经典服务器项目tinyhttpd详细源码注释

经典服务器项目tinyhttpd详细源码注释

函数关系图：

/* 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>
#include <stdint.h>

#define ISspace(x) isspace((int)(x))

#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"
#define STDIN   0
#define STDOUT  1
#define STDERR  2

void accept_request(void *);
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 *);
int startup(u_short *);
void unimplemented(int);

/**********************************************************************/
/* 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)  //处理连接的套接字中接收到的请求POST或GET
{
int client = (intptr_t)arg;
char buf[1024];
size_t 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;

//从连接中读出一行数据，numchars存放的是读到的数据长度
numchars = get_line(client, buf, sizeof(buf));
i = 0; j = 0;
//判断读取的buf[i]是否是空格，将buf中的http请求套接字复制到method中，遇到空格为止
while (!ISspace(buf[i]) && (i < sizeof(method) - 1))
{
method[i] = buf[i];
i++;
}
j=i;
method[i] = '\0';

//函数strcasecmp不区分大小写比较两个字符串，相同返回0，不同返回<0的数
if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
{
unimplemented(client); //如果不是GET和POST两种，调用unimplement函数通知客户端
return;
}

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

i = 0;
//循环去除空格
while (ISspace(buf[j]) && (j < numchars))
j++;
//从缓冲区中读取url
while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < numchars))
{
url[i] = buf[j];
i++; j++;
}
url[i] = '\0';

//如果是GET
if (strcasecmp(method, "GET") == 0)
{
query_string = url; //确定请求的路径
//处理url存储格式
while ((*query_string != '?') && (*query_string != '\0'))
query_string++;
if (*query_string == '?')
{
cgi = 1;                //遇到？，将cgi设置为1
*query_string = '\0';   //将地址从这里截断
query_string++;
}
}

sprintf(path, "htdocs%s", url);
if (path[strlen(path) - 1] == '/') //如果网址的最后以为是/，在末尾加上index.html
strcat(path, "index.html");
//获取文件信息，存放在st中
if (stat(path, &st) == -1) { //获取失败返回-1
while ((numchars > 0) && strcmp("\n", buf)) //缓冲区为空 /* read & discard headers */
numchars = get_line(client, buf, sizeof(buf)); //从客户端缓冲区读取一行
not_found(client); //直到缓冲区为空，且客户端读不到了？not_found函数，告诉客户端没找到
}
else //获取成功
{
if ((st.st_mode & S_IFMT) == S_IFDIR) //判断文件是否是目录，如果是目录在路径最后加上/index.html
strcat(path, "/index.html");
if ((st.st_mode & S_IXUSR) ||
(st.st_mode & S_IXGRP) ||
(st.st_mode & S_IXOTH) )    //确认各种执行权限，将cgi设为1
cgi = 1;
if (!cgi)                           //如果是一般的get请求，则调用server_file函数给返回那个文件的内容
serve_file(client, path);
else                                //否则调用execute_cgi执行cgi脚本
execute_cgi(client, path, method, query_string);
}

close(client);
}

/**********************************************************************/
/* Inform the client that a request it has made has a problem.
* Parameters: client socket */
/**********************************************************************/
//client客户套接字？（接口/描述符？），告诉客户端，请求有问题
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 */
/**********************************************************************/
//将文件内容写到客户端中
void cat(int client, FILE *resource)
{
char buf[1024];

fgets(buf, sizeof(buf), resource);
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. */
/**********************************************************************/
//服务器执行错误，向客户端发送500
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. */
/**********************************************************************/
//打印错误信息
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 */
/**********************************************************************/
//执行cgi
void execute_cgi(int client, const char *path,
const char *method, const char *query_string)
{
char buf[1024];
int cgi_output[2];
int cgi_input[2];
pid_t pid;
int status;
int i;
char c;
int numchars = 1;
int content_length = -1;

buf[0] = 'A'; buf[1] = '\0';
//如果是get请求，将请求头中剩余部分读出来
if (strcasecmp(method, "GET") == 0)
while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
numchars = get_line(client, buf, sizeof(buf));
//如果是是post请求
else if (strcasecmp(method, "POST") == 0) /*POST*/
{
numchars = get_line(client, buf, sizeof(buf)); //读出数据长度
while ((numchars > 0) && strcmp("\n", buf)) //数据长度为0，且缓冲区为空
{
buf[15] = '\0';
if (strcasecmp(buf, "Content-Length:") == 0) //缓冲区字段=="Content-Length:"
content_length = atoi(&(buf[16])); //
numchars = get_line(client, buf, sizeof(buf));//将客户端请求写入缓冲区？
}
if (content_length == -1) { //缓冲区末尾是-1？
bad_request(client); //告诉客户端，请求有问题
return;
}
}
else//其他请求
{
}


//给执行cgi脚本的进程创建输入输出管道
if (pipe(cgi_output) < 0) {
cannot_execute(client);
return;
}
if (pipe(cgi_input) < 0) {
cannot_execute(client);
return;
}

//fork子进程来执行cgi脚本
if ( (pid = fork()) < 0 ) {
cannot_execute(client);
return;
}
sprintf(buf, "HTTP/1.0 200 OK\r\n");
send(client, buf, strlen(buf), 0);
//子进程PID==0
if (pid == 0)  /* child: CGI script */
{
char meth_env[255];
char query_env[255];
char length_env[255];

//重定向子进程的标准输入和输出
dup2(cgi_output[1], STDOUT);
dup2(cgi_input[0], STDIN);
close(cgi_output[0]);
close(cgi_input[1]);
sprintf(meth_env, "REQUEST_METHOD=%s", method);

//设置环境变量
putenv(meth_env);
//如果是GET？
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);
}
execl(path, NULL);
exit(0);
} else {    /* parent */
close(cgi_output[1]);
close(cgi_input[0]);
//读POST请求传过来的消息，然后写到cgi脚本的输入管道cgi_input[1]中
if (strcasecmp(method, "POST") == 0)
for (i = 0; i < content_length; i++) {
recv(client, &c, 1, 0);
write(cgi_input[1], &c, 1);
}
while (read(cgi_output[0], &c, 1) > 0)
send(client, &c, 1, 0);

close(cgi_output[0]);
close(cgi_input[1]);
waitpid(pid, &status, 0); //等待子进程结束
}
}

/**********************************************************************/
/* 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) */
/**********************************************************************/
//从连接中读出一行数据
int get_line(int sock, char *buf, int size)
{
int i = 0;
char c = '\0';
int n;

while ((i < size - 1) && (c != '\n'))
{
//从套接字中接收到的信息长度？
n = recv(sock, &c, 1, 0);
/* DEBUG printf("%02X\n", c); */
if (n > 0)  //接收到的信息长度>0
{
if (c == '\r') //回车
{
n = recv(sock, &c, 1, MSG_PEEK);    // MSG_PEEK
/* DEBUG printf("%02X\n", c); */
if ((n > 0) && (c == '\n')) //c为换行
recv(sock, &c, 1, 0);
else
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 */
/**********************************************************************/
//将http头 写入连接
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. */
/**********************************************************************/
//客户端请求的地址不存在，返回404？
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 */
/**********************************************************************/
//返回客户端请求的文件
void serve_file(int client, const char *filename)
{
FILE *resource = NULL;
int numchars = 1;
char buf[1024];

buf[0] = 'A'; buf[1] = '\0';
//缓冲区内容是回车，从客户端读入一行数据到缓冲区
while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
numchars = get_line(client, buf, sizeof(buf));

//fopen()函数用于打开指定路径的文件，获取指向该文件的指针
resource = fopen(filename, "r"); //以只读的方式，打开指定路径filename的文件
if (resource == NULL) //函数返回指针指向NULL，调用not_found告诉客户端，没有找到请求的文件
not_found(client);
else
{
headers(client, filename); //向client标识的连接写入http头
cat(client, resource);      //用cat写入文件内容
}
fclose(resource);               //关闭文件？
}

/**********************************************************************/
/* 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 */
/**********************************************************************/
//程序建立socket，绑定ip地址，监听连接
int startup(u_short *port)
{
int httpd = 0;
int on = 1;
struct sockaddr_in name;

httpd = socket(PF_INET, SOCK_STREAM, 0);    //创建套接字
if (httpd == -1)                            //创建失败
error_die("socket");
memset(&name, 0, sizeof(name));             /*menset函数<string.h>，name指向内存块的指针，内存块大小为sizeof(name)，内存块中的值为0*/
name.sin_family = AF_INET;                  //初始化套接字
name.sin_port = htons(*port);
name.sin_addr.s_addr = htonl(INADDR_ANY);
//函数setsockopt，设置套接字状态，设置网络层，设置套接字选项，optval=on，
if ((setsockopt(httpd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on))) < 0)
{  
error_die("setsockopt failed");     //设置失败
}
//绑定ip地址和端口
if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
error_die("bind");
if (*port == 0)  /* if dynamically allocating a port */
{
socklen_t namelen = sizeof(name);
//通过套接字描述符取得与套接字关联的本地协议地址
if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
error_die("getsockname");
*port = ntohs(name.sin_port);       //将网络字节序转换为本子字节序
}
if (listen(httpd, 5) < 0)               //监听套接字，请求队列的最大长度为5
error_die("listen");
return(httpd);                          //返回套接字描述符
}

/**********************************************************************/
/* Inform the client that the requested web method has not been
* implemented.
* Parameter: the client socket */
/**********************************************************************/
//如果客户端发过来的不是get或post请求，会调用此函数
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 = 4000;
int client_sock = -1;
struct sockaddr_in client_name;
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)
{
client_sock = accept(server_sock,
(struct sockaddr *)&client_name,
&client_name_len);
if (client_sock == -1)
error_die("accept");
/* accept_request(&client_sock); */
//创建新的线程来处理请求
if (pthread_create(&newthread , NULL, (void *)accept_request, (void *)(intptr_t)client_sock) != 0)
perror("pthread_create");
}

close(server_sock);

return(0);
}