xref: /titanic_52/usr/src/cmd/sendmail/libsm/ungetc.c (revision cc7a88b54b4969574f03e1a1225bb13be487f5db)
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 #pragma ident	"%Z%%M%	%I%	%E% SMI"
16 
17 #include <sm/gen.h>
18 SM_IDSTR(id, "@(#)$Id: ungetc.c,v 1.30 2005/06/14 23:07:20 ca Exp $")
19 
20 #include <stdlib.h>
21 #include <string.h>
22 #include <signal.h>
23 #include <sm/time.h>
24 #include <errno.h>
25 #include <sm/io.h>
26 #include <sm/heap.h>
27 #include <sm/assert.h>
28 #include <sm/conf.h>
29 #include "local.h"
30 
31 static void	sm_submore_x __P((SM_FILE_T *));
32 
33 /*
34 **  SM_SUBMORE_X -- expand ungetc buffer
35 **
36 **  Expand the ungetc buffer `in place'.  That is, adjust fp->f_p when
37 **  the buffer moves, so that it points the same distance from the end,
38 **  and move the bytes in the buffer around as necessary so that they
39 **  are all at the end (stack-style).
40 **
41 **	Parameters:
42 **		fp -- the file pointer
43 **
44 **	Results:
45 **		none.
46 **
47 **	Exceptions:
48 **		F:sm_heap -- out of memory
49 */
50 
51 static void
52 sm_submore_x(fp)
53 	SM_FILE_T *fp;
54 {
55 	register int i;
56 	register unsigned char *p;
57 
58 	if (fp->f_ub.smb_base == fp->f_ubuf)
59 	{
60 		/* Get a buffer; f_ubuf is fixed size. */
61 		p = sm_malloc_x((size_t) SM_IO_BUFSIZ);
62 		fp->f_ub.smb_base = p;
63 		fp->f_ub.smb_size = SM_IO_BUFSIZ;
64 		p += SM_IO_BUFSIZ - sizeof(fp->f_ubuf);
65 		for (i = sizeof(fp->f_ubuf); --i >= 0;)
66 			p[i] = fp->f_ubuf[i];
67 		fp->f_p = p;
68 		return;
69 	}
70 	i = fp->f_ub.smb_size;
71 	p = sm_realloc_x(fp->f_ub.smb_base, i << 1);
72 
73 	/* no overlap (hence can use memcpy) because we doubled the size */
74 	(void) memcpy((void *) (p + i), (void *) p, (size_t) i);
75 	fp->f_p = p + i;
76 	fp->f_ub.smb_base = p;
77 	fp->f_ub.smb_size = i << 1;
78 }
79 
80 /*
81 **  SM_IO_UNGETC -- place a character back into the buffer just read
82 **
83 **	Parameters:
84 **		fp -- the file pointer affected
85 **		timeout -- time to complete ungetc
86 **		c -- the character to place back
87 **
88 **	Results:
89 **		On success, returns value of character placed back, 0-255.
90 **		Returns SM_IO_EOF if c == SM_IO_EOF or if last operation
91 **		was a write and flush failed.
92 **
93 **	Exceptions:
94 **		F:sm_heap -- out of memory
95 */
96 
97 int
98 sm_io_ungetc(fp, timeout, c)
99 	register SM_FILE_T *fp;
100 	int timeout;
101 	int c;
102 {
103 	SM_REQUIRE_ISA(fp, SmFileMagic);
104 	if (c == SM_IO_EOF)
105 		return SM_IO_EOF;
106 	if (timeout == SM_TIME_IMMEDIATE)
107 	{
108 		/*
109 		**  Ungetting the buffer will take time and we are wanted to
110 		**  return immediately. So...
111 		*/
112 
113 		errno = EAGAIN;
114 		return SM_IO_EOF;
115 	}
116 
117 	if (!Sm_IO_DidInit)
118 		sm_init();
119 	if ((fp->f_flags & SMRD) == 0)
120 	{
121 		/*
122 		**  Not already reading: no good unless reading-and-writing.
123 		**  Otherwise, flush any current write stuff.
124 		*/
125 
126 		if ((fp->f_flags & SMRW) == 0)
127 			return SM_IO_EOF;
128 		if (fp->f_flags & SMWR)
129 		{
130 			if (sm_flush(fp, &timeout))
131 				return SM_IO_EOF;
132 			fp->f_flags &= ~SMWR;
133 			fp->f_w = 0;
134 			fp->f_lbfsize = 0;
135 		}
136 		fp->f_flags |= SMRD;
137 	}
138 	c = (unsigned char) c;
139 
140 	/*
141 	**  If we are in the middle of ungetc'ing, just continue.
142 	**  This may require expanding the current ungetc buffer.
143 	*/
144 
145 	if (HASUB(fp))
146 	{
147 		if (fp->f_r >= fp->f_ub.smb_size)
148 			sm_submore_x(fp);
149 		*--fp->f_p = c;
150 		fp->f_r++;
151 		return c;
152 	}
153 	fp->f_flags &= ~SMFEOF;
154 
155 	/*
156 	**  If we can handle this by simply backing up, do so,
157 	**  but never replace the original character.
158 	**  (This makes sscanf() work when scanning `const' data.)
159 	*/
160 
161 	if (fp->f_bf.smb_base != NULL && fp->f_p > fp->f_bf.smb_base &&
162 	    fp->f_p[-1] == c)
163 	{
164 		fp->f_p--;
165 		fp->f_r++;
166 		return c;
167 	}
168 
169 	/*
170 	**  Create an ungetc buffer.
171 	**  Initially, we will use the `reserve' buffer.
172 	*/
173 
174 	fp->f_ur = fp->f_r;
175 	fp->f_up = fp->f_p;
176 	fp->f_ub.smb_base = fp->f_ubuf;
177 	fp->f_ub.smb_size = sizeof(fp->f_ubuf);
178 	fp->f_ubuf[sizeof(fp->f_ubuf) - 1] = c;
179 	fp->f_p = &fp->f_ubuf[sizeof(fp->f_ubuf) - 1];
180 	fp->f_r = 1;
181 
182 	return c;
183 }
184