//检查一个URL是否有效函数

//可用来检测网络连接是否正确，InternetCheckConnection函数检查不准确，有些情况无法检测到，而以下CheckUrl函数则不会。
//uses wininet;
function CheckUrl(url: string): Boolean;
var
  hSession, hfile, hRequest: hInternet;
  dwindex, dwcodelen: dword;
  dwcode: array[1..20] of Char;
  res: PChar;
begin
  Result := false;
  if Pos('http://', LowerCase(url)) = 0 then  url := 'http://' + url;
  hSession := InternetOpen('InetURL:/1.0', INTERNET_OPEN_TYPE_PRECONFIG,
    nil, nil, 0);
  if Assigned(hsession) then
  begin
    hfile := InternetOpenUrl(hsession, PChar(url), nil, 0, INTERNET_FLAG_RELOAD, 0);
    dwIndex := 0;
    dwCodeLen := 10;
    HttpQueryInfo(hfile, HTTP_QUERY_STATUS_CODE, @dwcode, dwcodeLen, dwIndex);
    res := PChar(@dwcode);
    Result := (res = '200') or (res = '302'); //200,302未重定位标志
    if Assigned(hfile) then
      InternetCloseHandle(hfile);
    InternetCloseHandle(hsession);
  end;
end;