Tinyhttpd C语言超轻量型 Http Server 开发精读解析

375次阅读

共计 16535 个字符，预计需要花费 42 分钟才能阅读完成。

tinyhttpd 是一个不到 500 行的超轻量型 Http Server，用来学习非常不错，可以帮助我们真正理解服务器程序的本质。

看完所有源码，真的感觉有很大收获，无论是 unix 的编程，还是 GET/POST 的 Web 处理流程，都清晰了不少。废话不说，开始我们的 Server 探索之旅。

项目主页:http://sourceforge.net/projects/tinyhttpd/

首先，本人刚刚开始开源代码精读，写的不对的地方，大家轻拍，一起进步。本文是对Tinyhttpd的一次精读，大家每天都在用着http服务，很多人也一直活跃在上层，使用IIS、Apache等，大家是否想看看http服务器大概是怎么运作的，通过一个500多行的源码加上完整的注释，和大家逛一逛http服务器。Tinyhttpd真的非常适合阅读尤其是刚入门的，清晰的代码，简单的makefile…其实有很多分析tinyghttpd的，这边抱着人家写的是人家，自己写的才是自己的态度，写的尽量详细，尽量简单，很多都写在代码注释里面，也把学习中的一些坑翻出来和大家一起读读，吸取将近20年前的大神通过500行代码带给我们的财富。不管你是写c的，或者C#，js亦或java，只要用到http的都欢迎读读。
大家看后如果觉得我有写的不对的地方，欢迎指出~~

附上注解代码的github地址：

https://github.com/nengm/Tinyhttpd

1.首先是一张图全解了Tinyhttp是如何运作的，我觉得图说明比我用文字描述的要清晰，语言功底不太给力。

Tinyhttpd C语言超轻量型 Http Server 开发精读解析

2. 主要函数简略说明，代码中进行了详细注释。

main 　　　　　　主函数
startup 　　　　　绑定监听套接字
accept_request 　每次收到请求，创建一个线程来处理接受到的请求
serve_file 　　　　接读取文件返回给请求的http客户端
execute_cgi 　　　执行cgi文件

3.注意点

注意点1：

index.html必须没有执行权限，否则看不到内容，并且会产生Program received signal SIGPIPE, Broken pipe，因为程序中如果有可执行权限会当cgi脚本处理。所以假如html有执行权限先把它去除了，chmod 600 index.html

color.cgi、date.cgi必须要有执行权限。

注意点2：

color.cgi是用perl写的，相信大家很少接触了。所以可以引用网上一个简单的例子，换成一个shell写的cgi测试

#!/bin/bash
echo “Content-Type: text/html”
echo
echo “<HTML><BODY>”
echo “<CENTER>Today is:</CENTER>”
echo “<CENTER><B>”
date
echo “</B></CENTER>”
echo “</BODY></HTML>”

4.操作

1.执行make，生成成功，./httpd启动成功。

Tinyhttpd C语言超轻量型 Http Server 开发精读解析

2.如果在当前linux下的firefox下执行。直接在浏览器中输入

Tinyhttpd C语言超轻量型 Http Server 开发精读解析

3.在windows中测试，

Tinyhttpd C语言超轻量型 Http Server 开发精读解析

4.测试执行自带的perl写的cgi脚本

Tinyhttpd C语言超轻量型 Http Server 开发精读解析

5.进入index2.html页面，测试shell写的cgi脚本。

Tinyhttpd C语言超轻量型 Http Server 开发精读解析

/* J. David's webserver */
/* This is a simple webserver.
 * Created November 1999 by J. David Blackstone.
 * CSE 4344 (Network concepts), Prof. Zeigler
 * University of Texas at Arlington
 */
/* This program compiles for Sparc Solaris 2.6.
 * To compile for Linux:
 *  1) Comment out the #include <pthread.h> line.
 *  2) Comment out the line that defines the variable newthread.
 *  3) Comment out the two lines that run pthread_create().
 *  4) Uncomment the line that runs accept_request().
 *  5) Remove -lsocket from the Makefile.
 */
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <sys/stat.h>
#include <pthread.h>
#include <sys/wait.h>
#include <stdlib.h>

//宏定义，是否是空格
#define ISspace(x) isspace((int)(x))

#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"

 //每次收到请求，创建一个线程来处理接受到的请求
 //把client_sock转成地址作为参数传入pthread_create
void accept_request(void *arg);

//错误请求
void bad_request(int);

//读取文件
void cat(int, FILE *);

//无法执行
void cannot_execute(int);

//错误输出
void error_die(const char *);

//执行cig脚本
void execute_cgi(int, const char *, const char *, const char *);

//得到一行数据,只要发现c为\n,就认为是一行结束，如果读到\r,再用MSG_PEEK的方式读入一个字符，如果是\n，从socket用读出
//如果是下个字符则不处理，将c置为\n，结束。如果读到的数据为0中断，或者小于0，也视为结束，c置为\n
int get_line(int, char *, int);

//返回http头
void headers(int, const char *);

//没有发现文件
void not_found(int);

//如果不是CGI文件，直接读取文件返回给请求的http客户端
void serve_file(int, const char *);

//开启tcp连接，绑定端口等操作
int startup(u_short *);

//如果不是Get或者Post，就报方法没有实现
void unimplemented(int);

// Http请求，后续主要是处理这个头
//
// GET / HTTP/1.1
// Host: 192.168.0.23:47310
// Connection: keep-alive
// Upgrade-Insecure-Requests: 1
// User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36
// Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*; q = 0.8
// Accept - Encoding: gzip, deflate, sdch
// Accept - Language : zh - CN, zh; q = 0.8
// Cookie: __guid = 179317988.1576506943281708800.1510107225903.8862; monitor_count = 5
//

// POST / color1.cgi HTTP / 1.1
// Host: 192.168.0.23 : 47310
// Connection : keep - alive
// Content - Length : 10
// Cache - Control : max - age = 0
// Origin : http ://192.168.0.23:40786
// Upgrade - Insecure - Requests : 1
// User - Agent : Mozilla / 5.0 (Windows NT 6.1; WOW64) AppleWebKit / 537.36 (KHTML, like Gecko) Chrome / 55.0.2883.87 Safari / 537.36
// Content - Type : application / x - www - form - urlencoded
// Accept : text / html, application / xhtml + xml, application / xml; q = 0.9, image / webp, */*;q=0.8
// Referer: http://192.168.0.23:47310/
// Accept-Encoding: gzip, deflate
// Accept-Language: zh-CN,zh;q=0.8
// Cookie: __guid=179317988.1576506943281708800.1510107225903.8862; monitor_count=281
// Form Data
// color=gray

/**********************************************************************/
/* A request has caused a call to accept() on the server port to
 * return.  Process the request appropriately.
 * Parameters: the socket connected to the client */
/**********************************************************************/
void accept_request(void *arg)
{
  //socket
 int client = (intptr_t)arg;
 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;
 //根据上面的Get请求，可以看到这边就是取第一行
 //这边都是在处理第一条http信息
 //"GET / HTTP/1.1\n"
 numchars = get_line(client, buf, sizeof(buf));
 i = 0; j = 0;

 //第一行字符串提取Get
 while (!ISspace(buf[j]) && (i < sizeof(method) - 1))
 {
  method[i] = buf[j];
  i++; j++;
 }
 //结束
 method[i] = '\0';

 //判断是Get还是Post
 if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
 {
  unimplemented(client);
  return;
 }

 //如果是POST，cgi置为1
 if (strcasecmp(method, "POST") == 0)
  cgi = 1;

 i = 0;
 //跳过空格
 while (ISspace(buf[j]) && (j < sizeof(buf)))
  j++;

 //得到 "/"   注意：如果你的http的网址为http://192.168.0.23:47310/index.html
 //               那么你得到的第一条http信息为GET /index.html HTTP/1.1，那么
 //               解析得到的就是/index.html
 while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))
 {
  url[i] = buf[j];
  i++; j++;
 }
 url[i] = '\0';

 //判断Get请求
 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++;
  }
 }

 //路径
 sprintf(path, "htdocs%s", url);

 //默认地址，解析到的路径如果为/，则自动加上index.html
 if (path[strlen(path) - 1] == '/')
  strcat(path, "index.html");

 //获得文件信息
 if (stat(path, &st) == -1) {
  //把所有http信息读出然后丢弃
  while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
   numchars = get_line(client, buf, sizeof(buf));

  //没有找到
  not_found(client);
 }
 else
 {
  if ((st.st_mode & S_IFMT) == S_IFDIR)
   strcat(path, "/index.html");
  //如果你的文件默认是有执行权限的，自动解析成cgi程序，如果有执行权限但是不能执行，会接受到报错信号
  if ((st.st_mode & S_IXUSR) ||
      (st.st_mode & S_IXGRP) ||
      (st.st_mode & S_IXOTH)    )
   cgi = 1;
  if (!cgi)
   //接读取文件返回给请求的http客户端
   serve_file(client, path);
  else
   //执行cgi文件
   execute_cgi(client, path, method, query_string);
 }
 //执行完毕关闭socket
 close(client);
}

/**********************************************************************/
/* Inform the client that a request it has made has a problem.
 * Parameters: client socket */
/**********************************************************************/
void bad_request(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "Content-type: text/html\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "<P>Your browser sent a bad request, ");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "such as a POST without a Content-Length.\r\n");
 send(client, buf, sizeof(buf), 0);
}

/**********************************************************************/
/* Put the entire contents of a file out on a socket.  This function
 * is named after the UNIX "cat" command, because it might have been
 * easier just to do something like pipe, fork, and exec("cat").
 * Parameters: the client socket descriptor
 *             FILE pointer for the file to cat */
/**********************************************************************/

//得到文件内容，发送
void cat(int client, FILE *resource)
{
 char buf[1024];

 fgets(buf, sizeof(buf), resource);
 //循环读
 while (!feof(resource))
 {
  send(client, buf, strlen(buf), 0);
  fgets(buf, sizeof(buf), resource);
 }
}

/**********************************************************************/
/* Inform the client that a CGI script could not be executed.
 * Parameter: the client socket descriptor. */
/**********************************************************************/
void cannot_execute(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<P>Error prohibited CGI execution.\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Print out an error message with perror() (for system errors; based
 * on value of errno, which indicates system call errors) and exit the
 * program indicating an error. */
/**********************************************************************/
void error_die(const char *sc)
{
 perror(sc);
 exit(1);
}

/**********************************************************************/
/* Execute a CGI script.  Will need to set environment variables as
 * appropriate.
 * Parameters: client socket descriptor
 *             path to the CGI script */
/**********************************************************************/
void execute_cgi(int client, const char *path,
                 const char *method, const char *query_string)
{
//缓冲区
 char buf[1024];

 //2根管道
 int cgi_output[2];
 int cgi_input[2];

 //进程pid和状态
 pid_t pid;
 int status;

 int i;
 char c;

 //读取的字符数
 int numchars = 1;

 //http的content_length
 int content_length = -1;

 //默认字符
 buf[0] = 'A'; buf[1] = '\0';

 //忽略大小写比较字符串
 if (strcasecmp(method, "GET") == 0)
 //读取数据，把整个header都读掉，以为Get写死了直接读取index.html，没有必要分析余下的http信息了
  while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
   numchars = get_line(client, buf, sizeof(buf));
 else    /* POST */
 {
  numchars = get_line(client, buf, sizeof(buf));
  while ((numchars > 0) && strcmp("\n", buf))
  {
   //如果是POST请求，就需要得到Content-Length，Content-Length：这个字符串一共长为15位，所以
   //取出头部一句后，将第16位设置结束符，进行比较
   //第16位置为结束
   buf[15] = '\0';
   if (strcasecmp(buf, "Content-Length:") == 0)
   //内存从第17位开始就是长度，将17位开始的所有字符串转成整数就是content_length
    content_length = atoi(&(buf[16]));
   numchars = get_line(client, buf, sizeof(buf));
  }
  if (content_length == -1) {
   bad_request(client);
   return;
  }
 }

 sprintf(buf, "HTTP/1.0 200 OK\r\n");
 send(client, buf, strlen(buf), 0);
 //建立output管道
 if (pipe(cgi_output) < 0) {
  cannot_execute(client);
  return;
 }

 //建立input管道
 if (pipe(cgi_input) < 0) {
  cannot_execute(client);
  return;
 }
 //       fork后管道都复制了一份，都是一样的
 //       子进程关闭2个无用的端口，避免浪费
 //       ×<------------------------->1    output
 //       0<-------------------------->×   input

 //       父进程关闭2个无用的端口，避免浪费
 //       0<-------------------------->×   output
 //       ×<------------------------->1    input
 //       此时父子进程已经可以通信


 //fork进程，子进程用于执行CGI
 //父进程用于收数据以及发送子进程处理的回复数据
 if ( (pid = fork()) < 0 ) {
  cannot_execute(client);
  return;
 }
 if (pid == 0)  /* child: CGI script */
 {
  char meth_env[255];
  char query_env[255];
  char length_env[255];

  //子进程输出重定向到output管道的1端
  dup2(cgi_output[1], 1);
  //子进程输入重定向到input管道的0端
  dup2(cgi_input[0], 0);

  //关闭无用管道口
  close(cgi_output[0]);
  close(cgi_input[1]);

  //CGI环境变量
  sprintf(meth_env, "REQUEST_METHOD=%s", method);
  putenv(meth_env);
  if (strcasecmp(method, "GET") == 0) {
   sprintf(query_env, "QUERY_STRING=%s", query_string);
   putenv(query_env);
  }
  else {   /* POST */
   sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
   putenv(length_env);
  }
  //替换执行path
  execl(path, path, NULL);
  //int m = execl(path, path, NULL);
  //如果path有问题，例如将html网页改成可执行的，但是执行后m为-1
  //退出子进程，管道被破坏，但是父进程还在往里面写东西，触发Program received signal SIGPIPE, Broken pipe.
  exit(0);
 } else {    /* parent */

  //关闭无用管道口
  close(cgi_output[1]);
  close(cgi_input[0]);
  if (strcasecmp(method, "POST") == 0)
   for (i = 0; i < content_length; i++) {
    //得到post请求数据，写到input管道中，供子进程使用
    recv(client, &c, 1, 0);
    write(cgi_input[1], &c, 1);
   }
  //从output管道读到子进程处理后的信息，然后send出去
  while (read(cgi_output[0], &c, 1) > 0)
   send(client, &c, 1, 0);

  //完成操作后关闭管道
  close(cgi_output[0]);
  close(cgi_input[1]);

  //等待子进程返回
  waitpid(pid, &status, 0);

 }
}

/**********************************************************************/
/* Get a line from a socket, whether the line ends in a newline,
 * carriage return, or a CRLF combination.  Terminates the string read
 * with a null character.  If no newline indicator is found before the
 * end of the buffer, the string is terminated with a null.  If any of
 * the above three line terminators is read, the last character of the
 * string will be a linefeed and the string will be terminated with a
 * null character.
 * Parameters: the socket descriptor
 *             the buffer to save the data in
 *             the size of the buffer
 * Returns: the number of bytes stored (excluding null) */
/**********************************************************************/

//得到一行数据,只要发现c为\n,就认为是一行结束，如果读到\r,再用MSG_PEEK的方式读入一个字符，如果是\n，从socket用读出
//如果是下个字符则不处理，将c置为\n，结束。如果读到的数据为0中断，或者小于0，也视为结束，c置为\n
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);
  /* DEBUG printf("%02X\n", c); */
  if (n > 0)
  {
   if (c == '\r')
   {
     //偷窥一个字节，如果是\n就读走
    n = recv(sock, &c, 1, MSG_PEEK);
    /* DEBUG printf("%02X\n", c); */
    if ((n > 0) && (c == '\n'))
     recv(sock, &c, 1, 0);
    else
    //不是\n（读到下一行的字符）或者没读到，置c为\n 跳出循环,完成一行读取
     c = '\n';
   }
   buf[i] = c;
   i++;
  }
  else
   c = '\n';
 }
 buf[i] = '\0';

 return(i);
}

/**********************************************************************/
/* Return the informational HTTP headers about a file. */
/* Parameters: the socket to print the headers on
 *             the name of the file */
/**********************************************************************/

//加入http的headers
void headers(int client, const char *filename)
{
 char buf[1024];
 (void)filename;  /* could use filename to determine file type */

 strcpy(buf, "HTTP/1.0 200 OK\r\n");
 send(client, buf, strlen(buf), 0);
 strcpy(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 strcpy(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Give a client a 404 not found status message. */
/**********************************************************************/

//如果资源没有找到得返回给客户端下面的信息
void not_found(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<BODY><P>The server could not fulfill\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "your request because the resource specified\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "is unavailable or nonexistent.\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</BODY></HTML>\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Send a regular file to the client.  Use headers, and report
 * errors to client if they occur.
 * Parameters: a pointer to a file structure produced from the socket
 *              file descriptor
 *             the name of the file to serve */
/**********************************************************************/

//如果不是CGI文件，直接读取文件返回给请求的http客户端
void serve_file(int client, const char *filename)
{
 FILE *resource = NULL;
 int numchars = 1;
 char buf[1024];

 //默认字符
 buf[0] = 'A'; buf[1] = '\0';
 while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
  numchars = get_line(client, buf, sizeof(buf));

 resource = fopen(filename, "r");
 if (resource == NULL)
  not_found(client);
 else
 {
  headers(client, filename);
  cat(client, resource);
 }
 fclose(resource);
}

/**********************************************************************/
/* This function starts the process of listening for web connections
 * on a specified port.  If the port is 0, then dynamically allocate a
 * port and modify the original port variable to reflect the actual
 * port.
 * Parameters: pointer to variable containing the port to connect on
 * Returns: the socket */
/**********************************************************************/
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));
 name.sin_family = AF_INET;
 name.sin_port = htons(*port);
 name.sin_addr.s_addr = htonl(INADDR_ANY);
 //绑定socket
 if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
  error_die("bind");
 //如果端口没有设置，提供个随机端口
 if (*port == 0)  /* if dynamically allocating a port */
 {
  socklen_t  namelen = sizeof(name);
  if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
   error_die("getsockname");
  *port = ntohs(name.sin_port);
 }
 //监听
 if (listen(httpd, 5) < 0)
  error_die("listen");
 return(httpd);
}

/**********************************************************************/
/* Inform the client that the requested web method has not been
 * implemented.
 * Parameter: the client socket */
/**********************************************************************/

//如果方法没有实现，就返回此信息
void unimplemented(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</TITLE></HEAD>\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</BODY></HTML>\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/

int main(void)
{
 int server_sock = -1;
 u_short port = 0;
 int client_sock = -1;
 struct sockaddr_in client_name;

 //这边要为socklen_t类型
 socklen_t client_name_len = sizeof(client_name);
 pthread_t newthread;

 server_sock = startup(&port);
 printf("httpd running on port %d\n", port);

 while (1)
 {
     //接受请求，函数原型
     //#include <sys/types.h>
     //#include <sys/socket.h>
     //int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
  client_sock = accept(server_sock,
                       (struct sockaddr *)&client_name,
                       &client_name_len);
  if (client_sock == -1)
      error_die("accept");
 /* accept_request(client_sock); */

  //每次收到请求，创建一个线程来处理接受到的请求
  //把client_sock转成地址作为参数传入pthread_create
  if (pthread_create(&newthread, NULL, (void *)accept_request, (void *)(intptr_t)client_sock) != 0)
      perror("pthread_create");
 }

 close(server_sock);

 return(0);
}

正文完