ftz - A small file transfer tool

Date: 04.03.2021

I created a new tool called ftz (File Transfer Zig) which allows to fetch or upload files onto another computed connected to network.

ftz Github Repository (and downloads)

What is ftz?

ftz (all lower case) is a file transfer tool that allows a client to connect to a server and fetch a file via a ftz url. It is also possible to upload files to a ftz server.

The tool and protocol is comparable to TFTP, but is based on TCP and provides an additional data integrity check.

To use ftz, just download an executable for your OS or build it yourself, then you can do the following:

# open the current directory for read/write access
ftz host .                             
# fetch file named "demo" from a ftz server "remote.machine"
ftz get  ftz://remote.machine/demo     
# upload the file "mode" to a ftz server "other.machine" with the name "demo"
ftz put  mode ftz://other.machine/demo

ftz has several command line options to adjust the port used for hosting as well as allow/deny get and put requests. You can find all usage options by invoking "ftz help" or checking out the GitHub link above.

Why another tool?

This question is answered easily: I didn't find a tool that fitted my requirements:

So as i could find no tool that satisfied my needs, i created a new one. It appeared to be easy and i actually got from the idea to a production-ready implementation in less than 24 hours.

The protocol

ftz uses a very simple tcp based protocol, defaulting to port 17457. A new transfer is initiated by a client by connecting to the server and sending a request line.

Fetching a file

The client opens the tcp connection and sends "GET " followed by a "/"-separated path to the file. The path can be either relative or absolute and will be normalized by the server. The path is then terminated by a CR LF sequence. After this, the server will respond with 32 byte containing the plain text hex-encoded MD5 checksum of the file in hexadecimal notation, followed by a CR LF sequence. After this sequence, the server will send the contents of the file and terminate the connection.

Example transfer for a file called "cat.jpg":

Client: "GET cat.jpg" CR LF
Server: "e1961be6e1370d615415a4354e08e131" CR LF
Server: <FILE DATA>

Here, a text in quotes will be sent as verbatim ASCII. CR is the ASCII carriage return character (0x0D), LF is the line feed character (0x0A). <FILE DATA> is the binary contents of the file. The length of this data is determined by how much data the server sends. When the connection is closed, the client should verify that the MD5 checksum actually fits the transferred checksum by the server. If not, the received file should be deleted/discarded and a error message should be shown.

Upload a file

The client opens the tcp connection and sends "PUT " followed by a "/"-separated path to the file and a CR LF sequence. The same rules as in "fetching a file" apply for the path. After the path was sent, the client will then send the hex-encoded MD5 checksum of the file, followed by the CR LF sequence. After this, the data of the file is sent, the connection is then terminated. The server can abort the transfer by just closing the TCP connection.

Example transfer for a file called "cat.jpg":

Client: "GET /cat.jpg" CR LF
Client: "e1961be6e1370d615415a4354e08e131" CR LF
Client: <FILE DATA>

The same notation style is in "fetching a file" is applied.

Design Rationale

Here are some bullet points that went through my mind while designing the tool and the protocol:

Known bugs