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The experimental SPDY protocol version 2, 3 and 3.1 implementation in C
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Fix doc for spdylay_select_next_protocol

We have to return this error code to notify OpenSSL that we have not
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Spdylay - SPDY C Library

This is an experimental implementation of Google's SPDY protocol in C.

This library provides SPDY version 2, 3 and 3.1 framing layer implementation. It does not perform any I/O operations. When the library needs them, it calls the callback functions provided by the application. It also does not include any event polling mechanism, so the application can freely choose the way of handling events. This library code does not depend on any particular SSL library (except for example programs which depend on OpenSSL 1.0.1 or later).

This project also develops SPDY client, server and proxy on top of Spdylay library. See SPDY Client and Server Programs section.

Development Status

Most of the SPDY/2, SPDY/3 and SPDY/3.1 functionality has been implemented. In both versions, the direct support of server-push has not been available yet. The application can achieve server-push using primitive APIs though.

As described below, we can create SPDY client and server with the current Spdylay API.


The following packages are needed to build the library:

  • pkg-config >= 0.20
  • zlib >= 1.2.3

To build and run the unit test programs, the following packages are needed:

  • cunit >= 2.1

To build and run the example programs, the following packages are needed:

  • OpenSSL >= 1.0.1

To enable -a option (getting linked assets from the downloaded resource) in spdycat (one of the example program), the following packages are needed:

  • libxml2 >= 2.7.7

To build SPDY/HTTPS to HTTP reverse proxy shrpx (one of the example program), the following packages are needed:

  • libevent-openssl >= 2.0.8

If you are using Ubuntu 12.04, you need the following packages installed:

$ apt-get install autoconf automake autotools-dev libtool pkg-config zlib1g-dev libcunit1-dev libssl-dev libxml2-dev libevent-dev

Build from git

Building from git is easy, but please be sure that at least autoconf 2.68 is used:

$ autoreconf -i
$ automake
$ autoconf
$ ./configure
$ make

Building documentation

To build documentation, run:

$ make html

The documents will be generated under doc/manual/html/.

The generated documents will not be installed with make install.

Building Android binary

In this section, we briefly describe how to build Android binary using Android NDK cross-compiler on Debian Linux.

We offer android-config and android-make scripts to make the build easier. To make these script work, NDK toolchain must be installed in the following way. First, let introduce ANDROID_HOME environment variable. We need to install toolchain under $ANDROID_HOME/toolchain. An user can freely choose the path for ANDROID_HOME. For example, to install toolchain under $ANDROID_HOME/toolchain, do this in the the directory where NDK is unpacked:

$ build/tools/ --platform=android-9 --install-dir=$ANDROID_HOME/toolchain

The platform level is not important here because we don't use Android specific C/C++ API.

The dependent libraries, such as OpenSSL and libevent should be built with the toolchain and installed under $ANDROID_HOME/usr/local. We recommend to build these libraries as static library to make the deployment easier. libxml2 support is currently disabled.

We use zlib which comes with Android NDK, so we don't have to build it by ourselves.

Before running android-config and android-make, ANDOIRD_HOME environment variable must be set to point to the correct path.

After android-config, run android-make to compile sources. android-make is just include path to cross compiler in PATH and run make. So if you include path to corss compiler by yourself, you can just run make to build spdylay and tools as usual.


The public API reference is available on online. Visit All public APIs are in spdylay/spdylay.h. All public API functions as well as the callback function typedefs are documented.

SPDY Client and Server Programs

The src directory contains SPDY client and server implementations using Spdylay library. These programs are intended to make sure that Spdylay API is acutally usable for real implementation and also for debugging purposes. Please note that OpenSSL with NPN support is required in order to build and run these programs. At the time of this writing, the OpenSSL 1.0.1 supports NPN.

Spdycat - SPDY client

The SPDY client is called spdycat. It is a dead simple downloader like wget/curl. It connects to SPDY server and gets resources given in the command-line:

$ src/spdycat -h
Usage: spdycat [-Oansv23] [-t <SECONDS>] [-w <WINDOW_BITS>] [--cert=<CERT>]
               [--key=<KEY>] [--no-tls] [-d <FILE>] [-m <N>] [-p <PROXY_HOST>]
               [-P <PROXY_PORT>] <URI>...

    -v, --verbose      Print debug information such as reception/
                       transmission of frames and name/value pairs.
    -n, --null-out     Discard downloaded data.
    -O, --remote-name  Save download data in the current directory.
                       The filename is dereived from URI. If URI
                       ends with '/', 'index.html' is used as a
                       filename. Not implemented yet.
    -2, --spdy2        Only use SPDY/2.
    -3, --spdy3        Only use SPDY/3.
    --spdy3-1          Only use SPDY/3.1.
    -t, --timeout=<N>  Timeout each request after <N> seconds.
    -w, --window-bits=<N>
                       Sets the initial window size to 2**<N>.
    -a, --get-assets   Download assets such as stylesheets, images
                       and script files linked from the downloaded
                       resource. Only links whose origins are the
                       same with the linking resource will be
    -s, --stat         Print statistics.
    -H, --header       Add a header to the requests.
    --cert=<CERT>      Use the specified client certificate file.
                       The file must be in PEM format.
    --key=<KEY>        Use the client private key file. The file
                       must be in PEM format.
    --no-tls           Disable SSL/TLS. Use -2, -3 or --spdy3-1 to
                       specify SPDY protocol version to use.
    -d, --data=<FILE>  Post FILE to server. If - is given, data
                       will be read from stdin.
    -m, --multiply=<N> Request each URI <N> times. By default, same
                       URI is not requested twice. This option
                       disables it too.
    -p, --proxy=<HOST> Use this host as a SPDY proxy
    -P, --proxy-port=<PORT>
                       Use this as the port of the SPDY proxy if
                       one is set
    --color            Force colored log output.

$ src/spdycat -nv
[  0.021] NPN select next protocol: the remote server offers:
          * spdy/4a4
          * spdy/3.1
          * spdy/3
          * http/1.1
          NPN selected the protocol: spdy/3.1
[  0.029] Handshake complete
[  0.029] recv SETTINGS frame <version=3, flags=0, length=20>
[  0.029] recv WINDOW_UPDATE frame <version=3, flags=0, length=8>
          (stream_id=0, delta_window_size=983040)
[  0.029] send SYN_STREAM frame <version=3, flags=1, length=221>
          (stream_id=1, assoc_stream_id=0, pri=3)
          :method: GET
          :path: /
          :scheme: https
          :version: HTTP/1.1
          accept: */*
          accept-encoding: gzip, deflate
          user-agent: spdylay/1.2.0-DEV
[  0.080] recv SYN_REPLY frame <version=3, flags=0, length=619>
          :status: 302 Found
          :version: HTTP/1.1
          alternate-protocol: 443:quic
          cache-control: private
          content-length: 262
          content-type: text/html; charset=UTF-8
          date: Tue, 19 Nov 2013 13:47:18 GMT
          server: gws
          x-frame-options: SAMEORIGIN
          x-xss-protection: 1; mode=block
[  0.080] recv DATA frame (stream_id=1, flags=1, length=262)
[  0.080] send GOAWAY frame <version=3, flags=0, length=8>

Spdyd - SPDY server

SPDY server is called spdyd and serves static files. It is single threaded and multiplexes connections using non-blocking socket. The static files are read using blocking I/O system call, read(2). It speaks SPDY/2 and SPDY/3:

$ src/spdyd --htdocs=/your/htdocs/ -v 3000 server.key server.crt
IPv4: listen on port 3000
IPv6: listen on port 3000
The negotiated next protocol: spdy/3.1
[id=1] [  1.296] send SETTINGS frame <version=3, flags=0, length=12>
[id=1] [  1.297] recv SYN_STREAM frame <version=3, flags=1, length=228>
          (stream_id=1, assoc_stream_id=0, pri=3)
          :host: localhost:3000
          :method: GET
          :path: /README
          :scheme: https
          :version: HTTP/1.1
          accept: */*
          accept-encoding: gzip, deflate
          user-agent: spdylay/1.2.0-DEV
[id=1] [  1.297] send SYN_REPLY frame <version=3, flags=0, length=116>
          :status: 200 OK
          :version: HTTP/1.1
          cache-control: max-age=3600
          content-length: 66
          date: Tue, 19 Nov 2013 14:35:24 GMT
          last-modified: Tue, 17 Jan 2012 15:39:01 GMT
          server: spdyd spdylay/1.2.0-DEV
[id=1] [  1.297] send DATA frame (stream_id=1, flags=0, length=66)
[id=1] [  1.297] send DATA frame (stream_id=1, flags=1, length=0)
[id=1] [  1.297] stream_id=1 closed
[id=1] [  1.297] recv GOAWAY frame <version=3, flags=0, length=8>
[id=1] [  1.297] closed

Currently, spdyd needs epoll or kqueue.

Shrpx - A reverse proxy for SPDY/HTTPS

For shrpx users who uses shrpx as SPDY proxy: Please consider migrating to nghttpx developed at nghttp2 project. nghttpx supports SPDY proxy too.

The shrpx is a multi-threaded reverse proxy for SPDY/HTTPS. It converts SPDY/HTTPS traffic to plain HTTP. It is initially developed as a reverse proxy, but now it has other operation modes such as a frontend forward proxy. For example, with --spdy-proxy (-s in shorthand) option, it can be used as secure SPDY proxy with a proxy (e.g., Squid) in the backend. With --cliet-proxy (-p) option, it acts like an ordinaly forward proxy but expects secure SPDY proxy in the backend. Thus it becomes an adapter to secure SPDY proxy for clients which does not support secure SPDY proxy. The another notable operation mode is --spdy-relay, which just relays SPDY/HTTPS traffic to the backend in SPDY. The following table summarizes the operation modes.

Mode option Frontend Backend Note
default SPDY/HTTPS HTTP Reverse proxy
--spdy-relay SPDY/HTTPS SPDY  
--client HTTP SPDY  
--client-proxy HTTP SPDY Forward proxy

The shrpx supports configuration file. See --conf option and sample configuration file shrpx.conf.sample.

We briefly describe the architecture of shrpx here. It has a dedicated thread which listens on server sockets. When it accepted the incoming connection, it passes the file descriptor of the incoming connection to one of the worker thread. Each worker thread has its own event loop and can handle many connections using non-blocking I/O. The number of worker thread can be specified using the command-line option. The libevent is used to handle low-level network I/O.

Here is the command-line options:

$ src/shrpx -h
Usage: shrpx [-Dh] [-s|--client|-p] [-b <HOST,PORT>]
             [-f <HOST,PORT>] [-n <CORES>] [-c <NUM>] [-L <LEVEL>]
             [OPTIONS...] [<PRIVATE_KEY> <CERT>]

A reverse proxy for SPDY/HTTPS.

Positional arguments:
    <PRIVATE_KEY>      Set path to server's private key. Required
                       unless either -p or --client is specified.
    <CERT>             Set path to server's certificate. Required
                       unless either -p or --client is specified.


    -b, --backend=<HOST,PORT>
                       Set backend host and port.
                       Default: ',80'
    -f, --frontend=<HOST,PORT>
                       Set frontend host and port.
                       Default: ',3000'
    --backlog=<NUM>    Set listen backlog size.
                       Default: 256
    --backend-ipv4     Resolve backend hostname to IPv4 address
    --backend-ipv6     Resolve backend hostname to IPv6 address

    -n, --workers=<CORES>
                       Set the number of worker threads.
                       Default: 1
    --read-rate=<RATE> Set maximum average read rate on frontend
                       connection. Setting 0 to this option means
                       read rate is unlimited.
                       Default: 1048576
                       Set maximum read burst size on frontend
                       connection. Setting 0 to this option means
                       read burst size is unlimited.
                       Default: 4194304
                       Set maximum average write rate on frontend
                       connection. Setting 0 to this option means
                       write rate is unlimited.
                       Default: 0
                       Set maximum write burst size on frontend
                       connection. Setting 0 to this option means
                       write burst size is unlimited.
                       Default: 0

                       Specify read timeout for SPDY frontend
                       connection. Default: 180
                       Specify read timeout for non-SPDY frontend
                       connection. Default: 180
                       Specify write timeout for both SPDY and
                       non-SPDY frontends.
                       connection. Default: 60
                       Specify read timeout for backend connection.
                       Default: 900
                       Specify write timeout for backend
                       connection. Default: 60
                       Specify keep-alive timeout for backend
                       connection. Default: 60
                       Specify proxy URI in the form
                       http://[<USER>:<PASS>@]<PROXY>:<PORT>. If
                       a proxy requires authentication, specify
                       <USER> and <PASS>. Note that they must be
                       properly percent-encoded. This proxy is used
                       when the backend connection is SPDY. First,
                       make a CONNECT request to the proxy and
                       it connects to the backend on behalf of
                       shrpx. This forms tunnel. After that, shrpx
                       performs SSL/TLS handshake with the
                       downstream through the tunnel. The timeouts
                       when connecting and making CONNECT request
                       can be specified by --backend-read-timeout
                       and --backend-write-timeout options.

    --ciphers=<SUITE>  Set allowed cipher list. The format of the
                       string is described in OpenSSL ciphers(1).
                       If this option is used, --honor-cipher-order
                       is implicitly enabled.
                       Honor server cipher order, giving the
                       ability to mitigate BEAST attacks.
    -k, --insecure     When used with -p or --client, don't verify
                       backend server's certificate.
    --cacert=<PATH>    When used with -p or --client, set path to
                       trusted CA certificate file.
                       The file must be in PEM format. It can
                       contain multiple certificates. If the
                       linked OpenSSL is configured to load system
                       wide certificates, they are loaded
                       at startup regardless of this option.
                       Path to file that contains password for the
                       server's private key. If none is given and
                       the private key is password protected it'll
                       be requested interactively.
                       Specify additional certificate and private
                       key file. Shrpx will choose certificates
                       based on the hostname indicated by client
                       using TLS SNI extension. This option can be
                       used multiple times.
                       Explicitly set the content of the TLS SNI
                       extension.  This will default to the backend
                       HOST name.
                       Path to file that contains DH parameters in
                       PEM format. Without this option, DHE cipher
                       suites are not available.
    --verify-client    Require and verify client certificate.
                       Path to file that contains CA certificates
                       to verify client certificate.
                       The file must be in PEM format. It can
                       contain multiple certificates.
                       Path to file that contains client private
                       key used in backend client authentication.
                       Path to file that contains client
                       certificate used in backend client
                       Comma delimited list of SSL/TLS protocol to
                       be enabled.
                       The following protocols are available:
                       TLSv1.2, TLSv1.1, TLSv1.0, SSLv3
                       The name matching is done in case-insensitive
                       The parameter must be delimited by a single
                       comma only and any white spaces are treated
                       as a part of protocol string.
                       Default: TLSv1.2,TLSv1.1,TLSv1.0

    -c, --spdy-max-concurrent-streams=<NUM>
                       Set the maximum number of the concurrent
                       streams in one SPDY session.
                       Default: 100
                       Sets the per-stream initial window size of
                       SPDY frontend connection to 2**<N>.
                       Default: 16
                       Sets the per-connection window size of SPDY
                       frontend connection to 2**<N>.
                       Default: 16
                       Disable SSL/TLS on frontend SPDY
                       connections. SPDY protocol must be specified
                       using --frontend-spdy-proto. This option
                       also disables frontend HTTP/1.1.
                       Specify SPDY protocol used in frontend
                       connection if --frontend-spdy-no-tls is
                       used. Default: spdy/3.1
                       Sets the per-stream initial window size of
                       SPDY backend connection to 2**<N>.
                       Default: 16
                       Sets the per-connection window size of SPDY
                       backend connection to 2**<N>.
                       Default: 16
                       Disable SSL/TLS on backend SPDY connections.
                       SPDY protocol must be specified using
                       Specify SPDY protocol used in backend
                       connection if --backend-spdy-no-tls is used.
                       Default: spdy/3.1

    -s, --spdy-proxy   Enable secure SPDY proxy mode.
    --spdy-bridge      Communicate with the backend in SPDY. Thus
                       the incoming SPDY/HTTPS connections are
                       converted to SPDY connection and relayed to
                       the backend. See --backend-http-proxy-uri
                       option if you are behind the proxy and want
                       to connect to the outside SPDY proxy.
    --client           Instead of accepting SPDY/HTTPS connection,
                       accept HTTP connection and communicate with
                       backend server in SPDY. To use shrpx as
                       a forward proxy, use -p option instead.
    -p, --client-proxy Like --client option, but it also requires
                       the request path from frontend must be
                       an absolute URI, suitable for use as a
                       forward proxy.

    -L, --log-level=<LEVEL>
                       Set the severity level of log output.
                       INFO, WARNING, ERROR and FATAL.
                       Default: WARNING
    --accesslog        Print simple accesslog to stderr.
    --syslog           Send log messages to syslog.
                       Set syslog facility.
                       Default: daemon

                       Append X-Forwarded-For header field to the
                       downstream request.
    --no-via           Don't append to Via header field. If Via
                       header field is received, it is left
    -D, --daemon       Run in a background. If -D is used, the
                       current working directory is changed to '/'.
    --pid-file=<PATH>  Set path to save PID of this program.
    --user=<USER>      Run this program as USER. This option is
                       intended to be used to drop root privileges.
    --conf=<PATH>      Load configuration from PATH.
                       Default: /etc/shrpx/shrpx.conf
    -v, --version      Print version and exit.
    -h, --help         Print this help and exit.

For those of you who are curious, shrpx is an abbreviation of "Spdy/https to Http Reverse ProXy".

Without any of -s, --spdy-bridge, -p and --client options, shrpx works as reverse proxy to the backend server:

Client <-- (SPDY, HTTPS) --> Shrpx <-- (HTTP) --> Web Server
                        [reverse proxy]

With -s option, it works as secure SPDY proxy:

Client <-- (SPDY, HTTPS) --> Shrpx <-- (HTTP) --> Proxy
                          [SPDY proxy]            (e.g., Squid)

The Client in the above is needs to be configured to use shrpx as secure SPDY proxy.

At the time of this writing, Chrome is the only browser which supports secure SPDY proxy. The one way to configure Chrome to use secure SPDY proxy is create proxy.pac script like this:

function FindProxyForURL(url, host) {

SERVERADDR and PORT is the hostname/address and port of the machine shrpx is running. Please note that Chrome requires valid certificate for secure SPDY proxy.

Then run chrome with the following arguments:

$ google-chrome --proxy-pac-url=file:///path/to/proxy.pac --use-npn


At the time of this writing, Chrome 24 limits the maximum concurrent connections to the proxy to 32. And due to the limitation of socket pool handling in Chrome, it is quickly filled up if SPDY proxy is used and many SPDY sessions are established. If it reaches the limit, the new connections are simply blocked until existing connections are timed out. (See Chrome Issue 92244). The workaround is make the number of maximum connections high, say, 99, which is the highest. To do this, you need to change so called Policy setup. See Policy Templates for details how to change Policy setup on the platform you use. The Policy name we are looking for is MaxConnectionsPerProxy For example, if you are using Linux, follow the instruction described in Linux Quick Start and create /etc/opt/chrome/policies/managed/test_policy.json file with the following content and restart Chrome:

    "MaxConnectionsPerProxy" :99

With --spdy-bridge, it accepts SPDY/HTTPS connections and communicates with backend in SPDY:

Client <-- (SPDY, HTTPS) --> Shrpx <-- (SPDY) --> Web or SPDY Proxy etc
                          [SPDY bridge]           (e.g., shrpx -s)

With -p option, it works as forward proxy and expects that the backend is secure SPDY proxy:

Client <-- (HTTP) --> Shrpx <-- (SPDY) --> Secure SPDY Proxy
                 [forward proxy]         (e.g., shrpx -s or node-spdyproxy)

The Client is needs to be configured to use shrpx as forward proxy.

In this configuration, clients which do not support secure SPDY proxy can use secure SPDY proxy through shrpx. Putting shrpx in the same box or same network with the clients, this configuration can bring the benefits of secure SPDY proxy to those clients. Since the maximum number of connections per server still applies in proxy connection, the performance gain is not obvious. For example, if the maximum number of connections per server is 6, after sending 6 requests to the proxy, client blocks further requests, which kills performance which might be gained in SPDY connection. For clients which can tweak these values (e.g., network.http.max-connections-per-server in Firefox), increasing them may improve the performance.

With --client option, it works as reverse proxy and expects that the backend is SPDY-enabled Web server:

Client <-- (HTTP) --> Shrpx <-- (SPDY) --> Web Server
                 [reverse proxy]

For the operation modes which talk to the backend in SPDY, the backend connections can be tunneled though HTTP proxy. The proxy is specified using --backend-http-proxy-uri option. The following figure illustrates the example of --spdy-bridge and --backend-http-proxy-uri option to talk to the outside SPDY proxy through HTTP proxy:

Client <-- (SPDY, HTTPS) --> Shrpx <-- (SPDY) --
                         [SPDY bridge]

        --===================---> SPDY Proxy
          (HTTP proxy tunnel)     (e.g., shrpx -s)


The examples directory contains a simple SPDY client implementation in C.

Python-Spdylay - Python Wrapper

The library comes with Python wrapper python-spdylay. See python directory.

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