SSH

Reference Manual

Version 4.7

Table of Contents

ssh_sftp

Module

ssh_sftp

Module Summary

SFTP client.

Description

This module implements an SSH FTP (SFTP) client. SFTP is a secure, encrypted file transfer service available for SSH.

DATA TYPES

Type definitions that are used more than once in this module, or abstractions to indicate the intended use of the data type, or both:

reason()

= atom() A description of the reason why an operation failed.

The value is formed from the sftp error codes in the protocol-level responses as defined in draft-ietf-secsh-filexfer-13.txt section 9.1.

The codes are named as SSH_FX_* which are transformed into lowercase of the star-part. E.g. the error code SSH_FX_NO_SUCH_FILE will cause the reason() to be no_such_file.

connection_ref() =

opaque() - as returned by ssh:connect/3

timeout()

= infinity | integer() in milliseconds. Default infinity.

Time-outs

If the request functions for the SFTP channel return {error, timeout}, no answer was received from the server within the expected time.

The request may have reached the server and may have been performed. However, no answer was received from the server within the expected time.

Exports

apread(ChannelPid, Handle, Position, Len) -> {async, N} | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Len = integer()
N = term()

The apread/4 function reads from a specified position, combining the position/3 and aread/3 functions.

apwrite(ChannelPid, Handle, Position, Data) -> {async, N} | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Len = integer()
Data = binary()
Timeout = timeout()
N = term()

The apwrite/4 function writes to a specified position, combining the position/3 and awrite/3 functions.

aread(ChannelPid, Handle, Len) -> {async, N} | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Len = integer()
N = term()

Reads from an open file, without waiting for the result. If the handle is valid, the function returns {async, N}, where N is a term guaranteed to be unique between calls of aread. The actual data is sent as a message to the calling process. This message has the form {async_reply, N, Result}, where Result is the result from the read, either {ok, Data}, eof, or {error, reason()}.

awrite(ChannelPid, Handle, Data) -> {async, N} | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Len = integer()
Data = binary()
Timeout = timeout()

Writes to an open file, without waiting for the result. If the handle is valid, the function returns {async, N}, where N is a term guaranteed to be unique between calls of awrite. The result of the write operation is sent as a message to the calling process. This message has the form {async_reply, N, Result}, where Result is the result from the write, either ok, or {error, reason()}.

close(ChannelPid, Handle) ->
close(ChannelPid, Handle, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Timeout = timeout()

Closes a handle to an open file or directory on the server.

delete(ChannelPid, Name) ->
delete(ChannelPid, Name, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Timeout = timeout()

Deletes the file specified by Name.

del_dir(ChannelPid, Name) ->
del_dir(ChannelPid, Name, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Timeout = timeout()

Deletes a directory specified by Name. The directory must be empty before it can be successfully deleted.

list_dir(ChannelPid, Path) ->
list_dir(ChannelPid, Path, Timeout) -> {ok, Filenames} | {error, reason()}

Types

ChannelPid = pid()
Path = string()
Filenames = [Filename]
Filename = string()
Timeout = timeout()

Lists the given directory on the server, returning the filenames as a list of strings.

make_dir(ChannelPid, Name) ->
make_dir(ChannelPid, Name, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Timeout = timeout()

Creates a directory specified by Name. Name must be a full path to a new directory. The directory can only be created in an existing directory.

make_symlink(ChannelPid, Name, Target) ->
make_symlink(ChannelPid, Name, Target, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Target = string()

Creates a symbolic link pointing to Target with the name Name.

open(ChannelPid, File, Mode) ->
open(ChannelPid, File, Mode, Timeout) -> {ok, Handle} | {error, reason()}

Types

ChannelPid = pid()
File = string()
Mode = [Modeflag]
Modeflag = read | write | creat | trunc | append | binary
Timeout = timeout()
Handle = term()

Opens a file on the server and returns a handle, which can be used for reading or writing.

opendir(ChannelPid, Path) ->
opendir(ChannelPid, Path, Timeout) -> {ok, Handle} | {error, reason()}

Types

ChannelPid = pid()
Path = string()
Timeout = timeout()

Opens a handle to a directory on the server. The handle can be used for reading directory contents.

open_tar(ChannelPid, Path, Mode) ->
open_tar(ChannelPid, Path, Mode, Timeout) -> {ok, Handle} | {error, reason()}

Types

ChannelPid = pid()
Path = string()
Mode = [read] | [write] | [read,EncryptOpt] | [write,DecryptOpt]
EncryptOpt = {crypto,{InitFun,EncryptFun,CloseFun}}
DecryptOpt = {crypto,{InitFun,DecryptFun}}
InitFun = (fun() -> {ok,CryptoState}) | (fun() -> {ok,CryptoState,ChunkSize})
CryptoState = any()
ChunkSize = undefined | pos_integer()
EncryptFun = (fun(PlainBin,CryptoState) -> EncryptResult)
EncryptResult = {ok,EncryptedBin,CryptoState} | {ok,EncryptedBin,CryptoState,ChunkSize}
PlainBin = binary()
EncryptedBin = binary()
DecryptFun = (fun(EncryptedBin,CryptoState) -> DecryptResult)
DecryptResult = {ok,PlainBin,CryptoState} | {ok,PlainBin,CryptoState,ChunkSize}
CloseFun = (fun(PlainBin,CryptoState) -> {ok,EncryptedBin})
Timeout = timeout()

Opens a handle to a tar file on the server, associated with ChannelPid. The handle can be used for remote tar creation and extraction, as defined by the erl_tar:init/3 function.

For code exampel see Section SFTP Client with TAR Compression and Encryption in the ssh Users Guide.

The crypto mode option is applied to the generated stream of bytes prior to sending them to the SFTP server. This is intended for encryption but can be used for other purposes.

The InitFun is applied once prior to any other crypto operation. The returned CryptoState is then folded into repeated applications of the EncryptFun or DecryptFun. The binary returned from those funs are sent further to the remote SFTP server. Finally, if doing encryption, the CloseFun is applied to the last piece of data. The CloseFun is responsible for padding (if needed) and encryption of that last piece.

The ChunkSize defines the size of the PlainBins that EncodeFun is applied to. If the ChunkSize is undefined, the size of the PlainBins varies, because this is intended for stream crypto, whereas a fixed ChunkSize is intended for block crypto. ChunkSizes can be changed in the return from the EncryptFun or DecryptFun. The value can be changed between pos_integer() and undefined.

position(ChannelPid, Handle, Location) ->
position(ChannelPid, Handle, Location, Timeout) -> {ok, NewPosition | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Location = Offset | {bof, Offset} | {cur, Offset} | {eof, Offset} | bof | cur | eof
Offset = integer()
Timeout = timeout()
NewPosition = integer()

Sets the file position of the file referenced by Handle. Returns {ok, NewPosition} (as an absolute offset) if successful, otherwise {error, reason()}. Location is one of the following:

Offset

The same as {bof, Offset}.

{bof, Offset}

Absolute offset.

{cur, Offset}

Offset from the current position.

{eof, Offset}

Offset from the end of file.

bof | cur | eof

The same as eariler with Offset 0, that is, {bof, 0} | {cur, 0} | {eof, 0}.

pread(ChannelPid, Handle, Position, Len) ->
pread(ChannelPid, Handle, Position, Len, Timeout) -> {ok, Data} | eof | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Len = integer()
Timeout = timeout()
Data = string() | binary()

The pread/3,4 function reads from a specified position, combining the position/3 and read/3,4 functions.

pwrite(ChannelPid, Handle, Position, Data) -> ok
pwrite(ChannelPid, Handle, Position, Data, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Data = iolist()
Timeout = timeout()

The pwrite/3,4 function writes to a specified position, combining the position/3 and write/3,4 functions.

read(ChannelPid, Handle, Len) ->
read(ChannelPid, Handle, Len, Timeout) -> {ok, Data} | eof | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Len = integer()
Timeout = timeout()
Data = string() | binary()

Reads Len bytes from the file referenced by Handle. Returns {ok, Data}, eof, or {error, reason()}. If the file is opened with binary, Data is a binary, otherwise it is a string.

If the file is read past eof, only the remaining bytes are read and returned. If no bytes are read, eof is returned.

read_file(ChannelPid, File) ->
read_file(ChannelPid, File, Timeout) -> {ok, Data} | {error, reason()}

Types

ChannelPid = pid()
File = string()
Data = binary()
Timeout = timeout()

Reads a file from the server, and returns the data in a binary.

read_file_info(ChannelPid, Name) ->
read_file_info(ChannelPid, Name, Timeout) -> {ok, FileInfo} | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Handle = term()
Timeout = timeout()
FileInfo = record()

Returns a file_info record from the file system object specified by Name or Handle. See file:read_file_info/2 for information about the record.

Depending on the underlying OS:es links might be followed and info on the final file, directory etc is returned. See ssh_sftp::read_link_info/2 on how to get information on links instead.

read_link(ChannelPid, Name) ->
read_link(ChannelPid, Name, Timeout) -> {ok, Target} | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Target = string()

Reads the link target from the symbolic link specified by name.

read_link_info(ChannelPid, Name) -> {ok, FileInfo} | {error, reason()}
read_link_info(ChannelPid, Name, Timeout) -> {ok, FileInfo} | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Handle = term()
Timeout = timeout()
FileInfo = record()

Returns a file_info record from the symbolic link specified by Name or Handle. See file:read_link_info/2 for information about the record.

rename(ChannelPid, OldName, NewName) ->
rename(ChannelPid, OldName, NewName, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
OldName = string()
NewName = string()
Timeout = timeout()

Renames a file named OldName and gives it the name NewName.

start_channel(ConnectionRef) ->
start_channel(ConnectionRef, Options) -> {ok, Pid} | {error, reason()|term()}
start_channel(Host, Options) ->
start_channel(Host, Port, Options) -> {ok, Pid, ConnectionRef} | {error, reason()|term()}
start_channel(TcpSocket) ->
start_channel(TcpSocket, Options) -> {ok, Pid, ConnectionRef} | {error, reason()|term()}

Types

Host = string()
ConnectionRef = connection_ref()
Port = integer()
TcpSocket = port()
The socket is supposed to be from gen_tcp:connect or gen_tcp:accept with option {active,false}
Options = [{Option, Value}]

If no connection reference is provided, a connection is set up, and the new connection is returned. An SSH channel process is started to handle the communication with the SFTP server. The returned pid for this process is to be used as input to all other API functions in this module.

Options:

{timeout, timeout()}

There are two ways to set a timeout for the underlying ssh connection:

  • If the connection timeout option connect_timeout is set, that value is used also for the negotiation timeout and this option (timeout) is ignored.
  • Otherwise, this option (timeout) is used as the negotiation timeout only and there is no connection timeout set

The value defaults to infinity.

{sftp_vsn, integer()}

Desired SFTP protocol version. The actual version is the minimum of the desired version and the maximum supported versions by the SFTP server.

All other options are directly passed to ssh:connect/3 or ignored if a connection is already provided.

stop_channel(ChannelPid) -> ok

Types

ChannelPid = pid()

Stops an SFTP channel. Does not close the SSH connection. Use ssh:close/1 to close it.

write(ChannelPid, Handle, Data) ->
write(ChannelPid, Handle, Data, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Data = iolist()
Timeout = timeout()

Writes data to the file referenced by Handle. The file is to be opened with write or append flag. Returns ok if successful or {error, reason()} otherwise.

write_file(ChannelPid, File, Iolist) ->
write_file(ChannelPid, File, Iolist, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
File = string()
Iolist = iolist()
Timeout = timeout()

Writes a file to the server. The file is created if it does not exist but overwritten if it exists.

write_file_info(ChannelPid, Name, Info) ->
write_file_info(ChannelPid, Name, Info, Timeout) -> ok | {error, reason()}

Types

ChannelPid = pid()
Name = string()
Info = record()
Timeout = timeout()

Writes file information from a file_info record to the file specified by Name. See file:write_file_info/[2,3] for information about the record.

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