sfreserve.c   [plain text]

#include	"sfhdr.h"

/*	Reserve a segment of data or buffer.
**
**	Written by Kiem-Phong Vo.
*/

#if __STD_C
Void_t* sfreserve(reg Sfio_t* f, ssize_t size, int type)
#else
Void_t* sfreserve(f,size,type)
reg Sfio_t*	f;	/* file to peek */
ssize_t		size;	/* size of peek */
int		type;	/* LOCKR: lock stream, LASTR: last record */
#endif
{
	reg ssize_t	n, sz;
	reg Sfrsrv_t*	rsrv;
	reg Void_t*	data;
	reg int		mode;

	SFMTXSTART(f,NIL(Void_t*));

	/* initialize io states */
	rsrv = NIL(Sfrsrv_t*);
	_Sfi = f->val = -1;

	/* return the last record */
	if(type == SF_LASTR )
	{	if((rsrv = f->rsrv) && (n = -rsrv->slen) > 0)
		{	rsrv->slen = 0;
			_Sfi = f->val = n;
			SFMTXRETURN(f, (Void_t*)rsrv->data);
		}
		else	SFMTXRETURN(f, NIL(Void_t*));
	}

	if(type > 0 && !(type == SF_LOCKR || type == 1) )
		SFMTXRETURN(f, NIL(Void_t*));

	if((sz = size) == 0 && type != 0)
	{	/* only return the current status and possibly lock stream */
		if((f->mode&SF_RDWR) != f->mode && _sfmode(f,0,0) < 0)
			SFMTXRETURN(f, NIL(Void_t*));

		SFLOCK(f,0);
		if((n = f->endb - f->next) < 0)
			n = 0;

		if(!f->data && type > 0)
			rsrv = _sfrsrv(f,0);

		goto done;
	}
	if(sz < 0)
		sz = -sz;

	/* iterate until get to a stream that has data or buffer space */
	for(;;)
	{	/* prefer read mode so that data is always valid */
		if(!(mode = (f->flags&SF_READ)) )
			mode = SF_WRITE;
		if((int)f->mode != mode && _sfmode(f,mode,0) < 0)
		{	n = -1;
			goto done;
		}

		SFLOCK(f,0);

		if((n = f->endb - f->next) < 0)	/* possible for string+rw */
			n = 0;

		if(n > 0 && n >= sz)	/* all done */
			break;

		/* do a buffer refill or flush */
		if(f->mode&SF_WRITE)
			(void)SFFLSBUF(f, -1);
		else if(type > 0 && f->extent < 0 && (f->flags&SF_SHARE) )
		{	if(n == 0) /* peek-read only if there is no buffered data */
			{	f->mode |= SF_RV;
				(void)SFFILBUF(f, sz == 0 ? -1 : (sz-n) );
			}
			if((n = f->endb - f->next) < sz)
			{	if(f->mode&SF_PKRD)
				{	f->endb = f->endr = f->next;
					f->mode &= ~SF_PKRD;
				}
				goto done;
			}
		}
		else	(void)SFFILBUF(f, sz == 0 ? -1 : (sz-n) );

		/* now have data */
		if((n = f->endb - f->next) > 0)
			break;
		else if(n < 0)
			n = 0;

		/* this test fails only if unstacked to an opposite stream */
		if((f->mode&mode) != 0)
			break;
	}

	if(n > 0 && n < sz && (f->mode&mode) != 0 )
	{	/* try to accomodate request size */	
		if(f->flags&SF_STRING)
		{	if((f->mode&SF_WRITE) && (f->flags&SF_MALLOC) )
			{	(void)SFWR(f,f->next,sz,f->disc);
				n = f->endb - f->next;
			}
		}
		else if(f->mode&SF_WRITE)
		{	if(type > 0 && (rsrv = _sfrsrv(f,sz)) )
				n = sz;
		}
		else /*if(f->mode&SF_READ)*/
		{	if(type <= 0 && (rsrv = _sfrsrv(f,sz)) &&
			   (n = SFREAD(f,(Void_t*)rsrv->data,sz)) < sz)
				rsrv->slen = -n;
		}
	}

done:
	/* return true buffer size */
	_Sfi = f->val = n;

	SFOPEN(f,0);

	if((sz > 0 && n < sz) || (n == 0 && type <= 0) )
		SFMTXRETURN(f, NIL(Void_t*));

	if((data = rsrv ? (Void_t*)rsrv->data : (Void_t*)f->next) )
	{	if(type > 0)
		{	f->mode |= SF_PEEK;
			f->endr = f->endw = f->data;
		}
		else if(data == (Void_t*)f->next)
			f->next += (size >= 0 ? size : n);
	}

	SFMTXRETURN(f, data);
}