xref: /illumos-gate/usr/src/cmd/sendmail/libsm/ungetc.c (revision 012e6ce759c490003aed29439cc47d3d73a99ad3)
1 /*
2  * Copyright (c) 2000-2001, 2004 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>
16 SM_IDSTR(id, "@(#)$Id: ungetc.c,v 1.30 2005/06/14 23:07:20 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 
29 static 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 
49 static void
50 sm_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 
95 int
96 sm_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