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libre README

libre is a Generic library for real-time communications with async IO support. Copyright (C) 2010 - 2019

Build Status


  • SIP Stack (RFC 3261)
  • SDP
  • RTP and RTCP
  • SRTP and SRTCP (Secure RTP)
  • DNS-Client
  • STUN/TURN/ICE stack
  • BFCP
  • HTTP-stack with client/server
  • Websockets
  • Jitter-buffer
  • Async I/O (poll, epoll, select, kqueue)
  • UDP/TCP/TLS/DTLS transport
  • JSON parser
  • Real Time Messaging Protocol (RTMP)


libre is using GNU makefiles. Make and OpenSSL development headers must be installed before building.

Build with debug enabled

$ make
$ sudo make install
$ sudo ldconfig

Build with release

$ make RELEASE=1
$ sudo make RELEASE=1 install
$ sudo ldconfig

Build with clang compiler

$ make CC=clang
$ sudo make CC=clang install
$ sudo ldconfig


The online documentation generated with doxygen is available in the main website


Coding examples are available from the redemo project


The libre project is using the BSD license.


Patches can sent via Github Pull-Requests or to the RE devel mailing-list. Currently we only accept small patches. Please send private feedback to libre [at]

Design goals

  • Portable POSIX source code (ANSI C89 and ISO C99 standard)
  • Robust, fast, low memory footprint
  • RFC compliance
  • IPv4 and IPv6 support


Name Status Description
aes unstable AES (Advanced Encryption Standard)
base64 testing Base-64 encoding/decoding functions
bfcp unstable The Binary Floor Control Protocol (BFCP)
conf testing Configuration file parser
crc32 testing 32-bit CRC defined in ITU V.42
dbg testing Debug printing
dns stable DNS resolving (NAPTR, SRV, A)
fmt testing Formatted printing and regular expression
hash testing Hashmap table
hmac testing HMAC: Keyed-Hashing for Message Authentication
http unstable HTTP parser (RFC 2616)
httpauth testing HTTP-based Authentication (RFC 2617)
ice unstable Interactive Connectivity Establishment (ICE)
jbuf testing Jitter buffer
json unstable JavaScript Object Notation (JSON)
list stable Sortable doubly-linked list handling
lock testing Resource locking functions
main testing Main poll loop
mbuf stable Linear memory buffers
md5 stable The MD5 Message-Digest Algorithm (RFC 1321)
mem stable Memory referencing
mod testing Run-time module loading
mqueue testing Thread-safe message queue
msg unstable Generic message component library
natbd unstable NAT Behavior Discovery using STUN
net testing Networking routines
odict unstable Ordered Dictionary
rtmp unstable Real Time Messaging Protocol
rtp testing Real-time Transport Protocol
sa stable Socket Address functions
sdp testing Session Description Protocol
sha testing Secure Hash Standard, NIST, FIPS PUB 180-1
sip stable Core SIP library
sipevent testing SIP Event framework
sipreg stable SIP register client
sipsess stable SIP Sessions
srtp unstable Secure Real-time Transport Protocol (SRTP)
stun stable Session Traversal Utilities for NAT (STUN)
sys testing System information
tcp testing TCP transport
telev testing Telephony Events (RFC 4733)
tls unstable Transport Layer Security
tmr stable Timer handling
turn stable Obtaining Relay Addresses from STUN (TURN)
udp testing UDP transport
uri testing Generic URI library
websock unstable WebSocket Client and Server


  • stable - code complete; stable code and stable API
  • testing - code complete, but API might change
  • unstable - code complete but not completely tested
  • development - code is under development


  • RFC 1321 - The MD5 Message-Digest Algorithm
  • RFC 1886 - DNS Extensions to support IP version 6
  • RFC 2032 - RTP Payload Format for H.261 Video Streams
  • RFC 2616 - Hypertext Transfer Protocol -- HTTP/1.1
  • RFC 2617 - HTTP Authentication: Basic and Digest Access Authentication
  • RFC 2782 - A DNS RR for Specifying the Location of Services (DNS SRV)
  • RFC 2915 - The Naming Authority Pointer (NAPTR) DNS Resource Record
  • RFC 3261 - SIP: Session Initiation Protocol
  • RFC 3263 - Locating SIP Servers
  • RFC 3264 - An Offer/Answer Model with SDP
  • RFC 3265 - SIP-Specific Event Notification
  • RFC 3327 - SIP Extension Header Field for Registering Non-Adjacent Contacts
  • RFC 3428 - SIP Extension for Instant Messaging
  • RFC 3489 - STUN - Simple Traversal of UDP Through NATs
  • RFC 3515 - The SIP Refer Method
  • RFC 3550 - RTP: A Transport Protocol for Real-Time Applications
  • RFC 3551 - RTP Profile for Audio and Video Conferences with Minimal Control
  • RFC 3555 - MIME Type Registration of RTP Payload Formats
  • RFC 3556 - SDP Bandwidth Modifiers for RTCP Bandwidth
  • RFC 3581 - An Extension to SIP for Symmetric Response Routing
  • RFC 3605 - RTCP attribute in SDP
  • RFC 3711 - The Secure Real-time Transport Protocol (SRTP)
  • RFC 3969 - The IANA URI Parameter Registry for SIP
  • RFC 3994 - Indication of Message Composition for Instant Messaging
  • RFC 4346 - The TLS Protocol Version 1.1
  • RFC 4566 - SDP: Session Description Protocol
  • RFC 4582 - The Binary Floor Control Protocol (BFCP)
  • RFC 4582bis - The Binary Floor Control Protocol (BFCP)
  • RFC 4585 - Extended RTP Profile for RTCP-Based Feedback
  • RFC 4733 - RTP Payload for DTMF Digits, Telephony Tones, and Teleph. Signals
  • RFC 4961 - Symmetric RTP / RTP Control Protocol (RTCP)
  • RFC 5118 - SIP Torture Test Messages for IPv6
  • RFC 5245 - Interactive Connectivity Establishment (ICE)
  • RFC 5389 - Session Traversal Utilities for NAT (STUN)
  • RFC 5626 - Managing Client-Initiated Connections in SIP
  • RFC 5761 - Multiplexing RTP Data and Control Packets on a Single Port
  • RFC 5766 - Traversal Using Relays around NAT (TURN)
  • RFC 5768 - Indicating Support for ICE in SIP
  • RFC 5769 - Test vectors for STUN
  • RFC 5780 - NAT Behaviour Discovery Using STUN
  • RFC 6026 - Correct Transaction Handling for 2xx Resp. to SIP INVITE Requests
  • RFC 6156 - TURN Extension for IPv6
  • RFC 6188 - The Use of AES-192 and AES-256 in Secure RTP
  • RFC 6455 - The WebSocket Protocol
  • RFC 7159 - JavaScript Object Notation (JSON)
  • RFC 7350 - DTLS as Transport for STUN
  • RFC 7714 - AES-GCM Authenticated Encryption in SRTP

Supported platforms

  • Linux
  • FreeBSD
  • OpenBSD
  • NetBSD
  • Solaris 11
  • Windows
  • Apple Mac OS X and iOS
  • Android (5.0 or later)

Supported versions of C Standard library

  • Android bionic
  • BSD libc
  • GNU C Library (glibc)
  • Windows C Run-Time Libraries (CRT)
  • uClibc

Supported compilers:

  • gcc 3.x
  • gcc 4.x
  • gcc 5.x
  • gcc 6.x
  • ms vc2003 compiler
  • clang

Supported versions of OpenSSL

  • OpenSSL version 1.0.1 (Not supported)
  • OpenSSL version 1.0.2
  • OpenSSL version 1.1.0
  • OpenSSL version 1.1.1
  • LibreSSL version 2.x

Coding guidelines

  • Use enum for constants where appropriate
  • Use const as much as possible (where appropriate)
  • Use C99 data types (intN_t, uintN_t, bool)
  • Hide data-types in .c files where possible (use struct foo)
  • Avoid malloc/free, use mem_alloc/mem_deref instead
  • CVS/svn/git tags are NOT allowed in the code!
  • Avoid bit-fields in structs which are not portable
  • Use dummy handlers for timing-critical callbacks
  • return err, return alloced objects as pointer-pointers
  • in allocating functions, first arg is always double pointer
  • Use POSIX error-codes; EINVAL for invalid args, EBADMSG for parse errors and EPROTO for protocol errors

Transport protocols

BFCP - yes - -
DNS yes yes - -
HTTP yes n/a yes n/a
ICE - yes - -
RTP - yes - -
RTCP - yes - -
RTMP yes - yes -
SIP yes yes yes -
STUN yes yes yes yes
TURN yes yes yes yes
WEBSOCK yes n/a yes n/a