自己动手学TCP/IP–http协议(http报文头)

我会带着你远行 2022-06-10 11:45 234阅读 0赞

在前面的一篇文章中，简单了介绍了HTTP报文格式，详情参考[http://www.firefoxbug.net/?cat=47][http_www.firefoxbug.net_cat_47]。  
  
这里大概介绍下基本的，常见的HTTP包头格式。

POST /report/getComment.jsp HTTP/1.1
    Host: yeeg.com
    Connection: keep-alive
    Content-Length: 161
    Origin: http://www.1g1g.com
    User-Agent: Mozilla/5.0 (X11; Linux i686) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.77 Safari/535.7
    content-type: application/x-www-form-urlencoded
    Accept: */*
    Referer: http://www.1g1g.com/player/loader.swf?uid=0.8106261373031884
    Accept-Encoding: gzip,deflate,sdch
    Accept-Language: en-US,en;q=0.8
    Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
    Cookie: JSESSIONID=C3F105F72E3602D6292D3E4561E8E400

上面是一个POST包的包头，其中Content-Length字段里面的值就是POST包数据段的长度。可以用

wireshark抓取POST包，会发现，post包是把报文头和数据内容分开来发的，会被TCP分片，然后重组。

具体这里不详细讨论。

GET /enclosure/2010-09-10T02_51_05-07_00.mp3 HTTP/1.1
    Host: 805665086.podomatic.com
    Connection: keep-alive
    User-Agent: Mozilla/5.0 (X11; Linux i686) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.77 Safari/535.7
    Accept: */*
    Referer: http://www.1g1g.com/player/loader.swf?uid=0.8106261373031884
    Accept-Encoding: gzip,deflate,sdch
    Accept-Language: en-US,en;q=0.8
    Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3

上面是一个GET包，GET包请求的资源都是在URL里面的，所以数据段也就没有了，可以通过抓包分析。

HTTP/1.1 200 OK
    Date: Tue, 10 Jul 2012 09:12:52 GMT
    Server: Apache/2.2.14 (Ubuntu)
    Last-Modified: Thu, 23 Dec 2010 19:29:26 GMT
    ETag: "960fcf-4a6459-49818e3486374"
    Accept-Ranges: bytes
    Content-Length: 487
    Keep-Alive: timeout=15, max=100
    Connection: Keep-Alive
    Content-Type: audio/mpeg

上面是一个http响应包，Content-Length指明了数据段的大小。

下面是我今天用C写了解析HTTP报文头的程序。注意：下面代码只主要用libcap实现实现了部分功能，具体

是解析GET包头，POST包头，还有HTTP相应包头，可能存在一些不足，希望大家多多交流。

/*
    	capture http packet by firefoxbug
    */
    #include <pcap.h>
    #include <stdio.h>
    #include <stdlib.h> 				
    #include <string.h>
    #include <sys/socket.h>
    #include <arpa/inet.h>		
    #include <net/ethernet.h>
    #include <netinet/ip_icmp.h>	//Provides declarations for icmp header
    #include <netinet/udp.h>		//Provides declarations for udp header
    #include <netinet/tcp.h>		//Provides declarations for tcp header
    #include <netinet/ip.h>		//Provides declarations for ip header
    
    #define BUFFSIZE 1500
    
    typedef struct port{
    	unsigned int src_port;
    	unsigned int des_port;
    }Port;
    
    Port port;
    int tcp=0;
    FILE *logfile;
    int size;
    
    void process_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *buffer);
    char *print_tcp_packet(const char *Buffer);
    void get_line(char *data,char *buff,int length);
    void print_http_req_packet(char *data);
    void print_http_ans_packet(char *data);
    
    int main(int argc,char *argv[])
    {
    	pcap_if_t *alldevsp , *device;
    	pcap_t *handle; //Handle of the device that shall be sniffed
    
    	char errbuf[100] , *devname , devs[100][100];
    	int count = 1 , n;
    
    	//First get the list of available devices
    	printf("Finding available devices ... ");
    	if( pcap_findalldevs( &alldevsp , errbuf) )
    	{
    		printf("Error finding devices : %s" , errbuf);
    		exit(1);
    	}
    	printf("Done");
    
    	//Print the available devices
    	printf("\nAvailable Devices are :\n");
    	for(device = alldevsp ; device != NULL ; device = device->next)
    	{
    		printf("%d. %s - %s\n" , count , device->name , device->description);
    		if(device->name != NULL)
    		{
    			strcpy(devs[count] , device->name);
    		}
    		count++;
    	}
    
    	//Ask user which device to sniff
    	printf("Enter the number of the device you want to sniff : ");
    	scanf("%d" , &n);
    	devname = devs[n];
    
    	//Open the device for sniffing
    	printf("Opening device %s for sniffing ... " , devname);
    	handle = pcap_open_live(devname , 65536 , 1 , 0 , errbuf);
    
    	if (handle == NULL)
    	{
    		fprintf(stderr, "Couldn't open device %s : %s\n" , devname , errbuf);
    		exit(1);
    	}
    	printf("Done\n");
    
    	logfile=fopen("log.txt","w");
    	if(logfile==NULL)
    	{
    		printf("Unable to create file.");
    	}
    
    	//Put the device in sniff loop
    	pcap_loop(handle , -1 , process_packet , NULL);
    
    	return 0;
    }
    
    void process_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *buffer)
    {
    	size = header->len;
    //	fprintf(logfile,"length of packet : %d \n",size);	
    	//Get the IP Header part of this packet , excluding the ethernet header
    	struct iphdr *iph = (struct iphdr*)(buffer + sizeof(struct ethhdr));
    	switch (iph->protocol) //Check the Protocol and do accordingly...
    	{
    
    		case 6:  //TCP Protocol
    			++tcp;	
    		//	printf("TCP : %d \n", tcp);
    			unsigned char *data = print_tcp_packet(buffer);	
    			if (size <= 0)
    				break;
    			if (port.des_port == 80)			
    			{
    				print_http_req_packet(data);
    			}
    			else if ( port.src_port == 80 )
    			{
    				print_http_ans_packet(data);
    			}
    			break;
    	}
    
    }
    
    char *print_tcp_packet(const char *Buffer)
    {
    	//IP header
    	struct iphdr *iph = (struct iphdr *)( Buffer  + sizeof(struct ethhdr) );
    	unsigned int iphdrlen = iph->ihl*4;
    	//TCP header
    	struct tcphdr *tcph=(struct tcphdr*)(Buffer + iphdrlen + sizeof(struct ethhdr));
    	
    	port.src_port = ntohs(tcph->source);
    	port.des_port = ntohs(tcph->dest);
    
    	// mac_header + ip_header + tcp_header
    	int header_size =  sizeof(struct ethhdr) + iphdrlen + tcph->doff*4;
    	size = size - header_size; 
    //	fprintf(logfile,"length of header : %d \n",header_size );
    	return (char *)(Buffer + header_size);
    }
    
    void print_http_req_packet(char *data)
    {	
    	if( strncmp(data,"GET",3) == 0 || strncmp(data,"POST",4) == 0 ) 
    	{
    		fprintf(logfile,"\n/***********************length of data : %d**********************/ \n",size);
    		fprintf(logfile,"From %d To %d \n",port.src_port,port.des_port);
    		int i = 0;	
    		for( ; i < size ; ++i)
    		{
    			fprintf(logfile,"%c",*(data + i));
    		}
    		fprintf(logfile,"/***************************** end *******************************/ \n\n");
    	}
    	return ;
    }
    
    void print_http_ans_packet(char *data)
    {
    	if( strncmp(data,"HTTP",4) == 0 ) 
    	{
    		fprintf(logfile,"\n/***********************length of data : %d**********************/ \n",size);
    		fprintf(logfile,"From %d To %d \n",port.src_port,port.des_port);
    		char buff[BUFFSIZE] = {'\0'};
    		get_line(data,buff,size);
    		fprintf(logfile,"%s",buff);
    		unsigned int off = strlen(buff);
    		size = size - off;
    		while(strcmp(buff,"\r\n") != 0)
    		{
    			memset(buff,'\0',sizeof(buff));
    			get_line(data + off,buff,size);
    			fprintf(logfile,"%s",buff);
    			off = off + strlen(buff);
    			size = size - off;
    		}
    		fprintf(logfile,"/***************************** end *******************************/ \n\n");
    	}
    }
    
    void get_line(char *data,char *buff,int length)
    {
    	int i = 0;
    	char ch;
    	for ( ; i < length;++i)
    	{
    		ch = *(data + i);
    		*(buff + i) = ch;
    		if(ch == '\n')
    			break;
    	}
    }

[http_www.firefoxbug.net_cat_47]: http://www.firefoxbug.net/?cat=47