File Transfer Service¶
The file transfer service is used to transfer files between the mission operations center and the OBC. It may also be used to transfer files between a developer’s system and the OBC when in a development environment.
The service provides file transfer functionality by implementing the file protocol. The file protocol is UDP-based which means a connection is required between the OBC and ground segment capable of transferring UDP packets. This should be established using a standard network connection.
The file transfer service listens for requests on its configured UDP socket.
When a message is received, it is then processed using the file protocol message engine. This logic keeps track of the current state of each client connection and takes the appropriate action depending on the current state and the particular message received.
Actions may also be taken if the service experiences a timeout while waiting for a follow-up message from a client. For example, if a client initiates an export operation and then stops communicating while in the middle of sending file chunks, the service will timeout, check the current status of the file, and then send a NAK to the client with the current missing chunks. Receiving this NAK should cause the client to resume transmitting file chunk data.
This timeout is currently hardcoded to two seconds.
In order to support simultaneous client connections, whenever a message is received on the main UDP socket, a new socket is spawned in order to handle the rest of the transaction. As a result, after sending the initial import or export request, the transfer client should listen for a reply and then use the new socket as the destination for future transmissions.
The file transfer service has several configuration options which may be defined in the system’s config.toml file:
storage_dir- Default: “file-transfer”. The directory which should be used for temporary storage of file chunks. Note: The directory will be created if it does not already exist.
timeout- Default: 2. The length of time, in seconds, for which the service should wait for new messages from the client once a file protocol transaction has been started
transfer_chunk_size- Default: 1024. Each file is broken up into equally sized chunks prior to transfer. This option specifies the size of those chunks in bytes.
hash_chunk_size- Default: 2048. Each file is broken up into equally sized chunks which are used to calculate the file’s hash. This option specifies the size of those chunks.
hold_count- Default: 5. The number of times the protocol waits for a new message before ending the transaction.
downlink_ip- Required. The IP address that the file service responds to.
downlink_port- Required. The port that the file service responds to.
inter_chunk_delay- Default: 1. The delay, in milliseconds, taken between the transmission of each chunk. This is to allow manual flow control.
max_chunks_transmit- Optional. The maximum number of chunks to transmit before waiting on a response. The default is to transmit the entire file.
ip- Specifies the service’s IP address
port- Specifies the port on which the service will be listening for UDP packets
[file-transfer-service] storage_dir = "my/storage/directory" timeout = 3600 downlink_ip = "127.0.0.1" downlink_port = 8080 [file-transfer-service.addr] ip = "0.0.0.0" port = 8040
Future configuration options:
- Maximum number of timeout-retry attempts
- Non-default destination IP/port
Running the Service from KubOS¶
The Kubos Linux distribution (as of v1.3.0) ships with the file transfer
service installed and configured to run on boot. This can be verified by
booting the KubOS system, running the
ps command and looking for the
file-service process. If the service is not running then it can
be started like so:
$ /etc/init.d/S90file-service start
Running the Service from Source¶
The file transfer service can also be run from source if required.
The source is located in the folder
in the KubOS source repo. The service can be started like so:
$ cd kubos/services/file-service $ cargo run -- -c config.toml
The service will look for the given
config.toml file in order to get the
needed configuration options.
Communicating with the File Service¶
Users should establish a ground-side client which implements the file protocol in order to transfer files over their communications device.
Kubos provides an example file transfer client to allow users to learn and experiment with the file transfer service prior to the formal file transfer client being developed. For more information, please refer to the file transfer tutorial.