《Linux网络开发必学教程》10_应用协议解析模块(下)

问题:如何通过 socket 文件描述符实时解析协议数据?
深度思考
从文件描述符是否能够获取足够的数据?(是否一定等到数量足够(如:消息头12字节),才能开始解析)
  • 数据量足够
    • 读取 12 字节解析消息头
    • 读取数据填充 payload (length)
  • 数据量不足
    • 无法获取消息头所需数据(如何处理?解析状态如何切换?)
    • 无法获取 payload 完整数据(如何处理?是否可追加?)
解决方案
策略:尽力获取数据,实时解析
  • 即便当前获取 1 字节,也可根据状态进行解析
  • 支持不同数据源多次接力解析(从内存或文件描述符交替获取数据)
充分利用解析器状态信息是实现解决方案的关键

解析器状态切换 【《Linux网络开发必学教程》10_应用协议解析模块(下)】《Linux网络开发必学教程》10_应用协议解析模块(下)
文章图片

状态切换函数
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; }

从文件描述符中获取数据
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; }

从文件描述符中实时解析消息头
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; } }

从文件描述符中获取 payload 数据
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); }

编程实验:从文件描述符解析协议消息
message.h
#ifndef MESSAGE_H #define MESSAGE_Htypedef 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 #include 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 #include #include #include #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); } }

测试一:test.c
#include #include #include #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; ilength; ++i) { printf("0x%02x ", m->payload[i]); }printf("\n"); free(m); }MParser_Del(p); return 0; }

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

测试2:
client.c
#include #include #include #include #include #include #include #include #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

server.c
#include #include #include #include #include #include #include #include #include #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; }

输出:
server start success client: 4 type = 128 cmd = 129 index = 0 total = 12 length = 2 payload = Dtype = 128 cmd = 129 index = 1 total = 12 length = 2 payload = .type = 128 cmd = 129 index = 2 total = 12 length = 2 payload = Tclient socket is closed

有了协议和协议解析器之后,可以干嘛?

    推荐阅读