ungetc.c revision 261363 
1/*
2 * Copyright (c) 2000-2001, 2004 Proofpoint, Inc. and its suppliers.
3 *      All rights reserved.
4 * Copyright (c) 1990, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Chris Torek.
9 *
10 * By using this file, you agree to the terms and conditions set
11 * forth in the LICENSE file which can be found at the top level of
12 * the sendmail distribution.
13 */
14
15#include <sm/gen.h>
16SM_IDSTR(id, "@(#)$Id: ungetc.c,v 1.31 2013/11/22 20:51:44 ca Exp $")
17
18#include <stdlib.h>
19#include <string.h>
20#include <signal.h>
21#include <sm/time.h>
22#include <errno.h>
23#include <sm/io.h>
24#include <sm/heap.h>
25#include <sm/assert.h>
26#include <sm/conf.h>
27#include "local.h"
28
29static void	sm_submore_x __P((SM_FILE_T *));
30
31/*
32**  SM_SUBMORE_X -- expand ungetc buffer
33**
34**  Expand the ungetc buffer `in place'.  That is, adjust fp->f_p when
35**  the buffer moves, so that it points the same distance from the end,
36**  and move the bytes in the buffer around as necessary so that they
37**  are all at the end (stack-style).
38**
39**	Parameters:
40**		fp -- the file pointer
41**
42**	Results:
43**		none.
44**
45**	Exceptions:
46**		F:sm_heap -- out of memory
47*/
48
49static void
50sm_submore_x(fp)
51	SM_FILE_T *fp;
52{
53	register int i;
54	register unsigned char *p;
55
56	if (fp->f_ub.smb_base == fp->f_ubuf)
57	{
58		/* Get a buffer; f_ubuf is fixed size. */
59		p = sm_malloc_x((size_t) SM_IO_BUFSIZ);
60		fp->f_ub.smb_base = p;
61		fp->f_ub.smb_size = SM_IO_BUFSIZ;
62		p += SM_IO_BUFSIZ - sizeof(fp->f_ubuf);
63		for (i = sizeof(fp->f_ubuf); --i >= 0;)
64			p[i] = fp->f_ubuf[i];
65		fp->f_p = p;
66		return;
67	}
68	i = fp->f_ub.smb_size;
69	p = sm_realloc_x(fp->f_ub.smb_base, i << 1);
70
71	/* no overlap (hence can use memcpy) because we doubled the size */
72	(void) memcpy((void *) (p + i), (void *) p, (size_t) i);
73	fp->f_p = p + i;
74	fp->f_ub.smb_base = p;
75	fp->f_ub.smb_size = i << 1;
76}
77
78/*
79**  SM_IO_UNGETC -- place a character back into the buffer just read
80**
81**	Parameters:
82**		fp -- the file pointer affected
83**		timeout -- time to complete ungetc
84**		c -- the character to place back
85**
86**	Results:
87**		On success, returns value of character placed back, 0-255.
88**		Returns SM_IO_EOF if c == SM_IO_EOF or if last operation
89**		was a write and flush failed.
90**
91**	Exceptions:
92**		F:sm_heap -- out of memory
93*/
94
95int
96sm_io_ungetc(fp, timeout, c)
97	register SM_FILE_T *fp;
98	int timeout;
99	int c;
100{
101	SM_REQUIRE_ISA(fp, SmFileMagic);
102	if (c == SM_IO_EOF)
103		return SM_IO_EOF;
104	if (timeout == SM_TIME_IMMEDIATE)
105	{
106		/*
107		**  Ungetting the buffer will take time and we are wanted to
108		**  return immediately. So...
109		*/
110
111		errno = EAGAIN;
112		return SM_IO_EOF;
113	}
114
115	if (!Sm_IO_DidInit)
116		sm_init();
117	if ((fp->f_flags & SMRD) == 0)
118	{
119		/*
120		**  Not already reading: no good unless reading-and-writing.
121		**  Otherwise, flush any current write stuff.
122		*/
123
124		if ((fp->f_flags & SMRW) == 0)
125			return SM_IO_EOF;
126		if (fp->f_flags & SMWR)
127		{
128			if (sm_flush(fp, &timeout))
129				return SM_IO_EOF;
130			fp->f_flags &= ~SMWR;
131			fp->f_w = 0;
132			fp->f_lbfsize = 0;
133		}
134		fp->f_flags |= SMRD;
135	}
136	c = (unsigned char) c;
137
138	/*
139	**  If we are in the middle of ungetc'ing, just continue.
140	**  This may require expanding the current ungetc buffer.
141	*/
142
143	if (HASUB(fp))
144	{
145		if (fp->f_r >= fp->f_ub.smb_size)
146			sm_submore_x(fp);
147		*--fp->f_p = c;
148		fp->f_r++;
149		return c;
150	}
151	fp->f_flags &= ~SMFEOF;
152
153	/*
154	**  If we can handle this by simply backing up, do so,
155	**  but never replace the original character.
156	**  (This makes sscanf() work when scanning `const' data.)
157	*/
158
159	if (fp->f_bf.smb_base != NULL && fp->f_p > fp->f_bf.smb_base &&
160	    fp->f_p[-1] == c)
161	{
162		fp->f_p--;
163		fp->f_r++;
164		return c;
165	}
166
167	/*
168	**  Create an ungetc buffer.
169	**  Initially, we will use the `reserve' buffer.
170	*/
171
172	fp->f_ur = fp->f_r;
173	fp->f_up = fp->f_p;
174	fp->f_ub.smb_base = fp->f_ubuf;
175	fp->f_ub.smb_size = sizeof(fp->f_ubuf);
176	fp->f_ubuf[sizeof(fp->f_ubuf) - 1] = c;
177	fp->f_p = &fp->f_ubuf[sizeof(fp->f_ubuf) - 1];
178	fp->f_r = 1;
179
180	return c;
181}
182