platform: modularize api/gui, add docs-tests-web foundation, and refresh root config

selective-vpn-api/app/egressutil/http.go

@@ -0,0 +1,48 @@
+package egressutil
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+)
+
+func HTTPGetBody(client *http.Client, rawURL string, timeout time.Duration, userAgent string, maxBytes int64) (string, error) {
+	if client == nil {
+		return "", fmt.Errorf("http client is nil")
+	}
+	limit := maxBytes
+	if limit <= 0 {
+		limit = 8 * 1024
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, rawURL, nil)
+	if err != nil {
+		return "", err
+	}
+	if strings.TrimSpace(userAgent) != "" {
+		req.Header.Set("User-Agent", strings.TrimSpace(userAgent))
+	}
+	req.Header.Set("Accept", "application/json, text/plain, */*")
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	body, _ := io.ReadAll(io.LimitReader(resp.Body, limit))
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		msg := strings.TrimSpace(string(body))
+		if msg == "" {
+			msg = resp.Status
+		}
+		return "", fmt.Errorf("%s -> %s", rawURL, msg)
+	}
+	return string(body), nil
+}