first commit of restructured project

trahn-trade-backend/internal/httputil/retry.go

@@ -0,0 +1,73 @@
+package httputil
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+type RetryConfig struct {
+	MaxAttempts int
+	BaseDelay   time.Duration
+	MaxDelay    time.Duration
+}
+
+var DefaultRetry = RetryConfig{
+	MaxAttempts: 3,
+	BaseDelay:   1 * time.Second,
+	MaxDelay:    10 * time.Second,
+}
+
+// Do executes an HTTP request with exponential backoff retry.
+// The buildReq function is called on each attempt to produce a fresh request
+// (required because request bodies are consumed on each attempt).
+func Do(ctx context.Context, client *http.Client, cfg RetryConfig, buildReq func() (*http.Request, error)) (*http.Response, error) {
+	if cfg.MaxAttempts <= 0 {
+		cfg.MaxAttempts = DefaultRetry.MaxAttempts
+	}
+
+	var lastErr error
+	delay := cfg.BaseDelay
+
+	for attempt := 1; attempt <= cfg.MaxAttempts; attempt++ {
+		req, err := buildReq()
+		if err != nil {
+			return nil, fmt.Errorf("build request: %w", err)
+		}
+
+		resp, err := client.Do(req)
+		if err == nil && resp.StatusCode < 500 {
+			return resp, nil
+		}
+
+		if err != nil {
+			lastErr = err
+		} else {
+			body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
+			resp.Body.Close()
+			lastErr = fmt.Errorf("HTTP %d: %s", resp.StatusCode, string(body))
+		}
+
+		if attempt == cfg.MaxAttempts {
+			break
+		}
+
+		fmt.Printf("[RETRY] Attempt %d/%d failed: %v — retrying in %s\n",
+			attempt, cfg.MaxAttempts, lastErr, delay)
+
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-time.After(delay):
+		}
+
+		delay *= 2
+		if delay > cfg.MaxDelay {
+			delay = cfg.MaxDelay
+		}
+	}
+
+	return nil, fmt.Errorf("all %d attempts failed, last error: %w", cfg.MaxAttempts, lastErr)
+}