Technical Q&A QA1078

Getting the User and Computer Name

static UInt32 gMoreCSSystemVersion = 0;

enum {
    kMoreCSMacOSX10point0 = 0x01000,
    kMoreCSMacOSX10point1 = 0x01010
};

static CFStringRef CreateCFStringFromStringResource(SInt16 rsrcID)
    // This routine is called on Mac OS 9 to create a CFString
    // from the system 'STR ' resource with ID of rsrcID.
{
    CFStringRef result;
    SInt8       s;
    Handle      stringH;

    result = nil;

    stringH = GetResource('STR ', rsrcID);
    if (stringH != nil) {
        s = HGetState(stringH);
        HLock(stringH);

        // CFStringGetSystemEncoding returns the CFStringEncoding of the
        // system as a whole.  We want the system text encoding because
        // the user/machine name is set by the File Sharing control panel
        // and the File Sharing control panel is localised in the system script.
        //
        // This only applies because we're reading a resource from the
        // System file.  If we were reading it from an application resource
        // we would have used GetApplicationTextEncoding (from "Processes.h")
        // instead.

        result = CFStringCreateWithPascalString(kCFAllocatorSystemDefault,
                                                (StringPtr) *stringH,
                                                CFStringGetSystemEncoding() );

        HSetState(stringH, s);
    }
    return result;
}

static CFStringRef ReadMachineNameFromFile(void)
    // This routine is called when the client tries to get the
    // machine name on Mac OS X 10.0.x.  Because CSCopyMachineName returns
    // un-useful information on those systems, w reads the name
    // directly from the System Configuration preferences file.
{
    CFStringRef     result;
    CFURLRef        url;
    CFDataRef       data;
    CFDictionaryRef dict;
    CFDictionaryRef systemDict;
    CFDictionaryRef system2Dict;

    assert( gMoreCSSystemVersion >= kMoreCSMacOSX10point0 );
    assert( gMoreCSSystemVersion <  kMoreCSMacOSX10point1 );

    // *** IMPORTANT ***
    //
    // The location and format of the System Configuration framework
    // preferences file in the code below is subject to change
    // at any time.  Do not write any code which makes any assumptions
    // on this file since your app WILL BREAK at some point in time.
    // The only reason we can do this safely in this code is because
    // we know we're running on Mac OS 10.0 through 10.0.4.  This is
    // enforced by the asserts above.  For Mac OS X 10.1 and above you
    // must use the public System Configuration framework APIs (or
    // APIs, like CSCopyMachineName, which are layered on top of
    // System Configuration framework).

    result = nil;

    url = CFURLCreateWithFileSystemPath(kCFAllocatorDefault,
                     CFSTR("/var/db/SystemConfiguration/preferences.xml"),
                     kCFURLPOSIXPathStyle,
                     false );
    if (url != nil) {
        if ( CFURLCreateDataAndPropertiesFromResource(kCFAllocatorDefault,
                                        url, &data, nil, nil, nil ) ) {
            dict = CFPropertyListCreateFromXMLData(kCFAllocatorSystemDefault,
                                        data, kCFPropertyListImmutable, nil);
            if (dict != nil) {
                systemDict = CFDictionaryGetValue(dict, CFSTR("System") );
                if (systemDict != nil) {
                    system2Dict = CFDictionaryGetValue(systemDict,
                                                       CFSTR("System") );
                    if ( system2Dict != nil ) {
                        result = CFDictionaryGetValue(system2Dict,
                                                       CFSTR("ComputerName") );
                        if (result != nil) {
                            // Increment the string's reference count so that
                            // releasing "dict" doesn't release the name.
                            CFRetain(result);
                        }
                        // Don't need to release system2Dict because it was "got".
                    }
                    // Don't need to release systemDict because it was "got".
                }
                CFRelease(dict);
            }
            CFRelease( data );
        }
        CFRelease( url );
    }

    return result;
}

extern pascal CFStringRef MoreCSCopyUserName(Boolean useShortName)
    // See comment in header file.
{
    CFStringRef result;

    if ( gMoreCSSystemVersion == 0 ) {
        (void) Gestalt(gestaltSystemVersion, (SInt32 *) &gMoreCSSystemVersion);
    }

    if ( gMoreCSSystemVersion < kMoreCSMacOSX10point0 ) {

        // Running on traditional Mac OS.  If we have a recent version
        // of CarbonLib (1.5 and above) that supports the routine, use
        // that.  Otherwise fall back to the Resource Manager.

        if ( CSCopyUserName != (void *) kUnresolvedCFragSymbolAddress) {
            result = CSCopyUserName(useShortName);
        } else {
            result = CreateCFStringFromStringResource(-16096);
        }

    } else {

        // Call the API.  However, if we're built CFM we can't just
        // call it directly because the routine isn't exported to
        // CFM on Mac OS 10.0.x.  So for CFM builds we have to call
        // through CFBundle.

        #if TARGET_RT_MAC_CFM
            {
                typedef CFStringRef (*CSCopyUserNameProc)(Boolean useShortName);
                CSCopyUserNameProc  csCopyUserName;
                CFBundleRef         bundle;

                result = nil;
                csCopyUserName = nil;

                bundle = CFBundleGetBundleWithIdentifier(
                                                 CFSTR("com.apple.Carbon" ) );
                if (bundle != nil) {
                    csCopyUserName =
                       (CSCopyUserNameProc) CFBundleGetFunctionPointerForName(
                                              bundle, CFSTR("CSCopyUserName") );
                }
                if (csCopyUserName != nil) {
                    result = csCopyUserName(useShortName);
                }
                // Both bundle and csCopyUserName got with "Get", so
                // no need to release.
            }
        #elif TARGET_RT_MAC_MACHO
            result = CSCopyUserName(useShortName);
        #else
            #error MoreCSCopyUserName: What runtime are you using?
        #endif

        // Mac OS 10.0 and 10.0.1 (which have the same gestaltSystemVersion
        // result -- this just gets better and better) have a bug [2665708]
        // where they fail to retain the user name and host name strings
        // each time they return it to the client.  The upshot is that
        // the client crashes the second time it calls CSCopyUserName or
        // CSCopyMachineName.  This extra CFRetain prevents this from happening.
        //
        // Note that we don't need a similar workaround in MoreCSCopyMachineName
        // because we never call the CSCopyMachineName on 10.0 or 10.0.1
        // because of another issue.

        if (result != nil && gMoreCSSystemVersion == kMoreCSMacOSX10point0) {
            CFRetain(result);
        }
    }

    return result;
}

extern pascal CFStringRef MoreCSCopyMachineName(void)
    // See comment in header file.
{
    CFStringRef result;

    if ( gMoreCSSystemVersion == 0 ) {
        (void) Gestalt(gestaltSystemVersion, (SInt32 *) &gMoreCSSystemVersion);
    }

    if ( gMoreCSSystemVersion < kMoreCSMacOSX10point0 ) {

        // Running on traditional Mac OS.  If we have a recent version
        // of CarbonLib (1.5 and above) that supports the routine, use
        // that.  Otherwise fall back to the Resource Manager.

        if ( CSCopyMachineName != (void *) kUnresolvedCFragSymbolAddress) {
            result = CSCopyMachineName();
        } else {
            result = CreateCFStringFromStringResource(-16413);
        }

    } else if ( gMoreCSSystemVersion < kMoreCSMacOSX10point1 ) {

        // Running on Mac OS X 10.0.x.  Read the file directly because
        // the API returns the wrong information (the BSD hostname rather
        // than the computer name) [2650897].

        result = ReadMachineNameFromFile();

    } else {

        // Running on Mac OS X 10.1 and above.  Let's just call the API.

        // The following checks that the CFM weak link worked.
        // It's benign for the Mach-O build.

        if ( CSCopyMachineName == (void *) kUnresolvedCFragSymbolAddress ) {
            result = nil;
        } else {
            result = CSCopyMachineName();
        }
    }

    return result;

Listing 1. Code for getting user and machine name