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Related Info: File Manager (PBxxx)

The Blessed Folder

By Donald Koscheka, Arthur Young & Co., MacTutor Contributing Editor

A colleague related an interesting experience that occurred to him at MacHacks this year. He asked an Apple Engineer whether he could mount Appleshare volumes under program control. The engineer asked him why he’d want to and went on to explain that it’s simply not something you do. If you need to mount Appleshare volumes, use the chooser.

This struck me as odd because I’ve always believed that your programs should be able to do anything that the user can do.

Imagine some inexperienced user being told that “the server has unexpectedly shut down”. Consider the options that this error message presents to the uninitiated: Ask someone what’s going on, call Apple’s customer service department or read the manual.

Each one of these options punishes the user for a mistake that he or she did not make! Why not have a little task running somewhere that tries to reconnect the user and, failing that, alerts the poor soul that they may have to visit the chooser to regain access to the server?

Perhaps too many people at Apple are falling into that old trap of believing in everything they read. The human interface guidelines should be just that, guidelines. When you start taking guidelines as gospel, you start closing the door on creativity and intuition.

It seems to me that the good people at Apple need to spend less time saying “You can’t do that” and spend more time asking, “Why can’t you do that?”

The file manager is another area where the Macintosh tends to dump problems in the user’s lap. Consider the “Where is ...” dialog that pops up in Hypercard from time to time. Imagine how intimidating that must be to the neophyte, “If the computer can’t find it, I’m sure not going to have any luck”.

A better user interface might suggest to the user that the Mac can search the disk on the user’s behalf. It might take a while, but if the user doesn’t have a clue as to where some file is, time really doesn’t become an issue.

The problem with the file manager is that it relies too heavily on the user. Giving control to the user is a wonderful idea. Nonetheless, the user should be able to delegate tasks like searching back to the Macintosh.

Perhaps you need to store a preferences or help file somewhere. If the user moves this file on you, are you supposed to pop a dialog asking the user to find the file for you again? Of course not, you’re going to store the file in a folder that you’re guaranteed to have access to at all times. That folder is the blessed folder, so called because it contains the system file and startup application (typically the Finder). All you need is access to the blessed folder under program control and your problem is solved.

Fortunately, Apple does have a champion for developers who would like to unload some of the file management stuff from the user. Jim Friedlander has published many useful tech notes for developer technical services describing how to do things like finding that blessed folder.

Listing 1 adds an interesting spin to this blessed folder business. This XCMD, called Volumes, returns a list of all mounted volumes. The volumes XCMD uses a handy little routine called pStrToField that adds a pascal format string to the end of a zero-terminated run of text. It’s a useful way of adding names that you get from the toolbox which are almost always Pascal strings to a container that you can return to Hypercard.

If you’re building a list, terminate each item with the ‘\r’ (carriage return) character. If you are building items, then use a comma. If you don’t want any delimiters, then pass a ‘\0’.

Because pStrToField is a general purpose routine, you should add it to whatever library you use to store such routines. If you are a regular reader of this column, you know that I use a file called “HyperUtils.c” for such routines.

Retrieving the list of volumes is simple. Set some index counter to 1. Then repeatedly call PBHGetVinfo with the following fields set in the parameter block:

  ioNamePtr = pointer to a string to store the name in
  ioVRefNum  = -1, tell file manager to use the volume index.
  ioVolIndex= your index counter.  

Keep incrementing ioVolIndex until PBHGetVInfo returns an error. That’s a good indication that no more volumes were found.

Each time that pbHGetVInfo succeeds, the name of the found volume will be returned in ioNamePtr as a Pascal string. We tack the obligatory colon to the end of this name and then add the new string to the volume list that we’re building in vList.

After all is said and done, we set the last character in the container to 0 because Hypercard expects containers to be null terminated.

Knowing the names of all mounted volumes may not seem useful at first blush but given a little time, I’m sure you’ll find many interesting ways to use this XCMD.

Once we know all the volume names on line, we can find all the blessed folders. A blessed folder is one that contains the system and startup application (usually the finder). You can find the blessed folder by inspection; it’s the one whose folder contains a very small image of a Macintosh.

Knowing the blessed folder does have applicability in very many cases. Perhaps your XCMD expects to store a preferences file in the blessed folder. At any rate, knowing how to find the blessed folder should be a part of every Mac programmer’s repertoire. The XCMD in listing 2, BlessedFolder, does just that. It’s based on tech note #129 by Jim Friedlander.

Note that this time we use PBHGetvinfo with the volume reference set to 0 and the index set to -1. By passing the name of a volume, we are telling the file manager to look up information about this volume using its name rather than a reference number or index.

The information returned by PBHGetVinfo gets a little fuzzy here. One of the fields returned is ioVFndrInfo which is an array of 8 ling integers. The first entry in this array is the id of the blessed folder. I’m sure this array is documented somewhere in tech notes and if you want to further explore this information, that’s a good place to start since IM volume IV seems to gloss over this field.

Once we know the directory id of the blessed folder, we can pass it to, climbtree (published last month), to reconstruct the full pathname of this folder. Climbtree works just as well for folders as it does for files. We start climbtree off with the directory id of the blessed folder which was assigned to theCPB.dirInfo.ioDrDirID. Climbtree also needs a volume reference number which we pass via ioVRefNum.

Climbtree requires that you declare a CInfoPBRec somewhere before calling it. This is because Climbtree is recursive, and I didn’t want stack space being consumed by a declaration of the relatively large catalog info record with each activation. If you’re a purist, you might take your chances with the heap and create a nonrelocatable block in each activation. If 8K seems like too much stack space to you, go ahead and declare theCPB as an automatic of climbtree.

This month’s XCMDs fall into the category of “Now that I have them, what can I do with them”. Play around for a while and see what you discover on your own. In the meantime, I’ll be cooking up some useful applications for these XCMDs.

/************************************/
/* File: Volumes.c */
/* */
/* Return a list of all on-line  */
/* Takes no input and returns */
/* a carrieage return delimited  */
/* list of all volumes currently */
/* on line*/
/* */
/* --------------------------------*/
/* ©1989, Donald Koscheka */
/* All Rights Reserved    */
/************************************/

#include<MacTypes.h>
#include<OSUtil.h>
#include<MemoryMgr.h>
#include<FileMgr.h>
#include<ResourceMgr.h>
#include<pascal.h>
#include<hfs.h>
#include<string.h>
#include  “HyperXCmd.h”
#include“HyperUtils.h”

#define nil 0L

char    colon[2] = “\p:”;

short pStrToField( str, delim, list )
 char *str; 
 char delim;
 Handle list;
/*********************************
* Given a pascal string, append it to
* the end of the handle passed in list
* which is assumed to be a valid handle
* of length >= 0.
*
* delim is some character to stick on the
* end of the string to delimit it.
* if you want to build a list for presentation
* in a field, pass ‘\r’ as the delimiter
*
* If you are building items pass a comma
* 
* A value of 0 for delim is ignored.  Pass
* 0 when you don’t want a delimiter.
*********************************/
{
 long   strlen;/* length of input string*/
 long   oldHSize;/* size of input handle*/
 char   *end;  /* pointer to end of data     */
 
 strlen = str[0];/* length of string is in first byte*/
 oldHSize = GetHandleSize( list );
 
 SetHandleSize( list, oldHSize + strlen );
 end = *list + oldHSize;

 BlockMove( (char *)&str[1] , end, strlen );
 
 if( delim ){
 oldHSize = GetHandleSize( list );
 SetHandleSize( list, oldHSize + 1 );
 end = *list + oldHSize;
 *end = delim;
 } 
}

pascal void main( paramPtr )
 XCmdBlockPtr  paramPtr;
{
 short  index;
 long   len; 
 char   *end;
 HParamBlockRec  theHPB;
 Handle vlist;
 char   vol_Name[256];
 OSErr  err;

 colon[0] = 1;
 colon[1] = ‘:’;
 
 /*** empty is the default answer ***/
 vlist = NewHandle( 0L );

 /*** Search for every volume that is on-line***/
 index = 1;
 do{  /*** Appeal to the volume manager      ***/
 /*** for the name of each volume  ***/
 /*** that is known to it ***/

 vol_Name[0] = ‘\0’;
 theHPB.volumeParam.ioNamePtr = (StringPtr)vol_Name;     
 theHPB.volumeParam.ioVRefNum = (short)-1;         
 theHPB.volumeParam.ioVolIndex   = index;                      
 err = PBHGetVInfo( &theHPB, 0);
 
 if ( !err ){/** Add each Volume to List **/
 Concat( vol_Name, colon );
 pStrToField( (char *)&vol_Name, ‘\r’, vlist );
 index += 1;
 }
 }while (err == noErr);

 /*** once done, tack a 0 onto the end of vlist ***/
 len = GetHandleSize( vlist );
 SetHandleSize( vlist, len+1 );
 end = *vlist + len;
 *end = ‘\0’;
 
 paramPtr->returnValue = vlist;
}

Listing 1. Volumes.c

/************************************/
/* File: Blessed Folder.c */
/* */
/* Given the name of a volume */
/* in params[0]  */
/* returns the id of the  */
/* blessed folder. */
/* --------------------------------*/
/* Based on tech note #129*/
/* by Jim Friedlander*/
/************************************/

#include<MacTypes.h>
#include<OSUtil.h>
#include<MemoryMgr.h>
#include<FileMgr.h>
#include<ResourceMgr.h>
#include<pascal.h>
#include<hfs.h>
#include<string.h>
#include  “HyperXCmd.h”
#include“HyperUtils.h”

#define nil 0L

char    colon[2] = “\p:”;
pascal void main( paramPtr )
 XCmdBlockPtr  paramPtr;
{
long    sid;/*** id of  blessed folder ***/
HParamBlockRec theHPB;  
CInfoPBRectheCPB;/**to reconstruct path name**/
char    vName[256];/*** volume we’re checking      ***/
char    fullPath[256];
OSErr   err;

 HLock( paramPtr->params[0] );
 ZeroToPas( paramPtr, *(paramPtr->params[0]), &vName );
 HUnlock( paramPtr->params[0] );
 /*** Given the name of a volume,  ***/
 /*** try to get the volume reference***/
 /*** number     ***/
 theHPB.volumeParam.ioNamePtr = (StringPtr)vName;  
 theHPB.volumeParam.ioVRefNum = (short)0;          
 theHPB.volumeParam.ioVolIndex = -1; 
 err = PBHGetVInfo( &theHPB, 0);

  fullPath[0] = ‘\0’;
 if ( !err ){
 theCPB.dirInfo.ioFDirIndex = -1;
 theCPB.dirInfo.ioDrDirID =theHPB.volumeParam.ioVFndrInfo[0]; 
 theCPB.dirInfo.ioVRefNum   = theHPB.volumeParam.ioVRefNum;    
 fullPath[0] = ‘\0’; 
 ClimbTree(theCPB.dirInfo.ioDrDirID,
 (CInfoPBPtr)&theCPB, (char *)fullPath );
 }
 paramPtr->returnValue = PasToZero( paramPtr, fullPath );
}

Listing 2. BlessedFolder.c