buffer.c revision 294693 
1/* $OpenBSD: buffer.c,v 1.35 2014/02/02 03:44:31 djm Exp $ */
2/*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 *                    All rights reserved
6 * Functions for manipulating fifo buffers (that can grow if needed).
7 *
8 * As far as I am concerned, the code I have written for this software
9 * can be used freely for any purpose.  Any derived versions of this
10 * software must be clearly marked as such, and if the derived work is
11 * incompatible with the protocol description in the RFC file, it must be
12 * called by a name other than "ssh" or "Secure Shell".
13 */
14
15#include "includes.h"
16
17#include <sys/param.h>
18
19#include <stdio.h>
20#include <string.h>
21#include <stdarg.h>
22#include <stdlib.h>
23
24#include "xmalloc.h"
25#include "buffer.h"
26#include "log.h"
27
28#define	BUFFER_MAX_CHUNK	0x100000
29#define	BUFFER_MAX_LEN		0xa00000
30#define	BUFFER_ALLOCSZ		0x008000
31
32/* Initializes the buffer structure. */
33
34void
35buffer_init(Buffer *buffer)
36{
37	const u_int len = 4096;
38
39	buffer->alloc = 0;
40	buffer->buf = xmalloc(len);
41	buffer->alloc = len;
42	buffer->offset = 0;
43	buffer->end = 0;
44}
45
46/* Frees any memory used for the buffer. */
47
48void
49buffer_free(Buffer *buffer)
50{
51	if (buffer->alloc > 0) {
52		explicit_bzero(buffer->buf, buffer->alloc);
53		buffer->alloc = 0;
54		free(buffer->buf);
55	}
56}
57
58/*
59 * Clears any data from the buffer, making it empty.  This does not actually
60 * zero the memory.
61 */
62
63void
64buffer_clear(Buffer *buffer)
65{
66	buffer->offset = 0;
67	buffer->end = 0;
68}
69
70/* Appends data to the buffer, expanding it if necessary. */
71
72void
73buffer_append(Buffer *buffer, const void *data, u_int len)
74{
75	void *p;
76	p = buffer_append_space(buffer, len);
77	memcpy(p, data, len);
78}
79
80static int
81buffer_compact(Buffer *buffer)
82{
83	/*
84	 * If the buffer is quite empty, but all data is at the end, move the
85	 * data to the beginning.
86	 */
87	if (buffer->offset > MIN(buffer->alloc, BUFFER_MAX_CHUNK)) {
88		memmove(buffer->buf, buffer->buf + buffer->offset,
89			buffer->end - buffer->offset);
90		buffer->end -= buffer->offset;
91		buffer->offset = 0;
92		return (1);
93	}
94	return (0);
95}
96
97/*
98 * Appends space to the buffer, expanding the buffer if necessary. This does
99 * not actually copy the data into the buffer, but instead returns a pointer
100 * to the allocated region.
101 */
102
103void *
104buffer_append_space(Buffer *buffer, u_int len)
105{
106	u_int newlen;
107	void *p;
108
109	if (len > BUFFER_MAX_CHUNK)
110		fatal("buffer_append_space: len %u not supported", len);
111
112	/* If the buffer is empty, start using it from the beginning. */
113	if (buffer->offset == buffer->end) {
114		buffer->offset = 0;
115		buffer->end = 0;
116	}
117restart:
118	/* If there is enough space to store all data, store it now. */
119	if (buffer->end + len < buffer->alloc) {
120		p = buffer->buf + buffer->end;
121		buffer->end += len;
122		return p;
123	}
124
125	/* Compact data back to the start of the buffer if necessary */
126	if (buffer_compact(buffer))
127		goto restart;
128
129	/* Increase the size of the buffer and retry. */
130	newlen = roundup(buffer->alloc + len, BUFFER_ALLOCSZ);
131	if (newlen > BUFFER_MAX_LEN)
132		fatal("buffer_append_space: alloc %u not supported",
133		    newlen);
134	buffer->buf = xrealloc(buffer->buf, 1, newlen);
135	buffer->alloc = newlen;
136	goto restart;
137	/* NOTREACHED */
138}
139
140/*
141 * Check whether an allocation of 'len' will fit in the buffer
142 * This must follow the same math as buffer_append_space
143 */
144int
145buffer_check_alloc(Buffer *buffer, u_int len)
146{
147	if (buffer->offset == buffer->end) {
148		buffer->offset = 0;
149		buffer->end = 0;
150	}
151 restart:
152	if (buffer->end + len < buffer->alloc)
153		return (1);
154	if (buffer_compact(buffer))
155		goto restart;
156	if (roundup(buffer->alloc + len, BUFFER_ALLOCSZ) <= BUFFER_MAX_LEN)
157		return (1);
158	return (0);
159}
160
161/* Returns the number of bytes of data in the buffer. */
162
163u_int
164buffer_len(const Buffer *buffer)
165{
166	return buffer->end - buffer->offset;
167}
168
169/* Gets data from the beginning of the buffer. */
170
171int
172buffer_get_ret(Buffer *buffer, void *buf, u_int len)
173{
174	if (len > buffer->end - buffer->offset) {
175		error("buffer_get_ret: trying to get more bytes %d than in buffer %d",
176		    len, buffer->end - buffer->offset);
177		return (-1);
178	}
179	memcpy(buf, buffer->buf + buffer->offset, len);
180	buffer->offset += len;
181	return (0);
182}
183
184void
185buffer_get(Buffer *buffer, void *buf, u_int len)
186{
187	if (buffer_get_ret(buffer, buf, len) == -1)
188		fatal("buffer_get: buffer error");
189}
190
191/* Consumes the given number of bytes from the beginning of the buffer. */
192
193int
194buffer_consume_ret(Buffer *buffer, u_int bytes)
195{
196	if (bytes > buffer->end - buffer->offset) {
197		error("buffer_consume_ret: trying to get more bytes than in buffer");
198		return (-1);
199	}
200	buffer->offset += bytes;
201	return (0);
202}
203
204void
205buffer_consume(Buffer *buffer, u_int bytes)
206{
207	if (buffer_consume_ret(buffer, bytes) == -1)
208		fatal("buffer_consume: buffer error");
209}
210
211/* Consumes the given number of bytes from the end of the buffer. */
212
213int
214buffer_consume_end_ret(Buffer *buffer, u_int bytes)
215{
216	if (bytes > buffer->end - buffer->offset)
217		return (-1);
218	buffer->end -= bytes;
219	return (0);
220}
221
222void
223buffer_consume_end(Buffer *buffer, u_int bytes)
224{
225	if (buffer_consume_end_ret(buffer, bytes) == -1)
226		fatal("buffer_consume_end: trying to get more bytes than in buffer");
227}
228
229/* Returns a pointer to the first used byte in the buffer. */
230
231void *
232buffer_ptr(const Buffer *buffer)
233{
234	return buffer->buf + buffer->offset;
235}
236
237/* Dumps the contents of the buffer to stderr. */
238
239void
240buffer_dump(const Buffer *buffer)
241{
242	u_int i;
243	u_char *ucp = buffer->buf;
244
245	for (i = buffer->offset; i < buffer->end; i++) {
246		fprintf(stderr, "%02x", ucp[i]);
247		if ((i-buffer->offset)%16==15)
248			fprintf(stderr, "\r\n");
249		else if ((i-buffer->offset)%2==1)
250			fprintf(stderr, " ");
251	}
252	fprintf(stderr, "\r\n");
253}
254