ssh_sftp

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

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

ssh_connection_ref() - opaque to the user returned by ssh:connect/3

timeout() = infinity | integer() - in milliseconds.

If the request functions for the SFTP channel return {error, timeout} it does not guarantee that the request did not reach the server and was not performed, it only means that we did not receive an answer from the server within the time that was expected.

Types:

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 should be used as input to all other API functions in this module.

Options are:

{timeout, timeout()}

The timeout is passed to the ssh_channel start function, and defaults to infinity.

{sftp_vsn, integer()}

Desired SFTP protocol version. The actual version will be 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.

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

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Reads a file from the server, and returns the data in a binary, like file:read_file/1.

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Writes a file to the server, like file:write_file/2. The file is created if it does not exist or is owerwritten if it does.

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

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

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

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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.

An example of writing and then reading a tar file:

          {ok,HandleWrite} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [write]),
          ok = erl_tar:add(HandleWrite, .... ),
          ok = erl_tar:add(HandleWrite, .... ),
              ...
          ok = erl_tar:add(HandleWrite, .... ),
          ok = erl_tar:close(HandleWrite),

          %% And for reading
          {ok,HandleRead} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [read]),
          {ok,NameValueList} = erl_tar:extract(HandleRead,[memory]),
          ok = erl_tar:close(HandleRead),
        

The crypto mode option is applied to the generated stream of bytes just prior to sending them to the sftp server. This is intended for encryption but could of course 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 inteded for stream crypto while a fixed ChunkSize is intended for block crypto. It is possible to change the ChunkSizes in the return from the EncryptFun or DecryptFun. It is in fact possible to change the value between pos_integer() and undefined.

The write and read example above can be extended with encryption and decryption:

          %% First three parameters depending on which crypto type we select:
          Key = <<"This is a 256 bit key. abcdefghi">>,
          Ivec0 = crypto:rand_bytes(16),
          DataSize = 1024,  % DataSize rem 16 = 0 for aes_cbc

          %% Initialization of the CryptoState, in this case it is the Ivector.
          InitFun = fun() -> {ok, Ivec0, DataSize} end,

          %% How to encrypt:
          EncryptFun = 
              fun(PlainBin,Ivec) -> 
                   EncryptedBin = crypto:block_encrypt(aes_cbc256, Key, Ivec, PlainBin),
                   {ok, EncryptedBin, crypto:next_iv(aes_cbc,EncryptedBin)}
              end,

          %% What to do with the very last block:
          CloseFun = 
              fun(PlainBin, Ivec) ->
                    EncryptedBin = crypto:block_encrypt(aes_cbc256, Key, Ivec, 
                                                     pad(16,PlainBin) %% Last chunk
                                                     ),
                    {ok, EncryptedBin} 
            end,

          Cw = {InitFun,EncryptFun,CloseFun},
          {ok,HandleWrite} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [write,{crypto,Cw}]),
          ok = erl_tar:add(HandleWrite, .... ),
          ok = erl_tar:add(HandleWrite, .... ),
              ...
          ok = erl_tar:add(HandleWrite, .... ),
          ok = erl_tar:close(HandleWrite),

          %% And for decryption (in this crypto example we could use the same InitFun
          %% as for encryption):
          DecryptFun = 
              fun(EncryptedBin,Ivec) ->
                   PlainBin = crypto:block_decrypt(aes_cbc256, Key, Ivec, EncryptedBin),
                   {ok, PlainBin, crypto:next_iv(aes_cbc,EncryptedBin)}
              end,

          Cr = {InitFun,DecryptFun},
          {ok,HandleRead} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [read,{crypto,Cw}]),
          {ok,NameValueList} = erl_tar:extract(HandleRead,[memory]),
          ok = erl_tar:close(HandleRead),
        

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

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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 will be read and returned. If no bytes are read, eof is returned.

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

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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}, or eof, or {error, Error}.

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

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Writesdata to the file referenced by Handle. The file should be opened with write or append flag. Returns ok if successful or S{error, Reason} otherwise.

Typical error reasons are:

ebadf

The file is not opened for writing.

enospc

There is a no space left on the device.

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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, Error}.

The apwrite writes on a specified position, combining the position and awrite operations.

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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 above with Offset 0.

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Returns a file_info record from the file specified by Name or Handle, like file:read_file_info/2.

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Returns a file_info record from the symbolic link specified by Name or Handle, like file:read_link_info/2.

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Writes file information from a file_info record to the file specified by Name, like file:write_file_info.

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Reads the link target from the symbolic link specified by name, like file:read_link/1.

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Creates a symbolic link pointing to Target with the name Name, like file:make_symlink/2.

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Renames a file named OldName, and gives it the name NewName, like file:rename/2

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Deletes the file specified by Name, like file:delete/1

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

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Deletes a directory specified by Name. Note that the directory must be empty before it can be successfully deleted