BBC BASIC Programmers' Reference

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=====Downloading a file from a URL=====

//by Richard Russell, August 2007; amended July 2009//\\ \\  The simplest method of downloading a file (e.g. a web page) from an internet URL is to use the **URLDownloadToFile** API function as described in the main [[http://www.bbcbasic.co.uk/bbcwin/manual/bbcwine.html#urlmon|documentation]]. The following program segment illustrates how to do that:\\ \\ 
<code bb4w>
        url$ = "http://www.bbcbasic.co.uk/bbcwin/bbcwin.html"
        file$ = @tmp$+"bbcwin.html"
        PROCurldownload(url$, file$)
        END

        DEF PROCurldownload(url$, file$)
        LOCAL urlmon%, res%
        SYS "LoadLibrary", "urlmon.dll" TO urlmon%
        SYS "GetProcAddress", urlmon%, "URLDownloadToFileA" TO `URLDownloadToFile`
        SYS `URLDownloadToFile`, 0, url$, file$, 0, 0 TO res%
        SYS "FreeLibrary", urlmon%
        IF res% ERROR 100, "Couldn't download "+url$
        ENDPROC
</code>
If you need to flush the cache to ensure you retrieve the latest version (e.g. it's a webcam picture) then it becomes slightly more complicated:\\ \\ 
<code bb4w>
        url$ = "http://www.bbcbasic.co.uk/bbcwin/bbcwin.html"
        file$ = @tmp$+"bbcwin.html"
        PROCurldownloadflush(url$, file$)
        END

        DEF PROCurldownloadflush(url$, file$)
        LOCAL urlmon%, wininet%, res%
        SYS "LoadLibrary", "URLMON.DLL" TO urlmon%
        SYS "GetProcAddress", urlmon%, "URLDownloadToFileA" TO `URLDownloadToFile`
        SYS "LoadLibrary", "WININET.DLL" TO wininet%
        SYS "GetProcAddress", wininet%, "DeleteUrlCacheEntryA" TO `DeleteUrlCacheEntry`
        SYS `DeleteUrlCacheEntry`, url$
        SYS `URLDownloadToFile`, 0, url$, file$, 0, 0 TO res%
        SYS "FreeLibrary", wininet%
        SYS "FreeLibrary", urlmon%
        IF res% ERROR 100, "Couldn't download "+url$
        ENDPROC
</code>
These routines can be used for both **HTTP** and **FTP** downloads.\\ \\  However under some circumstances the above methods do not work reliably. In that case you may find the following routine to be more successful:\\ \\ 
<code bb4w>
        url$ = "http://www.bbcbasic.co.uk/bbcwin/bbcwin.html"
        file$ = @tmp$+"bbcwin.html"
        PROCurldownload(url$, file$)
        END

        DEF PROCurldownload(url$, file$)
        LOCAL wininet%, buffer%, hinet%, hreq%, file%, nbr%, nbw%, ok%
        DIM buffer% LOCAL 511

        _INTERNET_OPEN_TYPE_PRECONFIG = 0
        _INTERNET_FLAG_RELOAD = &80000000

        SYS "LoadLibrary", "WININET.DLL" TO wininet%
        SYS "GetProcAddress", wininet%, "InternetOpenA"       TO `InternetOpen`
        SYS "GetProcAddress", wininet%, "InternetOpenUrlA"    TO `InternetOpenUrl`
        SYS "GetProcAddress", wininet%, "InternetReadFile"    TO `InternetReadFile`
        SYS "GetProcAddress", wininet%, "InternetCloseHandle" TO `InternetCloseHandle`

        SYS `InternetOpen`, "BB4W", _INTERNET_OPEN_TYPE_PRECONFIG, 0, 0, 0 TO hinet%
        IF hinet% = 0 ERROR 100, "Couldn't open internet services"

        SYS `InternetOpenUrl`, hinet%, url$, "", 0, _INTERNET_FLAG_RELOAD, 0 TO hreq%
        IF hreq% = 0 THEN
          PROCinetcleanup
          ERROR 100, "Couldn't open "+url$
        ENDIF

        file% = OPENOUT(file$)
        IF file% = 0 THEN
          PROCinetcleanup
          ERROR 100, "Couldn't create "+file$
        ENDIF

        REPEAT
          SYS `InternetReadFile`, hreq%, buffer%, 512, ^nbr% TO ok%
          IF ok% = 0 THEN
            PROCinetcleanup
            ERROR 100, "Couldn't read from "+url$
          ENDIF
          SYS "WriteFile", @hfile%(file%), buffer%, nbr%, ^nbw%, 0 TO ok%
          IF ok% = 0 THEN
            PROCinetcleanup
            ERROR 100, "Couldn't write "+file$
          ENDIF
        UNTIL nbr% = 0

        CLOSE #file%

        PROCinetcleanup
        ENDPROC

        DEF PROCinetcleanup
        hreq% += 0  : IF hreq%  SYS `InternetCloseHandle`, hreq%  : hreq% = 0
        hinet% += 0 : IF hinet% SYS `InternetCloseHandle`, hinet% : hinet% = 0
        wininet% += 0 : IF wininet% SYS "FreeLibrary", wininet% : wininet% = 0
        ENDPROC
</code>
Unfortunately with early versions of Internet Explorer (pre 4.0) the above code results in a memory leak when used for **http** downloads (see http://support.microsoft.com/kb/174897). If you need your code to work with such old versions you can use the following routine instead (note that because the HTTP protocol is implied, you must **not** include the **<nowiki>"http://"</nowiki>** in the supplied **server$**):\\ \\ 
<code bb4w>
        server$ = "www.bbcbasic.co.uk"
        request$ = "bbcwin/bbcwin.html"
        file$ = @tmp$+"bbcwin.html"
        PROChttpdownload(server$, request$, file$)
        END

        DEF PROChttpdownload(server$, request$, file$)
        LOCAL wininet%, buffer%, hinet%, hsess%, hreq%, file%, nbr%, nbw%, ok%
        DIM buffer% LOCAL 511

        _INTERNET_OPEN_TYPE_PRECONFIG = 0
        _INTERNET_DEFAULT_HTTP_PORT = 80
        _INTERNET_SERVICE_HTTP = 3
        _INTERNET_FLAG_RELOAD = &80000000

        SYS "LoadLibrary", "WININET.DLL" TO wininet%
        SYS "GetProcAddress", wininet%, "InternetOpenA"       TO `InternetOpen`
        SYS "GetProcAddress", wininet%, "InternetConnectA"    TO `InternetConnect`
        SYS "GetProcAddress", wininet%, "HttpOpenRequestA"    TO `HttpOpenRequest`
        SYS "GetProcAddress", wininet%, "HttpSendRequestA"    TO `HttpSendRequest`
        SYS "GetProcAddress", wininet%, "InternetReadFile"    TO `InternetReadFile`
        SYS "GetProcAddress", wininet%, "InternetCloseHandle" TO `InternetCloseHandle`

        SYS `InternetOpen`, "BB4W", _INTERNET_OPEN_TYPE_PRECONFIG, 0, 0, 0 TO hinet%
        IF hinet% = 0 ERROR 100, "Couldn't open internet services"

        SYS `InternetConnect`, hinet%, server$, _INTERNET_DEFAULT_HTTP_PORT, \
        \                      "", "", _INTERNET_SERVICE_HTTP, 0, 0 TO hsess%
        IF hsess% = 0 THEN
          PROCinetcleanup
          ERROR 100, "Couldn't connect to "+server$
        ENDIF

        SYS `HttpOpenRequest`, hsess%, 0, request$, 0, 0, 0, _INTERNET_FLAG_RELOAD, \
        \                      0 TO hreq%
        IF hreq% = 0 THEN
          PROCinetcleanup
          ERROR 100, "Couldn't open "+request$
        ENDIF

        SYS `HttpSendRequest`, hreq%, 0, 0, 0, 0 TO ok%
        IF ok% = 0 THEN
          PROCinetcleanup
          ERROR 100, "Couldn't request "+request$
        ENDIF

        file% = OPENOUT(file$)
        IF file% = 0 THEN
          PROCinetcleanup
          ERROR 100, "Couldn't create "+file$
        ENDIF

        REPEAT
          SYS `InternetReadFile`, hreq%, buffer%, 512, ^nbr% TO ok%
          IF ok% = 0 THEN
            PROCinetcleanup
            ERROR 100, "Couldn't read "+request$
          ENDIF
          SYS "WriteFile", @hfile%(file%), buffer%, nbr%, ^nbw%, 0 TO ok%
          IF ok% = 0 THEN
            PROCinetcleanup
            ERROR 100, "Couldn't write "+file$
          ENDIF
        UNTIL nbr% = 0

        CLOSE #file%

        PROCinetcleanup
        ENDPROC

        DEF PROCinetcleanup
        hreq% += 0  : IF hreq%  SYS `InternetCloseHandle`, hreq%  : hreq% = 0
        hsess% += 0 : IF hsess% SYS `InternetCloseHandle`, hsess% : hsess% = 0
        hinet% += 0 : IF hinet% SYS `InternetCloseHandle`, hinet% : hinet% = 0
        wininet% += 0 : IF wininet% SYS "FreeLibrary", wininet% : wininet% = 0
        ENDPROC
</code>