tinyhttpd源码详解
tinyhttpd是一轻量级的web 服务器,最近几天终于抽出时间来研究研究了。其源码百度即可下载,500多行,确实是学习linux编程的好材料。很多网友都写了关于tinyhttpd的博文,但是我还是觉得不够深入,严格说是写得不够深入,往往就是把500多行代码一扔,分析下主要过程,画个流程图就完事了。我怎么觉得还有很多东西可以挖一挖呢,也许还可再调整一下代码,虽然目前也不清楚可调整多少,待我细细道来。
我分析的过程就按主要路线走,也就是这样一个主干道流程:服务器创建socket并监听某一端口->浏览器输入url发出请求->服务器收到请求,创建线程处理请求,主线程继续等待->新线程读取http请求,并解析相关字段,读取文件内容或者执行CGI程序并返回给浏览器->关闭客户端套接字,新线程退出
咱们先来看看main函数
int main(void) { int server_sock = -1; u_short port = 0; int client_sock = -1; struct sockaddr_in client_name; int client_name_len = sizeof(client_name); pthread_t newthread; server_sock = startup(&port); printf("httpd running on port %d\n", port); while (1) { client_sock = accept(server_sock, (struct sockaddr *)&client_name, &client_name_len); if (client_sock == -1) error_die("accept"); if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0) perror("pthread_create"); } close(server_sock); return(0); }
这段代码,只要是稍微了解linux的网络编程就很好懂,创建服务端socket,绑定、监听、等待客户端连接。只不过作者把这些步骤都放在了一个叫startup的函数里。那来看startup
int startup(u_short *port) { int httpd = 0; struct sockaddr_in name; httpd = socket(PF_INET, SOCK_STREAM, 0); if (httpd == -1) error_die("socket"); memset(&name, 0, sizeof(name));//也可以用bzero name.sin_family = AF_INET; name.sin_port = htons(*port); name.sin_addr.s_addr = htonl(INADDR_ANY);//任何网络接口 if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0) error_die("bind"); if (*port == 0) /* if dynamically allocating a port */ { int namelen = sizeof(name); if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1) error_die("getsockname"); *port = ntohs(name.sin_port);//系统动态分配一个端口号 } if (listen(httpd, 5) < 0) error_die("listen"); return(httpd);//返回服务套接字描述符 }很常见的步骤,就不多说了。
此后,服务端就accept等待连接,作者其实没有关心客户端来自哪里,那accept的第二、第三参数完全可以为NULL。接着就创建线程把客户端套接字作为参数传过去了,由新线程处理请求,这是服务器编程的常用手段,提高并发性。注意这里的线程函数并不完全合法,至少在linux上就不符合线程函数的原型定义,编译时编译器也只是警告而未报错。
接下来重点就在线程函数accept_request上了
void accept_request(int client) { char buf[1024]; int numchars; char method[255]; char url[255]; char path[512]; size_t i, j; struct stat st; int cgi = 0; /* becomes true if server decides this is a CGI * program */ char *query_string = NULL; numchars = get_line(client, buf, sizeof(buf)); i = 0; j = 0; while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) { method[i] = buf[j]; i++; j++; } method[i] = '\0'; if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) { unimplemented(client); return; } if (strcasecmp(method, "POST") == 0) cgi = 1; i = 0; while (ISspace(buf[j]) && (j < sizeof(buf))) j++; while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf))) { url[i] = buf[j]; i++; j++; } url[i] = '\0'; if (strcasecmp(method, "GET") == 0) { query_string = url; while ((*query_string != '?') && (*query_string != '\0')) query_string++; if (*query_string == '?') { cgi = 1; *query_string = '\0'; query_string++; } } sprintf(path, "htdocs%s", url); if (path[strlen(path) - 1] == '/') strcat(path, "index.html"); if (stat(path, &st) == -1) { while ((numchars > 0) && strcmp("\n", buf)) /* read & discard headers */ numchars = get_line(client, buf, sizeof(buf)); not_found(client); } else { if ((st.st_mode & S_IFMT) == S_IFDIR) strcat(path, "/index.html"); if ((st.st_mode & S_IXUSR) || (st.st_mode & S_IXGRP) || (st.st_mode & S_IXOTH) ) cgi = 1; if (!cgi) serve_file(client, path); else execute_cgi(client, path, method, query_string); } close(client); }
首先很关键一点要理解get_line的意思。我们要知道当在浏览器中输入url后enter之后,它发给服务器是文本型的字符串,遵循http请求格式,类似下面的:
GET / HTTP/1.1
HOST:www.abc.com
Content-type:text/html
...
get_line干的事就是读取一行,并且不管原来是以\n还是\r\n结束,均转化为以\n再加\0字符结束。其实现如下:
int get_line(int sock, char *buf, int size) { int i = 0; char c = '\0'; int n; while ((i < size - 1) && (c != '\n')) { n = recv(sock, &c, 1, 0);//从sock中一次读一个字符,循环读 if (n > 0) { if (c == '\r') //如果读到回车,一般紧接着字符就是\n { n = recv(sock, &c, 1, MSG_PEEK); if ((n > 0) && (c == '\n')) recv(sock, &c, 1, 0);//这时再读,c还是\n,循环跳出 else c = '\n'; } buf[i] = c; i++; } else c = '\n'; } buf[i] = '\0'; return(i);//返回读取的字符数 }
get_line完后,就是开始解析第一行,判断是GET方法还是POST方法,目前只支持这两种。如果是POST,还是把cgi置1,表明要运行CGI程序;如果是GET方法且附带以?开头的参数时,也认为是执行CGI程序
还是获取要访问的url,可以是很常见的/,/index.html等等。该程序默认为根目录是在htdocs下的,且默认文件是index.html。另外还判断了给定文件是否有可执权限,如果有,则认为是CGI程序。最后根据变量cgi的值来进行相应选择:读取静态文件或者执行CGI程序返回结果。
我们首先看看最简单的静态文件情况,调用函数serve_file
void serve_file(int client, const char *filename) { FILE *resource = NULL; int numchars = 1; char buf[1024]; buf[0] = 'A'; buf[1] = '\0'; while ((numchars > 0) && strcmp("\n", buf)) /* read & discard headers */ numchars = get_line(client, buf, sizeof(buf));//必须要读完客户端发来的头部,否则后来的send不能正常显示在浏览器中。 resource = fopen(filename, "r"); if (resource == NULL) not_found(client); else { headers(client, filename); cat(client, resource); } fclose(resource); }
将文件名作为参数,首先读完客户端的头部,然后打开创建文件流。为了模拟http响应,首先向客户端发送头部,头部信息至少包含以下几点:
http/1.0 200 ok
server:
content-type:
\r\n(一个空白行,标识头部结束)
最后发送数据体部分,即文件内容,在cat方法中,fgets每读入一行,就send,直到末尾。headers和cat函数就不在这里列出了。下面,我们来看看一个具体测试例子,紧接着在gdb中调试
我在根目录下的htdocs下建立一个新文件index2.html,内容如下:
<a href="http://10.108.222.96:54205/test.sh">Display Date</a>
我在这里放了一个链接,href部分是关于cgi的,先不管,就只看文本部分能否显示在浏览器中。
首先编译之后直接运行./httpd,程序打印"httpd running on port 53079"
我们在浏览器中访问index2.html文件,如下图所示:
文本能正确显示了。那如何在gdb中调试观察呢?
xiaoqiang@ljq-Lenovo:~/chenshi/tinyhttpd-0.1.0$ gdb attach 7029 【通过ps查看httpd进程的PID,然后gdb attach之】 Attaching to process 7029 Reading symbols from /home/xiaoqiang/chenshi/tinyhttpd-0.1.0/httpd...done. Reading symbols from /lib/i386-linux-gnu/libpthread.so.0...(no debugging symbols found)...done. [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1". Loaded symbols for /lib/i386-linux-gnu/libpthread.so.0 Reading symbols from /lib/i386-linux-gnu/libc.so.6...(no debugging symbols found)...done. Loaded symbols for /lib/i386-linux-gnu/libc.so.6 Reading symbols from /lib/ld-linux.so.2...(no debugging symbols found)...done. Loaded symbols for /lib/ld-linux.so.2 0xb7750424 in __kernel_vsyscall () (gdb) bt #0 0xb7750424 in __kernel_vsyscall () #1 0xb772dc08 in accept () from /lib/i386-linux-gnu/libpthread.so.0 #2 0x0804a8d6 in main () at httpd.c:516 (gdb) l accept_request warning: Source file is more recent than executable. 47 /* A request has caused a call to accept() on the server port to 48 * return. Process the request appropriately. 49 * Parameters: the socket connected to the client */ 50 /**********************************************************************/ 51 void accept_request(int client) 52 { 53 char buf[1024]; 54 int numchars; 55 char method[255]; 56 char url[255]; (gdb) l 57 char path[512]; 58 size_t i, j; 59 struct stat st; 60 int cgi = 0; /* becomes true if server decides this is a CGI 61 * program */ 62 char *query_string = NULL; 63 64 numchars = get_line(client, buf, sizeof(buf));//从套接字中读取一行 65 i = 0; j = 0; 66 while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) (gdb) b 64 【在64行设置断点,观察读到的是什么】 Breakpoint 1 at 0x8048b3f: file httpd.c, line 64. (gdb) c Continuing. 【直到在浏览器中发起了请求,后面的才会打印出来】 [New Thread 0xb63feb40 (LWP 7655)] [Switching to Thread 0xb63feb40 (LWP 7655)] Breakpoint 1, accept_request (client=4) at httpd.c:64 64 numchars = get_line(client, buf, sizeof(buf));//从套接字中读取一行 (gdb) n 65 i = 0; j = 0; (gdb) p buf 【打印读到的一行】 $1 = "GET /index2.html HTTP/1.1\n", '\000' <repeats 997 times> 【果真是HTTP GET请求的第一行】 (gdb) l 60 int cgi = 0; /* becomes true if server decides this is a CGI 61 * program */ 62 char *query_string = NULL; 63 64 numchars = get_line(client, buf, sizeof(buf));//从套接字中读取一行 65 i = 0; j = 0; 66 while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) 67 { 68 method[i] = buf[j]; 69 i++; j++; (gdb) l 70 } 71 method[i] = '\0';//获取到了HTTP方法 72 73 if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) 74 { 75 //忽略大小写比较 76 unimplemented(client); 77 return;//尚未支持的请求方法,线程返回 78 } 79 (gdb) l serve_file 【其它的细节调试就不在这里演示了,直接跳到serve_file里】 412 * Parameters: a pointer to a file structure produced from the socket 413 * file descriptor 414 * the name of the file to serve */ 415 /**********************************************************************/ 416 void serve_file(int client, const char *filename) 417 { 418 FILE *resource = NULL; 419 int numchars = 1; 420 char buf[1024]; 421 (gdb) l 422 buf[0] = 'A'; buf[1] = '\0'; 423 while ((numchars > 0) && strcmp("\n", buf)) /* read & discard headers */ 424 numchars = get_line(client, buf, sizeof(buf)); 425 426 resource = fopen(filename, "r"); 427 if (resource == NULL) 428 not_found(client); 429 else 430 { 431 headers(client, filename); (gdb) b 426 【在426行设置断点】 Breakpoint 2 at 0x804a247: file httpd.c, line 426. (gdb) c Continuing. Breakpoint 2, serve_file (client=4, filename=0xb63fdf4e "htdocs/index2.html") at httpd.c:426 426 resource = fopen(filename, "r"); (gdb) p filename $2 = 0xb63fdf4e "htdocs/index2.html" (gdb) n 427 if (resource == NULL) (gdb) n 431 headers(client, filename); (gdb) n 432 cat(client, resource); (gdb) s 【进入cat里面看看】 cat (client=4, resource=0xb6c00468) at httpd.c:170 170 { (gdb) l 165 * easier just to do something like pipe, fork, and exec("cat"). 166 * Parameters: the client socket descriptor 167 * FILE pointer for the file to cat */ 168 /**********************************************************************/ 169 void cat(int client, FILE *resource) 170 { 171 char buf[1024]; 172 173 fgets(buf, sizeof(buf), resource); 174 while (!feof(resource)) (gdb) n 173 fgets(buf, sizeof(buf), resource); (gdb) n 174 while (!feof(resource)) (gdb) p buf 【讲到了index2.html的一行,然后send】 $3 = "<a href=\"http://10.108.222.96:54205/test.sh\">Display Date</a>\n", '\000' <repeats 306 times>, "\"\225^\267\000\000\000\000 \312q\267\000\320t\267 \000\000\000 \312q\267\304Re\267 \000\000\000El^\267\001\000\000\000\000\320t\267 \000\000\000\364\277q\267\360\331?\266V\003_\267\364\277q\267 \000\000\000 \312q\267\000\320t\267\000\000\000\000$k^\267 \312q\267\000\320t\267 ", '\000' <repeats 15 times>, "A\252\004\b\364\277q\267 \000\000\000\377\377\377\377\000\000\000\000\236\201^\267 ", '\000' <repeats 23 times>, " \312q\267U\205^\267 \312q\267\000\320t\267 ", '\000' <repeats 19 times>"\364, \277q\267\001\000\000\000R\252\004\b\000\000\000\000\343v^\267"... (gdb) n 176 send(client, buf, strlen(buf), 0); (gdb) n 177 fgets(buf, sizeof(buf), resource); (gdb) n 174 while (!feof(resource)) (gdb) n 179 } (gdb) n serve_file (client=4, filename=0xb63fdf4e "htdocs/index2.html") at httpd.c:434 434 fclose(resource); (gdb) bt #0 serve_file (client=4, filename=0xb63fdf4e "htdocs/index2.html") at httpd.c:434 #1 0x08048f83 in accept_request (client=4) at httpd.c:130 #2 0xb7726d4c in start_thread () from /lib/i386-linux-gnu/libpthread.so.0 #3 0xb7665b8e in clone () from /lib/i386-linux-gnu/libc.so.6 (gdb) n 435 } (gdb) s accept_request (client=4) at httpd.c:139 139 close(client); <span style="background-color: rgb(255, 255, 255);">【直到运行在这里,浏览器的请求才会真正停止,意味着标签栏那个不断旋转的标志就停了】</span> (gdb) s 140 } (gdb) s 0xb7726d4c in start_thread () from /lib/i386-linux-gnu/libpthread.so.0 (gdb) s Single stepping until exit from function start_thread, which has no line number information. [New Thread 0xb5bfdb40 (LWP 7656)] [Switching to Thread 0xb5bfdb40 (LWP 7656)] Breakpoint 1, accept_request (client=4) at httpd.c:64 64 numchars = get_line(client, buf, sizeof(buf));//从套接字中读取一行 (gdb) n [Thread 0xb63feb40 (LWP 7655) exited] 65 i = 0; j = 0; (gdb) p buf $4 = "GET /favicon.ico HTTP/1.1\n", '\000' <repeats 997 times> 【再读一行时,竟读到favicon.ico,目前没弄明白这怎么回事】 (gdb)
前面已说过,tinyhttpd目前就支持两种请求形式,纯get请求或者带?的get和直接POST请求。了解到源码htdocs目录下的cgi都是perl写的,不知读者你懂不懂,反正博主我不懂,所以就改一改,改成自己的需求,用shell写。正如index2.html所示:
<a href="http://10.108.222.96:54205/test.sh">Display Date</a>
test.sh脚本如下:
#!/bin/sh
#echo "Content-type:text/html"
echo
echo "<html><head><meta charset="utf-8"><title>MyTitle</title></head><body>"
time=`date`
echo "<p>Server Time:$time"
echo "</body></html>"
即包括服务器响应给客户的字符数据,顺便把服务器时间传过去。注意要加test.sh添加执行权限,才会被视为执行cgi程序,且href中的端口号要改为你具体的端口号,这里只是个示例。来看当在浏览器中点击“Display Date”时,服务器作出的响应:
(gdb) l execute_cgi 【为了节省空间,以下内容我删除了无关内容】 warning: Source file is more recent than executable. 214 * Parameters: client socket descriptor 215 * path to the CGI script */ 216 /**********************************************************************/ 217 void execute_cgi(int client, const char *path, 218 const char *method, const char *query_string) 219 { 220 char buf[1024]; 229 230 buf[0] = 'A'; buf[1] = '\0'; 231 if (strcasecmp(method, "GET") == 0) (gdb) b 231 【在execute_cgi处设置断点】 Breakpoint 1 at 0x8049555: file httpd.c, line 231. (gdb) c Continuing. 【当在浏览器发起请求时,serve_file被调用,但此时断点在execute_cgi处,所以此处没有反应直到鼠标点击链接】 [New Thread 0xb7567b40 (LWP 7708)] [Thread 0xb7567b40 (LWP 7708) exited] [New Thread 0xb6bffb40 (LWP 7709)] [Thread 0xb6bffb40 (LWP 7709) exited] [New Thread 0xb63feb40 (LWP 7710)] [Switching to Thread 0xb63feb40 (LWP 7710)] Breakpoint 1, execute_cgi (client=4, path=0xb63fdf4e "htdocs/test.sh", method=0xb63fe14e "GET", query_string=0xb63fe255 "") at httpd.c:231 231 if (strcasecmp(method, "GET") == 0) (gdb) info args 【查看此函数调用参数值】 client = 4 path = 0xb63fdf4e "htdocs/test.sh" 【文件为test.sh脚本】 method = 0xb63fe14e "GET" query_string = 0xb63fe255 "" 257 258 if (pipe(cgi_output) < 0) { 259 cannot_execute(client); 260 return; 261 } 262 if (pipe(cgi_input) < 0) { 263 cannot_execute(client); 264 return; 265 } 266 (gdb) b 258 【在创建管道处设置断点】 Breakpoint 2 at 0x804973e: file httpd.c, line 258. (gdb) c Continuing. Breakpoint 2, execute_cgi (client=4, path=0xb63fdf4e "htdocs/test.sh", method=0xb63fe14e "GET", query_string=0xb63fe255 "") at httpd.c:258 258 if (pipe(cgi_output) < 0) { (gdb) n 262 if (pipe(cgi_input) < 0) { (gdb) n 267 if ( (pid = fork()) < 0 ) { (gdb) l 262 if (pipe(cgi_input) < 0) { 263 cannot_execute(client); 264 return; 265 } 266 267 if ( (pid = fork()) < 0 ) { 268 cannot_execute(client); 269 return; 270 } 271 if (pid == 0) /* child: CGI script */ (gdb) l 272 { 273 char meth_env[255]; 274 char query_env[255]; 275 char length_env[255]; 276 277 dup2(cgi_output[1], 1); 278 dup2(cgi_input[0], 0); 279 close(cgi_output[0]); 280 close(cgi_input[1]); 281 sprintf(meth_env, "REQUEST_METHOD=%s", method); (gdb) l 282 putenv(meth_env); 283 if (strcasecmp(method, "GET") == 0) { 【我的测试例子虽说是get请求,但不需要设置什么环境变量】 284 sprintf(query_env, "QUERY_STRING=%s", query_string); 285 putenv(query_env); 286 } 287 else { /* POST */ 288 sprintf(length_env, "CONTENT_LENGTH=%d", content_length); 289 putenv(length_env); 290 } 291 execl(path, path, NULL); 【子进程执行test.sh】 (gdb) l 292 exit(0); 293 } 294 295 else { /* parent */ 296 close(cgi_output[1]); 297 close(cgi_input[0]); 298 if (strcasecmp(method, "POST") == 0) 299 for (i = 0; i < content_length; i++) { 300 recv(client, &c, 1, 0); 301 write(cgi_input[1], &c, 1); (gdb) b 298 【由于子进程执行test.sh,父进程发送响应给浏览器,所以先进入父进程,看发的是什么】 Breakpoint 3 at 0x80498ec: file httpd.c, line 298. (gdb) c Continuing. Breakpoint 3, execute_cgi (client=4, path=0xb63fdf4e "htdocs/test.sh", method=0xb63fe14e "GET", query_string=0xb63fe255 "") at httpd.c:298 298 if (strcasecmp(method, "POST") == 0) (gdb) n 304 while (read(cgi_output[0], &c, 1) > 0) (gdb) l 299 for (i = 0; i < content_length; i++) { 【如果是POST,则还要继续从cgi_input中读取数据体,它被导入到标准输入,从而经由管道进入cgi_output[1]】 300 recv(client, &c, 1, 0); 301 write(cgi_input[1], &c, 1); 302 } 303 304 while (read(cgi_output[0], &c, 1) > 0) 305 send(client, &c, 1, 0); 306 307 close(cgi_output[0]); 308 close(cgi_input[1]); (gdb) s 【单步从cgi_output[0]中读】 305 send(client, &c, 1, 0); (gdb) p c $1 = 10 '\n' (gdb) s 305 send(client, &c, 1, 0); (gdb) p c 【以下部分刚好读到的是test脚本的"<html"】 $2 = 60 '<' (gdb) s 305 send(client, &c, 1, 0); (gdb) p c $3 = 104 'h' (gdb) s 305 send(client, &c, 1, 0); (gdb) p c $4 = 116 't' (gdb) s 305 send(client, &c, 1, 0); (gdb) p c $5 = 109 'm' (gdb) s 305 send(client, &c, 1, 0); (gdb) p c $6 = 108 'l' (gdb) l 300 recv(client, &c, 1, 0); 301 write(cgi_input[1], &c, 1); 302 } 303 304 while (read(cgi_output[0], &c, 1) > 0) 305 send(client, &c, 1, 0); 306 307 close(cgi_output[0]); 308 close(cgi_input[1]); 309 waitpid(pid, &status, 0); (gdb) b 307 Breakpoint 4 at 0x80499be: file httpd.c, line 307. (gdb) c Continuing. Breakpoint 4, execute_cgi (client=4, path=0xb63fdf4e "htdocs/test.sh", method=0xb63fe14e "GET", query_string=0xb63fe255 "") at httpd.c:307 307 close(cgi_output[0]); (gdb) n 308 close(cgi_input[1]); (gdb) n 309 waitpid(pid, &status, 0); (gdb) n 311 } (gdb) p status $7 = 0 (gdb) n accept_request (client=4) at httpd.c:139 139 close(client); <span style="background-color: rgb(255, 255, 255);">【直到这里,浏览器才显示了返回结果】</span> (gdb) n 140 } (gdb)结果显示: 当然我在这里只是演示了其中的一种情况,至于情况如get请求带?查询的,POST请求带数据体的,只有靠读者自己去尝试了,博主暂时抛砖引玉于此。
呃,感觉讲解至此结束了呢。貌似还有一点点细节博主还得继续研究下,总之通过这个例子确实对Linux编程了解了更多了,感谢开源,哈哈!
参考链接
1 http://blog.csdn.net/jcjc918/article/details/42129311
2 http://blog.sina.com.cn/s/blog_a5191b5c0102v9yr.html
3 CGI介绍:http://www.jdon.com/idea/cgi.htm
4 http://www.scholat.com/vpost.html?pid=7337
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