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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 is always started as part of the ftp application and legacy start_service function, is
deprecated in OTP-24
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 provided 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 START/STOP
The FTP client can be started and stopped dynamically in runtime by calling the ftp application API
ftp:open(Host, Options) and ftp:close(Client).
The available configuration options are as follows:
{host, Host}:
Host = string() | ip_address()
{port, Port}:
Port = integer() > 0
Default is 0 which aliases to 21 or 990 when used with {tls_sec_method,ftps}).
{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 ASCII 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()}
| {tls_sec_method, tls_sec_method()} | {tls_ctrl_session_reuse, boolean() (default is false)} |
{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() = non_neg_integer() (default is 0 which aliases to 21 or 990 when used with
{tls_sec_method,ftps})
mode() = active | passive (default is passive)
tls_options() = [ssl:tls_option()]
tls_sec_method() = ftps | ftpes (default is ftpes)
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)
progress() = ignore | {module(), function(), initial_data()} (default is ignore)
module() = atom()
function() = atom()
initial_data() = term()
Reason = ehost | term()
Starts a FTP client process 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 suboption {tls_sec_method, tls_sec_method()} (defaults to ftpes) when set to ftps will connect
immediately with SSL instead of upgrading with STARTTLS. This suboption is ignored unless the
suboption tls is also set.
The option {tls_ctrl_session_reuse, boolean()} (defaults to false) when set to true the client
will re-use the TLS session from the control channel on the data channel as enforced by many FTP
servers as (proposed and implemented first by vsftpd).
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).