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.
* 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
* 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.
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.
Note that this implementation offers additional functionality to supplement that in the [official getdns API](https://getdnsapi.net/documentation/spec/). Some additions are convenient utility functions but other functionality is experimental prior to be being recommended for inclusion in the official API. The [Doxygen documentation](https://getdnsapi.net/doxygen/modules.html) provides the details of the full API for this implementation.
The project home page at [getdnsapi.net](https://getdnsapi.net) provides documentation, binary downloads, and news regarding the getdns API implementation. This README 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.
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.
External dependencies are linked outside the getdns API build tree (we rely on CMake to find them). We would like to keep the dependency tree short, see [Minimising Dependancies](#minimizing-dependancies) for more details.
* [libssl and libcrypto from the OpenSSL Project](https://www.openssl.org/) version 1.0.2 or later. Using OpenSSL 1.1 is recommended due to TSL 1.3 support.
Required for all builds that include recursive functionality:
* [libunbound from NLnet Labs](https://unbound.net/) version 1.5.9 or later. (Note: linking to libunbound is not yet supported on Windows, see [Windows 10](#microsoft-windows-10))
* [Doxygen](http://www.doxygen.nl) is used to generate documentation; while this is not technically necessary for the build it makes things a lot more pleasant.
If you are unfamiliar with CMake, see our [CMake Quick Start](https://getdnsapi.net/quick-start/cmake-quick-start/) for how to use CMake options to customise the getdns build.
* getdns_query: a command line test script wrapper for getdns. This can be used to quickly check the functionality of the library, see (#using-getdnsquery)
Additionally `Stubby` a DNS Privacy enabled client can also be built and installed by using the `BUILD_STUBBY` option when running `cmake`, see [Stubby](#stubby).
* 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 by setting the`USE_LIBIDN2` option to `cmake` to OFF.
* When `ENABLE_STUB_ONLY` is ON, and `USE_LIBIDN2` is OFF, getdns has only one dependency left, which is OpenSSL.
The implementation works with a variety of event loops, each built as a separate shared library. See [this Doxygen page](https://getdnsapi.net/doxygen/group__eventloops.html) and [this man page](https://getdnsapi.net/documentation/manpages/#ASYNCHRONOUS USE) for more details.
Example test queries using `getdns_query` (pointed at Google Public DNS) and requesting the `call_reporting` extension which provides information on the transport and query time:
getdns_query -s example.com A @8.8.8.8 +return_call_reporting (UDP)
getdns_query -s example.com A @8.8.8.8 -T +return_call_reporting (TCP)
getdns_query -s example.com A @8.8.8.8 -L +return_call_reporting (TLS without authentication)
getdns_query -s getdnsapi.net A +dnssec_return_status +return_call_reporting (DNSSEC)
* Stubby is an implementation of a DNS Privacy enabled stub resolver that encrypts DNS queries using TLS. It is currently suitable for advanced/technical users - all feedback is welcome!
A project to allow user selection of either OpenSSL or GnuTLS is currently a work in progress. At present a user may select to use GnuTLS for the majority of the supported functionality, however, OpenSSL is still required for some cryptographic functions.
to install [libcheck](https://libcheck.github.io/check/). The check library is also available from many of the package repositories for the more popular operating systems.
When the root trust anchor is not installed in the default location and a DNSSEC query is done, getdns will try to use the trust anchors published here: http://data.iana.org/root-anchors/root-anchors.xml .
It will validate these anchors with the ICANN Certificate Authority certificate following the procedure described in [RFC7958].
The `root-anchors.xml` and `root-anchors.p7s` S/MIME signature will be cached in the `$HOME/.getdns` directory on Unixes, and the `%appdata%\getdns` directory on Windows.
When using trust-anchors from the `root-anchors.xml` file, getdns will track the keys in the root DNSKEY rrset and store a copy in `$HOME/.getdns/root.key` on Unixes, and `%appdata%\getdns\root.key` on Windows.
Only when the KSK DNSKEY's change, a new version of `root-anchors.xml` is tried to be retrieved from [data.iana.org](https://data.iana.org/root-anchors/).
A installed trust-anchor from the default location (`/etc/unbound/getdns-root.key`) that fails to validate the root DNSKEY RRset, will also trigger the "Zero configuration DNSSEC" procedure described above.
If you're using [FreeBSD](https://www.freebsd.org/), you may install getdns via the [ports tree](https://www.freshports.org/dns/getdns/) by running: `cd /usr/ports/dns/getdns && make install clean`
getdns should also work on Ubuntu 16.04, however if you require IDN functionality you will have to install a recent version of libidn2 via a ppa e.g. from https://launchpad.net/~ondrej/+archive/ubuntu/php
A self-compiled version of OpenSSL or the version installed via Homebrew is required and the options OPENSSL_ROOT_DIR, OPENSSL_CRYPTO_LIBRARY and OPENSSL_SSL_LIBRARY can be used to specify the location of the libraries.
Note: If using a self-compiled version, manual configuration of certificates into /usr/local/etc/openssl/certs is required for TLS authentication to work.
If you're using [Homebrew](http://brew.sh/), 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](https://getdnsapi.net/doxygen/group__eventloops.html) that enable support for libevent, libuv, and libev, run: `brew install getdns --with-libevent --with-libuv --with-libev`. All switches are optional.
Additionally, getdns is linked against the the OpenSSL library installed by Homebrew. 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.
Once these are installed, set CMake variables CMAKE_INCLUDE_PATH and CMAKE_LIBRARY_PATH to the vcpkg include and library directories e.g. `../vcpkg/installed/x64-windows/include` and `../vcpkg/installed/x64-windows/lib`.
To generate a project suitable for use in Visual Studio, select the appropriate Visual Studio generator in CMake. Once generated, the cmake-gui Open Project button can be used to load the project into Visual Studio.
* At present, no native Windows DLL version of libunbound exists; support for linking against libunbound is not currently available. The default build option for ENABLE_STUB_ONLY_ is ON for Windows.
* The detection of the location of the `/etc/hosts` file should be optimised - it currently assumes Windows is installed in the default directory on the C: drive
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 getdns-api mailing list (discontinued) for their contributions.
