Announcing qcp

Posted on in software with tags network, debian.

The QUIC Copier (qcp) is an experimental high-performance remote file copy utility for long-distance internet connections.

Source repository: https://github.com/crazyscot/qcp

📋 Features

  • 🔧 Drop-in replacement for scp
  • 🛡️ Similar security to scp, using existing, well-known mechanisms
  • 🚀 Better throughput on congested networks

📖 About qcp

qcp is a hybrid protocol combining ssh and QUIC.

We use ssh to establish a control channel to the target machine, then spin up the QUIC protocol to transfer data.

This has the following useful properties:

  • User authentication is handled entirely by ssh
  • Data is transmitted over UDP, avoiding known issues with TCP over “long, fat pipe” connections
  • Data in transit is protected by TLS using ephemeral keys
  • The security mechanisms all use existing, well-known cryptographic algorithms

For full documentation refer to qcp on docs.rs.

Motivation

I needed to copy multiple large (3+ GB) files from a server in Europe to my home in New Zealand.

I’ve got nothing against ssh or scp. They’re brilliant. I’ve been using them since the 1990s. However they run on top of TCP, which does not perform very well when the network is congested. With a fast fibre internet connection, a long round-trip time and noticeable packet loss, I was right in the sour spot. TCP did its thing and slowed down, but when the congestion cleared it was very slow to get back up to speed.

If you’ve ever been frustrated by download performance from distant websites, you might have been experiencing this same issue. Friends with satellite (pre-Starlink) internet connections seem to be particularly badly affected.

💻 Getting qcp

The project is a Rust binary crate.

You can install it:

  • as a Debian package or pre-compiled binary from the latest qcp release page (N.B. the Linux builds are static musl binaries);
  • with cargo install qcp (you will need to have a rust toolchain and capnpc installed);
  • by cloning and building the source repository.

You will need to install qcp on both machines. Please refer to the README for more.

See also