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# [![c-ares logo](https://c-ares.org/art/c-ares-logo.svg)](https://c-ares.org/)
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[![Build Status](https://api.cirrus-ci.com/github/c-ares/c-ares.svg?branch=main)](https://cirrus-ci.com/github/c-ares/c-ares)
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[![Windows Build Status](https://ci.appveyor.com/api/projects/status/aevgc5914tm72pvs/branch/main?svg=true)](https://ci.appveyor.com/project/c-ares/c-ares/branch/main)
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[![Coverage Status](https://coveralls.io/repos/github/c-ares/c-ares/badge.svg?branch=main)](https://coveralls.io/github/c-ares/c-ares?branch=main)
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[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/291/badge)](https://bestpractices.coreinfrastructure.org/projects/291)
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[![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/c-ares.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:c-ares)
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[![Bugs](https://sonarcloud.io/api/project_badges/measure?project=c-ares_c-ares&metric=bugs)](https://sonarcloud.io/summary/new_code?id=c-ares_c-ares)
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[![Coverity Scan Status](https://scan.coverity.com/projects/c-ares/badge.svg)](https://scan.coverity.com/projects/c-ares)
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- [Overview](#overview)
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- [Code](#code)
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- [Communication](#communication)
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- [Release Keys](#release-keys)
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- [Verifying signatures](#verifying-signatures)
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- [Features](#features)
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- [RFCs and Proposals](#supported-rfcs-and-proposals)
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## Overview
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[c-ares](https://c-ares.org) is a modern DNS (stub) resolver library, written in
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C. It provides interfaces for asynchronous queries while trying to abstract the
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intricacies of the underlying DNS protocol. It was originally intended for
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applications which need to perform DNS queries without blocking, or need to
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perform multiple DNS queries in parallel.
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One of the goals of c-ares is to be a better DNS resolver than is provided by
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your system, regardless of which system you use. We recommend using
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the c-ares library in all network applications even if the initial goal of
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asynchronous resolution is not necessary to your application.
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c-ares will build with any C89 compiler and is [MIT licensed](LICENSE.md),
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which makes it suitable for both free and commercial software. c-ares runs on
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Linux, FreeBSD, OpenBSD, MacOS, Solaris, AIX, Windows, Android, iOS and many
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more operating systems.
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c-ares has a strong focus on security, implementing safe parsers and data
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builders used throughout the code, thus avoiding many of the common pitfalls
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of other C libraries. Through automated testing with our extensive testing
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framework, c-ares is constantly validated with a range of static and dynamic
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analyzers, as well as being constantly fuzzed by [OSS Fuzz](https://github.com/google/oss-fuzz).
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While c-ares has been around for over 20 years, it has been actively maintained
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both in regards to the latest DNS RFCs as well as updated to follow the latest
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best practices in regards to C coding standards.
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## Code
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The full source code and revision history is available in our
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[GitHub repository](https://github.com/c-ares/c-ares). Our signed releases
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are available in the [release archives](https://c-ares.org/download/).
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See the [INSTALL.md](INSTALL.md) file for build information.
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## Communication
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**Issues** and **Feature Requests** should be reported to our
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[GitHub Issues](https://github.com/c-ares/c-ares/issues) page.
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**Discussions** around c-ares and its use, are held on
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[GitHub Discussions](https://github.com/c-ares/c-ares/discussions/categories/q-a)
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or the [Mailing List](https://lists.haxx.se/mailman/listinfo/c-ares). Mailing
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List archive [here](https://lists.haxx.se/pipermail/c-ares/).
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Please, do not mail volunteers privately about c-ares.
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**Security vulnerabilities** are treated according to our
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[Security Procedure](SECURITY.md), please email c-ares-security at
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haxx.se if you suspect one.
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## Release keys
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Primary GPG keys for c-ares Releasers (some Releasers sign with subkeys):
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* **Daniel Stenberg** <<daniel@haxx.se>>
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`27EDEAF22F3ABCEB50DB9A125CC908FDB71E12C2`
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* **Brad House** <<brad@brad-house.com>>
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`DA7D64E4C82C6294CB73A20E22E3D13B5411B7CA`
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To import the full set of trusted release keys (including subkeys possibly used
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to sign releases):
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```bash
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gpg --keyserver hkps://keyserver.ubuntu.com --recv-keys 27EDEAF22F3ABCEB50DB9A125CC908FDB71E12C2 # Daniel Stenberg
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gpg --keyserver hkps://keys.openpgp.org --recv-keys DA7D64E4C82C6294CB73A20E22E3D13B5411B7CA # Brad House
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```
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### Verifying signatures
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For each release `c-ares-X.Y.Z.tar.gz` there is a corresponding
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`c-ares-X.Y.Z.tar.gz.asc` file which contains the detached signature for the
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release.
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After fetching all of the possible valid signing keys and loading into your
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keychain as per the prior section, you can simply run the command below on
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the downloaded package and detached signature:
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```bash
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% gpg -v --verify c-ares-1.29.0.tar.gz.asc c-ares-1.29.0.tar.gz
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gpg: enabled compatibility flags:
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gpg: Signature made Fri May 24 02:50:38 2024 EDT
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gpg: using RSA key 27EDEAF22F3ABCEB50DB9A125CC908FDB71E12C2
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gpg: using pgp trust model
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gpg: Good signature from "Daniel Stenberg <daniel@haxx.se>" [unknown]
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: 27ED EAF2 2F3A BCEB 50DB 9A12 5CC9 08FD B71E 12C2
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gpg: binary signature, digest algorithm SHA512, key algorithm rsa2048
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```
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## Features
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### Supported RFCs and Proposals
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- [RFC1035](https://datatracker.ietf.org/doc/html/rfc7873).
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Initial/Base DNS RFC
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- [RFC2671](https://datatracker.ietf.org/doc/html/rfc2671),
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[RFC6891](https://datatracker.ietf.org/doc/html/rfc6891).
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EDNS0 option (meta-RR)
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- [RFC3596](https://datatracker.ietf.org/doc/html/rfc3596).
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IPv6 Address. `AAAA` Record.
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- [RFC2782](https://datatracker.ietf.org/doc/html/rfc2782).
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Server Selection. `SRV` Record.
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- [RFC3403](https://datatracker.ietf.org/doc/html/rfc3403).
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Naming Authority Pointer. `NAPTR` Record.
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- [RFC6698](https://datatracker.ietf.org/doc/html/rfc6698).
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DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS) Protocol.
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`TLSA` Record.
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- [RFC9460](https://datatracker.ietf.org/doc/html/rfc9460).
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General Purpose Service Binding, Service Binding type for use with HTTPS.
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`SVCB` and `HTTPS` Records.
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- [RFC7553](https://datatracker.ietf.org/doc/html/rfc7553).
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Uniform Resource Identifier. `URI` Record.
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- [RFC6844](https://datatracker.ietf.org/doc/html/rfc6844).
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Certification Authority Authorization. `CAA` Record.
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- [RFC2535](https://datatracker.ietf.org/doc/html/rfc2535),
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[RFC2931](https://datatracker.ietf.org/doc/html/rfc2931).
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`SIG0` Record. Only basic parser, not full implementation.
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- [RFC7873](https://datatracker.ietf.org/doc/html/rfc7873),
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[RFC9018](https://datatracker.ietf.org/doc/html/rfc9018).
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DNS Cookie off-path dns poisoning and amplification mitigation.
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- [draft-vixie-dnsext-dns0x20-00](https://datatracker.ietf.org/doc/html/draft-vixie-dnsext-dns0x20-00).
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DNS 0x20 query name case randomization to prevent cache poisioning attacks.
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- [RFC7686](https://datatracker.ietf.org/doc/html/rfc7686).
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Reject queries for `.onion` domain names with `NXDOMAIN`.
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- [RFC2606](https://datatracker.ietf.org/doc/html/rfc2606),
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[RFC6761](https://datatracker.ietf.org/doc/html/rfc6761).
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Special case treatment for `localhost`/`.localhost`.
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- [RFC2308](https://datatracker.ietf.org/doc/html/rfc2308),
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[RFC9520](https://datatracker.ietf.org/doc/html/rfc9520).
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Negative Caching of DNS Resolution Failures.
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- [RFC6724](https://datatracker.ietf.org/doc/html/rfc6724).
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IPv6 address sorting as used by `ares_getaddrinfo()`.
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- [RFC7413](https://datatracker.ietf.org/doc/html/rfc7413).
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TCP FastOpen (TFO) for 0-RTT TCP Connection Resumption.
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