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"Call it TCP/2. One More Time."

ngtcp2 project is an effort to implement RFC9000 QUIC protocol.


Online documentation is available.

Public test server

The following endpoints are available to try out ngtcp2 implementation:


The libngtcp2 C library itself does not depend on any external libraries. The example client, and server are written in C++20, and should compile with the modern C++ compilers (e.g., clang >= 11.0, or gcc >= 11.0).

The following packages are required to configure the build system:

  • pkg-config >= 0.20
  • autoconf
  • automake
  • autotools-dev
  • libtool

libngtcp2 uses cunit for its unit test frame work:

  • cunit >= 2.1

To build sources under the examples directory, libev and nghttp3 are required:

ngtcp2 crypto helper library, and client and server under examples directory require at least one of the following TLS backends:

  • OpenSSL with QUIC support
  • GnuTLS >= 3.7.2
  • BoringSSL (commit b2536a2c6234496ef609e7c909936bbf828dac6d)
  • Picotls (commit 67ba66e91728316152fc2c2172710ca4c2236027)
  • wolfSSL >= 5.5.0

Build from git

$ git clone --depth 1 -b OpenSSL_1_1_1s+quic
$ cd openssl
$ # For Linux
$ ./config enable-tls1_3 --prefix=$PWD/build
$ make -j$(nproc)
$ make install_sw
$ cd ..
$ git clone
$ cd nghttp3
$ autoreconf -i
$ ./configure --prefix=$PWD/build --enable-lib-only
$ make -j$(nproc) check
$ make install
$ cd ..
$ git clone
$ cd ngtcp2
$ autoreconf -i
$ # For Mac users who have installed libev with MacPorts, append
$ # ',-L/opt/local/lib' to LDFLAGS, and also pass
$ # CPPFLAGS="-I/opt/local/include" to ./configure.
$ # For OpenSSL >= v3.0.0, replace "openssl/build/lib" with
$ # "openssl/build/lib64".
$ ./configure PKG_CONFIG_PATH=$PWD/../openssl/build/lib/pkgconfig:$PWD/../nghttp3/build/lib/pkgconfig LDFLAGS="-Wl,-rpath,$PWD/../openssl/build/lib"
$ make -j$(nproc) check


After successful build, the client and server executable should be found under examples directory. They talk HTTP/3.


$ examples/client [OPTIONS] <HOST> <PORT> [<URI>...]

The notable options are:

  • -d, --data=<PATH>: Read data from <PATH> and send it to a peer.



The notable options are:

  • -V, --validate-addr: Enforce stateless address validation.


There are h09client and h09server which speak HTTP/0.9. They are written just for quic-interop-runner. They share the basic functionalities with HTTP/3 client and server but have less functions (e.g., h09client does not have a capability to send request body, and h09server does not understand numeric request path, like /1000).

Resumption and 0-RTT

In order to resume a session, a session ticket, and a transport parameters must be fetched from server. First, run examples/client with --session-file, and --tp-file options which specify a path to session ticket, and transport parameter files respectively to save them locally.

Once these files are available, run examples/client with the same arguments again. You will see that session is resumed in your log if resumption succeeds. Resuming session makes server's first Handshake packet pretty small because it does not send its certificates.

To send 0-RTT data, after making sure that resumption works, use -d option to specify a file which contains data to send.

Token (Not something included in Retry packet)

QUIC server might send a token to client after connection has been established. Client can send this token in subsequent connection to the server. Server verifies the token and if it succeeds, the address validation completes and lifts some restrictions on server which might speed up transfer. In order to save and/or load a token, use --token-file option of examples/client. The given file is overwritten if it already exists when storing a token.

Crypto helper library

In order to make TLS stack integration less painful, we provide a crypto helper library which offers the basic crypto operations.

The header file exists under crypto/includes/ngtcp2 directory.

Each library file is built for a particular TLS backend. The available crypto helper libraries are:

  • libngtcp2_crypto_openssl: Use OpenSSL as TLS backend
  • libngtcp2_crypto_gnutls: Use GnuTLS as TLS backend
  • libngtcp2_crypto_boringssl: Use BoringSSL as TLS backend
  • libngtcp2_crypto_picotls: Use Picotls as TLS backend
  • libngtcp2_crypto_wolfssl: Use wolfSSL as TLS backend

Because BoringSSL and Picotls are an unversioned product, we only tested their particular revision. See Requirements section above.

We use Picotls with OpenSSL as crypto backend. It does not work with OpenSSL >= 3.0.0.

The examples directory contains client and server that are linked to those crypto helper libraries and TLS backends. They are only built if their corresponding crypto helper library is built:

  • client: OpenSSL client
  • server: OpenSSL server
  • gtlsclient: GnuTLS client
  • gtlsserver: GnuTLS server
  • bsslclient: BoringSSL client
  • bsslserver: BoringSSL server
  • ptlsclient: Picotls client
  • ptlsserver: Picotls server
  • wsslclient: wolfSSL client
  • wsslserver: wolfSSL server

QUIC protocol extensions

The library implements the following QUIC protocol extensions:

Configuring Wireshark for QUIC

Wireshark can be configured to analyze QUIC traffic using the following steps:

  1. Set SSLKEYLOGFILE environment variable:

    $ export SSLKEYLOGFILE=quic_keylog_file
  2. Set the port that QUIC uses

    Go to Preferences->Protocols->QUIC and set the port the program listens to. In the case of the example application this would be the port specified on the command line.

  3. Set Pre-Master-Secret logfile

    Go to Preferences->Protocols->TLS and set the Pre-Master-Secret log file to the same value that was specified for SSLKEYLOGFILE.

  4. Choose the correct network interface for capturing

    Make sure you choose the correct network interface for capturing. For example, if using localhost choose the loopback network interface on macos.

  5. Create a filter

    Create A filter for the udp.port and set the port to the port the application is listening to. For example:

    udp.port == 7777


The MIT License

Copyright (c) 2016 ngtcp2 contributors