ANTOOZA-BACKEND/Infrastructure/StockData/KrxCoKrHttp.cs

using System.Net.Http.Headers;
using Microsoft.Extensions.Logging;

namespace Infrastructure.StockData;

/// <summary>KRX OpenAPI(data-dbg.krx.co.kr) 호출 공통 — AUTH_KEY 헤더 인증 + 간단 3회 재시도 (2s/4s 백오프)</summary>
internal static class KrxCoKrHttp
{
    public const string ClientName = "KRXCoKr";

    /// <summary>KRX OpenAPI 인증 헤더명 (라이브 검증: 헤더 있으면 "Unauthorized API Call", 없으면 "Unauthorized Key")</summary>
    public const string AuthHeader = "AUTH_KEY";

    private const int MaxAttempts = 3;

    public static async Task<string> GetStringWithRetryAsync(HttpClient client, string url, string apiKey, ILogger logger, CancellationToken ct)
    {
        for (var attempt = 1; ; attempt++)
        {
            try
            {
                using var request = new HttpRequestMessage(HttpMethod.Get, url);
                request.Headers.TryAddWithoutValidation(AuthHeader, apiKey);
                request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

                using var response = await client.SendAsync(request, ct);
                response.EnsureSuccessStatusCode();
                return await response.Content.ReadAsStringAsync(ct);
            }
            catch (Exception ex) when (ex is not OperationCanceledException && attempt < MaxAttempts)
            {
                logger.LogWarning(ex, "[KRXCoKr] HTTP 실패 — 재시도 {Attempt}/{Max}", attempt, MaxAttempts);
                await Task.Delay(TimeSpan.FromSeconds(2 * attempt), ct);
            }
        }
    }
}