Un-Mapping Mapped Network Drives Andrew Coates - dFPUG-Portal

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What the article does mention, though, is a couple of workarounds. The first involves about 30 lines of C code that calls another couple of functions in MPR.DLL. The second mentions in passing that there’s yet another function in MPR.DLL called WNetGetConnection(). WNetGetConnection() is not quite as versatile as WNetGetUniversalName(). It only accepts a drive letter and a colon (for instance, H:) rather than a full path. With a little string manipulation, however, it’s pretty easy to split up a mapped path, pass the function what it wants, and then re-assemble a complete UNC path from the pieces. To take the drudgery out of calling the Windows API, I wrote a wrapper function called GetUNCPath() that I include in any project in which I call either getdir() or getfile(). You could, of course, write wrappers for getfile() and getdir() that called GetUNCPath(). For example, if the pub share on the server_pdc server were mapped as drive s: ? GetUNCPath('s:\documents') \\server_pdc\pub\documents ? GetUNCPath('c:\temp') c:\temp ? GetUNCPath('s:\documents\myfile.doc') \\server_pdc\pub\documents\myfile.doc The wrapper function itself is pretty straightforward. The complete function is shown in Listing 1 and is available in this month’s Subscriber Downloads at www.pinpub.com/foxtalk. It accepts the mapped drive path as a compulsory parameter and optionally a length for the UNC version of the path. This second parameter is most often passed by the function itself in a recursive call if the default buffer size guess isn’t large enough (more on this later). Listing 1. The complete GetUNCPath source code. * Program....: GetUNCPath.prg * Version....: 1.0 * Author.....: Andrew Coates * Date.......: September 28, 1998 * Notice.....: Copyright © 1998 Civil Solutions, All * Rights Reserved. * Compiler...: Visual FoxPro 05.00.00.0415 for Windows * Abstract...: Wrapper to the API call that converts a * mapped drive path to the UNC path * Changes....: * Originally used WNetGetUniversalName, but that * doesn't work under Win95 (see KB Q131416). Now uses * WNetGetConnection, which uses a string rather than a * structure so STRUCTURE_HEADER is now 0. lParameters tcMappedPath, tnBufferSize * from winnetwk.h #define UNIVERSAL_NAME_INFO_LEVEL 0x00000001 #define REMOTE_NAME_INFO_LEVEL 0x00000002 * from winerror.h #define NO_ERROR 0 #define ERROR_BAD_DEVICE 1200 #define ERROR_CONNECTION_UNAVAIL 1201 #define ERROR_EXTENDED_ERROR 1208 #define ERROR_MORE_DATA 234 #define ERROR_NOT_SUPPORTED 50 #define ERROR_NO_NET_OR_BAD_PATH 1203 Returning a UNC Path from getdir() If you pass getdir() an initial folder in UNC format, then that folder will be the initially selected folder, but it won’t appear in the list of drives in the dialog box (see Figure 1). If that folder or one of its subfolders is selected, then the string returned will be in UNC. Be careful, though. If you navigate to a mapped drive from the drive’s drop-down box, there’s no way to get back to the UNC drive. #define ERROR_NO_NETWORK 1222 #define ERROR_NOT_CONNECTED 2250 * Local decision - paths aren't likely to be longer * than this - if they are, this function calls itself * recursively with the appropriate buffer size as the * second parameter. #DEFINE MAX_BUFFER_SIZE 500 * String length at the beginning of the structure * returned before the UNC path. * ACC changed to 0 on 9/10/98 - Now using * WNetGetConnection, which uses a string rather than a * struct. #DEFINE STRUCTURE_HEADER 0 local lcReturnValue if type('tcMappedPath') = "C" and ; ! isnull(tcMappedPath) Figure 1. Passing getdir() a UNC path will initially display the UNC path in the dialog box, but the unmapped drive won’t appear in the drop-down list. * Split up the passed path to get just the drive. local lcDrive, lcPath * Just take the first two characters - we'll put it * all back together later. If the first two * characters aren't a valid drive, that's okay. The * error value returned from the function call will * handle it. * Case statement ensures we don't get the "cannot * access beyond end of string" error. do case case len(tcMappedPath) > 2 lcDrive = left(tcMappedPath, 2) lcPath = substr(tcMappedPath, 3) case len(tcMappedPath)
lcPath = "" endcase declare INTEGER WNetGetConnection IN WIN32API ; STRING @lpLocalPath, ; STRING @lpBuffer, ; INTEGER @lpBufferSize * Set up some variables so the appropriate call can * be made. local lcLocalPath, lcBuffer, lnBufferSize, ; lnResult, lcStructureString * Set to +1 to allow for the null terminator. lnBufferSize = ; iif(pcount() = 1 or ; type('tnBufferSize') # "N" or ; isnull(tnBufferSize), ; MAX_BUFFER_SIZE, ; tnBufferSize) + ; 1 lcLocalPath = lcDrive lcBuffer = space(lnBufferSize) * Now call the dll function. lnResult = WNetGetConnection(@lcLocalPath, ; @lcBuffer, @lnBufferSize) do case * String translated sucessfully. case lnResult = NO_ERROR * Actually, this structure-stripping is no longer * required because WNetGetConnection() returns a * string rather than a struct. lcStructureString = alltrim(substr(lcBuffer, ; STRUCTURE_HEADER + 1)) lcReturnValue = left(lcStructureString, ; at(chr(0), lcStructureString) - 1) + lcPath * The string pointed to by lpLocalPath is invalid. case lnResult = ERROR_BAD_DEVICE lcReturnValue = tcMappedPath * There's no current connection to the remote * device, but there's a remembered (persistent) * connection to it. case lnResult = ERROR_CONNECTION_UNAVAIL lcReturnValue = tcMappedPath * A network-specific error occurred. Use the * WNetGetLastError function to obtain a description * of the error. case lnResult = ERROR_EXTENDED_ERROR lcReturnValue = tcMappedPath * The buffer pointed to by lpBuffer is too small. * The function sets the variable pointed to by * lpBufferSize to the required buffer size. case lnResult = ERROR_MORE_DATA lcReturnValue = getuncpath(tcMappedPath, ; lnBufferSize) * None of the providers recognized this local name * as having a connection. However, the network is * not available for at least one provider to whom * the connection may belong. case lnResult = ERROR_NO_NET_OR_BAD_PATH lcReturnValue = tcMappedPath * There's no network present. case lnResult = ERROR_NO_NETWORK lcReturnValue = tcMappedPath * The device specified by lpLocalPath isn't * redirected. case lnResult = ERROR_NOT_CONNECTED lcReturnValue = tcMappedPath otherwise lcReturnValue = tcMappedPath endcase else lcReturnValue = tcMappedPath http://www.pinpub.com FoxTalk December 1998 5 endif return lcReturnValue Constants from the corresponding API header files are reproduced in the function rather than in a standalone header to make it more portable, and a couple of local constants are also #DEFINEd for clarity later in the code. The mapped drive parameter is checked, and if it’s not a character expression, or if it’s .NULL., then the function simply returns whatever was passed to it. If the tests are passed, then the API function is DECLAREd. Note the use of the Win32API rather than the specific MPR.DLL. Splitting up the mapped path parameter into its component pieces is simply a matter of taking the first two characters and calling them the mapped drive, and taking the rest of the expression and calling them the path. There’s no problem if that’s not a valid assumption because the API function will return an error value and we’ll take the appropriate action. Next I call the API function and check the return value. The two important values I’m looking for are NO_ERROR (my personal favorite ) and ERROR_MORE_DATA. The NO_ERROR code means just that: The drive mapping was decoded successfully, and the result is in the lcBuffer variable. The value placed in lcBuffer is a null-terminated string. This means that the string is terminated by a chr(0) that needs to be stripped before we use it in VFP. I just append the path part of the original mapped path parameter to the translated drive returned by the PAI call and voila—a UNC version of the mapped path. The ERROR_MORE_DATA return value tells me that I didn’t allocate enough space in the return buffer, and I need to call the function again. Fortunately, once I get this error, I no longer need to guess how long to make the buffer. In addition to returning the error, the API function sets lnBufferSize to the value required so I can call GetUNCPath() recursively with the original mapped drive path and lnBufferSize. Each of the other error states indicates that the mapping couldn’t be decoded for some reason or other. I’ve decided to treat them all the same way: Simply return the mapped path passed to the function. While VFP is a wonderful development environment, it does have some limitations. Fortunately, it provides enough access to the Windows API to be able to work around most of them. ▲ 12COASC2.ZIP at www.pinpub.com/foxtalk Andrew Coates is an independent developer/data consultant living in the Olympic City—Sydney, Australia. He specializes in PC database applications, particularly integrating tools and visualizing spatial data. a.coates@civilsolutions.com.au.
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Un-Mapping Mapped Network Drives Andrew Coates - dFPUG-Portal

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