ungetc.c revision 90792 
1/*
2 * Copyright (c) 2000-2001 Sendmail, 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 1.28 2001/09/11 04:04:49 gshapiro Exp $")
17
18#include <stdlib.h>
19#include <string.h>
20#include <signal.h>
21#include <sys/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
29/*
30**  SM_SUBMORE_X -- expand ungetc buffer
31**
32**  Expand the ungetc buffer `in place'.  That is, adjust fp->f_p when
33**  the buffer moves, so that it points the same distance from the end,
34**  and move the bytes in the buffer around as necessary so that they
35**  are all at the end (stack-style).
36**
37**	Parameters:
38**		fp -- the file pointer
39**
40**	Results:
41**		none.
42**
43**	Exceptions:
44**		F:sm_heap -- out of memory
45*/
46
47static void
48sm_submore_x(fp)
49	register SM_FILE_T *fp;
50{
51	register int i;
52	register unsigned char *p;
53
54	if (fp->f_ub.smb_base == fp->f_ubuf)
55	{
56		/* Get a buffer; f_ubuf is fixed size. */
57		p = sm_malloc_x((size_t) SM_IO_BUFSIZ);
58		fp->f_ub.smb_base = p;
59		fp->f_ub.smb_size = SM_IO_BUFSIZ;
60		p += SM_IO_BUFSIZ - sizeof(fp->f_ubuf);
61		for (i = sizeof(fp->f_ubuf); --i >= 0;)
62			p[i] = fp->f_ubuf[i];
63		fp->f_p = p;
64		return;
65	}
66	i = fp->f_ub.smb_size;
67	p = sm_realloc_x(fp->f_ub.smb_base, i << 1);
68
69	/* no overlap (hence can use memcpy) because we doubled the size */
70	(void) memcpy((void *) (p + i), (void *) p, (size_t) i);
71	fp->f_p = p + i;
72	fp->f_ub.smb_base = p;
73	fp->f_ub.smb_size = i << 1;
74}
75
76/*
77**  SM_IO_UNGETC -- place a character back into the buffer just read
78**
79**	Parameters:
80**		fp -- the file pointer affected
81**		timeout -- time to complete ungetc
82**		c -- the character to place back
83**
84**	Results:
85**		On success, returns value of character placed back, 0-255.
86**		Returns SM_IO_EOF if c == SM_IO_EOF or if last operation
87**		was a write and flush failed.
88**
89**	Exceptions:
90**		F:sm_heap -- out of memory
91*/
92
93int
94sm_io_ungetc(fp, timeout, c)
95	register SM_FILE_T *fp;
96	int timeout;
97	int c;
98{
99	SM_REQUIRE_ISA(fp, SmFileMagic);
100	if (c == SM_IO_EOF)
101		return SM_IO_EOF;
102	if (timeout == SM_TIME_IMMEDIATE)
103	{
104		/*
105		**  Ungetting the buffer will take time and we are wanted to
106		**  return immediately. So...
107		*/
108
109		errno = EAGAIN;
110		return SM_IO_EOF;
111	}
112
113	if (!Sm_IO_DidInit)
114		sm_init();
115	if ((fp->f_flags & SMRD) == 0)
116	{
117		/*
118		**  Not already reading: no good unless reading-and-writing.
119		**  Otherwise, flush any current write stuff.
120		*/
121
122		if ((fp->f_flags & SMRW) == 0)
123			return SM_IO_EOF;
124		if (fp->f_flags & SMWR)
125		{
126			if (sm_flush(fp, &timeout))
127				return SM_IO_EOF;
128			fp->f_flags &= ~SMWR;
129			fp->f_w = 0;
130			fp->f_lbfsize = 0;
131		}
132		fp->f_flags |= SMRD;
133	}
134	c = (unsigned char) c;
135
136	/*
137	**  If we are in the middle of ungetc'ing, just continue.
138	**  This may require expanding the current ungetc buffer.
139	*/
140
141	if (HASUB(fp))
142	{
143		if (fp->f_r >= fp->f_ub.smb_size)
144			sm_submore_x(fp);
145		*--fp->f_p = c;
146		fp->f_r++;
147		return c;
148	}
149	fp->f_flags &= ~SMFEOF;
150
151	/*
152	**  If we can handle this by simply backing up, do so,
153	**  but never replace the original character.
154	**  (This makes sscanf() work when scanning `const' data.)
155	*/
156
157	if (fp->f_bf.smb_base != NULL && fp->f_p > fp->f_bf.smb_base &&
158	    fp->f_p[-1] == c)
159	{
160		fp->f_p--;
161		fp->f_r++;
162		return c;
163	}
164
165	/*
166	**  Create an ungetc buffer.
167	**  Initially, we will use the `reserve' buffer.
168	*/
169
170	fp->f_ur = fp->f_r;
171	fp->f_up = fp->f_p;
172	fp->f_ub.smb_base = fp->f_ubuf;
173	fp->f_ub.smb_size = sizeof(fp->f_ubuf);
174	fp->f_ubuf[sizeof(fp->f_ubuf) - 1] = c;
175	fp->f_p = &fp->f_ubuf[sizeof(fp->f_ubuf) - 1];
176	fp->f_r = 1;
177
178	return c;
179}
180