qcdm: add DM protocol utilities and testcases
Bits for CRC calculation and frame escaping/unescaping.
This commit is contained in:
Dan Williams
169
libqcdm/src/utils.c
Normal file
169
libqcdm/src/utils.c
Normal file
@@ -0,0 +1,169 @@
|
||||
/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
|
||||
/*
|
||||
* Copyright (C) 2010 Red Hat, Inc.
|
||||
*
|
||||
* This program is free software: you can redistribute it and/or
|
||||
* modify it under the terms of version 2 of the GNU General Public
|
||||
* License as published by the Free Software Foundation
|
||||
*
|
||||
* This program is distributed in the hope that it will be useful,
|
||||
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||||
* GNU General Public License for more details.
|
||||
*
|
||||
* You should have received a copy of the GNU General Public License
|
||||
* along with this program. If not, see <http://www.gnu.org/licenses/>.
|
||||
*/
|
||||
|
||||
#include <stdio.h>
|
||||
#include <sys/types.h>
|
||||
#include <unistd.h>
|
||||
#include <malloc.h>
|
||||
#include <fcntl.h>
|
||||
#include <string.h>
|
||||
|
||||
#include "utils.h"
|
||||
|
||||
/* QCDM protocol frames are pseudo Async HDLC frames which end with a 3-byte
|
||||
* trailer. This trailer consists of the 16-bit CRC of the frame plus an ending
|
||||
* "async control character" whose value is 0x7E. The frame *and* the CRC are
|
||||
* escaped before adding the trailing control character so that the control
|
||||
* character (0x7E) and the escape marker (0x7D) are never seen in the frame.
|
||||
*/
|
||||
|
||||
/* Table of CRCs for each possible byte, with a generator polynomial of 0x8408 */
|
||||
const guint16 crc_table[256] = {
|
||||
0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
|
||||
0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
|
||||
0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
|
||||
0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
|
||||
0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
|
||||
0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
|
||||
0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
|
||||
0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
|
||||
0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
|
||||
0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
|
||||
0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
|
||||
0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
|
||||
0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
|
||||
0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
|
||||
0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
|
||||
0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
|
||||
0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
|
||||
0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
|
||||
0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
|
||||
0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
|
||||
0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
|
||||
0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
|
||||
0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
|
||||
0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
|
||||
0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
|
||||
0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
|
||||
0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
|
||||
0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
|
||||
0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
|
||||
0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
|
||||
0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
|
||||
0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
|
||||
};
|
||||
|
||||
/* Calculate the CRC for a buffer using a seed of 0xffff */
|
||||
guint16
|
||||
crc16 (const char *buffer, gsize len)
|
||||
{
|
||||
guint16 crc = 0xffff;
|
||||
|
||||
while (len--)
|
||||
crc = crc_table[(crc ^ *buffer++) & 0xff] ^ (crc >> 8);
|
||||
return ~crc;
|
||||
}
|
||||
|
||||
#define DIAG_CONTROL_CHAR 0x7E
|
||||
#define DIAG_ESC_CHAR 0x7D /* Escape sequence 1st character value */
|
||||
#define DIAG_ESC_MASK 0x20 /* Escape sequence complement value */
|
||||
|
||||
/* Performs DM escaping on inbuf putting the result into outbuf, and returns
|
||||
* the final length of the buffer.
|
||||
*/
|
||||
gsize
|
||||
dm_escape (const char *inbuf,
|
||||
gsize inbuf_len,
|
||||
char *outbuf,
|
||||
gsize outbuf_len)
|
||||
{
|
||||
const char *src = inbuf;
|
||||
char *dst = outbuf;
|
||||
size_t i = inbuf_len;
|
||||
|
||||
g_return_val_if_fail (inbuf != NULL, 0);
|
||||
g_return_val_if_fail (inbuf_len > 0, 0);
|
||||
g_return_val_if_fail (outbuf != NULL, 0);
|
||||
g_return_val_if_fail (outbuf_len > inbuf_len, 0);
|
||||
|
||||
/* Since escaping potentially doubles the # of bytes, short-circuit the
|
||||
* length check if destination buffer is clearly large enough. Note the
|
||||
*
|
||||
*/
|
||||
if (outbuf_len <= inbuf_len << 1) {
|
||||
size_t outbuf_required = inbuf_len + 1; /* +1 for the trailing control char */
|
||||
|
||||
/* Each escaped character takes up two bytes in the output buffer */
|
||||
while (i--) {
|
||||
if (*src == DIAG_CONTROL_CHAR || *src == DIAG_ESC_CHAR)
|
||||
outbuf_required++;
|
||||
src++;
|
||||
}
|
||||
|
||||
if (outbuf_len < outbuf_required)
|
||||
return 0;
|
||||
}
|
||||
|
||||
/* Do the actual escaping. Replace both the control character and
|
||||
* the escape character in the source buffer with the following sequence:
|
||||
*
|
||||
* <escape_char> <src_byte ^ escape_mask>
|
||||
*/
|
||||
src = inbuf;
|
||||
i = inbuf_len;
|
||||
while (i--) {
|
||||
if (*src == DIAG_CONTROL_CHAR || *src == DIAG_ESC_CHAR) {
|
||||
*dst++ = DIAG_ESC_CHAR;
|
||||
*dst++ = *src ^ DIAG_ESC_MASK;
|
||||
} else
|
||||
*dst++ = *src;
|
||||
src++;
|
||||
}
|
||||
|
||||
return (dst - outbuf);
|
||||
}
|
||||
|
||||
gsize
|
||||
dm_unescape (const char *inbuf,
|
||||
gsize inbuf_len,
|
||||
char *outbuf,
|
||||
gsize outbuf_len,
|
||||
gboolean *escaping)
|
||||
{
|
||||
size_t i, outsize;
|
||||
|
||||
g_return_val_if_fail (inbuf_len > 0, 0);
|
||||
g_return_val_if_fail (outbuf_len >= inbuf_len, 0);
|
||||
g_return_val_if_fail (escaping != NULL, 0);
|
||||
|
||||
for (i = 0, outsize = 0; i < inbuf_len; i++) {
|
||||
if (*escaping) {
|
||||
outbuf[outsize++] = inbuf[i] ^ DIAG_ESC_MASK;
|
||||
*escaping = FALSE;
|
||||
} else if (inbuf[i] == DIAG_ESC_CHAR)
|
||||
*escaping = TRUE;
|
||||
else
|
||||
outbuf[outsize++] = inbuf[i];
|
||||
|
||||
/* About to overrun output buffer size */
|
||||
if (outsize >= outbuf_len)
|
||||
return 0;
|
||||
}
|
||||
|
||||
return outsize;
|
||||
}
|
||||
|
||||
Reference in New Issue
Block a user