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Async-friendly QUIC implementation in Rust


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Quinn is a pure-Rust, async-compatible implementation of the IETF QUIC transport protocol. The project was founded by Dirkjan Ochtman and Benjamin Saunders as a side project in 2018, and has seen more than 30 releases since then. If you're using Quinn in a commercial setting, please consider sponsoring the project.


  • Simultaneous client/server operation
  • Ordered and unordered stream reads for improved performance
  • Works on stable Rust, tested on Linux, macOS and Windows
  • Pluggable cryptography, with a standard implementation backed by rustls and ring
  • Application-layer datagrams for small, unreliable messages
  • Future-based async API
  • Minimum supported Rust version of 1.66


  • quinn: High-level async API based on tokio, see examples for usage. This will be used by most developers. (Basic benchmarks are included.)
  • quinn-proto: Deterministic state machine of the protocol which performs no I/O internally and is suitable for use with custom event loops (and potentially a C or C++ API).
  • quinn-udp: UDP sockets with ECN information tuned for the protocol.
  • bench: Benchmarks without any framework.
  • fuzz: Fuzz tests.

Getting Started


$ cargo run --example server ./
$ cargo run --example client https://localhost:4433/Cargo.toml

This launches an HTTP 0.9 server on the loopback address serving the current working directory, with the client fetching ./Cargo.toml. By default, the server generates a self-signed certificate and stores it to disk, where the client will automatically find and trust it.


Usage Notes

Click to show the notes


A Quinn endpoint corresponds to a single UDP socket, no matter how many connections are in use. Handling high aggregate data rates on a single endpoint can require a larger UDP buffer than is configured by default in most environments. If you observe erratic latency and/or throughput over a stable network link, consider increasing the buffer sizes used. For example, you could adjust the SO_SNDBUF and SO_RCVBUF options of the UDP socket to be used before passing it in to Quinn. Note that some platforms (e.g. Linux) require elevated privileges or modified system configuration for a process to increase its UDP buffer sizes.


By default, Quinn clients validate the cryptographic identity of servers they connect to. This prevents an active, on-path attacker from intercepting messages, but requires trusting some certificate authority. For many purposes, this can be accomplished by using certificates from Let's Encrypt for servers, and relying on the default configuration for clients.

For some cases, including peer-to-peer, trust-on-first-use, deliberately insecure applications, or any case where servers are not identified by domain name, this isn't practical. Arbitrary certificate validation logic can be implemented by enabling the dangerous_configuration feature of rustls and constructing a Quinn ClientConfig with an overridden certificate verifier by hand.

When operating your own certificate authority doesn't make sense, rcgen can be used to generate self-signed certificates on demand. To support trust-on-first-use, servers that automatically generate self-signed certificates should write their generated certificate to persistent storage and reuse it on future runs.


All feedback welcome. Feel free to file bugs, requests for documentation and any other feedback to the issue tracker.

The quinn-proto test suite uses simulated IO for reproducibility and to avoid long sleeps in certain timing-sensitive tests. If the SSLKEYLOGFILE environment variable is set, the tests will emit UDP packets for inspection using external protocol analyzers like Wireshark, and NSS-compatible key logs for the client side of each connection will be written to the path specified in the variable.

The minimum supported Rust version for published releases of our crates will always be at least 6 months old at the time of release.