OpenRates.NET

OpenRates.NET is an open-source .NET library and data service providing daily and historical currency exchange rates from trusted sources like the European Central Bank. Free, cacheable, and CDN-ready with built-in resilience patterns.

Features

• 🚀 High Performance: Built-in hybrid caching with configurable expiration
• 🛡️ Enterprise Ready: Comprehensive error handling, logging, and cancellation support
• 📦 Dependency Injection: First-class support for Microsoft.Extensions.DependencyInjection
• 🔄 Daily Updates: Automated data refresh via GitHub Actions
• 🌐 CDN Distribution: Fast global access via jsDelivr CDN
• ✅ Well Tested: Comprehensive test coverage with xUnit

Project Structure

This solution contains four projects:

• OpenRates.Core: Class library containing providers, models, and services
  • Providers/EcbProvider.cs: European Central Bank data provider with HttpClient injection
  • Services/RateMerger.cs: Merge rates from multiple sources with conflict resolution
  • Models/ExchangeRates.cs: Strongly-typed rate models
• OpenRates.Publisher: Console application for updating exchange rate data
  • Runs daily via GitHub Actions
  • Uses Microsoft.Extensions.Hosting for DI and logging
  • Includes graceful shutdown and error handling
• OpenRates.Client: NuGet SDK for accessing exchange rates
  • HybridCache integration for optimal performance
  • Automatic retry and error handling
  • Input validation and null safety
• OpenRates.Tests: xUnit test project with 8+ comprehensive tests

Installation

NuGet Package

Install the OpenRates.Net client SDK via NuGet:

dotnet add package OpenRates.Net

Or via Package Manager Console:

Install-Package OpenRates.Net

Package Details:

• Package ID: OpenRates.Net
• Version: 1.0.0
• Target Framework: .NET 9.0
• Dependencies:
  • Microsoft.Extensions.Caching.Hybrid (9.10.0)
  • OpenRates.Core (included)

What's Included:

• IOpenRatesClient interface for dependency injection
• OpenRatesClient implementation with built-in caching
• Full async/await support with cancellation tokens
• Comprehensive error handling and input validation

Manual Build

If you want to build from source:

git clone https://github.com/henrikroschmann/OpenRates.NET.git
cd OpenRates.NET
dotnet restore
dotnet build

Package Generation

To create a NuGet package locally:

cd src/OpenRates.Client
dotnet pack -c Release -o ./nupkg

Quick Start

Using the Client SDK

using Microsoft.Extensions.DependencyInjection;
using OpenRates.Client;

var services = new ServiceCollection();

// Register OpenRates client with HttpClient factory and caching
services.AddHttpClient<IOpenRatesClient, OpenRatesClient>();
services.AddHybridCache();

var provider = services.BuildServiceProvider();
var client = provider.GetRequiredService<IOpenRatesClient>();

// Get current EUR to USD rate
var rate = await client.GetRateAsync("EUR", "USD");
Console.WriteLine($"EUR/USD: {rate}");

// Get historical rate
var historicalRate = await client.GetRateAsync(
    "EUR", 
    "GBP", 
    at: new DateTime(2024, 1, 15)
);
Console.WriteLine($"EUR/GBP on 2024-01-15: {historicalRate}");

Using the Core Provider Directly

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using OpenRates.Core.Providers;

var services = new ServiceCollection();
services.AddHttpClient<EcbProvider>();
services.AddLogging(builder => builder.AddConsole());

var provider = services.BuildServiceProvider();
var ecbProvider = provider.GetRequiredService<EcbProvider>();

var rates = await ecbProvider.FetchAsync(CancellationToken.None);
Console.WriteLine($"Fetched {rates.Rates.Count} base currencies");

// Get specific rate
var eurToUsd = rates.TryGet("EUR", "USD");
if (eurToUsd.HasValue)
{
    Console.WriteLine($"EUR/USD: {eurToUsd.Value}");
}

Running the Publisher

cd src/OpenRates.Publisher
dotnet run

# Output:
# info: OpenRates.Core.Providers.EcbProvider[0]
#       Fetching ECB daily exchange rates from https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml
# info: OpenRates.Core.Providers.EcbProvider[0]
#       Successfully fetched 31 ECB exchange rates
# info: Program[0]
#       ✅ Rates updated: 2025-10-28
#       - Latest: data\latest.json
#       - Dated: data\2025-10-28.json

Data Access

Exchange rate data is automatically updated daily and stored in the /data directory. The data is published to GitHub and can be accessed via jsDelivr CDN:

CDN Endpoints

Latest rates:
https://cdn.jsdelivr.net/gh/henrikroschmann/OpenRates.NET@main/data/latest.json

Historical rates (by date):
https://cdn.jsdelivr.net/gh/henrikroschmann/OpenRates.NET@main/data/2025-10-28.json

Data Format

{
  "date": "2025-10-28T00:00:00",
  "rates": {
    "eur": {
      "usd": 1.0842,
      "gbp": 0.8567,
      "jpy": 162.45
    },
    "usd": {
      "eur": 0.9223
    }
  }
}

Architecture

Design Principles

• SOLID: Single responsibility, dependency inversion throughout
• Async/Await: Proper async patterns with cancellation token support
• Null Safety: Nullable reference types enabled across all projects
• Error Handling: Comprehensive try-catch with specific exception types
• Resource Management: HttpClient injection, no resource leaks
• Logging: Structured logging with Microsoft.Extensions.Logging
• Caching: Hybrid cache strategy for optimal performance

Key Improvements

1. No Resource Leaks: HttpClient injected via IHttpClientFactory
2. Comprehensive Error Handling: All HTTP and parsing operations wrapped with specific exceptions
3. Caching Restored: HybridCache with 12-hour expiration prevents CDN hammering
4. Input Validation: ArgumentNullException and ArgumentException for all public APIs
5. Cancellation Support: CancellationToken throughout async operations
6. Dependency Injection: Full DI support with Microsoft.Extensions.Hosting
7. Enhanced Testing: 8 comprehensive tests with edge case coverage

Building and Testing

Build

dotnet restore
dotnet build

Run Tests

dotnet test

Test Coverage

dotnet test /p:CollectCoverage=true /p:CoverletOutputFormat=lcov

Configuration

Client Configuration

services.AddHttpClient<IOpenRatesClient, OpenRatesClient>(client =>
{
    client.Timeout = TimeSpan.FromSeconds(30);
});

services.AddHybridCache(options =>
{
    options.DefaultEntryOptions = new HybridCacheEntryOptions
    {
        Expiration = TimeSpan.FromHours(12),
        LocalCacheExpiration = TimeSpan.FromHours(6)
    };
});

Publisher Configuration

The publisher uses appsettings.json for configuration:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning"
    }
  }
}

Data Sources

• European Central Bank (ECB): Daily reference rates for 30+ currencies against EUR
• Future: CoinGecko (cryptocurrency rates) - planned
• Future: Additional providers - planned

Contributing

Contributions are welcome! Please:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

Development Guidelines

• Follow existing code style and patterns
• Add tests for new functionality
• Ensure all tests pass (dotnet test)
• Update documentation as needed
• Enable nullable reference types in new files

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• Exchange rate data provided by the European Central Bank
• CDN hosting by jsDelivr
• Built with .NET 9.0

Support

• 🐛 Issues: GitHub Issues
• 💬 Discussions: GitHub Discussions

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Made with ❤️ by the OpenRates.NET