getdns

Overview of getdns

• GitHub: https://github.com/getdnsapi/getdns

getdns is an implementation of a modern asynchronous DNS API; the specification was originally edited by Paul Hoffman. It is intended to make all types of DNS information easily available to application developers and non-DNS experts.

Why you might want getdns

Traditional access to DNS data from applications has several limitations:

• APIs require applications to have considerable sophistication about DNS data and data types

• Some kinds of data about the response (notably, the resource record set time to live) is not exposed via any API, so applications need to process raw protocol responses to get such data

• APIs are often blocking, meaning asynchronous access is not possible without some work

• Sophisticated uses of the DNS (things like IDNA and DNSSEC validation) require considerable application work, possibly by application developers with little experience with the vagaries of DNS.

getdns also provides a experimental DNS Privacy enabled client called 'stubby' - see below for more details.

Motivation for providing the API

The developers are of the opinion that DNSSEC offers a unique global infrastructure for establishing and enhancing cryptographic trust relations. With the development of this API we intend to offer application developers a modern and flexible interface that enables end-to-end trust in the DNS architecture, and which will inspire application developers to implement innovative security solutions in their applications.

License

This implementation is licensed under the New BSD License (BSD-new).

Obtaining and getting started with getdns

The project home page at getdnsapi.net provides documentation, binary downloads, and news regarding the getdns API implementation. This file captures the goals and direction of the project and the current state of the implementation.

If you are just getting started with the library take a look at the section below that describes building and handling external dependencies for the library. Once it is built you should take a look at src/examples to see how the library is used.

Download

Download the sources from our github repo or from getdnsapi.net and verify the download using the checksums (SHA1 or MD5) or using gpg to verify the signature. Our keys are available from the pgp keyservers

• willem@nlnetlabs.nl, key id E5F8F8212F77A498

Releases

Release numbering follows the Semantic Versioning approach. The code is currently under active development.

The following requirements were met as conditions for the present release:

• code compiles cleanly on at least the primary target platforms: OSX, RHEL/CentOS Linux, FreeBSD
• examples must compile and run cleanly
• there must be clear documentation of supported and unsupported elements of the API

Building and External Dependencies

External dependencies are linked outside the getdns API build tree (we rely on configure to find them). We would like to keep the dependency tree short. Please refer to section for building on Windows for separate dependency and build instructions for that platform.

• libunbound from NLnet Labs version 1.4.16 or later.
• libidn from the FSF version 1. (Note that the libidn version means the conversions between A-labels and U-labels may permit conversion of formally invalid labels under IDNA2008.)
• libssl and libcrypto from the OpenSSL Project version 0.9.7 or later. (Note: version 1.0.1 or later is required for TLS support, version 1.0.2 or later is required for TLS hostname authentication)
• Doxygen is used to generate documentation; while this is not technically necessary for the build it makes things a lot more pleasant.

If you are installing from packages, you have to install the library and also the library-devel (or -dev) for your package management system to get the the necessary compile time files. If you checked out from git you need to copy the libtool helper scripts and rebuild configure thus:

# libtoolize -ci (use glibtoolize for OS X, libtool is installed as glibtool to avoid name conflict on OS X)
# autoreconf -fi

If you want to make use of the configuration files that utilise a JSON-like format, you must do

# git submodule update --init

before building.

As well as building the getdns library 2 other tools are installed by default by the above process:

• getdns_query: a command line test script wrapper for getdns
• stubby: a experimental DNS Privacy enabled client

Note: If you only want to build stubby, then use the --enable-stub-only and --without-libidn options when running 'configure'.

Minimizing dependencies

• getdns can be configured for stub resolution mode only with the --enable-stub-only option to configure. This removes the dependency on libunbound.
• Currently getdns only offers two helper functions to deal with IDN: getdns_convert_ulabel_to_alabel and getdns_convert_alabel_to_ulabel. If you do not need these functions, getdns can be configured to compile without them with the --without-libidn option to configure.
• When both --enable-stub-only and --without-libidn options are used, getdns has only one dependency left, which is OpenSSL.

Extensions and Event loop dependencies

The implementation works with a variety of event loops, each built as a separate shared library. See the wiki for more details.

• libevent. Note: the examples require this and should work with either libevent 1.x or 2.x. 2.x is preferred.
• libuv
• libev

Stubby

• Stubby is an experimental implementation of a DNS Privacy enabled stub resolver. It is currently suitable for advanced/technical users - all feedback is welcome! Also see dnsprivacy.org for more information on DNS Privacy and stubby.
• By default stubby will attempt to use 'Opportunistic' Privacy for DNS queries.
• A sample configuration file is available in the source code (src/tools/stubby.conf) which uses 'Strict' Privacy and some of the available test DNS Privacy servers to resolve queries. Note these servers are test servers that offer no service guarantees. The location of a configuration file can be specified with the '-C' flag
• RECOMMENDED: Minimal logging output from Stubby is available (e.g. which servers are used and connection level statistics) by also using the '--enable-debug-daemon' flag when running 'configure'.

To use stubby

• Start stubby from the command line
• Test it by doing, for example, 'dig @127.0.0.1 www.example.com'
• Alter the default DNS resolvers on your system to point at localhost (127.0.0.1, ::1)

Regression Tests

A suite of regression tests are included with the library, if you make changes or just want to sanity check things on your system take a look at src/test. You will need to install libcheck. The check library is also available from many of the package repositories for the more popular operating systems.

The regression tests do not work with --enable-stub-only.

DNSSEC dependencies

For the library to be DNSSEC capable, it needs to know the root trust anchor. The library will try to load the root trust anchor from /etc/unbound/getdns-root.key by default. This file is expected to have one or more DS or DNSKEY resource records in presentation (i.e. zone file) format. Note that this is different than the format of BIND.keys.

The best way to setup or update the root trust anchor is by using unbound-anchor. To setup the library with the root trust anchor at the default location, execute the following steps as root:

# mkdir -p /etc/unbound
# unbound-anchor -a /etc/unbound/getdns-root.key

Support

Mailing lists

We have a getdns users list for this implementation.

The getdns-api mailing list is a good place to engage in discussions regarding the design of the API.

Tickets and Bug Reports

Tickets and bug reports should be reported via the GitHub issues list.

Features of this release

Goals

The goals of this implementation of the getdns API are:

• Provide an open source implementation, in C, of the formally described getdns API by getdns API team at https://getdnsapi.net/spec.html
• Support FreeBSD, OSX, Linux (CentOS/RHEL, Ubuntu) via functional "configure" script
• Support Windows 8.1
• Include examples and tests as part of the build
• Document code using doxygen
• Leverage github as much as possible for project coordination
• Follow the BSD coding style/standards ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-current/src/share/misc/style

Non-goals (things we will not be doing at least initially) include:

• implementation of the traditional DNS related routines (gethostbyname, etc.)

Official and Additional API

Note that this implementation offers additional functionality to supplement that in the official getdns API. Some additions are convenient utility functions but other functionality is experimental prior to be being recommended for inclusion in the official API. The 'Modules' page in the doxygen documentation provides a guide to both the official API and the additional functionality.

Language Bindings

In parallel, the team is actively developing bindings for various languages. For more information, visit the wiki.

Unsupported getDNS Features

The following API calls are documented in getDNS but not supported by the implementation at this time:

• Disabling following of CNAMEs with getdns_context_set_follow_redirects()
• Detecting changes to resolv.conf and hosts
• MDNS, NIS and NetBIOS namespaces (only DNS and LOCALFILES are supported)

Minor omissions

The following minor implementation omissions are noted:

Recursive mode does not support:

• TLS as a transport
• Non-zero connection idle timeouts or query pipelining

Stub mode does not support:

• Non zero idle timeouts for synchronous calls
• Limit on number of outstanding queries

Known Issues

• The synchronous lookup functions will not work when new file descriptors needed for the lookup will be larger than FD_SETSIZE. This is because the synchronous functions use a "default" event loop under the hood which is based on select() and thus inherits the limits that select() has.

  If you need only slightly more file descriptors, it is possible to enlarge the FD_SETSIZE with the --with-fd-setsize=size flag to configure.

  To resolve, use the asynchronous functions with an event loop extension for libevent, libev or libuv. Note that the asynchronous functions will have the same problem when used in combination with getdns_context_run(), which also uses the default event loop.

Supported Platforms

The primary platforms targeted are Linux and FreeBSD, other platform are supported as we get time. The names listed here are intended to help ensure that we catch platform specific breakage, not to limit the work that folks are doing.

• RHEL/CentOS 6.4
• OSX 10.8
• Ubuntu 14.04
• Microsoft Windows 8.1

We intend to add Android and other platforms to future releases as we have time to port it.

Platform Specific Build Reports

FreeBSD

If you're using FreeBSD, you may install getdns via the ports tree by running: cd /usr/ports/dns/getdns && make install clean

If you are using FreeBSD 10 getdns can be intalled via 'pkg install getdns'.

CentOS and RHEL 6.5

We rely on the most excellent package manager fpm to build the linux packages, which means that the packaging platform requires ruby 2.1.0. There are other ways to build the packages; this is simply the one we chose to use.

# cat /etc/redhat-release
CentOS release 6.5 (Final)
# uname -a
Linux host-10-1-1-6 2.6.32-358.el6.x86_64 #1 SMP Fri Feb 22 00:31:26 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
# cd getdns-0.2.0rc1
# ./configure --prefix=/home/deploy/build
# make; make install
# cd /home/deploy/build
# mv lib lib64
# . /usr/local/rvm/config/alias
# fpm -x "*.la" -a native -s dir -t rpm -n getdns -v 0.2.0rc1 -d "unbound" -d "libevent" -d "libidn" --prefix /usr --vendor "Verisign Inc., NLnet Labs" --license "BSD New" --url "https://getdnsapi.net" --description "Modern asynchronous API to the DNS" .

OSX

# sw_vers
ProductName:	Mac OS X
ProductVersion:	10.8.5
BuildVersion:	12F45

Built using PackageMaker, libevent2.

# ./configure --with-libevent --prefix=$HOME/getdnsosx/export
# make
# make install

edit/fix hardcoded paths in lib/*.la to reference /usr/local

update getdns.pmdoc to match release info

build package using PackageMaker

create dmg

A self-compiled version of OpenSSL or the version installed via Homebrew is required.
Note: If using a self-compiled version, manual configuration of certificates into /usr/local/etc/openssl/certs is required for TLS authentication to work.

Homebrew

If you're using Homebrew, you may run brew install getdns. By default, this will only build the core library without any 3rd party event loop support.

To install the event loop integration libraries that enable support for libevent, libuv, and libev, run: brew install getdns --with-libevent --with-libuv --with-libev. All switches are optional.

Note that in order to compile the examples, the --with-libevent switch is required.

As of the 0.2.0 release, when installing via Homebrew, the trust anchor is expected to be located at $(brew --prefix)/etc/getdns-root.key. Additionally, the OpenSSL library installed by Homebrew is linked against. Note that the Homebrew OpenSSL installation clones the Keychain certificates to the default OpenSSL location so TLS certificate authentication should work out of the box.

Microsoft Windows 8.1

The build has been tested using the following: 32 bit only Mingw: Mingw(3.21.0) and Msys 1.0 on Windows 8.1 32 bit build on a 64 bit Mingw [Download latest from: http://mingw-w64.org/doku.php/download/mingw-builds and http://msys2.github.io/]. IMPORTANT: Install tested ONLY on the "x86_64" for 64-bit installer of msys2.

Dependencies

The following dependencies are

• openssl-1.0.2j
• libidn

Instructions to build openssl-1.0.2j: Open the mingw32_shell.bat from msys2 in order to build:

If necessary, install the following using pacman:

pacman -S pkg-config  libtool automake
pacman -S autoconf automake-wrapper

tar -xvf openssl-1.0.2j.tar 
cd openssl-1.0.2j/
./Configure --prefix=${LOCALDESTDIR} --openssldir=${LOCALDESTDIR}/etc/ssl --libdir=lib shared zlib-dynamic mingw
make
make install

To configure:

./configure --enable-stub-only --with-trust-anchor="c:\\\MinGW\\\msys\\\1.0\\\etc\\\unbound\\\getdns-root.key" --with-ssl=<location of openssl from above> --with-getdns_query

The trust anchor is also installed by unbound on c:\program Files (X86)\unbound\root.key and can be referenced from there or anywhere else that the user chooses to configure it.

After configuring, do a make and make install to build getdns for Windows.

Example test queries:

./getdns_query.exe -s gmadkat.com A @64.6.64.6  +return_call_reporting (UDP)
./getdns_query.exe -s gmadkat.com A @64.6.64.6 -T  +return_call_reporting (TCP)
./getdns_query.exe -s gmadkat.com A -l L @185.49.141.37  +return_call_reporting (TLS without authentication)
./getdns_query.exe -s www.huque.com A +dnssec_return_status +return_call_reporting (DNSSEC)

Contributors

• Claus Assman
• Theogene Bucuti
• Andrew Cathrow, Verisign Labs
• Neil Cook
• Saúl Ibarra Corretgé
• Craig Despeaux, Verisign, Inc.
• John Dickinson, Sinodun
• Sara Dickinson, Sinodun
• Robert Edmonds
• Angelique Finan, Verisign, Inc.
• Simson Garfinkel
• Daniel Kahn Gillmor
• Neel Goyal, Verisign, Inc.
• Bryan Graham, Verisign, Inc.
• Robert Groenenberg
• Paul Hoffman
• Scott Hollenbeck, Verising, Inc.
• Shumon Huque, Verisign Labs
• Jelte Janssen
• Guillem Jover
• Shane Kerr
• Anthony Kirby
• Olaf Kolkman, NLnet Labs
• Sanjay Mahurpawar, Verisign, Inc.
• Allison Mankin, Verisign, Inc. - Verisign Labs.
• Sai Mogali, Verisign, Inc.
• Linus Nordberg
• Benno Overeinder, NLnet Labs
• Joel Purra
• Tom Pusateri
• Prithvi Ranganath, Verisign, Inc.
• Rushi Shah, Verisign, Inc.
• Vinay Soni, Verisign, Inc.
• Melinda Shore, No Mountain Software LLC
• Bob Steagall, Verisign, Inc.
• Andrew Sullivan
• Ondřej Surý
• Willem Toorop, NLnet Labs
• Gowri Visweswaran, Verisign Labs
• Wouter Wijngaards, NLnet Labs
• Glen Wiley, Verisign, Inc.
• Paul Wouters

Acknowledgements

The development team explicitly acknowledges Paul Hoffman for his initiative and efforts to develop a consensus based DNS API. We would like to thank the participants of the mailing list for their contributions.