c-ares

Daniel Stenberg – Open Source

c-ares: Efficient Asynchronous DNS Client Library

Boris Weber

03/04/2025

c-ares is a powerful library that simplifies asynchronous DNS requests, making it easier for developers to handle DNS lookups efficiently without blocking the main application thread.

Overview of c-ares

c-ares is a C library that provides asynchronous capabilities for DNS resolution. Developed by Daniel Stenberg, who is also the creator of cURL, this library is focused on facilitating non-blocking DNS lookups. This feature is particularly beneficial for applications that must maintain high performance and require the ability to handle multiple tasks simultaneously without interruptions. The library enables developers to integrate DNS resolution into their applications seamlessly while managing other tasks concurrently.

Key Features

Asynchronous DNS Resolution: c-ares allows for non-blocking DNS queries, enabling applications to maintain responsiveness without waiting for network operations to complete.
Support for IPv4 and IPv6: The library supports both Internet Protocol versions, ensuring compatibility with modern networking standards.
Multiple Resolver Types: Offers various resolver types including both A and AAAA records, enhancing flexibility in handling different domain queries.
Built-in Parsing: Automatically parses returned DNS data, which simplifies the application development process by reducing the need for manual data handling.
Error Handling: Provides detailed error codes that aid developers in diagnosing issues related to DNS queries.
Cross-Platform Compatibility: Supports multiple operating systems including Windows, MacOS, and Linux environments, making it a versatile choice for developers worldwide.

Installation

The installation process for c-ares is straightforward. Users can choose to build from source or utilize package managers on their respective platforms. Here’s a quick guide on how to get started:

Clone the Repository: git clone https://github.com/c-ares/c-ares.git
Navigate to the Directory: cd c-ares
Build the Library: This can be done using CMake: cmake .
Compile and Install: make && sudo make install

Usage

C-ares provides a simple API that allows developers to initiate DNS lookups with minimal setup. Below is a basic example demonstrating how to use c-ares to resolve a hostname:

#include <ares.h>
#include <stdio.h>

void callback(void *data, int status, int timeouts, struct hostent *host) {
    if (status == ARES_SUCCESS) {
        printf("Resolved IP: %s\n", inet_ntoa(*(struct in_addr *)host->h_addr));
    } else {
        fprintf(stderr, "Error resolving: %d\n", status);
    }
}

int main() {
    ares_channel channel;
    ares_init(&channel);
    
    char *hostname = "www.example.com";
    struct ares_options options;
    options.sock_state = NULL;
    
    ares_gethostbyname(channel, hostname, AF_INET, callback, NULL);
    
    // Process events
    // (Include event loop code here to handle callbacks)
    
    ares_destroy(channel);
}

Performance

C-ares is designed for high efficiency in DNS resolution. Its non-blocking nature allows applications to handle numerous resolutions concurrently without being stalled by any one lookup. This performance-oriented architecture benefits applications like web browsers or servers where multiple hostname lookups are conducted in parallel.

Error Handling and Debugging

Error management within c-ares is robust. When an error occurs during a DNS query, the library returns specific error codes which developers can leverage for detailed diagnostics. The provided error management capabilities facilitate easier debugging and enhance the reliability of applications that utilize the library.

Documentation and Community Support

C-ares comes with comprehensive documentation that covers all aspects of its API along with examples illustrating its usage. The library has an active community contributing to its development through GitHub and mailing lists where users can seek assistance or share improvements.

The c-ares library stands out as a highly performant solution for asynchronous DNS resolution in C programming languages. Its extensive features and ease of use make it ideal for modern applications requiring efficient network operations. Developers looking for a reliable library that minimizes blocking operations while performing DNS queries will find c-ares invaluable.

Overview

c-ares is a Open Source software in the category Miscellaneous developed by Daniel Stenberg.

The latest version of c-ares is currently unknown. It was initially added to our database on 10/16/2009.

c-ares runs on the following operating systems: Windows.

c-ares has not been rated by our users yet.

Pros

Lightweight and fast asynchronous DNS resolver library
Designed for high performance and low latency
Supports both IPv4 and IPv6
Easy integration with C/C++ projects
Well-documented API and usage examples
Cross-platform compatibility, works on various operating systems
Highly portable due to minimal dependencies
Good support for DNS over HTTPS (DoH)
Active community and regular updates from the original author

Cons

Limited features compared to more comprehensive DNS libraries
Mainly focused on DNS, lacking broader networking functionality
Asynchronous model can be complex for developers new to it
Requires familiarity with C/C++ development practices
May have a steeper learning curve for beginners
No built-in caching mechanism; caching must be implemented separately if needed

FAQ

What is c-ares?

c-ares is a C library that performs DNS requests and name resolutions asynchronously.

Who is the author of c-ares?

Daniel Stenberg is the author of c-ares.

Is c-ares open source?

Yes, c-ares is open source and distributed under the MIT License.

What platforms does c-ares support?

c-ares is designed to work on various platforms including Linux, Windows, and macOS.

Can c-ares handle multiple DNS requests concurrently?

Yes, c-ares can handle multiple DNS requests concurrently in an asynchronous manner.

Does c-ares support caching of DNS responses?

Yes, c-ares provides support for caching DNS responses to improve performance.

Is c-ares actively maintained?

Yes, c-ares is actively maintained with updates and bug fixes provided by the community.

Can c-ares be used in commercial projects?

Yes, c-ares can be used in commercial projects as it is licensed under the MIT License.

Does c-ares have support for IPv6?

Yes, c-ares includes support for both IPv4 and IPv6 address resolutions.

Is there a mailing list or forum for c-ares users?

Yes, there is a mailing list available for c-ares users to ask questions and discuss issues.

Boris Weber

I am an editor at UpdateStar. I started as a support engineer, and am now specialized in writing about general software topics from a usability and performance angle among others. I telecommute from UpdateStar’s Berlin office, when I am not working remote as a digital nomad for UpdateStar. When I'm not analyzing the latest software updates, you can find me exploring new cities, immersing myself in local cultures, and discovering innovative tech trends across the globe.

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