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/*
* Copyright 2013 Google Inc.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* 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, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*/
/*
* Author: ncardwell@google.com (Neal Cardwell)
*
* Implementation for generating human-readable representations of TCP options.
*/
#include "tcp_options_to_string.h"
#include "tcp_options_iterator.h"
/* If the MD5 digest option is in the valid range of sizes, print the MD5
* option and digest and return STATUS_OK. Otherwise, return STATUS_ERR.
*/
static int tcp_md5_option_to_string(FILE *s, struct tcp_option *option)
{
int digest_bytes, i;
if (option->length < TCPOLEN_MD5_BASE ||
option->length > TCPOLEN_MD5SIG)
return STATUS_ERR;
digest_bytes = option->length - TCPOLEN_MD5_BASE;
fprintf(s, "md5");
if (digest_bytes > 0)
fprintf(s, " ");
for (i = 0; i < digest_bytes; ++i)
fprintf(s, "%02x", option->data.md5.digest[i]);
return STATUS_OK;
}
/* See if the given experimental option is a TFO option, and if so
* then print the TFO option and return STATUS_OK. Otherwise, return
* STATUS_ERR.
*/
static int tcp_fast_open_option_to_string(FILE *s, struct tcp_option *option,
bool exp)
{
if (exp && ((option->length < TCPOLEN_EXP_FASTOPEN_BASE) ||
(ntohs(option->data.fast_open_exp.magic) != TCPOPT_FASTOPEN_MAGIC)))
return STATUS_ERR;
fprintf(s, exp ? "FOEXP" : "FO");
int cookie_bytes = option->length - (exp ? TCPOLEN_EXP_FASTOPEN_BASE :
TCPOLEN_FASTOPEN_BASE);
assert(cookie_bytes >= 0);
assert(cookie_bytes <= (exp ? MAX_TCP_FAST_OPEN_EXP_COOKIE_BYTES :
MAX_TCP_FAST_OPEN_COOKIE_BYTES));
if (cookie_bytes > 0)
fprintf(s, " ");
int i;
for (i = 0; i < cookie_bytes; ++i)
fprintf(s, "%02x", exp ? option->data.fast_open_exp.cookie[i] :
option->data.fast_open.cookie[i]);
return STATUS_OK;
}
int tcp_options_to_string(struct packet *packet,
char **ascii_string, char **error)
{
int result = STATUS_ERR; /* return value */
size_t size = 0;
FILE *s = open_memstream(ascii_string, &size); /* output string */
int index = 0; /* number of options seen so far */
struct tcp_options_iterator iter;
struct tcp_option *option = NULL;
for (option = tcp_options_begin(packet, &iter);
option != NULL; option = tcp_options_next(&iter, error)) {
if (index > 0)
fputc(',', s);
switch (option->kind) {
case TCPOPT_EOL:
fputs("eol", s);
break;
case TCPOPT_NOP:
fputs("nop", s);
break;
case TCPOPT_MAXSEG:
fprintf(s, "mss %u", ntohs(option->data.mss.bytes));
break;
case TCPOPT_WINDOW:
fprintf(s, "wscale %u",
option->data.window_scale.shift_count);
break;
case TCPOPT_SACK_PERMITTED:
fputs("sackOK", s);
break;
case TCPOPT_SACK:
fprintf(s, "sack ");
int num_blocks = 0;
if (num_sack_blocks(option->length,
&num_blocks, error))
goto out;
int i = 0;
for (i = 0; i < num_blocks; ++i) {
if (i > 0)
fputc(' ', s);
fprintf(s, "%u:%u",
ntohl(option->data.sack.block[i].left),
ntohl(option->data.sack.block[i].right));
}
break;
case TCPOPT_TIMESTAMP:
fprintf(s, "TS val %u ecr %u",
ntohl(option->data.time_stamp.val),
ntohl(option->data.time_stamp.ecr));
break;
case TCPOPT_MD5SIG:
tcp_md5_option_to_string(s, option);
break;
case TCPOPT_FASTOPEN:
tcp_fast_open_option_to_string(s, option, false);
break;
case TCPOPT_EXP:
if (tcp_fast_open_option_to_string(s, option, true)) {
asprintf(error,
"unknown experimental option");
goto out;
}
break;
default:
asprintf(error, "unexpected TCP option kind: %u",
option->kind);
goto out;
}
++index;
}
if (*error != NULL) /* bogus TCP options prevented iteration */
goto out;
result = STATUS_OK;
out:
fclose(s);
return result;
}
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