View Source tftp behaviour (tftp v1.2.1)
Trivial FTP.
Interface module for the tftp
application.
Overwiew
This is a complete implementation of the following IETF standards:
RFC 1350, The TFTP Protocol (revision 2).
RFC 2347, TFTP Option Extension.
RFC 2348, TFTP Blocksize Option.
RFC 2349, TFTP Timeout Interval and Transfer Size Options.
The only feature that not is implemented in this release is the "netascii" transfer mode.
The start function starts a daemon process which, listens for UDP packets on a port. When it receives a request for read or write it spawns a temporary server process which handles the actual transfer of the file. On the client side the read_file/3 and write_file/3 functions spawns a temporary client process which establishes contact with a TFTP daemon and performs the actual transfer of the file.
Most of the options are common for both the client and the server side, but some of them differs a little.
Callbacks
A tftp
callback module is to be implemented as a tftp
behavior and export
the functions listed in the following.
On the server side, the callback interaction starts with a call to open/5
with
the registered initial callback state. open/5
is expected to open the
(virtual) file. Then either function Module:read/1
or
Module:write/2
is invoked repeatedly, once per transferred block. At
each function call, the state returned from the previous call is obtained. When
the last block is encountered, function Module:read/1
or
Module:write/2
is expected to close the (virtual) file and return its
last state. Function Module:abort/3
is only used in error situations.
Function prepare/5
is not used on the server side.
On the client side, the callback interaction is the same, but it starts and ends
a bit differently. It starts with a call to prepare/5
with the same arguments
as open/5
takes. prepare/5
is expected to validate the TFTP options
suggested by the user and to return the subset of them that it accepts. Then the
options are sent to the server, which performs the same TFTP option negotiation
procedure. The options that are accepted by the server are forwarded to function
open/5
on the client side. On the client side, function open/5
must accept
all option as-is or reject the transfer. Then the callback interaction follows
the same pattern as described for the server side. When the last block is
encountered in Module:read/1
or Module:write/2
, the returned
state is forwarded to the user and returned from read_file
/3 or
write_file/3
.
If a callback (performing the file access in the TFTP server) takes too long time (more than the double TFTP time-out), the server aborts the connection and sends an error reply to the client. The server simply assumes that the client has given up.
If the TFTP server receives yet another request from the same client (same host and port) while it already has an active connection to the client, it ignores the new request if the request is equal to the first one (same filename and options). This implies that the (new) client will be served by the already ongoing connection on the server side. By not setting up yet another connection, in parallel with the ongoing one, the server consumes less resources.
Summary
Types
Access mode.
All options most of them common to the client and server.
Error reason codes.
Specific TFTP protocol options
Information about the peer provided for callback.
Callbacks
Invoked when the file transfer is aborted.
Opens a file for read or write access.
Prepares to open a file on the client side.
Reads a chunk from the file.
Writes a chunk to the file.
Client API
Reads a (virtual) file RemoteFilename
from a TFTP server.
Writes a (virtual) file RemoteFilename
to a TFTP server.
Server API
Changes configuration a TFTP Server
Returns information about all TFTP server.
Starts a daemon process listening for UDP packets on a port.
Types
-type access() :: read | write.
Access mode.
All options most of them common to the client and server.
{debug, Level::none | error | warning | brief | normal | verbose | all}
Controls the level of debug printouts. Default is
none
.{host, Host::inet:hostname()}
-The name or IP address of the host where the TFTP daemon resides. This option is only used by the client.
{port, Port::inet:port_number()}
The TFTP port where the daemon listens. Defaults is the standardized number 69. On the server side, it can sometimes make sense to set it to 0, meaning that the daemon just picks a free port (which one is returned by function
info/1
).If a socket is connected already, option
{udp, [{fd, integer()}]}
can be used to pass the open file descriptor togen_udp
. This can be automated by using a command-line argument stating the prebound file descriptor number. For example, if the port is 69 and file descriptor 22 is opened bysetuid_socket_wrap
, the command-line argument "-tftpd_69 22" triggers the prebound file descriptor 22 to be used instead of opening port 69. The UDP option{udp, [{fd, 22}]}
is automatically added. Seeinit:get_argument/
about command-line arguments andgen_udp:open/2
about UDP options.{port_policy, random | inet:port_number() | {range, Min::inet:port_number(), Max::inet:port_nuber()}
Policy for the selection of the temporary port that is used by the server/client during the file transfer. Default is
random
, which is the standardized policy. With this policy a randomized free port is used. A single port or a range of ports can be useful if the protocol passes through a firewall.{udp, Options::gen_udp:option}
{use_tsize, boolean()}
Flag for automated use of option
tsize
. With this set totrue
, thewrite_file/3
client determines the filesize and sends it to the server as the standardizedtsize
option. Aread_file/3
client acquires only a filesize from the server by sending a zerotsize
.{max_tsize, MaxTsize::pos_integer() | infinity}
Threshold for the maximal filesize in bytes. The transfer is aborted if the limit is exceeded. Default is
infinity
.{max_conn, MaxConn::pos_integer() | infinity}
Threshold for the maximal number of active connections. The daemon rejects the setup of new connections if the limit is exceeded. Default is
infinity
.TftpOption::option()
Name and value of a TFTP option.
{reject, Feature:: access() | TftpKey::string()}
Controls which features to reject. This is mostly useful for the server as it can restrict the use of certain TFTP options or read/write access.
{callback, {RegExp ::string(), Module::module(), State :: term()}}
Registration of a callback module. When a file is to be transferred, its local filename is matched to the regular expressions of the registered callbacks. The first matching callback is used during the transfer. See
read_file/3
andwrite_file/3
.The callback module must implement the
tftp
behavior, see callbacks.{logger, module()}
Callback module for customized logging of errors, warnings, and info messages. The callback module must implement the
tftp_logger
behavior. The default module istftp_logger
.{max_retries, MaxRetries::non_neg_integer()}
Threshold for the maximal number of retries. By default the server/client tries to resend a message up to five times when the time-out expires.
-type error_code() :: undef | enoent | eacces | enospc | badop | eexist | baduser | badopt | pos_integer().
Error reason codes.
Specific TFTP protocol options
-type peer() :: {PeerType :: inet | inet6, PeerHost :: inet:ip_address(), PeerPort :: port()}.
Information about the peer provided for callback.
Callbacks
-callback abort(Code :: error_code(), string(), State :: term()) -> ok.
Invoked when the file transfer is aborted.
The callback function is expected to clean up its used resources after the aborted file transfer, such as closing open file descriptors and so on. The function is not invoked if any of the other callback functions returns an error, as it is expected that they already have cleaned up the necessary resources. However, it is invoked if the functions fail (crash).
open(Peer, Access, Filename, Mode, SuggestedOptions, State)
View Source (since OTP 18.1)-callback open(Peer :: peer(), Access :: access(), Filename :: file:name(), Mode :: string(), SuggestedOptions :: [option()], State :: [] | [{root_dir, string()}] | term()) -> {ok, AcceptedOptions :: [option()], NewState :: term()} | {error, {Code :: error_code(), string()}}.
Opens a file for read or write access.
On the client side, where the open/5
call has been preceded by a call to
prepare/5
, all options must be accepted or rejected.
On the server side, where there is no preceding prepare/5
call, no new options
can be added, but those present in SuggestedOptions
can be omitted or replaced
with new values in AcceptedOptions
.
prepare(Peer, Access, Filename, Mode, SuggestedOptions, InitialState)
View Source (since OTP 18.1)-callback prepare(Peer :: peer(), Access :: access(), Filename :: file:name(), Mode :: string(), SuggestedOptions :: [option()], InitialState :: [] | [{root_dir, string()}]) -> {ok, AcceptedOptions :: [option()], NewState :: term()} | {error, {Code :: error_code(), string()}}.
Prepares to open a file on the client side.
No new options can be added, but those present in SuggestedOptions
can be
omitted or replaced with new values in AcceptedOptions
.
This is followed by a call to open/4
before any read/write access is
performed. AcceptedOptions
is sent to the server, which replies with the
options that it accepts. These are then forwarded to open/4
as
SuggestedOptions
.
-callback read(State :: term()) -> {more, binary(), NewState :: term()} | {last, binary(), integer()} | {error, {Code :: error_code(), string()}}.
Reads a chunk from the file.
The callback function is expected to close the file when the last file chunk is encountered. When an error is encountered, the callback function is expected to clean up after the aborted file transfer, such as closing open file descriptors, and so on. In both cases there will be no more calls to any of the callback functions.
-callback write(binary(), State :: term()) -> {more, NewState :: term()} | {last, FileSize :: integer()} | {error, {Code :: error_code(), string()}}.
Writes a chunk to the file.
The callback function is expected to close the file when the last file chunk is encountered. When an error is encountered, the callback function is expected to clean up after the aborted file transfer, such as closing open file descriptors, and so on. In both cases there will be no more calls to any of the callback functions.
Client API
-spec read_file(RemoteFilename, LocalFilename, Options) -> {ok, LastCallbackState} | {error, Reason} when RemoteFilename :: file:filename(), LocalFilename :: file:filename_all(), Options :: [connection_option()], LastCallbackState :: term(), Reason :: term().
Reads a (virtual) file RemoteFilename
from a TFTP server.
If LocalFilename
is the atom binary
, tftp_binary
is used as callback
module. It concatenates all transferred blocks and returns them as one single
binary in LastCallbackState
.
If LocalFilename
is a string and there are no registered callback modules,
tftp_file
is used as callback module. It writes each transferred block to the
file named LocalFilename
and returns the number of transferred bytes in
LastCallbackState
.
If LocalFilename
is a string and there are registered callback modules,
LocalFilename
is tested against the regexps of these and the callback module
corresponding to the first match is used, or an error tuple is returned if no
matching regexp is found.
-spec write_file(RemoteFilename, LocalFilename, Options) -> {ok, LastCallbackState} | {error, Reason} when RemoteFilename :: file:filename(), LocalFilename :: file:filename_all() | binary, Options :: [option()], LastCallbackState :: term(), Reason :: term().
Writes a (virtual) file RemoteFilename
to a TFTP server.
If LocalFilename
is a binary, tftp_binary
is used as callback module. The
binary is transferred block by block and the number of transferred bytes is
returned in LastCallbackState
.
If LocalFilename
is a string and there are no registered callback modules,
tftp_file
is used as callback module. It reads the file named LocalFilename
block by block and returns the number of transferred bytes in
LastCallbackState
.
If LocalFilename
is a string and there are registered callback modules,
LocalFilename
is tested against the regexps of these and the callback module
corresponding to the first match is used, or an error tuple is returned if no
matching regexp is found.
Server API
Changes configuration a TFTP Server
Returns information about all TFTP server.
-spec start(Options) -> {ok, Pid} | {error, Reason} when Options :: [connection_option()], Pid :: pid(), Reason :: term().
Starts a daemon process listening for UDP packets on a port.
When it receives a request for read or write, it spawns a temporary server process handling the actual transfer of the (virtual) file.