_tcp:option()  except for ipv6_v6only, active, packet, mode,
                 packet_size and header
                 timeout() = integer() > 0 (default is 60000 milliseconds)
                 dtimeout() = integer() > 0 | infinity (default is infinity)
                 pogress() = ignore | {module(), function(), initial_data()} (default is ignore)
                 module() = atom()
                 function() = atom()
                 initial_data() = term()
                 Reason = ehost | term()

              Starts a standalone FTP client process (without  the  ftp  service  framework)  and
              opens a session with the FTP server at Host.

              If  option {tls, tls_options()} is present, the FTP session is transported over tls
              (ftps,  see  RFC  4217).  The  list  tls_options()  can  be  empty.  The   function
              ssl:connect/3  is  used  for  securing  both  the  control  connection and the data
              sessions.

              The options sock_ctrl, sock_data_act and sock_data_pass passes options down to  the
              underlying  transport  layer  (tcp).  The  default  value for sock_ctrl is []. Both
              sock_data_act and sock_data_pass uses the value of sock_ctrl as default value.

              A session opened in this way is closed using function close.

       pwd(Pid) -> {ok, Dir} | {error, Reason}

              Types:

                 Pid = pid()
                 Reason = restriction_reason() | common_reason()

              Returns the current working directory at the remote server.

       recv(Pid, RemoteFile) ->
       recv(Pid, RemoteFile, LocalFile) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 RemoteFile = LocalFile = string()
                 Reason = restriction_reason() | common_reason() | file_write_error_reason()
                 file_write_error_reason() = see file:write/2

              Transfers the file RemoteFile from the remote server to  the  file  system  of  the
              local  client.  If  LocalFile  is  specified,  the  local  file  will be LocalFile,
              otherwise RemoteFile.

              If the file write fails (for example, enospc), the command is aborted  and  {error,
              file_write_error_reason()} is returned. However, the file is not removed.

       recv_bin(Pid, RemoteFile) -> {ok, Bin} | {error, Reason}

              Types:

                 Pid = pid()
                 Bin = binary()
                 RemoteFile = string()
                 Reason = restriction_reason() | common_reason()

              Transfers the file RemoteFile from the remote server and receives it as a binary.

       recv_chunk_start(Pid, RemoteFile) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 RemoteFile = string()
                 Reason = restriction_reason() | common_reason()

              Starts transfer of the file RemoteFile from the remote server.

       recv_chunk(Pid) -> ok | {ok, Bin} | {error, Reason}

              Types:

                 Pid = pid()
                 Bin = binary()
                 Reason = restriction_reason() | common_reason()

              Receives  a  chunk  of the remote file (RemoteFile of recv_chunk_start). The return
              values have the following meaning:

                * ok = the transfer is complete.

                * {ok, Bin} = just another chunk of the file.

                * {error, Reason} = transfer failed.

       rename(Pid, Old, New) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 CurrFile = NewFile = string()
                 Reason = restriction_reason() | common_reason()

              Renames Old to New at the remote server.

       rmdir(Pid, Dir) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Dir = string()
                 Reason = restriction_reason() | common_reason()

              Removes directory Dir at the remote server.

       send(Pid, LocalFile) ->
       send(Pid, LocalFile, RemoteFile) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 LocalFile = RemoteFile = string()
                 Reason = restriction_reason() | common_reason() | shortage_reason()

              Transfers the file LocalFile to the remote server. If RemoteFile is specified,  the
              name of the remote file is set to RemoteFile, otherwise to LocalFile.

       send_bin(Pid, Bin, RemoteFile) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Bin = binary()
                 RemoteFile = string()
                 Reason = restriction_reason() | common_reason() | shortage_reason()

              Transfers the binary Bin into the file RemoteFile at the remote server.

       send_chunk(Pid, Bin) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Bin = binary()
                 Reason = echunk | restriction_reason() | common_reason()

              Transfers  the  chunk  Bin  to  the  remote  server,  which writes it into the file
              specified in the call to send_chunk_start/2.

              For some errors, for example,  file  system  full,  it  is  necessary  to  to  call
              send_chunk_end to get the proper reason.

       send_chunk_start(Pid, File) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 File = string()
                 Reason = restriction_reason() | common_reason()

              Starts transfer of chunks into the file File at the remote server.

       send_chunk_end(Pid) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Reason = restriction_reason() | common_reason() | shortage_reason()

              Stops  transfer  of  chunks  to  the  remote server. The file at the remote server,
              specified in the call to send_chunk_start/2 is closed by the server.

       start_service(ServiceConfig) -> {ok, Pid} | {error, Reason}

              Types:

                 ServiceConfig = [{Option, Value}]
                 Option = property()
                 Value = term()

              Dynamically starts an FTP session after the ftp application has been started.

          Note:
              As long as the ftp application is operational, the FTP sessions are supervised  and
              can be soft code upgraded.

       stop_service(Reference) -> ok | {error, Reason}

              Types:

                 Reference = pid() | term() - service-specified reference
                 Reason = term()

              Stops a started FTP session.

       type(Pid, Type) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 Type = ascii | binary
                 Reason = etype | restriction_reason() | common_reason()

              Sets  the file transfer type to ascii or binary. When an FTP session is opened, the
              default transfer type of the server is used, most often  ascii,  which  is  default
              according to RFC 959.

       user(Pid, User, Password) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 User = Password = string()
                 Reason = euser | common_reason()

              Performs login of User with Password.

       user(Pid, User, Password, Account) -> ok | {error, Reason}

              Types:

                 Pid = pid()
                 User = Password = string()
                 Reason = euser | common_reason()

              Performs login of User with Password to the account specified by Account.

       quote(Pid, Command) -> [FTPLine]

              Types:

                 Pid = pid()
                 Command = string()
                 FTPLine = string(

          Note:
              The  telnet  end  of  line  characters, from the FTP protocol definition, CRLF, for
              example, "\\r\\n" has been removed.

              Sends an arbitrary FTP command and returns verbatim a list of the lines  sent  back
              by  the  FTP  server. This function is intended to give application accesses to FTP
              commands that are server-specific or that cannot be provided by this FTP client.

          Note:
              FTP commands requiring a data connection cannot be successfully  issued  with  this
              function.

ERRORS

       The   possible  error  reasons  and  the  corresponding  diagnostic  strings  returned  by
       formaterror/1 are as follows:

         echunk:
           Synchronization error during chunk sending according to one of the following:

           * A  call  is  made  to  send_chunk/2   or   send_chunk_end/1   before   a   call   to
             send_chunk_start/2.

           * A  call  has  been  made to another transfer function during chunk sending, that is,
             before a call to send_chunk_end/1.

         eclosed:
           The session is closed.

         econn:
           Connection to the remote server is prematurely closed.

         ehost:
           Host is not found, FTP server is not found, or connection is rejected by FTP server.

         elogin:
           User is not logged in.

         enotbinary:
           Term is not a binary.

         epath:
           No such file or directory, or directory already exists, or permission denied.

         etype:
           No such type.

         euser:
           Invalid username or password.

         etnospc:
           Insufficient storage space in system [452].

         epnospc:
           Exceeded storage allocation (for current directory or dataset) [552].

         efnamena:
           Filename not allowed [553].

SEE ALSO

       file(3erl) filename(3erl) and J. Postel and J. Reynolds: File Transfer Protocol (RFC 959).