【源代码分析】tinyhttpd学习

首先介绍下服务器的共性：工作流程

1.收包（服务器接收客户端数据包）---------------->2.解析（服务器判断解析客户端的数据包，通过分析url，可以得到客户端的请求资源是静态资源即html, 还是动态资源java,jsp,asp,php,cgi等等）-----------------------------3.业务逻辑处理（根据解析的结果调用相应的业务逻辑处理，例如tomcat）--------------------------------------------->4.回包，将静态文件或者服务器网关处理后的资源响应给客户端

正题：tinyhttpd是一轻量级的web 服务器 ，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

主要函数：

         

 int startup(u_short *);
 void accept_request(int);
 void bad_request(int);
 void cat(int, FILE *);
 void cannot_execute(int);
 void error_die(const char *);
 void execute_cgi(int, const char *, const char *, const char *);
 int get_line(int, char *, int);
 void headers(int, const char *);
 void not_found(int);
 void serve_file(int, const char *);
 void unimplemented(int);

1.首先看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;
   /*在对应端口建立 httpd 服务*/
  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);
 }

2.startup 初始化函数，这段代码，主要完成：创建服务端socket，绑定、监听、等待客户端连接。 [cpp]   view plain  copy

 int startup(u_short *port)
 {
  int httpd = 0;
  struct sockaddr_in name;
   //1 .创建监听套接字
  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
 //2.将监听套接字与服务器的端口，IP进行绑定
  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
  }
 //3监听套接字
  if (listen(httpd, 5) < 0)
   error_die("listen");
  return(httpd);//返回服务套接字描述符
 }

此后，服务端就accept等待连接。

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);
 }

 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
 }

 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);
 }

 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'  【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】
 $3 = "Display Date\n", '\000' , "\"\225^\267\000\000\000\000 \312q\267\000\320t\267 \000\000\000 \312q\267\304Re\267 \000\000\000El^\267\001\000\000\000\000\320t\267 \000\000\000\364\277q\267\360\331?\266V\003_\267\364\277q\267 \000\000\000 \312q\267\000\320t\267\000\000\000\000$k^\267 \312q\267\000\320t\267 ", '\000' , "A\252\004\b\364\277q\267 \000\000\000\377\377\377\377\000\000\000\000\236\201^\267 ", '\000' , " \312q\267U\205^\267 \312q\267\000\320t\267 ", '\000' "\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); 【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】
 (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'  【再读一行时，竟读到favicon.ico，目前没弄明白这怎么回事】
 (gdb)

Display Date

test.sh脚本如下：

#!/bin/sh 
#echo "Content-type:text/html"
echo
echo ""
time=`date`
echo "

Server Time:$time"
echo ""

 (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"
 $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); 【直到这里，浏览器才显示了返回结果】
 (gdb) n
 140 }
 (gdb)