You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: download.go
    path of file: ./repos/shiori/internal/core
    
    the code of the file until where you have to start completion: package core

import (
	"io"
	"net/http"
	"time"
)

var httpClient = &http.Client{Timeout: time.
    
func DownloadBookmark(url string) (io.ReadCloser, string, error) {
	// Prepare download request
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return nil, "", err
	}

	// Send download request
	req.Header.Set("User-Agent", userAgent)
	resp, err := httpClient.Do(req)
	if err != nil {
		return nil, "", err
	}

	// Get content type
	contentType := resp.Header.Get("Content-Type")

	return resp.Body, contentType, nil
}