"Linux Network Development Required Course" 10_Application Protocol Analysis Module (Part 2)

Question: How to parse protocol data in real time through socket file descriptor?

Deep thinking

Is it possible to get enough data from the file descriptor? (Whether it must wait until the number is sufficient (eg: 12 bytes in the message header) before parsing can begin)

• enough data

  • Read 12 bytes to parse the message header
  • Read data to fill payload (length)

• Insufficient amount of data

  • The data required by the message header cannot be obtained (how to deal with it? How to switch the parsing state?)
  • Failed to get the complete payload data (how to handle? Can it be appended?)

solution

Strategy: Do your best to obtain data and analyze it in real time

• Even if 1 byte is currently obtained, it can be parsed according to the status
• Support multiple relay parsing of different data sources (obtain data alternately from memory or file descriptors)

 充分利用解析器状态信息是实现解决方案的关键

Parser state toggle

State switching function

 static void InitState(MsgParser *p) 
{
    p->header = 0;
    p->need = sizeof(p->cache);
    free(p->msg);
    p->msg = NULL;
}

 static int ToMidState(MsgParser *p)
{
    p->header = 1;
    p->need = p->cache.length;
    
    p->msg = malloc(sizeof(p->cache) + p->need);

    if (p->msg) {
        *p->msg = p->cache;
    }

    return !!p->msg;
}

 static Message *ToLastState(MsgParser *p)
{
    Message *ret = NULL;
    
    if (p->header && !p->need) {
        ret = p->msg;
        p->msg = NULL;
    }

    return ret;
}

get data from file descriptor

 static int ToRecv(int fd, char *buf, int size)
{
    int retry = 0;
    int i = 0;

    while (i < size) {
        int len = read(fd, buf + i, size - i);

        if (len > 0) {
            i += len;
        }
        else {
            if (retry++ > 5) {
                break;
            }

            usleep(200 * 10000);
        }
    }

    return i;
}

Real-time parsing of message headers from file descriptors

 if (!p->header) {
    int offset = sizeof(p->cache) - p->need;
    int len = ToRecv(fd, (char*)&p->cache + offset/* 计算存放位置并读取消息头数据 */, p->need);

    if (len == p->need) {
        ntoh(&p->cache);

        if (ToMidState(p)) {
            ret = MParser_ReadFd(p, fd);
        }
    } else {
        p->need -= len;
    }
}

Get payload data from file descriptor

 if (p->msg) {
    int len = ToRecv(fd, p->msg->payload, p->need);
    p->need -= len;
}

/* 尝试切换到最终状态，如果成功，则可获得协议消息；之后切换到初始状态 */
if (ret = ToLastState(p)) {
    InitState(p);
}

Programming Lab: Parsing Protocol Messages from File Descriptors

message.h

 #ifndef MESSAGE_H
#define MESSAGE_H

typedef struct message {
    unsigned short type;
    unsigned short cmd;
    unsigned short index;
    unsigned short total;
    unsigned int length;
    unsigned char payload[];
}Message;

Message *Message_New(unsigned short type,
                    unsigned short cmd,
                    unsigned short index,
                    unsigned short total,
                    unsigned char *payload,
                    unsigned int length);

#endif

message.c

 #include "message.h"

#include <malloc.h>
#include <string.h>

Message *Message_New(unsigned short type, unsigned short cmd, unsigned short index, unsigned short total, unsigned char *payload, unsigned int length)
{
    Message *ret = malloc(sizeof(Message) + length);

    if (ret) {
        ret->type   = type;
        ret->cmd    = cmd;
        ret->index  = index;
        ret->total  = total;
        ret->length = length;

        if (payload) {
            memcpy(ret + 1, payload, length);
        }
    }

    return ret;
}

msg_parser.h

 #ifndef MSG_PARSER_H
#define MSG_PARSER_H

#include "message.h"

typedef void MParser;

MParser *MParser_New();
Message *MParser_ReadMem(MParser *parser, unsigned char *mem, unsigned int length);
Message *MParser_ReadFd(MParser *parser, int fd);
void MParser_Reset(MParser *parse);
void MParser_Del(MParser *parse);

#endif

msg_parser.c

 #include <malloc.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>

#include "msg_parser.h"

typedef struct msg_parser {
    Message cache;
    int header;
    int need;
    Message *msg;
}MsgParser;

static void InitState(MsgParser *p)
{
    p->header = 0;
    p->need = sizeof(p->cache);
    
    free(p->msg);

    p->msg = NULL;
}

static int ToMidState(MsgParser *p)
{
    p->header = 1;
    p->need = p->cache.length;

    p->msg = malloc(sizeof(p->cache) + p->need);

    if (p->msg) {
        *p->msg = p->cache;
    }

    return !!p->msg;
}

static Message *ToLastState(MsgParser *p)
{
    Message *ret = NULL;

    if (p->header && !p->need) {
        ret = p->msg;
        p->msg = NULL;
    }

    return ret;
}

static void ntoh(Message *m)
{
    m->type = ntohs(m->type);
    m->cmd = ntohs(m->cmd);
    m->index = ntohs(m->index);
    m->total = ntohs(m->total);
    m->length = ntohl(m->length);    
}

static int ToRecv(int fd, char *buf, int size)
{
    int retry = 0;
    int i = 0;

    while (i < size) {
        int len = read(fd, buf + i, size - i);
        if (len > 0) {
            i += len;
        } else if (len < 0) {
            break;
        } else {
            if (retry++ > 5) {
                break;
            }

            usleep(200 * 1000);
        }
    }

    return i;
}

MParser *MParser_New()
{
    MsgParser *ret = calloc(1,  sizeof(MsgParser));

    InitState(ret);

    return ret;
}

Message *MParser_ReadMem(MParser *parser, unsigned char *mem, unsigned int length)
{
    Message *ret = NULL;
    MsgParser *p = (MsgParser*)parser;

    if (!p || !mem || !length) {
        return ret;
    }

    if (!p->header) {
        int len = (p->need < length) ? p->need : length;
        int offset = sizeof(p->cache) - p->need;

        memcpy((char*)&p->cache + offset, mem, len);

        if (p->need == len) {
            ntoh(&p->cache);

            mem += p->need;
            length -= p->need;

            if (ToMidState(p)) {
                ret = MParser_ReadMem(p, mem, length);
            } else {
                InitState(p);
            }
        } else {
            p->need -= len;
        }
    } else {
        if (p->msg) {
            int len = (p->need < length) ? p->need : length;
            int offset = p->msg->length - p->need;

            memcpy(p->msg->payload + offset, mem, len);

            p->need -= len;

            if (ret = ToLastState(p)) {
                InitState(p);
            }
        }  
    }

    return ret;
}

Message *MParser_ReadFd(MParser *parser, int fd)
{
    Message *ret = NULL;
    MsgParser *p = (MsgParser*)parser;

    if (fd == -1 || !p) {
        return ret;
    }

    if (!p->header) {
        int offset = sizeof(p->cache) - p->need;
        int len = ToRecv(fd, (char*)&p->cache + offset, p->need);

        if (len == p->need) {
            ntoh(&p->cache);
            if (ToMidState(p)) {
                ret = MParser_ReadFd(p, fd);
            }
            else {
                InitState(p);
            }
        }
        else {
            p->need -= len;
        }
    } else {
        if (p->msg) {
            int offset = p->msg->length - p->need;
            int len = ToRecv(fd, p->msg->payload + offset, p->need);

            p->need -= len;
        }

        if (ret = ToLastState(p)) {
            InitState(p);
        }
    } 

    return ret;
}

void MParser_Reset(MParser *parse)
{
    MsgParser *p = (MsgParser*)parse;

    if (p) {
        InitState(p);
    }
}

void MParser_Del(MParser *parse)
{
    MsgParser *p = (MsgParser*)parse;

    if (p) {
        free(p->msg);
        free(p);
    }
}

Test 1: test.c

 #include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#include "msg_parser.h"

int main()
{   
    MParser *p = MParser_New();
    char buf[] = {0x00, 0x01, 0x00, 0x02, 0x00};
    char another[] = {0x03, 0x00, 0x04, 0x00, 0x00, 0x00, 0x04};
    char data[] = {0x11, 0x12, 0x13, 0x14};
    Message *m = MParser_ReadMem(p, buf, sizeof(buf));
    int i = 0;

    if (!m) {
        printf("parse again...\n");

        m = MParser_ReadMem(p, another, sizeof(another));
    }

        if (!m) {
        printf("parse again again...\n");

        m = MParser_ReadMem(p, data, sizeof(data));
    }

    printf("m = %p\n", m);

    if (m) {
        printf("type = %d\n", m->type);
        printf("cmd = %d\n", m->cmd);
        printf("index = %d\n", m->index);
        printf("total = %d\n", m->total);
        printf("length = %d\n", m->length);

        for (i=0; i<m->length; ++i) {
            printf("0x%02x ", m->payload[i]);
        }

        printf("\n");

        free(m);
    }

    MParser_Del(p);

    return 0;    
}

output:

 parse again...
parse again again...
m = 0x555e21dd56a0
type = 1
cmd = 2
index = 3
total = 4
length = 4
0x11 0x12 0x13 0x14

Test 2:
client.c

 #include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <malloc.h>

#include "message.h"

static void hton(Message *m)
{
    m->type = htons(m->type);
    m->cmd = htons(m->cmd);
    m->index = htons(m->index);
    m->total = htons(m->total);
    m->length = htonl(m->length);    
}

int main()
{
    int sock = 0;
    struct sockaddr_in addr = {0};
    int i = 0;
    char *test = "D.T.Software";
    Message *pm = NULL;

    sock = socket(PF_INET, SOCK_STREAM, 0);

    if (sock == -1) {
        printf("socket error\n");
        return -1;
    }

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    addr.sin_port = htons(8888);

    if (connect(sock, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
        printf("connect error\n");
        return -1;
    }

    printf("connect success\n");

    for (i=0; i<strlen(test); ++i) {
        char buf[2] = {0};

        buf[0] = test[i];

        pm = Message_New(128, 129, i, strlen(test), buf, 2);

        hton(pm);

        send(sock, pm, sizeof(Message) + 2, 0);

        free(pm);
    }
    
    getchar();

    close(sock);

    return 0;
}

server.c

 #include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/tcp.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <malloc.h>

#include "msg_parser.h"

int main()
{
    int server = 0;
    struct sockaddr_in saddr = {0};
    int client = 0;
    struct sockaddr_in caddr = {0};
    socklen_t asize = 0;
    int len = 0;
    char buf[32] = {0};
    int r = 0;
    MParser *parser = MParser_New();

    server = socket(PF_INET, SOCK_STREAM, 0);

    if (server == -1) {
        printf("server socket error\n");
        return -1;
    }

    saddr.sin_family = AF_INET;
    saddr.sin_addr.s_addr = htonl(INADDR_ANY);
    saddr.sin_port = htons(8888);

    if (bind(server, (struct sockaddr*)&saddr, sizeof(saddr)) == -1) {
        printf("server bind error\n");
        return -1;
    }

    if (listen(server, 1) == -1) {
        printf("server listen error\n");
        return -1;
    }

    printf("server start success\n");

    while (1) {
        struct tcp_info info = {0};
        int l = sizeof(info);

        asize = sizeof(caddr);
        client = accept(server, (struct sockaddr*)&caddr, &asize);

        if (client == -1) {
            printf("client accept error\n");
            return -1;
        }

        printf("client: %d\n", client);

        do {
            getsockopt(client, IPPROTO_TCP, TCP_INFO, &info, (socklen_t*)&l);

            Message *m = MParser_ReadFd(parser, client);

            if (m) {
                printf("type = %d\n", m->type);
                printf("cmd = %d\n", m->cmd);
                printf("index = %d\n", m->index);
                printf("total = %d\n", m->total);
                printf("length = %d\n", m->length);
                printf("payload = %s\n", m->payload);
                printf("\n");
                free(m);
            }
        } while (info.tcpi_state == TCP_ESTABLISHED);

        printf("client socket is closed\n");

        close(client);
    }

    close(server);

    MParser_Del(parser);

    return 0;
}

output:

 server start success
client: 4
type = 128
cmd = 129
index = 0
total = 12
length = 2
payload = D

type = 128
cmd = 129
index = 1
total = 12
length = 2
payload = .

type = 128
cmd = 129
index = 2
total = 12
length = 2
payload = T

type = 128
cmd = 129
index = 3
total = 12
length = 2
payload = .

type = 128
cmd = 129
index = 4
total = 12
length = 2
payload = S

type = 128
cmd = 129
index = 5
total = 12
length = 2
payload = o

type = 128
cmd = 129
index = 6
total = 12
length = 2
payload = f

type = 128
cmd = 129
index = 7
total = 12
length = 2
payload = t

type = 128
cmd = 129
index = 8
total = 12
length = 2
payload = w

type = 128
cmd = 129
index = 9
total = 12
length = 2
payload = a

type = 128
cmd = 129
index = 10
total = 12
length = 2
payload = r

type = 128
cmd = 129
index = 11
total = 12
length = 2
payload = e

client socket is closed

---

After you have a protocol and a protocol parser, what can you do?