I am having an issue with my HTTP requests in my app, such that if the remote file is the same size as the local file (even though its modified time is different, as its contents have been changed), attempts to download it return quickly and the newer file is not downloaded.
In short, the process I am following is: Setting up an HTTP connection with the INTERNET_FLAG_RESYNCHRONIZE flag and calling HttpSendRequest(); then checking the HTTP status code and finding it to be "200".
If the remote file is updated, but remains the same size as the local copy: The local file is unchanged after running the app. If I call HttpQueryInfo() with HTTP_QUERY_LAST_MODIFIED after sending the request, it gives me the actual last modified time of the server's file, which I can see is different from the local file I am trying to have it overwrite.
If the remote file is updated, and the file size becomes different from the local copy: It is downloaded and overwrites the local copy as expected.
Here's a fairly abridged version of the code, to cut out helpers and error checking:
// szAppName = our app name
HINTERNET hInternetHandle = InternetOpen( szAppName,
INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0 );
// szServerName = our server name
hInternetHandle = InternetConnect( hInternetHandle, szServerName,
INTERNET_DEFAULT_HTTP_PORT, NULL, NULL, INTERNET_SERVICE_HTTP, NULL, 0 );
// szPath = the file to download
LPCSTR aszDefault[2] = { "*/*", NULL };
DWORD dwFlags = 0
| INTERNET_FLAG_IGNORE_REDIRECT_TO_HTTP
| INTERNET_FLAG_IGNORE_REDIRECT_TO_HTTPS
| INTERNET_FLAG_KEEP_CONNECTION
| INTERNET_FLAG_NO_AUTH
| INTERNET_FLAG_NO_AUTO_REDIRECT
| INTERNET_FLAG_NO_COOKIES
| INTERNET_FLAG_NO_UI
| INTERNET_FLAG_RESYNCHRONIZE;
HINTERNET hHandle = HttpOpenRequest( hInternetHandle, "GET", szPath, NULL,
NULL, aszDefault, dwFlags, 0 );
DWORD dwTimeOut = 10 * 1000; // In milliseconds
InternetSetOption( hInternetHandle, INTERNET_OPTION_CONNECT_TIMEOUT,
&dwTimeOut, sizeof( dwTimeOut ) );
InternetSetOption( hInternetHandle, INTERNET_OPTION_RECEIVE_TIMEOUT,
&dwTimeOut, sizeof( dwTimeOut ) );
InternetSetOption( hInternetHandle, INTERNET_OPTION_SEND_TIMEOUT,
&dwTimeOut, sizeof( dwTimeOut ) );
DWORD dwRetries = 5;
InternetSetOption( hInternetHandle, INTERNET_OPTION_CONNECT_RETRIES,
&dwRetries, sizeof( dwRetries ) );
HttpSendRequest( hInternetHandle, NULL, 0, NULL, 0 );
Since I have found I can query the remote file's last modified time, and find it to be accurate, I know it's actually getting to the server. I thought that specifying INTERNET_FLAG_RESYNCHRONIZE would force the file to resynch if it's out of date. Do I have it all wrong? Is this just how it's supposed to work?
