CNB Exchange Rate Provider

[matteobusnelli]

Overview

Production-ready ExchangeRateProvider that fetches daily exchange rates from the Czech National Bank (CNB) public API and outputs them in CZK/XXX format.

Architecture

Core Components

• ExchangeRateProvider - Orchestrates fetching, filtering, and rate conversion (CNB format → 1 CZK = X Foreign)
• CnbHttpClient - HTTP communication with 30s timeout and domain-specific error handling
• CnbDataParser - Parses pipe-separated format with validation and culture-invariant decimal parsing

Tech Stack

• .NET 10.0
• Microsoft.Extensions.* - DI, Configuration, Logging, HttpClient factory
• Polly - Retry policy (3 attempts, 2s delays) for transient HTTP failures
• xUnit, Moq, FluentAssertions - Testing

Key Features

Resilience

• Polly retry for 5xx/network errors with exponential backoff
• Configurable timeouts and retry behavior via appsettings.json

Error Handling

• HTTP/timeout errors → domain-specific exceptions with clear messages
• Parsing errors → CnbDataParsingException with line-number context
• Missing currencies → silently ignored (per requirements)

Configuration

• Environment-specific config (appsettings.json, appsettings.{env}.json)
• CNB endpoint: https://www.cnb.cz/en/financial-markets/.../daily.txt

Design Principles

• Simple architecture: HTTP client → Parser → Provider (no over-engineering)
• Immutable models: Currency and ExchangeRate are record types
• Separation of concerns: Network, parsing, and business logic cleanly separated
• Returns only explicit rates - no inverse or cross-rate calculations

[wiz-mewssystems]

Wiz Scan Summary

Scanner	Findings
Vulnerabilities	-
Sensitive Data	-
Secrets	-
IaC Misconfigurations	-
SAST Findings	1
Software Supply Chain Findings	-
Total	1

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