[PROPOSAL] Remove unsafe Fortran API calls

[derobins]

PROBLEM

The HDF4 Fortran API has some API wrappers that store pointers in 32-bit Fortran integers, which is fundamentally unsafe on 64-bit systems.

Example (from: hdf/src/dff.c)

/*-----------------------------------------------------------------------------  
 * Name:    dfiopen                                                              
 * Purpose: call DFopen to open HDF file                                         
 * Inputs:  name: name of file to open                                           
 *      acc_mode: access mode - integer with value DFACC_READ etc.               
 *      defdds: default number of DDs per header block                           
 *      namelen: length of name                                                  
 * Returns: 0 on success, -1 on failure with DFerror set                         
 * Users:   HDF Fortran programmers                                              
 * Invokes: DFopen                                                               
 * Method:  Convert filename to C string, call DFopen                            
 * Note: DFopen actually return *DF.  In machines that a pointer                 
 *       is bigger than a Fortran INTEGER, this routine would fail.              
 *       This is a design error and has no easy portable solution.               
 *---------------------------------------------------------------------------*/  
FRETVAL(intf)                                                                    
ndfiopen(_fcd name, intf *acc_mode, intf *defdds, intf *namelen)                 
{                                                                                
    char *fn;                                                                    
    intf  ret;                                                                   
                                                                                 
    fn = DFIf2cstring(name, (intn)*namelen);                                     
    /* For compiler warning, see note above. */                                  
    ret = (intf)DFopen(fn, (intn)*acc_mode, (intn)*defdds);                      
    free(fn);                                                                    
    return (ret);                                                                
} 

We do not have a list of unsafe API calls at this time. We'd have to compile this list and any affected wrapper calls would have to be either removed or the integer type would have to match the pointer size.

PROPOSED FIX

• Remove the unsafe Fortran wrapper calls or change the API so that the integer size matches the pointer size.
• At the very least, the unsafe calls need to be documented

HOW WOULD USERS BE AFFECTED?

PRO
➕ Fortran interface would no longer be unsafe

CON
➖ Unsafe Fortran calls might be removed
➖ Might require Fortran 95, which would make Fortran 77 users sad

NEUTRAL
✔️ If this breaks important code, we could make the HDF4 4.2 line a maintenance branch that gets critical bugfixes