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      1 /*	$OpenBSD: fread.c,v 1.12 2014/05/01 16:40:36 deraadt Exp $ */
      2 /*-
      3  * Copyright (c) 1990, 1993
      4  *	The Regents of the University of California.  All rights reserved.
      5  *
      6  * This code is derived from software contributed to Berkeley by
      7  * Chris Torek.
      8  *
      9  * Redistribution and use in source and binary forms, with or without
     10  * modification, are permitted provided that the following conditions
     11  * are met:
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  * 2. Redistributions in binary form must reproduce the above copyright
     15  *    notice, this list of conditions and the following disclaimer in the
     16  *    documentation and/or other materials provided with the distribution.
     17  * 3. Neither the name of the University nor the names of its contributors
     18  *    may be used to endorse or promote products derived from this software
     19  *    without specific prior written permission.
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     31  * SUCH DAMAGE.
     32  */
     33 
     34 #include <stdio.h>
     35 #include <string.h>
     36 #include <stdint.h>
     37 #include <errno.h>
     38 #include <sys/param.h>
     39 #include "local.h"
     40 
     41 #define MUL_NO_OVERFLOW	(1UL << (sizeof(size_t) * 4))
     42 
     43 size_t
     44 fread(void *buf, size_t size, size_t count, FILE *fp)
     45 {
     46 	/*
     47 	 * Extension:  Catch integer overflow.
     48 	 */
     49 	if ((size >= MUL_NO_OVERFLOW || count >= MUL_NO_OVERFLOW) &&
     50 	    size > 0 && SIZE_MAX / size < count) {
     51 		errno = EOVERFLOW;
     52 		fp->_flags |= __SERR;
     53 		return (0);
     54 	}
     55 
     56 	const size_t desired_total = count * size;
     57 	size_t total = desired_total;
     58 
     59 	/*
     60 	 * ANSI and SUSv2 require a return value of 0 if size or count are 0.
     61 	 */
     62 	if (total == 0) {
     63 		return (0);
     64 	}
     65 
     66 	FLOCKFILE(fp);
     67 	_SET_ORIENTATION(fp, -1);
     68 
     69 	// TODO: how can this ever happen?!
     70 	if (fp->_r < 0)
     71 		fp->_r = 0;
     72 
     73 	/*
     74 	 * Ensure _bf._size is valid.
     75 	 */
     76 	if (fp->_bf._base == NULL) {
     77 		__smakebuf(fp);
     78 	}
     79 
     80 	char* dst = buf;
     81 
     82 	while (total > 0) {
     83 		/*
     84 		 * Copy data out of the buffer.
     85 		 */
     86 		size_t buffered_bytes = MIN((size_t) fp->_r, total);
     87 		memcpy(dst, fp->_p, buffered_bytes);
     88 		fp->_p += buffered_bytes;
     89 		fp->_r -= buffered_bytes;
     90 		dst += buffered_bytes;
     91 		total -= buffered_bytes;
     92 
     93 		/*
     94 		 * Are we done?
     95 		 */
     96 		if (total == 0) {
     97 			goto out;
     98 		}
     99 
    100 		/*
    101 		 * Do we have so much more to read that we should
    102 		 * avoid copying it through the buffer?
    103 		 */
    104 		if (total > (size_t) fp->_bf._size) {
    105 			/*
    106 			 * Make sure that fseek doesn't think it can
    107 			 * reuse the buffer since we are going to read
    108 			 * directly from the file descriptor.
    109 			 */
    110 			fp->_flags |= __SMOD;
    111 			break;
    112 		}
    113 
    114 		/*
    115 		 * Less than a buffer to go, so refill the buffer and
    116 		 * go around the loop again.
    117 		 */
    118 		if (__srefill(fp)) {
    119 			goto out;
    120 		}
    121 	}
    122 
    123 	/*
    124 	 * Read directly into the caller's buffer.
    125 	 */
    126 	while (total > 0) {
    127 		ssize_t bytes_read = (*fp->_read)(fp->_cookie, dst, total);
    128 		if (bytes_read <= 0) {
    129 			fp->_flags |= (bytes_read == 0) ? __SEOF : __SERR;
    130 			break;
    131 		}
    132 		dst += bytes_read;
    133 		total -= bytes_read;
    134 	}
    135 
    136 out:
    137 	FUNLOCKFILE(fp);
    138 	return ((desired_total - total) / size);
    139 }
    140