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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 first goal of this project was to provide feedback on the development of a QUIC standard in the IETF QUIC WG. Information on the WG is available at QUIC has been published as RFC 9000, but there is still ongoing work, for example on multipath. Picoquic enables developers to test this new work.

The second goal is to experiment with API for non-HTTP development, such as DNS over QUIC -- see RFC 9250. Then there are plenty of other features we may dream off, such as support for peer-to-peer applications or forward error correction. That's on the horizon, but not there now.

The current version of Picoquic supports the QUIC specifications per RFC 9000, RFC 9001, RFC 9002, and RFC 8999. It also implements the following extensions:

The distribution also includes a minimal implementation of HTTP3 per RFC 9114, including a static implementation of QPACK, compatible with RFC9204 with support for the following extensions:

The code in this repo is stable. Performance work is ongoing -- recent tests showed picoquic sending data at up to 5Gbps.

There are many implementations of Quic, listed at 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 version 1, RFC 9000.

An implemention of DNS over QUIC is available 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 protocol. Suggestions for documentation, API, performance and more are wellcome. Feel free to open an issue.

Planned developments include support for the standard version of multipath, improved support for Real Time Media over QUIC, as well as various other research issues, in particular related to congestion control.

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 evolved recently to support the latest version of QUIC. The current code is tested against the Picotls version of Sat Dec 10 01:56:28 2022 +0900, after commit 7d294ab4f2e0ed749b4bcfaf533225a4e0c096f7. (Note that these last commits changed the Picotls API by removing code for the now obsolete ESNI draft; prior versions will not work with Picoquic.) The code can use OpenSSL version 1.1.1 or OpenSSL version 3.0.

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

Thanks to check-ins from Deb Banerjee and Igor Lubashev for the build experience on Linux.

To build Picoquic on Linux, you need can either build picotls separately or use an integrated option. In both cases, you need first to install and build Openssl on your machine

To build step by step, you should:

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

  • Clone and compile Picoquic:

   cmake .

Instead of building picotls separately, you can use an integrated option (thanks to Paul E. Jones and Suhas Nandakumar for developing that):

  • Clone and compile Picoquic and Picotls in a single command:

Either way, you can verify that everything worked:

  • Run the test program picoquic_ct to verify the port.

The tests verify that the code compiles and runs correctly under Ubuntu, using GitHub actions on Intel 64 bit VMs. We rely on user reports to verify behavior on other architecture, e.g. ARM. Thanks to @defermelowie for testing on ARM 32 bits.

Picoquic on MacOSX

Thanks to Frederik Deweerdt for ensuring that Picoquic runs on MacOSX. The build steps are the same as for Linux. The tests verify that the code compiles and runs correctly under MacOS, using GitHub actions on Intel 64 bit VMs. We rely on user reports to verify behavior on other architecture, e.g. M1. Thanks to @defermelowie for testing on M1.

Picoquic on FreeBSD

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

Using Picoquic in CLI mode

See Usage for how to use various commands from shell.

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 Version 1, and will negotiate support for the corresponding version 0x00000001 -- that is, QUIC Transport version 1. Picoquic will also accept negotiation of previous versions down to draft-27.

Creating QLOG Log Files

See How To Produce QLOG files with picoquic