ANTOOZA-BACKEND/Infrastructure/StockData/KoreaEximHttp.cs

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

namespace Infrastructure.StockData;

/// <summary>
/// 한국수출입은행(koreaexim.go.kr) OpenAPI 호출 공통 — 인증은 URL query param authkey (헤더 아님, OpenDART 와 동일 방식).
/// 호출부가 authkey + searchdate + data 를 붙인 완성 URL 을 넘기며, 여기선 Accept json + 간단 3회 재시도(2s/4s 백오프)만 담당.
/// </summary>
internal static class KoreaEximHttp
{
    public const string ClientName = "KoreaExim";

    private const int MaxAttempts = 3;

    public static async Task<string> GetStringWithRetryAsync(HttpClient client, string url, ILogger logger, CancellationToken ct)
    {
        for (var attempt = 1; ; attempt++)
        {
            try
            {
                using var request = new HttpRequestMessage(HttpMethod.Get, url);
                request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                // 일부 공공 게이트웨이는 UA 없는 요청을 봇으로 차단(OpenDART 사례) — 방어적으로 UA 부여
                request.Headers.UserAgent.ParseAdd("antooza/1.0 (+https://antooza.com)");

                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, "[KoreaExim] HTTP 실패 — 재시도 {Attempt}/{Max}", attempt, MaxAttempts);
                await Task.Delay(TimeSpan.FromSeconds(2 * attempt), ct);
            }
        }
    }
}