ftp

A File Transfer Protocol client.

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

Functions

account(Pid, Account) -> ok | {error, Reason}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • Pid = pid()
  • Dir = string()
  • Reason = restriction_reason() | common_reason()

Changes the working directory at the remote server to Dir.

close(Pid) -> ok
  • Pid = pid()

Ends an FTP session, created using function open.

delete(Pid, File) -> ok | {error, Reason}
  • Pid = pid()
  • File = string()
  • Reason = restriction_reason() | common_reason()

Deletes the file File at the remote server.

formaterror(Tag) -> string()
  • 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}
  • Pid = pid()
  • Dir = string()
  • Reason = restriction_reason()

Changes the working directory to Dir for the local client.

lpwd(Pid) -> {ok, Dir}
  • Pid = pid()

Returns the current working directory at the local client.

ls(Pid) -> ls(Pid, Pathname) -> {ok, Listing} | {error, Reason}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • Pid = pid()
  • CurrFile = NewFile = string()
  • Reason = restriction_reason() | common_reason()

Renames Old to New at the remote server.

rmdir(Pid, Dir) -> ok | {error, Reason}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • 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}
  • Reference = pid() | term() - service-specified reference
  • Reason = term()

Stops a started FTP session.

type(Pid, Type) -> ok | {error, Reason}
  • 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}
  • Pid = pid()
  • User = Password = string()
  • Reason = euser | common_reason()

Performs login of User with Password.

user(Pid, User, Password, Account) -> ok | {error, Reason}
  • 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]
  • 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(3) filename(3) and J. Postel and J. Reynolds: File Transfer Protocol (RFC 959).