CSAPP2e: Proxy lab 解答
这次的Proxy lab 是要求实现一个简单的web 代理。与此相关的章节是网络编程和并发编程，其实之前零零星星的看过一些讲HTTP协议的书，但是对于套接字这些都是一知半解，跟着课堂学完这两章突然柳暗花明，再看一些更详细更深入的书，像《HTTP权威指南》，《计算机网络-自顶向下的方法》就明白的多了。
下面就说一下这次lab，共有3个部分，第一部分是实现一个单线程代理，接收客户端请求，连接服务器然后转发。第二部分是实现并发，为每一个请求新建一个进程。第三部分是最有趣的，为每个请求建立独立的进程之后，该怎么共享进程之间的数据，也就是缓存呢？这里用到了书上介绍的写者-读者模型。源代码如下（已经通过了测试）。
1 /* 2 * justforyeah@yeah.net 3 * 2014.12.28 18:24 4 */ 5 6 #include "csapp.h" 7 8 #define MAX_CACHE_SIZE 1049000 9 #define MAX_OBJECT_SIZE 102400 10 11 /* argument for each thread */ 12 struct arg { 13 int connfd; /* client socked */ 14 int turn; /* the time of current request */ 15 }; 16 /* cache block */ 17 struct cache_block { 18 char data[MAX_OBJECT_SIZE]; /* store the response head and body */ 19 sem_t mutex; /* 模仿书上P673,使用写者-读者模型解决并发冲突 */ 20 sem_t w; 21 int readcnt; 22 23 int turn; /* the time of request */ 24 sem_t t_mutex; 25 sem_t t_w; 26 int t_readcnt; 27 28 char url[300]; /* the url of request */ 29 sem_t url_mutex; 30 sem_t url_w; 31 int url_readcnt; 32 33 }; 34 /* total 10 cache block */ 35 struct cache_block cache[10]; 36 37 /* init the block */ 38 void cache_erase(int index); 39 40 /* because of concurrency, all operation on cache use following 4 function */ 41 /* write data, url and turn on cache[index] */ 42 void cache_write(int index, char *url,char *data, int turn); 43 /* read data on cache[index] */ 44 void cache_data_read(int index, char *dst, int turn); 45 /* read url on cache[index] */ 46 void cache_url_read(int index,char *dst); 47 /* read turn on cache[index] */ 48 int cache_turn_read(int index); 49 50 /* thread for each request */ 51 void *thread(void *connfdp); 52 53 /* parse the request line */ 54 void parse_url(char *url, char *hostname, char *query_path, int *port); 55 56 /* connect to server, if failed return -1 */ 57 int connect_server(char *hostname,int port,char *query_path); 58 59 60 int main(int argc,char **argv) 61 { 62 Signal(SIGPIPE, SIG_IGN); 63 struct sockaddr_in clientaddr; 64 int port,listenfd,clientlen; 65 int turn=1; 66 pthread_t tid; 67 struct arg *p; 68 69 /* check port */ 70 if(argc!=2) { 71 fprintf(stderr, "usage: %s <port>\n", argv[0]); 72 exit(0); 73 } 74 75 // init 10 cache blocks 76 int i; 77 for(i=0;i<10;i++) 78 cache_erase(i); 79 80 port=atoi(argv[1]); 81 listenfd=Open_listenfd(port); 82 clientlen=sizeof(clientaddr); 83 84 while(1) { 85 p=(int*)Malloc(sizeof(struct arg)); 86 p->connfd=Accept(listenfd,(SA*)&clientaddr,&clientlen); 87 p->turn =turn++; 88 /* create thread */ 89 Pthread_create(&tid,NULL,thread,(void *)p); 90 } 91 return 0; 92 } 93 94 /* parse request url */ 95 void parse_url(char *ur, char *hostname, char *query_path, int *port) 96 { 97 char url[100]; 98 url[0]='\0'; 99 strcat(url,ur); 100 hostname[0]=query_path[0]='\0'; 101 char *p=strstr(url,"//"); /* skip "http://" and "https://" */ 102 if(p!=NULL) { 103 p=p+2; 104 } else { 105 p=url; 106 } 107 char *q=strstr(p,":"); /* read ":<port>" and "/index.html" */ 108 if(q!=NULL) { 109 *q='\0'; 110 sscanf(p,"%s",hostname); 111 sscanf(q+1,"%d%s",port,query_path); 112 } else { 113 q=strstr(p,"/"); 114 if(q!=NULL) { 115 *q='\0'; 116 sscanf(p,"%s",hostname); 117 *q='/'; 118 sscanf(q,"%s",query_path); 119 } else { 120 sscanf(p,"%s",hostname); 121 } 122 *port=80; 123 } 124 /* the default path */ 125 if(strlen(query_path)<=1) 126 strcpy(query_path,"/index.html"); 127 128 return; 129 } 130 131 /* connect to server and return socket fd */ 132 int connect_server(char *hostname,int port,char *query_path) 133 { 134 static const char *user_agent = "User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.3) Gecko/20120305 Firefox/10.0.3\r\n"; 135 static const char *accept_str= "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\nAccept-Encoding: gzip, deflate\r\n"; 136 static const char *connection = "Connection: close\r\nProxy-Connection: close\r\n"; 137 138 char buf[MAXLINE]; 139 /* connect to server */ 140 int proxy_clientfd; 141 proxy_clientfd=open_clientfd(hostname,port); 142 143 /* if failed return */ 144 if(proxy_clientfd<0) 145 return proxy_clientfd; 146 147 /* write request to server */ 148 sprintf(buf,"GET %s HTTP/1.0\r\n",query_path); 149 Rio_writen(proxy_clientfd,buf,strlen(buf)); 150 sprintf(buf,"Host: %s\r\n",hostname); 151 Rio_writen(proxy_clientfd,buf,strlen(buf)); 152 Rio_writen(proxy_clientfd,user_agent,strlen(user_agent)); 153 Rio_writen(proxy_clientfd,accept_str,strlen(accept_str)); 154 Rio_writen(proxy_clientfd,connection,strlen(connection)); 155 Rio_writen(proxy_clientfd,"\r\n",strlen("\r\n")); 156 return proxy_clientfd; 157 } 158 159 /* 160 * if there is a finished cache, read and response. 161 * else connect to server 162 */ 163 void *thread(void *p) 164 { 165 Pthread_detach(pthread_self()); 166 int connfd=((struct arg*)p)->connfd,turn=((struct arg*)p)->turn; 167 free(p); 168 169 char buf[MAXLINE]; 170 char method[MAXLINE],version[MAXLINE],url[MAXLINE]; 171 char host[MAXLINE],query[MAXLINE]; 172 char url_tmp[300],*data_tmp; 173 rio_t rio; 174 int index,port,content_length; 175 int serverfd; 176 177 /* read request line */ 178 rio_readinitb(&rio,connfd); 179 rio_readlineb(&rio,buf,MAXLINE); 180 sscanf(buf,"%s %s %s",method,url,version); 181 182 if(strcasecmp(method,"GET")) { 183 /* ignore */ 184 printf("Not GET\r\n"); 185 Close(connfd); 186 return NULL; 187 } 188 /* ignore client request */ 189 do { 190 rio_readlineb(&rio,buf,MAXLINE-1); 191 }while(strcmp(buf,"\r\n")); 192 193 /* find cache block */ 194 for(index=0;index<10;index++) { 195 cache_url_read(index,url_tmp); 196 /* the block'url is same as current url */ 197 if(!strcmp(url,url_tmp)) 198 break; 199 } 200 201 data_tmp=(char*)Malloc(MAX_OBJECT_SIZE); 202 data_tmp[0]='\0'; 203 204 if(index <10) { /* if have cached */ 205 cache_data_read(index,data_tmp,turn); 206 rio_writen(connfd,data_tmp,strlen(data_tmp)); 207 Close(connfd); 208 free(data_tmp); 209 return NULL; 210 } 211 212 /* connect to server */ 213 parse_url(url,host,query,&port); 214 if((serverfd=connect_server(host,port,query))<0) { 215 /* connect to server failed, return */ 216 free(data_tmp); 217 Close(connfd); 218 return NULL; 219 } 220 221 rio_readinitb(&rio,serverfd); 222 content_length=0; 223 /* read response head line */ 224 do { 225 int t=rio_readlineb(&rio,buf,MAXLINE-1); 226 if(t<=0) 227 break; 228 strncat(data_tmp,buf,t); 229 if(strstr(buf,"Content-length")!=NULL) 230 sscanf(buf,"Content-length: %d\r\n",&content_length); 231 rio_writen(connfd,buf,t); 232 }while(strcmp(buf,"\r\n")); 233 234 /* read response body */ 235 /* response is small enough to cache */ 236 if(content_length+strlen(data_tmp)<MAX_OBJECT_SIZE) { 237 while(content_length>0) { 238 int t= rio_readnb(&rio,buf,(content_length<MAXLINE-1)?content_length:MAXLINE-1); 239 if(t<=0) 240 continue; 241 content_length-=t; 242 strncat(data_tmp,buf,t); 243 rio_writen(connfd,buf,t); 244 } 245 index=0; 246 int i; 247 /* least-recently-used */ 248 for(i=1;i<10;i++) { 249 if(cache_turn_read(i)<cache_turn_read(index)) { 250 index=i; 251 } 252 } 253 /* cache write */ 254 cache_write(index,url,data_tmp,turn); 255 } 256 /* ignore store and write to client */ 257 else { 258 while(content_length>0) { 259 int t= rio_readnb(&rio,buf,(content_length<MAXLINE-1)?content_length:MAXLINE-1); 260 if(t<=0) 261 break; 262 content_length-=t; 263 rio_writen(connfd,buf,t); 264 } 265 } 266 Close(connfd); 267 Close(serverfd); 268 free(data_tmp); 269 return NULL; 270 } 271 272 void cache_erase(int index) 273 { 274 /* init all var */ 275 cache[index].turn=0; 276 cache[index].url[0]='\0'; 277 cache[index].data[0]='\0'; 278 Sem_init(&cache[index].t_mutex,0,1); 279 Sem_init(&cache[index].t_w,0,1); 280 cache[index].t_readcnt=0; 281 Sem_init(&cache[index].url_mutex,0,1); 282 Sem_init(&cache[index].url_w,0,1); 283 cache[index].url_readcnt=0; 284 Sem_init(&cache[index].mutex,0,1); 285 Sem_init(&cache[index].w,0,1); 286 cache[index].readcnt=0; 287 } 288 289 void cache_write(int index,char *url, char *data, int turn) 290 { 291 /* semaphore */ 292 P(&cache[index].url_w); 293 P(&cache[index].w); 294 P(&cache[index].t_w); 295 /* begin write operation */ 296 cache[index].turn=turn; 297 strcpy(cache[index].data,data); 298 strcpy(cache[index].url,url); 299 /* end write operation */ 300 301 /* semaphore */ 302 V(&cache[index].t_w); 303 V(&cache[index].w); 304 V(&cache[index].url_w); 305 return ; 306 } 307 308 void cache_data_read(int index, char *dst, int turn) 309 { 310 /* semaphore */ 311 P(&cache[index].mutex); 312 cache[index].readcnt++; 313 if(cache[index].readcnt==1) 314 P(&cache[index].w); 315 V(&cache[index].mutex); 316 P(&cache[index].t_w); 317 318 /* begin read operation */ 319 cache[index].turn=turn; 320 strcpy(dst,cache[index].data); 321 /* end read operation */ 322 323 /* semphore */ 324 V(&cache[index].t_w); 325 P(&cache[index].mutex); 326 cache[index].readcnt--; 327 if(cache[index].readcnt==0) 328 V(&cache[index].w); 329 V(&cache[index].mutex); 330 331 return; 332 } 333 334 void cache_url_read(int index,char *dst) 335 { 336 /* semaphore */ 337 P(&cache[index].url_mutex); 338 cache[index].url_readcnt++; 339 if(cache[index].url_readcnt==1) 340 P(&cache[index].url_w); 341 V(&cache[index].url_mutex); 342 343 /* begin read operation */ 344 strcpy(dst,cache[index].url); 345 /* end read operation */ 346 347 /* semphore */ 348 P(&cache[index].url_mutex); 349 cache[index].url_readcnt--; 350 if(cache[index].url_readcnt==0) 351 V(&cache[index].url_w); 352 V(&cache[index].url_mutex); 353 354 return; 355 } 356 357 int cache_turn_read(int index) 358 { 359 int t; 360 /* semaphore */ 361 P(&cache[index].t_mutex); 362 cache[index].t_readcnt++; 363 if(cache[index].t_readcnt==1) 364 P(&cache[index].t_w); 365 V(&cache[index].t_mutex); 366 367 /* begin read operation */ 368 t=cache[index].turn; 369 /* end read operation */ 370 371 /* semphore */ 372 P(&cache[index].t_mutex); 373 cache[index].t_readcnt--; 374 if(cache[index].t_readcnt==0) 375 V(&cache[index].t_w); 376 V(&cache[index].t_mutex); 377 378 return t; 379 }
