tinyhttpd源码阅读

tinythhpd是一个超精简的web服务器,作者是1999年写的,到现在仍然能正常运行。
这个web服务器涉及到进程、线程、管道、socket等内容,源码只有五六百行,非常适合初学者阅读。

运行项目

我直接运行make httpd的时候报错说找不到-lsocket,从网上搜到说,这个库会自动链接上,并且也不叫这个名字了。
于是删掉-lsocket,但是又提示未定义的引用pthread_create,原来-lpthread的参数要放到最后边才行。
然后最终运行以下命令,就生成httpd了。

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gcc -o httpd httpd.c

因为我本机的per在/usr/bin目录下,所以改一下perl脚本中的第一行。
然后执行:

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./httpd &

然后在浏览器地址栏输入下面地址测试web服务器。

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127.0.0.1:<端口号>

函数功能分析

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void accept_request(int);//每次创建一个线程,执行这个函数,用来处理一次http请求。
void bad_request(int);//当客户端发来的请求格式错误时(比如http协议的某些字段印错了),会向客户端发送400信息。
void cat(int, FILE *);//把某个文件的内容全部写入到与客户端的那个连接中。
void cannot_execute(int)//;当服务器身程序执行错误时(比如服务器自己在建立管道,或者fork进程时发生错误),会调用此函数,会向客户端发送500的信息。
void error_die(const char *);//打印错误信息的函数
void execute_cgi(int, const char *, const char *, const char *);//如果是post请求,这个函数用来执行cgi脚本。
int get_line(int, char *, int);//从连接中读出一行数据。
void headers(int, const char *);//将http的开头的字段写入连接。
void not_found(int);//如果客户端请求的地址不存在,调用此函数,并给客户端返回404.
void serve_file(int, const char *);//负责给返回客户端所请求的文件,通过调用headers(),cat(),not_found,gen_line()几个函数来实现。
int startup(u_short *);//负责程序刚开始建立socket、绑定ip地址、监听连接等工作。
void unimplemented(int);//如果客户端发过来的不死get或post请求,会调用此函数。

程序阅读顺序:可以先大概看看这些函数的功能,再从主函数顺着看一下主体,主函数中先调用startup创建socket连接。
然后监听到连接请求之后再创建新线程执行accept_request来处理请求。

函数关系图

函数流程图

注释版代码

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/* 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>

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

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

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 *);
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(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;

//从连接中读出一行数据,numchars存放所读到的数据长度。
numchars = get_line(client, buf, sizeof(buf));
i = 0; j = 0;

//将buf中的http“请求方式”字段复制到method中,遇到空格停止。
while (!ISspace(buf[j]) && (i < sizeof(method) - 1))
{
method[i] = buf[j];
i++; j++;
}
method[i] = '\0';

//如果不是get或post这两种,就会调用unimplement函数通知客户端。
if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
{
unimplemented(client);
return;
}

//如果请求方式是post,就把cgi设置为1,一会再调用cgi脚本
if (strcasecmp(method, "POST") == 0)
cgi = 1;

i = 0;
//循环吸收空格。
while (ISspace(buf[j]) && (j < sizeof(buf)))
j++;
//再用类似上面获取method的方式从buf中获取url。
while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))
{
url[i] = buf[j];
i++; j++;
}
url[i] = '\0';

//这个if语句用来把url中存储的地址的格式处理一下,如果中间有问号,
//就设置cgi为1,随后会调用cgi脚本来处理这个请求(所以get请求也会调用cgi)
//如果请求方式是get
if (strcasecmp(method, "GET") == 0)
{
query_string = url;
while ((*query_string != '?') && (*query_string != '\0'))
query_string++;
//如果请求的网址中有问号,那就从这里截断(因为本web服务器除了返回页面只有用cgi脚本来处理请求)
if (*query_string == '?')
{
cgi = 1;
*query_string = '\0';
query_string++;
}
}

sprintf(path, "htdocs%s", url);
//如果网址最后一位是"/",那就在后面加上index.html
if (path[strlen(path) - 1] == '/')
strcat(path, "index.html");
//获取那个文件的信息,存放在st中
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
{
//判断这个文件是不是一个目录,如果是目录在后面加上"/index.html"。
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;
//如果是一般的get请求,那就调用server_file函数给返回那个文件的内容,
//否则就执行调用execute_cgi执行cgi脚本
if (!cgi)
serve_file(client, path);
else
execute_cgi(client, path, method, query_string);
}

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 */
/**********************************************************************/
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. */
/**********************************************************************/
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)
{
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';
if (strcasecmp(method, "GET") == 0)
//如果是get请求,那就把请求头中剩余的内容都读出来(相当于丢弃)
while ((numchars > 0) && strcmp("\n", buf)) /* read & discard headers */
numchars = get_line(client, buf, sizeof(buf));
else//如果是post请求,那么读出数据长度来
{
numchars = get_line(client, buf, sizeof(buf));
while ((numchars > 0) && strcmp("\n", buf))
{
buf[15] = '\0';
if (strcasecmp(buf, "Content-Length:") == 0)
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);

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

//fork出子进程来执行cgi脚本
if ( (pid = fork()) < 0 ) {
cannot_execute(client);
return;
}
//如果是子进程
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输出
dup2(cgi_output[1], 1);
dup2(cgi_input[0], 0);
close(cgi_output[0]);
close(cgi_input[1]);
sprintf(meth_env, "REQUEST_METHOD=%s", method);
//设置环境变量
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);
}
execl(path, path, NULL);
exit(0);
} else { /* parent */
close(cgi_output[1]);
close(cgi_input[0]);
//读出post请求所传过来的消息,然后写入到cgi脚本的"输入管道"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]);
//等待子进程结束
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) */
/**********************************************************************/
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')
{
n = recv(sock, &c, 1, MSG_PEEK);
/* DEBUG printf("%02X\n", c); */
if ((n > 0) && (c == '\n'))
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 */
/**********************************************************************/
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. */
/**********************************************************************/
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 */
/**********************************************************************/
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));

resource = fopen(filename, "r");
if (resource == NULL)
not_found(client);
else//向client所标识的连接写入http头,然后是用cat写入文件内容
{
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;

//创建socket
httpd = socket(PF_INET, SOCK_STREAM, 0);
if (httpd == -1)
error_die("socket");
memset(&name, 0, sizeof(name));
name.sin_family = AF_INET;
//主机字节序转变为网络字节序(即大顶端和小顶端之间的相互转换)
name.sin_port = htons(*port);
name.sin_addr.s_addr = htonl(INADDR_ANY);
//给socket绑定上地址和端口
if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
error_die("bind");
if (*port == 0) /* if dynamically allocating a port */
{
int namelen = sizeof(name);
if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
error_die("getsockname");
*port = ntohs(name.sin_port);
}
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 */
/**********************************************************************/
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;
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");
/* accept_request(client_sock); */
//创建新的线程来处理请求
if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0)
perror("pthread_create");
}

close(server_sock);

return(0);
}

参考