Add RequestCached and RequestCachedBytes functions for caching HTTP requests

main.go

@@ -1,7 +1,12 @@
 package cyutils
 
 import (
+	"encoding/json"
+	"fmt"
+	"io"
 	"net/http"
+	"os"
+	"path/filepath"
 	"sync"
 
 	"golang.org/x/time/rate"
@@ -77,3 +82,50 @@ func LimitedHttp(rps float64, burst int) *http.Client {
 		Transport: transport,
 	}
 }
+
+func RequestCached[T any](req *http.Request, filename string) (T, error) {
+	var zero T
+
+	data, err := os.ReadFile(filename)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return zero, fmt.Errorf("failed to read cache: %w", err)
+		}
+
+		resp, httpErr := http.DefaultClient.Do(req)
+		if httpErr != nil {
+			return zero, fmt.Errorf("HTTP request failed: %w", httpErr)
+		}
+		defer resp.Body.Close()
+
+		body, readErr := io.ReadAll(resp.Body)
+		if readErr != nil {
+			return zero, fmt.Errorf("failed to read response body: %w", readErr)
+		}
+
+		dir := filepath.Dir(filename)
+		if dir != "." && dir != "" {
+			if mkErr := os.MkdirAll(dir, 0o755); mkErr != nil {
+				return zero, fmt.Errorf("failed to create cache dir %s: %w", dir, mkErr)
+			}
+		}
+		if writeErr := os.WriteFile(filename, body, 0o644); writeErr != nil {
+			return zero, fmt.Errorf("failed to write cache %s: %w", filename, writeErr)
+		}
+		data = body
+	}
+
+	if _, ok := any(zero).([]byte); ok {
+		return any(data).(T), nil
+	}
+
+	var out T
+	if err := json.Unmarshal(data, &out); err != nil {
+		return zero, fmt.Errorf("failed to unmarshal cached response: %w", err)
+	}
+	return out, nil
+}
+
+func RequestCachedBytes(req *http.Request, filename string) ([]byte, error) {
+	return RequestCached[[]byte](req, filename)
+}