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Minimalist implementation of the QUIC protocol, as defined by the IETF. The IETF spec started with the version of QUIC defined by Google and implemented in Chrome, but the IETF spec is independent of Chrome, and does not attempt to be backward compatible. The main developer is Christian Huitema.

The first goal of this project is to provide feedback on the development of a QUIC standard in the IETF QUIC WG. Information on the WG is available at The in-progress version of the spec is available on GitHub at

The second goal is to experiment with API for non-HTTP development, such as DNS over QUIC. Then there are plenty of other features we may dream off, such as support for multipath, or support for peer-to-peer applications. That's on the horizon, but not there now.

The code in this repo is getting stable, just like the specification itself. The version 34 of the QUIC draft has passed all IETF reviews, and publication as an RFc is imminent. At this stage the changes in Picoquic are mostly driven by performance issues, or API improvements. And bug fixing, too. The goal is to have the "1.0" version of picoquic ready as soon as the RFC are published.

There are many implementations of Quic, listed at The interop goals are defined at, which points to the current interoperability matrix. Several implementations provide docker images to the "Quic Interop Runner" project, with results updated daily at

Bastian Köcher has developed bindings of the picoquic library to RUST. His repository can be found here. You may want to check it.


Picoquic is currently developed as a Visual Studio 2017 project, and simultaneously tested on Windows and on Linux. It has a dependency on the Picotls implementation of TLS 1.3. Picotls has two modes, a feature rich version that depends on OpenSSL, and a leaner version that only depends on the "minicrypto" library. For now, Picoquic uses the OpenSSL version, and has a dependency on OpenSSL.

The project consists of a core library (picoquic), of a test library (picoquictest), and of a test program (picoquicdemo). All these are written in C. In the Visual Studio project, the test library is wrapped up in the Visual Studio unittest framework, which makes for convenient regression testing during development. In the Linux builds, the tests are run through a command line program.


As explained in the Wiki, Picoquic is actively tested against other implementations during the QUIC Interop days. See

The current version is aligned with draft 34. All big features are supported, including the interface between QUIC and TLS, 0-RTT, migration and key rollover. The state of development is tracked in the list of issues in this repository.

We have started an implementation of DNS over QUIC as Quicdoq. DNS over Quic is interesting by itself, but it also provides an example for building an application different than HTTP on top of Picoquic.

We are spending time bettering the implementation, and the documentation, including a first pass at documenting architecture and API. Initially the focus has been on correctness rather than performance. We will keep correctness, but we will improve performance, especially in light of practical experience with applications. To facilitate performance tests, the demo program includes an implementation of the quic performance test. Suggestions for documentation, API, performance and more are wellcome. Feel free to open an issue!

Building Picoquic

Picoquic is developed in C, and can be built under Windows or Linux. Building the project requires first managing the dependencies, Picotls and OpenSSL. Please note that you will need a recent version of Picotls -- the Picotls API has eveolved recently to support the latest version of QUIC. The current code is tested against the Picotls version of Fri Mar 26 06:55:11 2021 +0900, after commit 86ccc558004c6808d6605d2c0e6f8dd13ebd1376. The code uses OpenSSL version 1.1.1.

Picoquic on Windows

To build Picoquic on Windows, you need to:

  • Install and build Openssl on your machine

  • Document the location of the Openssl install in the environment variable OPENSSLDIR (OPENSSL64DIR for the x64 builds)

  • Make sure that a copy of libcrypto.lib is available at that location, and that a copy of applink.c is available at the include location: $(OPENSSLDIR)\include
    for win32 builds, $(OPENSSL64DIR)\include\ for the x64 builds.

  • Clone and compile Picotls, using the Picotls for Windows options. The picotls project should be in the same directory level as the picoquic project, and the folder name should be kept as picotls.

  • Clone and compile Picoquic, using the Visual Studio 2017 solution picoquic.sln included in the sources.

  • You can use the unit tests included in the Visual Studio solution to verify the port.

Picoquic on Linux

The build experience on Linux is now much improved, thanks to check-ins from Deb Banerjee and Igor Lubashev.

To build Picoquic on Linux, you need to:

  • Install and build Openssl on your machine

  • Clone and compile Picotls, using cmake as explained in the Picotls documentation.

  • Clone and compile Picoquic:

   cmake .
  • Run the test program picoquic_ct to verify the port.

Picoquic on MacOSX

Thanks to Frederik Deweerdt for ensuring that Picoquic runs on MacOSX. The build steps are the same as for Linux.

Picoquic on FreeBSD

Same build steps as Linux. Picoquic probably also works on other BSD variants, but only FreeBSD has been tested so far.

Developing applications

Sorry, not all that much documentation yet. This will come as we populate the wiki. Your best bet is to look at the demonstration program "picoquicdemo" that is included in the release. The sources are in "picoquicfirst/picoquicdemo.c". The sample folder contains a code sample for a simplistic file transfer protocol, which might be a good place to start. Look at the file in the sample folder for more details.

Testing previous versions

The code is constantly updated to track the latest version of the specification. It currently conforms to draft-34, and will negotiate support for the corresponding version 0x00000001 -- that is, QUIC Transport version 1. The version 1 RFC is not published yet, but it is not expected to be much different from draft-34. Picoquic will also accept negotiation of previous versions down to draft-27.

Creating QLOG Log Files

See How To Produce QLOG files with picoquic