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本章主要是通过对packet-ftp.c源码，讲解wireshark源码中解析器的解析方式方法。具体内容请直接看注释即可。
/* packet-ftp.c
* Routines for ftp packet dissection
* Copyright 1999, Richard Sharpe <[email protected]>
* Copyright 2001, Juan Toledo <[email protected]> (Passive FTP)
*
* Wireshark - Network traffic analyzer
* By Gerald Combs <[email protected]>
* Copyright 1998 Gerald Combs
*
* Copied from packet-pop.c
*
* 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.
*/
#include "config.h"
#include <stdio.h>
#include <stdlib.h> /* for atoi() and strtoul() */
#include <epan/packet.h>
#include <epan/strutil.h>
#include <epan/conversation.h>
#include <epan/expert.h>
#include <epan/addr_resolv.h>
void proto_register_ftp(void);
void proto_reg_handoff_ftp(void);
/* 协议解析单元索引，默认为-1，注册以后会有相应的返回值，
标记其在protocol_tree中的位置。
解析到相应的数据后，会将其挂载到固定的位置
*/
static int proto_ftp = -1;
static int proto_ftp_data = -1;
static int hf_ftp_response = -1;
static int hf_ftp_request = -1;
static int hf_ftp_request_command = -1;
static int hf_ftp_request_arg = -1;
static int hf_ftp_response_code = -1;
static int hf_ftp_response_arg = -1;
static int hf_ftp_pasv_ip = -1 ;
static int hf_ftp_pasv_port = -1;
static int hf_ftp_pasv_nat = -1;
static int hf_ftp_active_ip = -1;
static int hf_ftp_active_port = -1;
static int hf_ftp_active_nat = -1;
static int hf_ftp_eprt_af = -1;
static int hf_ftp_eprt_ip = -1;
static int hf_ftp_eprt_ipv6 = -1;
static int hf_ftp_eprt_port = -1;
static int hf_ftp_epsv_ip = -1;
static int hf_ftp_epsv_ipv6 = -1;
static int hf_ftp_epsv_port = -1;
/*折叠用到的信息，主要是为了wireshark界面展示用的*/
static gint ett_ftp = -1;
static gint ett_ftp_reqresp = -1;
static expert_field ei_ftp_eprt_args_invalid = EI_INIT;
static expert_field ei_ftp_epsv_args_invalid = EI_INIT;
static dissector_handle_t ftpdata_handle;
/*指明端口，用在handoff注册中*/
#define TCP_PORT_FTPDATA 20
#define TCP_PORT_FTP 21
/*
ftp响应值(tp.response.code)翻译，比如在协议树上的tp.response.code填上了202值
则在显示的时候，会自动翻译为"Command not implemented, superfluous at this site"
提高界面的人性化阅读
*/
static const value_string response_table[] = {
{ 110, "Restart marker reply" },
{ 120, "Service ready in nnn minutes" },
{ 125, "Data connection already open; transfer starting" },
{ 150, "File status okay; about to open data connection" },
{ 200, "Command okay" },
{ 202, "Command not implemented, superfluous at this site" },
{ 211, "System status, or system help reply" },
{ 212, "Directory status" },
{ 213, "File status" },
{ 214, "Help message" },
{ 215, "NAME system type" },
{ 220, "Service ready for new user" },
{ 221, "Service closing control connection" },
{ 225, "Data connection open; no transfer in progress" },
{ 226, "Closing data connection" },
{ 227, "Entering Passive Mode" },
{ 229, "Entering Extended Passive Mode" },
{ 230, "User logged in, proceed" },
{ 232, "User logged in, authorized by security data exchange" },
{ 234, "Security data exchange complete" },
{ 235, "Security data exchange completed successfully" },
{ 250, "Requested file action okay, completed" },
{ 257, "PATHNAME created" },
{ 331, "User name okay, need password" },
{ 332, "Need account for login" },
{ 334, "Requested security mechanism is ok" },
{ 335, "Security data is acceptable, more is required" },
{ 336, "Username okay, need password. Challenge is ..." },
{ 350, "Requested file action pending further information" },
{ 421, "Service not available, closing control connection" },
{ 425, "Can't open data connection" },
{ 426, "Connection closed; transfer aborted" },
{ 431, "Need some unavailable resource to process security" },
{ 450, "Requested file action not taken" },
{ 451, "Requested action aborted: local error in processing" },
{ 452, "Requested action not taken. Insufficient storage space in system" },
{ 500, "Syntax error, command unrecognized" },
{ 501, "Syntax error in parameters or arguments" },
{ 502, "Command not implemented" },
{ 503, "Bad sequence of commands" },
{ 504, "Command not implemented for that parameter" },
{ 522, "Network protocol not supported" },
{ 530, "Not logged in" },
{ 532, "Need account for storing files" },
{ 533, "Command protection level denied for policy reasons" },
{ 534, "Request denied for policy reasons" },
{ 535, "Failed security check (hash, sequence, etc)" },
{ 536, "Requested PROT level not supported by mechanism" },
{ 537, "Command protection level not supported by security mechanism" },
{ 550, "Requested action not taken: File unavailable" },
{ 551, "Requested action aborted: page type unknown" },
{ 552, "Requested file action aborted: Exceeded storage allocation" },
{ 553, "Requested action not taken: File name not allowed" },
{ 631, "Integrity protected reply" },
{ 632, "Confidentiality and integrity protected reply" },
{ 633, "Confidentiality protected reply" },
{ 0, NULL }
};
static value_string_ext response_table_ext = VALUE_STRING_EXT_INIT(response_table);
#define EPRT_AF_IPv4 1
#define EPRT_AF_IPv6 2
static const value_string eprt_af_vals[] = {
{ EPRT_AF_IPv4, "IPv4" },
{ EPRT_AF_IPv6, "IPv6" },
{ 0, NULL }
};
/*
* Parse the address and port information in a PORT command or in the
* response to a PASV command. Return TRUE if we found an address and
* port, and supply the address and port; return FALSE if we didn't find
* them.
*
* We ignore the IP address in the reply, and use the address from which
* the request came.
*
* XXX - are there cases where they differ? What if the FTP server is
* behind a NAT box, so that the address it puts into the reply isn't
* the address at which you should contact it? Do all NAT boxes detect
* FTP PASV replies and rewrite the address? (I suspect not.)
*
* RFC 959 doesn't say much about the syntax of the 227 reply.
*
* A proposal from Dan Bernstein at
*
* http://cr.yp.to/ftp/retr.html
*
* "recommend[s] that clients use the following strategy to parse the
* response line: look for the first digit after the initial space; look
* for the fourth comma after that digit; read two (possibly negative)
* integers, separated by a comma; the TCP port number is p1*256+p2, where
* p1 is the first integer modulo 256 and p2 is the second integer modulo
* 256."
*
* wget 1.5.3 looks for a digit, although it doesn't handle negative
* integers.
*
* The FTP code in the source of the cURL library, at
*
* http://curl.haxx.se/lxr/source/lib/ftp.c
*
* says that cURL "now scans for a sequence of six comma-separated numbers
* and will take them as IP+port indicators"; it loops, doing "sscanf"s
* looking for six numbers separated by commas, stepping the start pointer
* in the scanf one character at a time - i.e., it tries rather exhaustively.
*
* An optimization would be to scan for a digit, and start there, and if
* the scanf doesn't find six values, scan for the next digit and try
* again; this will probably succeed on the first try.
*
* The cURL code also says that "found reply-strings include":
*
* "227 Entering Passive Mode (127,0,0,1,4,51)"
* "227 Data transfer will passively listen to 127,0,0,1,4,51"
* "227 Entering passive mode. 127,0,0,1,4,51"
*
* so it appears that you can't assume there are parentheses around
* the address and port number.
*/
/*
ftp协议因为会涉及到父子连接，通过命令通道的信息，解析出下一步的子连接
信息(IP，端口)是这个函数的主要功能
*/
static gboolean
parse_port_pasv(const guchar *line, int linelen, guint32 *ftp_ip, guint16 *ftp_port,
guint32 *pasv_offset, guint *ftp_ip_len, guint *ftp_port_len)
{
char *args;
char *p;
guchar c;
int i;
int ip_address[4], port[2];
gboolean ret = FALSE;
/*
* Copy the rest of the line into a null-terminated buffer.
*/
args = wmem_strndup(wmem_packet_scope(), line, linelen);
p = args;
for (;;) {
/*
* Look for a digit.
*/
while ((c = *p) != '\0' && !g_ascii_isdigit(c))
p++;
if (*p == '\0') {
/*
* We ran out of text without finding anything.
*/
break;
}
/*
* See if we have six numbers.
*/
i = sscanf(p, "%d,%d,%d,%d,%d,%d",
&ip_address[0], &ip_address[1], &ip_address[2], &ip_address[3],
&port[0], &port[1]);
if (i == 6) {
/*
* We have a winner!
*/
*ftp_port = ((port[0] & 0xFF)<<8) | (port[1] & 0xFF);
*ftp_ip = g_htonl((ip_address[0] << 24) | (ip_address[1] <<16) | (ip_address[2] <<8) | ip_address[3]);
*pasv_offset = (guint32)(p - args);
*ftp_port_len = (port[0] < 10 ? 1 : (port[0] < 100 ? 2 : 3 )) + 1 +
(port[1] < 10 ? 1 : (port[1] < 100 ? 2 : 3 ));
*ftp_ip_len = (ip_address[0] < 10 ? 1 : (ip_address[0] < 100 ? 2 : 3)) + 1 +
(ip_address[1] < 10 ? 1 : (ip_address[1] < 100 ? 2 : 3)) + 1 +
(ip_address[2] < 10 ? 1 : (ip_address[2] < 100 ? 2 : 3)) + 1 +
(ip_address[3] < 10 ? 1 : (ip_address[3] < 100 ? 2 : 3));
ret = TRUE;
break;
}
/*
* Well, that didn't work. Skip the first number we found,
* and keep trying.
*/
while ((c = *p) != '\0' && g_ascii_isdigit(c))
p++;
}
return ret;
}
static gboolean
isvalid_rfc2428_delimiter(const guchar c)
{
/* RFC2428 sect. 2 states rules for a valid delimiter */
const gchar *forbidden = "0123456789abcdef.:";
if (!g_ascii_isgraph(c))
return FALSE;
if (strchr(forbidden, g_ascii_tolower(c)))
return FALSE;
return TRUE;
}
/*
* RFC2428 states...
*
* AF Number Protocol
* --------- --------
* 1 Internet Protocol, Version 4
* 2 Internet Protocol, Version 6
*
* AF Number Address Format Example
* --------- -------------- -------
* 1 dotted decimal 132.235.1.2
* 2 IPv6 string 1080::8:800:200C:417A
* representations
* defined in
*
* The following are sample EPRT commands:
* EPRT |1|132.235.1.2|6275|
* EPRT |2|1080::8:800:200C:417A|5282|
*
* The first command specifies that the server should use IPv4 to open a
* data connection to the host "132.235.1.2" on TCP port 6275. The
* second command specifies that the server should use the IPv6 network
* protocol and the network address "1080::8:800:200C:417A" to open a
* TCP data connection on port 5282.
*
* ... which means in fact that RFC2428 is capable to handle both,
* IPv4 and IPv6 so we have to care about the address family and properly
* act depending on it.
*
*/
static gboolean
parse_eprt_request(const guchar* line, gint linelen, guint32 *eprt_af,
guint32 *eprt_ip, guint16 *eprt_ipv6, guint16 *ftp_port,
guint32 *eprt_ip_len, guint32 *ftp_port_len)
{
gint delimiters_seen = 0;
gchar delimiter;
gint fieldlen;
gchar *field;
gint n;
gint lastn;
char *args, *p;
gboolean ret = TRUE;
/* line contains the EPRT parameters, we need at least the 4 delimiters */
if (!line || linelen<4)
return FALSE;
/* Copy the rest of the line into a null-terminated buffer. */
args = wmem_strndup(wmem_packet_scope(), line, linelen);
p = args;
/*
* Handle a NUL being in the line; if there's a NUL in the line,
* strlen(args) will terminate at the NUL and will thus return
* a value less than linelen.
*/
if ((gint)strlen(args) < linelen)
linelen = (gint)strlen(args);
/*
* RFC2428 sect. 2 states ...
*
* The EPRT command keyword MUST be followed by a single space (ASCII
* 32). Following the space, a delimiter character (<d>) MUST be
* specified.
*
* ... the preceding <space> is already stripped so we know that the first
* character must be the delimiter and has just to be checked to be valid.
*/
if (!isvalid_rfc2428_delimiter(*p))
return FALSE; /* EPRT command does not follow a vaild delimiter;
* malformed EPRT command - immediate escape */
delimiter = *p;
/* Validate that the delimiter occurs 4 times in the string */
for (n = 0; n < linelen; n++) {
if (*(p+n) == delimiter)
delimiters_seen++;
}
if (delimiters_seen != 4)
return FALSE; /* delimiter doesn't occur 4 times
* probably no EPRT request - immediate escape */
/* we know that the first character is a delimiter... */
delimiters_seen = 1;
lastn = 0;
/* ... so we can start searching from the 2nd onwards */
for (n=1; n < linelen; n++) {
if (*(p+n) != delimiter)
continue;
/* we found a delimiter */
delimiters_seen++;
fieldlen = n - lastn - 1;
if (fieldlen<=0)
return FALSE; /* all fields must have data in them */
field = p + lastn + 1;
if (delimiters_seen == 2) { /* end of address family field */
gchar *af_str;
af_str = wmem_strndup(wmem_packet_scope(), field, fieldlen);
*eprt_af = atoi(af_str);
}
else if (delimiters_seen == 3) {/* end of IP address field */
gchar *ip_str;
ip_str = wmem_strndup(wmem_packet_scope(), field, fieldlen);
if (*eprt_af == EPRT_AF_IPv4) {
if (str_to_ip(ip_str, eprt_ip))
ret = TRUE;
else
ret = FALSE;
}
else if (*eprt_af == EPRT_AF_IPv6) {
if (str_to_ip6(ip_str, eprt_ipv6))
ret = TRUE;
else
ret = FALSE;
}
else
return FALSE; /* invalid/unknown address family */
*eprt_ip_len = fieldlen;
}
else if (delimiters_seen == 4) {/* end of port field */
gchar *pt_str;
pt_str = wmem_strndup(wmem_packet_scope(), field, fieldlen);
*ftp_port = atoi(pt_str);
*ftp_port_len = fieldlen;
}
lastn = n;
}
return ret;
}
/*
* RFC2428 states ....
*
* The first two fields contained in the parenthesis MUST be blank. The
* third field MUST be the string representation of the TCP port number
* on which the server is listening for a data connection.
*
* The network protocol used by the data connection will be the same network
* protocol used by the control connection. In addition, the network
* address used to establish the data connection will be the same
* network address used for the control connection.
*
* An example response string follows:
*
* Entering Extended Passive Mode (|||6446|)
*
* ... which in fact means that again both address families IPv4 and IPv6
* are supported. But gladly it's not necessary to parse because it doesn't
* occur in EPSV responses. We can leverage ftp_ip_address which is
* protocol independent and already set.
*
*/
static gboolean
parse_extended_pasv_response(const guchar *line, gint linelen, guint16 *ftp_port,
guint *pasv_offset, guint *ftp_port_len)
{
gint n;
gchar *args;
gchar *p;
gchar *e;
guchar c;
gboolean ret = FALSE;
gboolean delimiters_seen = FALSE;
/*
* Copy the rest of the line into a null-terminated buffer.
*/
args = wmem_strndup(wmem_packet_scope(), line, linelen);
p = args;
/*
* Look for ( <d> <d> <d>
(Try to cope with '(' in description)
*/
for (; !delimiters_seen;) {
guchar delimiter = '\0';
while ((c = *p) != '\0' && (c != '('))
p++;
if (*p == '\0') {
return FALSE;
}
/* Skip '(' */
p++;
/* Make sure same delimiter is used 3 times */
for (n=0; n<3; n++) {
if ((c = *p) != '\0') {
if (delimiter == '\0' && isvalid_rfc2428_delimiter(c)) {
delimiter = c;
}
if (c != delimiter) {
break;
}
p++;
}
else {
break;
}
}
delimiters_seen = TRUE;
}
/*
* Should now be at digits.
*/
if (*p != '\0') {
/*
* We didn't run out of text without finding anything.
*/
*ftp_port = atoi(p);
*pasv_offset = (guint32)(p - args);
ret = TRUE;
/* get port string length */
if ((e=strchr(p,')')) == NULL) {
ret = FALSE;
}
else {
*ftp_port_len = (guint)(--e - p);
}
}
return ret;
}
/*
解析函数
tvbuff_t是wireshark中的一个主要结构体，数据报文即都放在这里面，然后使用偏移的方式查找具体数据
packet_info主要是包的一些信息，描述包的具体内容。tvbuff_t是纯报文，packet_info则是具体报文信息
proto_tree是wireshark中的协议数，用来挂载解析到的数据
*/
static int
dissect_ftp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
gboolean is_request;
proto_tree *ftp_tree;
proto_tree *reqresp_tree;
proto_item *ti, *hidden_item;
gint offset;
const guchar *line;
guint32 code;
gchar code_str[4];
gboolean is_port_request = FALSE;
gboolean is_eprt_request = FALSE;
gboolean is_pasv_response = FALSE;
gboolean is_epasv_response = FALSE;
gint next_offset;
int linelen;
int tokenlen = 0;
const guchar *next_token;
guint32 pasv_ip;
guint32 pasv_offset;
guint32 ftp_ip;
guint32 ftp_ip_len;
guint32 eprt_offset;
guint32 eprt_af = 0;
guint32 eprt_ip;
guint16 eprt_ipv6[8];
guint32 eprt_ip_len = 0;
guint16 ftp_port;
guint32 ftp_port_len;
address ftp_ip_address;
gboolean ftp_nat;
conversation_t *conversation;
/*拷贝源地址信息*/
copy_address_shallow(&ftp_ip_address, &pinfo->src);
if (pinfo->match_uint == pinfo->destport)/*match_uint是被调用该解析器时候的int，通过他来判定方向*/
is_request = TRUE;
else
is_request = FALSE;
col_set_str(pinfo->cinfo, COL_PROTOCOL, "FTP");/*设置wireshark第一区域，COL_PROTOCOL列的数据*/
/*
* Find the end of the first line.
*
* Note that "tvb_find_line_end()" will return a value that is
* not longer than what's in the buffer, so the "tvb_get_ptr()"
* call won't throw an exception.
*/
/*ftp命令通道的特点是第一行肯定是命令信息，所以在这里提取命令信息*/
linelen = tvb_find_line_end(tvb, 0, -1, &next_offset, FALSE);
line = tvb_get_ptr(tvb, 0, linelen);
/*
* Put the first line from the buffer into the summary
* (but leave out the line terminator).
*/
col_add_fstr(pinfo->cinfo, COL_INFO, "%s: %s",
is_request ? "Request" : "Response",
format_text(line, linelen));/*将命令信息打印到wireshark第一区域，COL_INFO列上*/
/*在wireshark的tree上添加proto_ftp的值，即在界面展示的File Transfer Protocol (FTP)信息*/
ti = proto_tree_add_item(tree, proto_ftp, tvb, 0, -1, ENC_NA);
/*在ti上创建一个subtree，也就是再建一个折叠，以方便在里面显示内容*/
ftp_tree = proto_item_add_subtree(ti, ett_ftp);
hidden_item = proto_tree_add_boolean(ftp_tree,
hf_ftp_request, tvb, 0, 0, is_request);/*t在tree上添加请求或者响应的一个item，但是是隐藏的*/
PROTO_ITEM_SET_HIDDEN(hidden_item);
hidden_item = proto_tree_add_boolean(ftp_tree,
hf_ftp_response, tvb, 0, 0, is_request == FALSE);
PROTO_ITEM_SET_HIDDEN(hidden_item);
/* Put the line into the protocol tree. */
/*将一行信息添加到树上，所以第九个包为USER test\r\n*/
ti = proto_tree_add_format_text(ftp_tree, tvb, 0, next_offset);
/*在树上再加一个subtree，则下面还可以展开*/
reqresp_tree = proto_item_add_subtree(ti, ett_ftp_reqresp);
if (is_request) {
/*
* Extract the first token, and, if there is a first
* token, add it as the request.
将一行数据按照空格截开
*/
tokenlen = get_token_len(line, line + linelen, &next_token);
if (tokenlen != 0) {
/*将截开的第一半赋给hf_ftp_request_command，第九个包里则为USER*/
proto_tree_add_item(reqresp_tree, hf_ftp_request_command,
tvb, 0, tokenlen, ENC_ASCII|ENC_NA);
/*PORT和EPRT都需要特殊对待，因为涉及到子连接*/
if (strncmp(line, "PORT", tokenlen) == 0)
is_port_request = TRUE;
/*
* EPRT request command, as per RFC 2428
*/
else if (strncmp(line, "EPRT", tokenlen) == 0)
is_eprt_request = TRUE;
}
} else {
/*
* This is a response; the response code is 3 digits,
* followed by a space or hyphen, possibly followed by
* text. 响应一般是跟三个数字，然后是空格加一段描述
*
* If the line doesn't start with 3 digits, it's part of
* a continuation.如果不是三个数字，则可能只是一部分了
*
* XXX - keep track of state in the first pass, and
* treat non-continuation lines not beginning with digits
* as errors?
*/
if (linelen >= 3 && g_ascii_isdigit(line[0]) && g_ascii_isdigit(line[1])
&& g_ascii_isdigit(line[2])) {/*三个数字，正常数据*/
/*
* One-line reply, or first or last line
* of a multi-line reply.
*/
/*获取字符串---这里是获得三个数字的字符串*/
tvb_get_nstringz0(tvb, 0, sizeof(code_str), code_str);
code = (guint32)strtoul(code_str, NULL, 10);/*转化为十进制*/
/*将响应编码赋值给hf_ftp_response_code
会根据response_table翻译展现
*/
proto_tree_add_uint(reqresp_tree,
hf_ftp_response_code, tvb, 0, 3, code);
/*
* See if it's a passive-mode response.
*
* XXX - does anybody do FOOBAR, as per RFC
* 1639, or has that been supplanted by RFC 2428?
*/
if (code == 227)/*也是子连接，被动连接*/
is_pasv_response = TRUE;
/*
* Responses to EPSV command, as per RFC 2428
*/
if (code == 229)
is_epasv_response = TRUE;
/*
* Skip the 3 digits and, if present, the
* space or hyphen.
*/
if (linelen >= 4)
next_token = line + 4;
else
next_token = line + linelen;
} else {
/*
* Line doesn't start with 3 digits; assume it's
* a line in the middle of a multi-line reply.
*/
next_token = line;
}
}
offset = (gint) (next_token - line);
linelen -= (int) (next_token - line);
line = next_token;
/*
* Add the rest of the first line as request or
* reply data.
上面解析的是request的command部分，和response的code部分。
剩余的是argument，参数部分，所以调用下面的展现。
*/
if (linelen != 0) {
if (is_request) {
proto_tree_add_item(reqresp_tree,
hf_ftp_request_arg, tvb, offset,
linelen, ENC_ASCII|ENC_NA);
} else {
proto_tree_add_item(reqresp_tree,
hf_ftp_response_arg, tvb, offset,
linelen, ENC_ASCII|ENC_NA);
}
}
offset = next_offset;
/*
* If this is a PORT request or a PASV response, handle it.
父子连接的特殊处理
*/
if (is_port_request) {
/*port命令情况下，解析出ip地址和端口*/
if (parse_port_pasv(line, linelen, &ftp_ip, &ftp_port, &pasv_offset, &ftp_ip_len, &ftp_port_len)) {
/*展示ip地址*/
proto_tree_add_ipv4(reqresp_tree, hf_ftp_active_ip,
tvb, pasv_offset + (tokenlen+1) , ftp_ip_len, ftp_ip);
/*展示端口*/
proto_tree_add_uint(reqresp_tree, hf_ftp_active_port,
tvb, pasv_offset + 1 + (tokenlen+1) + ftp_ip_len, ftp_port_len, ftp_port);
/*获取ip地址，判断是否跟包的ip地址相同，如果不同则是走了ftp的nat，即接收方ip地址是变的*/
set_address(&ftp_ip_address, AT_IPv4, 4, (const guint8 *)&ftp_ip);
ftp_nat = !addresses_equal(&pinfo->src, &ftp_ip_address);
if (ftp_nat) {
proto_tree_add_boolean(reqresp_tree, hf_ftp_active_nat,
tvb, 0, 0, ftp_nat);
}
}
}
if (is_pasv_response) {
if (linelen != 0) {
/*
* This frame contains a PASV response; set up a
* conversation for the data.
相应方向包出现父子连接是对pasv（被动模式）的响应
*/
/*仍然是解析出ip地址和端口，不过这里的地址是服务器端的*/
if (parse_port_pasv(line, linelen, &pasv_ip, &ftp_port, &pasv_offset, &ftp_ip_len, &ftp_port_len)) {
proto_tree_add_ipv4(reqresp_tree, hf_ftp_pasv_ip,
tvb, pasv_offset + 4, ftp_ip_len, pasv_ip);
proto_tree_add_uint(reqresp_tree, hf_ftp_pasv_port,
tvb, pasv_offset + 4 + 1 + ftp_ip_len, ftp_port_len, ftp_port);
set_address(&ftp_ip_address, AT_IPv4, 4,
(const guint8 *)&pasv_ip);
ftp_nat = !addresses_equal(&pinfo->src, &ftp_ip_address);
if (ftp_nat) {
proto_tree_add_boolean(reqresp_tree, hf_ftp_pasv_nat,
tvb, 0, 0, ftp_nat);
}
/*
* We use "ftp_ip_address", so that if
* we're NAT'd we look for the un-NAT'd
* connection.
*
* XXX - should this call to
* "find_conversation()" just use
* "ftp_ip_address" and "server_port", and
* wildcard everything else?
先根据解析出的服务器ip地址+客户端ip地址+端口去检索是否存在了，
如果不存在，则创建。
创建出来后，设置这个互联的解析要调用ftpdata_handle解析器。
也就是他们的父子连接是建立在conversation上。
*/
conversation = find_conversation(pinfo->num, &ftp_ip_address,
&pinfo->dst, PT_TCP, ftp_port, 0,
NO_PORT_B);
if (conversation == NULL) {
/*
* XXX - should this call to "conversation_new()"
* just use "ftp_ip_address" and "server_port",
* and wildcard everything else?
*
* XXX - what if we did find a conversation? As
* we create it only on the first pass through the
* packets, if we find one, it's presumably an
* unrelated conversation. Should we remove the
* old one from the hash table and put this one in
* its place? Can the conversation code handle
* conversations not in the hash table? Or should
* we make conversations support start and end
* frames, as circuits do, and treat this as an
* indication that one conversation was closed and
* a new one was opened?
*/
conversation = conversation_new(
pinfo->num, &ftp_ip_address, &pinfo->dst,
PT_TCP, ftp_port, 0, NO_PORT2);
/*设置子连接的解析方式，直接传解析handle过去*/
conversation_set_dissector(conversation, ftpdata_handle);
}
}
}
}
if (is_eprt_request) {
/*
* RFC2428 - sect. 2
* This frame contains a EPRT request; let's dissect it and set up a
* conversation for the data connection.
*/
if (parse_eprt_request(line, linelen,
&eprt_af, &eprt_ip, eprt_ipv6, &ftp_port,
&eprt_ip_len, &ftp_port_len)) {
/* since parse_eprt_request() returned TRUE,
we know that we have a valid address family */
eprt_offset = tokenlen + 1 + 1; /* token, space, 1st delimiter */
proto_tree_add_uint(reqresp_tree, hf_ftp_eprt_af, tvb,
eprt_offset, 1, eprt_af);
eprt_offset += 1 + 1; /* addr family, 2nd delimiter */
if (eprt_af == EPRT_AF_IPv4) {
proto_tree_add_ipv4(reqresp_tree, hf_ftp_eprt_ip,
tvb, eprt_offset, eprt_ip_len, eprt_ip);
set_address(&ftp_ip_address, AT_IPv4, 4,
(const guint8 *)&eprt_ip);
}
else if (eprt_af == EPRT_AF_IPv6) {
proto_tree_add_ipv6(reqresp_tree, hf_ftp_eprt_ipv6,
tvb, eprt_offset, eprt_ip_len, (const struct e_in6_addr *)eprt_ipv6);
set_address(&ftp_ip_address, AT_IPv6, 16, eprt_ipv6);
}
eprt_offset += eprt_ip_len + 1; /* addr, 3rd delimiter */
proto_tree_add_uint(reqresp_tree, hf_ftp_eprt_port,
tvb, eprt_offset, ftp_port_len, ftp_port);
/* Find/create conversation for data */
conversation = find_conversation(pinfo->num,
&pinfo->src, &ftp_ip_address,
PT_TCP, ftp_port, 0, NO_PORT_B);
if (conversation == NULL) {
conversation = conversation_new(
pinfo->num, &pinfo->src, &ftp_ip_address,
PT_TCP, ftp_port, 0, NO_PORT2);
conversation_set_dissector(conversation,
ftpdata_handle);
}
}
else {
proto_tree_add_expert(reqresp_tree, pinfo, &ei_ftp_eprt_args_invalid,
tvb, offset - linelen - 1, linelen);
}
}
if (is_epasv_response) {
if (linelen != 0) {
proto_item *addr_it;
/*
* RFC2428 - sect. 3
* This frame contains an EPSV response; set up a
* conversation for the data.
*/
/*因IPV6的出现，地址信息变长，所以RFC2428增加了EPRT和EPSV，以扩展对IPV6的支持*/
if (parse_extended_pasv_response(line, linelen,
&ftp_port, &pasv_offset, &ftp_port_len)) {
/* Add IP address and port number to tree */
if (ftp_ip_address.type == AT_IPv4) {
guint32 addr;
memcpy(&addr, ftp_ip_address.data, 4);
addr_it = proto_tree_add_ipv4(reqresp_tree,
hf_ftp_epsv_ip, tvb, 0, 0, addr);
PROTO_ITEM_SET_GENERATED(addr_it);
}
else if (ftp_ip_address.type == AT_IPv6) {
addr_it = proto_tree_add_ipv6(reqresp_tree,
hf_ftp_epsv_ipv6, tvb, 0, 0,
(const struct e_in6_addr *)ftp_ip_address.data);
PROTO_ITEM_SET_GENERATED(addr_it);
}
proto_tree_add_uint(reqresp_tree,
hf_ftp_epsv_port, tvb, pasv_offset + 4,
ftp_port_len, ftp_port);
/* Find/create conversation for data */
conversation = find_conversation(pinfo->num, &ftp_ip_address,
&pinfo->dst, PT_TCP, ftp_port, 0,
NO_PORT_B);
if (conversation == NULL) {
conversation = conversation_new(
pinfo->num, &ftp_ip_address, &pinfo->dst,
PT_TCP, ftp_port, 0, NO_PORT2);
conversation_set_dissector(conversation,
ftpdata_handle);
}
}
else {
proto_tree_add_expert(reqresp_tree, pinfo, &ei_ftp_epsv_args_invalid,
tvb, offset - linelen - 1, linelen);
}
}
}
/*
* Show the rest of the request or response as text,
* a line at a time.
* XXX - only if there's a continuation indicator?
*/
while (tvb_offset_exists(tvb, offset)) {
/*
* Find the end of the line.
*/
tvb_find_line_end(tvb, offset, -1, &next_offset, FALSE);
/*
* Put this line.
*/
proto_tree_add_format_text(ftp_tree, tvb, offset,
next_offset - offset);
offset = next_offset;
}
return tvb_captured_length(tvb);
}
/*data解析器*/
static int
dissect_ftpdata(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
proto_item *ti;
int data_length;
gboolean is_text = TRUE;
gint check_chars, i;
col_set_str(pinfo->cinfo, COL_PROTOCOL, "FTP-DATA");
col_add_fstr(pinfo->cinfo, COL_INFO, "FTP Data: %u bytes",
tvb_reported_length(tvb));
data_length = tvb_captured_length(tvb);
ti = proto_tree_add_item(tree, proto_ftp_data, tvb, 0, -1, ENC_NA);
/* Check the first few chars to see whether it looks like a text file or not */
check_chars = MIN(10, data_length);
for (i=0; i < check_chars; i++) {
if (!g_ascii_isprint(tvb_get_guint8(tvb, i))) {
is_text = FALSE;
break;
}
}
if (is_text) {
/* Show as string, but don't format more text than will be displayed */
proto_item_append_text(ti, " (%s)", tvb_format_text(tvb, 0, MIN(data_length, ITEM_LABEL_LENGTH)));
}
else {
/* Assume binary, just show the number of bytes */
proto_item_append_text(ti, " (%u bytes data)", data_length);
}
return tvb_captured_length(tvb);
}
/*
协议解析注册函数
注册解析器能够解析的协议参数，以及参数的名称、路径、类型、显示方式等信息给协议树。
*/
void
proto_register_ftp(void)
{
static hf_register_info hf[] = {
{ &hf_ftp_response,/*在协议树中的id*/
{ "Response",/*参数全称*/ "ftp.response",/*参数的简写名称*/
FT_BOOLEAN,/*参数的数据类型*/ BASE_NONE,/*参数的显示方式*/
NULL,/*参数格式化对照表例如response_table_ext*/ 0x0,/*参数掩码，不足一个字节的参数需要使用，如tcp的flag标记*/
"TRUE if FTP response",/*参数的简短描述*/ HFILL/*set by proto routines (prefilled by HFILL macro, see below)*/ }},
{ &hf_ftp_request,
{ "Request", "ftp.request",
FT_BOOLEAN, BASE_NONE, NULL, 0x0,
"TRUE if FTP request", HFILL }},
{ &hf_ftp_request_command,
{ "Request command", "ftp.request.command",
FT_STRING, BASE_NONE, NULL, 0x0,
NULL, HFILL }},
{ &hf_ftp_request_arg,
{ "Request arg", "ftp.request.arg",
FT_STRING, BASE_NONE, NULL, 0x0,
NULL, HFILL }},
{ &hf_ftp_response_code,
{ "Response code", "ftp.response.code",
FT_UINT32, BASE_DEC|BASE_EXT_STRING, &response_table_ext, 0x0,
NULL, HFILL }},
{ &hf_ftp_response_arg,
{ "Response arg", "ftp.response.arg",
FT_STRING, BASE_NONE, NULL, 0x0,
NULL, HFILL }},
{ &hf_ftp_pasv_ip,
{ "Passive IP address", "ftp.passive.ip",
FT_IPv4, BASE_NONE, NULL,0x0,
"Passive IP address (check NAT)", HFILL}},
{ &hf_ftp_pasv_port,
{ "Passive port", "ftp.passive.port",
FT_UINT16, BASE_DEC, NULL,0x0,
"Passive FTP server port", HFILL }},
{ &hf_ftp_pasv_nat,
{"Passive IP NAT", "ftp.passive.nat",
FT_BOOLEAN, BASE_NONE, NULL, 0x0,
"NAT is active SIP and passive IP different", HFILL }},
{ &hf_ftp_active_ip,
{ "Active IP address", "ftp.active.cip",
FT_IPv4, BASE_NONE, NULL, 0x0,
"Active FTP client IP address", HFILL }},
{ &hf_ftp_active_port,
{"Active port", "ftp.active.port",
FT_UINT16, BASE_DEC, NULL, 0x0,
"Active FTP client port", HFILL }},
{ &hf_ftp_active_nat,
{ "Active IP NAT", "ftp.active.nat",
FT_BOOLEAN, BASE_NONE, NULL, 0x0,
"NAT is active", HFILL}},
{ &hf_ftp_eprt_af,
{ "Extended active address family", "ftp.eprt.af",
FT_UINT8, BASE_DEC, VALS(eprt_af_vals), 0,
NULL, HFILL }},
{ &hf_ftp_eprt_ip,
{ "Extended active IP address", "ftp.eprt.ip",
FT_IPv4, BASE_NONE, NULL, 0,
"Extended active FTP client IPv4 address", HFILL }},
{ &hf_ftp_eprt_ipv6,
{ "Extended active IPv6 address", "ftp.eprt.ipv6",
FT_IPv6, BASE_NONE, NULL, 0,
"Extended active FTP client IPv6 address", HFILL }},
{ &hf_ftp_eprt_port,
{ "Extended active port", "ftp.eprt.port",
FT_UINT16, BASE_DEC, NULL, 0,
"Extended active FTP client listener port", HFILL }},
{ &hf_ftp_epsv_ip,
{ "Extended passive IPv4 address", "ftp.epsv.ip",
FT_IPv4, BASE_NONE, NULL, 0,
"Extended passive FTP server IPv4 address", HFILL }},
{ &hf_ftp_epsv_ipv6,
{ "Extended passive IPv6 address", "ftp.epsv.ipv6",
FT_IPv6, BASE_NONE, NULL, 0,
"Extended passive FTP server IPv6 address", HFILL }},
{ &hf_ftp_epsv_port,
{ "Extended passive port", "ftp.epsv.port",
FT_UINT16, BASE_DEC, NULL, 0,
"Extended passive FTP server port", HFILL }}
};
/*子树标记*/
static gint *ett[] = {
&ett_ftp,
&ett_ftp_reqresp
};
static ei_register_info ei[] = {
{ &ei_ftp_eprt_args_invalid, { "ftp.eprt.args_invalid", PI_MALFORMED, PI_WARN, "EPRT arguments must have the form: |<family>|<addr>|<port>|", EXPFILL }},
{ &ei_ftp_epsv_args_invalid, { "ftp.epsv.args_invalid", PI_MALFORMED, PI_WARN, "EPSV arguments must have the form (|||<port>|)", EXPFILL }},
};
expert_module_t* expert_ftp;
/*注册ftp协议*/
proto_ftp = proto_register_protocol("File Transfer Protocol (FTP)", "FTP", "ftp");
/*注册ftp协议解析器*/
register_dissector("ftp", dissect_ftp, proto_ftp);
/*注册ftp_data协议*/
proto_ftp_data = proto_register_protocol("FTP Data", "FTP-DATA", "ftp-data");
/*注册ftp_data协议解析器*/
register_dissector("ftp-data", dissect_ftpdata, proto_ftp_data);
/*注册ftp协议的协议参数*/
proto_register_field_array(proto_ftp, hf, array_length(hf));
/*注册ftp协议解析中的子树*/
proto_register_subtree_array(ett, array_length(ett));
expert_ftp = expert_register_protocol(proto_ftp);
expert_register_field_array(expert_ftp, ei, array_length(ei));
}
/*注册协议到协议树下，方便后续解析*/
void
proto_reg_handoff_ftp(void)
{
dissector_handle_t ftp_handle;
/*注册ftp-data到tcp.port下，如果tcp.port==TCP_PORT_FTPDATA,则执行ftpdata_handle解析器*/
ftpdata_handle = find_dissector("ftp-data");
dissector_add_uint("tcp.port", TCP_PORT_FTPDATA, ftpdata_handle);
/*注册ftp-data到tcp.port下，如果tcp.port==TCP_PORT_FTP,则执行ftp_handle解析器*/
ftp_handle = find_dissector("ftp");
dissector_add_uint("tcp.port", TCP_PORT_FTP, ftp_handle);
}
/*
* Editor modelines - http://www.wireshark.org/tools/modelines.html
*
* Local variables:
* c-basic-offset: 4
* tab-width: 8
* indent-tabs-mode: nil
* End:
*
* vi: set shiftwidth=4 tabstop=8 expandtab:
* :indentSize=4:tabSize=8:noTabs=true:
*/
如果你有耐心看完了这个代码示例，并阅读了wireshark的源代码，那我们就正式进入了wireshark的殿堂。
每一份代码都有一条主线，有的主线可能是main函数里面的1、2、3、4，也有可能是一个输入的层层处理，输入数据就是主线。在数据包解析过程中，我认为会话才是协议解析主线，网络中，一条回话建立一个网络互联，互联两段分别是客户端和服务器。一条会话连接两端，并承载其中大量的数据报文。也许只要做过网络协议解析产品的都对这个有直观的认识。
那么wireshark的会话是什么样的，是怎么建立的，是怎么维护的，是我们后续分析的一个重点。分析完会话，就可以将wireshark整个串联起来，理解他的设计理念。