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Diffstat (limited to 'libqcdm/src/utils.c')
| -rw-r--r-- | libqcdm/src/utils.c | 311 |
1 files changed, 311 insertions, 0 deletions
diff --git a/libqcdm/src/utils.c b/libqcdm/src/utils.c new file mode 100644 index 0000000..b581548 --- /dev/null +++ b/libqcdm/src/utils.c @@ -0,0 +1,311 @@ +/* -*- 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_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; +} + +/** + * dm_encapsulate_buffer: + * @inbuf: buffer in which a valid QCDM packet exists + * @cmd_len: size of the QCDM packet contained in @inbuf + * @inbuf_len: total size of @inbuf itself (not just the packet) + * @outbuf: buffer in which to put the encapsulated QCDM packet + * @outbuf_len: total size of @outbuf + * + * Escapes and CRCs a QCDM packet, and finally adds the trailing control + * character that denotes the end of the QCDM packet. + * + * Returns: size of the encapsulated QCDM command writted to @outbuf. + **/ +gsize +dm_encapsulate_buffer (char *inbuf, + gsize cmd_len, + gsize inbuf_len, + char *outbuf, + gsize outbuf_len) +{ + guint16 crc; + gsize escaped_len; + + g_return_val_if_fail (inbuf != NULL, 0); + g_return_val_if_fail (cmd_len >= 1, 0); + g_return_val_if_fail (inbuf_len >= cmd_len + 2, 0); /* space for CRC */ + g_return_val_if_fail (outbuf != NULL, 0); + + /* Add the CRC */ + crc = crc16 (inbuf, cmd_len); + inbuf[cmd_len++] = crc & 0xFF; + inbuf[cmd_len++] = (crc >> 8) & 0xFF; + + escaped_len = dm_escape (inbuf, cmd_len, outbuf, outbuf_len); + g_return_val_if_fail (outbuf_len > escaped_len, 0); + outbuf[escaped_len++] = DIAG_CONTROL_CHAR; + + return escaped_len; +} + +/** + * dm_decapsulate_buffer: + * @inbuf: buffer in which to look for a QCDM packet + * @inbuf_len: length of valid data in @inbuf + * @outbuf: buffer in which to put decapsulated QCDM packet + * @outbuf_len: max size of @outbuf + * @out_decap_len: on success, size of the decapsulated QCDM packet + * @out_used: on either success or failure, amount of data used; caller should + * discard this much data from @inbuf before the next call to this function + * @out_need_more: when TRUE, indicates that more data is required before + * and determination about a valid QCDM packet can be made; caller should add + * more data to @inbuf before calling this function again. + * + * Attempts to retrieve, unescape, and CRC-check a QCDM packet from the given + * buffer. + * + * Returns: FALSE on error (packet was invalid or malformed, or the CRC check + * failed, etc) and places number of bytes to discard from @inbuf in @out_used. + * When TRUE, either more data is required (in which case @out_need_more will + * be TRUE), or a QCDM packet was successfully retrieved from @inbuf and the + * decapsulated packet of length @out_decap_len was placed into @outbuf. In + * all cases the caller should advance the buffer by the number of bytes + * returned in @out_used before calling this function again. + **/ +gboolean +dm_decapsulate_buffer (const char *inbuf, + gsize inbuf_len, + char *outbuf, + gsize outbuf_len, + gsize *out_decap_len, + gsize *out_used, + gboolean *out_need_more) +{ + gboolean escaping = FALSE; + gsize i, pkt_len = 0, unesc_len; + guint16 crc, pkt_crc; + + g_return_val_if_fail (inbuf != NULL, FALSE); + g_return_val_if_fail (outbuf != NULL, FALSE); + g_return_val_if_fail (outbuf_len > 0, FALSE); + g_return_val_if_fail (out_decap_len != NULL, FALSE); + g_return_val_if_fail (out_used != NULL, FALSE); + g_return_val_if_fail (out_need_more != NULL, FALSE); + + *out_decap_len = 0; + *out_used = 0; + *out_need_more = FALSE; + + if (inbuf_len < 4) { + *out_need_more = TRUE; + return TRUE; + } + + /* Find the async control character */ + for (i = 0; i < inbuf_len; i++) { + if (inbuf[i] == DIAG_CONTROL_CHAR) { + /* If the control character shows up in a position before a valid + * QCDM packet length (4), the packet is malformed. + */ + if (i < 3) { + /* Tell the caller to advance the buffer past the control char */ + *out_used = i + 1; + return FALSE; + } + + pkt_len = i; + break; + } + } + + /* No control char yet, need more data */ + if (!pkt_len) { + *out_need_more = TRUE; + return TRUE; + } + + /* Unescape first; note that pkt_len */ + unesc_len = dm_unescape (inbuf, pkt_len, outbuf, outbuf_len, &escaping); + if (!unesc_len) { + /* Tell the caller to advance the buffer past the control char */ + *out_used = pkt_len + 1; + return FALSE; + } + + if (escaping) { + *out_need_more = TRUE; + return TRUE; + } + + /* Check the CRC of the packet's data */ + crc = crc16 (outbuf, unesc_len - 2); + pkt_crc = outbuf[unesc_len - 2] & 0xFF; + pkt_crc |= (outbuf[unesc_len - 1] & 0xFF) << 8; + if (crc != pkt_crc) { + *out_used = pkt_len + 1; /* packet + CRC + 0x7E */ + return FALSE; + } + + *out_used = pkt_len + 1; /* packet + CRC + 0x7E */ + *out_decap_len = unesc_len - 2; /* decap_len should not include the CRC */ + return TRUE; +} + |