Linux下用C编写WebSocet服务以响应HTML5的WebSocket请求

在HTML5中新增了WebSocket，使得通讯变得更加方便。这样一来，Web与硬件的交互除了CGI和XHR的方式外，又有了一个新的方式。那么使用WebSocket又如何与下层通信呢？看看WebSocket的相关介绍就会发现，其类似于HTTP协议的通信，但又不同于HTTP协议通信，其最终使用的是TCP通信。具体的可以参照该文WebScoket 规范 + WebSocket 协议。

我们先来看看通信的效果图

下面是实现的步骤

1.建立SOCKET监听

WebSocket也是TCP通信，所以服务端需要先建立监听，下面是实现的代码。

/* server.c */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

#include "base64.h"
#include "sha1.h"
#include "intLib.h"


#define REQUEST_LEN_MAX 1024
#define DEFEULT_SERVER_PORT 8000
#define WEB_SOCKET_KEY_LEN_MAX 256
#define RESPONSE_HEADER_LEN_MAX 1024
#define LINE_MAX 256


void shakeHand(int connfd,const char *serverKey);
char * fetchSecKey(const char * buf);
char * computeAcceptKey(const char * buf);
char * analyData(const char * buf,const int bufLen);
char * packData(const char * message,unsigned long * len);
void response(const int connfd,const char * message);

int main(int argc, char *argv[])
{
	struct sockaddr_in servaddr, cliaddr;
	socklen_t cliaddr_len;
	int listenfd, connfd;
	char buf[REQUEST_LEN_MAX];
	char *data;
	char str[INET_ADDRSTRLEN];
	char *secWebSocketKey;
	int i,n;
	int connected=0;//0:not connect.1:connected.
	int port= DEFEULT_SERVER_PORT;

	if(argc>1)
	  {
	    port=atoi(argv[1]);
	  }
	if(port<=0||port>0xFFFF)
	  {
	    printf("Port(%d) is out of range(1-%d)
",port,0xFFFF);
	    return;
	  }
	listenfd = socket(AF_INET, SOCK_STREAM, 0);

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(port);
    
	bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

	listen(listenfd, 20);

	printf("Listen %d
Accepting connections ...
",port);
	cliaddr_len = sizeof(cliaddr);
	connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &cliaddr_len);
	printf("From %s at PORT %d
",
		       inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)),
		       ntohs(cliaddr.sin_port));

	while (1)
	  {
	
		memset(buf,0,REQUEST_LEN_MAX);
		n = read(connfd, buf, REQUEST_LEN_MAX);	
		printf("---------------------
");
	
	
		if(0==connected)
		  {
		    printf("read:%d
%s
",n,buf);
		    secWebSocketKey=computeAcceptKey(buf);	
		    shakeHand(connfd,secWebSocketKey);
		    connected=1;
		    continue;
		  }

		data=analyData(buf,n);
		response(connfd,data);
	}
	close(connfd);
}

2.握手

在建立监听后，网页向服务端发现WebSocket请求，这时需要先进行握手。握手时，客户端会在协议中包含一个握手的唯一Key，服务端在拿到这个Key后，需要加入一个GUID，然后进行sha1的加密，再转换成base64，最后再发回到客户端。这样就完成了一次握手。此种握手方式是针对chrome websocket 13的版本，其他版本的可能会有所不同。下面是实现的代码。

char * fetchSecKey(const char * buf)
{
  char *key;
  char *keyBegin;
  char *flag="Sec-WebSocket-Key: ";
  int i=0, bufLen=0;

  key=(char *)malloc(WEB_SOCKET_KEY_LEN_MAX);
  memset(key,0, WEB_SOCKET_KEY_LEN_MAX);
  if(!buf)
    {
      return NULL;
    }
 
  keyBegin=strstr(buf,flag);
  if(!keyBegin)
    {
      return NULL;
    }
  keyBegin+=strlen(flag);

  bufLen=strlen(buf);
  for(i=0;i<bufLen;i++)
    {
      if(keyBegin[i]==0x0A||keyBegin[i]==0x0D)
	{
	  break;
	}
      key[i]=keyBegin[i];
    }
  
  return key;
}

char * computeAcceptKey(const char * buf)
{
  char * clientKey;
  char * serverKey; 
  char * sha1DataTemp;
  char * sha1Data;
  short temp;
  int i,n;
  const char * GUID="258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
 

  if(!buf)
    {
      return NULL;
    }
  clientKey=(char *)malloc(LINE_MAX);
  memset(clientKey,0,LINE_MAX);
  clientKey=fetchSecKey(buf);
 
  if(!clientKey)
    {
      return NULL;
    }

 
  strcat(clientKey,GUID);

  sha1DataTemp=sha1_hash(clientKey);
  n=strlen(sha1DataTemp);


  sha1Data=(char *)malloc(n/2+1);
  memset(sha1Data,0,n/2+1);
 
  for(i=0;i<n;i+=2)
    {      
      sha1Data[i/2]=htoi(sha1DataTemp,i,2);    
    } 

  serverKey = base64_encode(sha1Data, strlen(sha1Data)); 

  return serverKey;
}

void shakeHand(int connfd,const char *serverKey)
{
  char responseHeader [RESPONSE_HEADER_LEN_MAX];

  if(!connfd)
    {
      return;
    }

  if(!serverKey)
    {
      return;
    }

  memset(responseHeader,'',RESPONSE_HEADER_LEN_MAX);

  sprintf(responseHeader, "HTTP/1.1 101 Switching Protocols
");
  sprintf(responseHeader, "%sUpgrade: websocket
", responseHeader);
  sprintf(responseHeader, "%sConnection: Upgrade
", responseHeader);
  sprintf(responseHeader, "%sSec-WebSocket-Accept: %s

", responseHeader, serverKey);
 
  printf("Response Header:%s
",responseHeader);

  write(connfd,responseHeader,strlen(responseHeader));
}

注意：

1.Connection后面的值与HTTP通信时的不一样了，是Upgrade，而Upgrade又对应到了websocket，这样就标识了该通信协议是websocket的方式。

2.在sha1加密后进行base64编码时，使用sha1加密后的串必须将其当成16进制的字符串，将每两个字符合成一个新的码(0-0xFF间)来进一步计算后，才可以进行base64换算(我开始时就在这里折腾了很久，后面才弄明白还要加上这一步)，如果是直接就base64，那就会握手失败。

3.对于sha1和base64网上有很多，后面也附上我所使用的代码。

3.数据传输

握手成功后就可以进行数据传输了，只要按照WebSocket的协议来解就可以了。下面是实现的代码

char * analyData(const char * buf,const int bufLen)
{
  char * data;
  char fin, maskFlag,masks[4];
  char * payloadData;
  char temp[8];
  unsigned long n, payloadLen=0;
  unsigned short usLen=0;
  int i=0; 


 if (bufLen < 2) 
   {
     return NULL;
   }

  fin = (buf[0] & 0x80) == 0x80; // 1bit，1表示最后一帧  
  if (!fin)
   {
       return NULL;// 超过一帧暂不处理 
   }

   maskFlag = (buf[1] & 0x80) == 0x80; // 是否包含掩码  
   if (!maskFlag)
   {
       return NULL;// 不包含掩码的暂不处理
   }

   payloadLen = buf[1] & 0x7F; // 数据长度 
   if (payloadLen == 126)
   {      
     memcpy(masks,buf+4, 4);      
     payloadLen =(buf[2]&0xFF) << 8 | (buf[3]&0xFF);  
     payloadData=(char *)malloc(payloadLen);
     memset(payloadData,0,payloadLen);
     memcpy(payloadData,buf+8,payloadLen);
    }
    else if (payloadLen == 127)
    {
     memcpy(masks,buf+10,4);  
     for ( i = 0; i < 8; i++)
     {
         temp[i] = buf[9 - i];
     } 

     memcpy(&n,temp,8);  
     payloadData=(char *)malloc(n); 
     memset(payloadData,0,n); 
     memcpy(payloadData,buf+14,n);//toggle error(core dumped) if data is too long.
     payloadLen=n;    
     }
     else
     {   
      memcpy(masks,buf+2,4);    
      payloadData=(char *)malloc(payloadLen);
      memset(payloadData,0,payloadLen);
      memcpy(payloadData,buf+6,payloadLen); 
     }

     for (i = 0; i < payloadLen; i++)
     {
       payloadData[i] = (char)(payloadData[i] ^ masks[i % 4]);
     }
 
     printf("data(%d):%s
",payloadLen,payloadData);
     return payloadData;
}

char *  packData(const char * message,unsigned long * len)
 {
         char * data=NULL;
	 unsigned long n;

	 n=strlen(message);
            if (n < 126)
            {
	      data=(char *)malloc(n+2);
	      memset(data,0,n+2);	 
	      data[0] = 0x81;
	      data[1] = n;
	      memcpy(data+2,message,n);
	      *len=n+2;
            }
            else if (n < 0xFFFF)
            {
	      data=(char *)malloc(n+4);
	      memset(data,0,n+4);
	      data[0] = 0x81;
	      data[1] = 126;
	      data[2] = (n>>8 & 0xFF);
	      data[3] = (n & 0xFF);
	      memcpy(data+4,message,n);    
	      *len=n+4;
            }
            else
            {
	 
                // 暂不处理超长内容  
	      *len=0;
            }
  

        return data;
 }

void response(int connfd,const char * message)
{
  char * data;
  unsigned long n=0;
  int i;
  if(!connfd)
    {
      return;
    }

  if(!data)
    {
      return;
    }
  data=packData(message,&n); 
 
  if(!data||n<=0)
    {
      printf("data is empty!
");
      return;
    } 
 
  write(connfd,data,n);
  
}

注意：

1.对于超过0xFFFF长度的数据在分析数据部分虽然作了处理，但是在memcpy时会报core dumped的错误，没有解决，请过路的大牛帮忙指点。在packData部分也未对这一部分作处理。

2.在这里碰到了一个郁闷的问题，在命名函数时，将函数名写的过长了(fetchSecWebSocketAcceptkey)，结果导致编译通过，但在运行时却莫名其妙的报core dumped的错误，试了很多方法才发现是这个原因，后将名字改短后就OK了。

3.在回复数据时，只要按websocket的协议进行回应就可以了。

附上sha1、base64和intLib的代码（sha1和base64是从网上摘来的）

sha1.h

//sha1.h：对字符串进行sha1加密
#ifndef _SHA1_H_
#define _SHA1_H_

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


typedef struct SHA1Context{
	unsigned Message_Digest[5];      
	unsigned Length_Low;             
	unsigned Length_High;            
	unsigned char Message_Block[64]; 
	int Message_Block_Index;         
	int Computed;                    
	int Corrupted;                   
} SHA1Context;

void SHA1Reset(SHA1Context *);
int SHA1Result(SHA1Context *);
void SHA1Input( SHA1Context *,const char *,unsigned);
#endif


#define SHA1CircularShift(bits,word) ((((word) << (bits)) & 0xFFFFFFFF) | ((word) >> (32-(bits))))

void SHA1ProcessMessageBlock(SHA1Context *);
void SHA1PadMessage(SHA1Context *);

void SHA1Reset(SHA1Context *context){// 初始化动作
	context->Length_Low             = 0;
	context->Length_High            = 0;
	context->Message_Block_Index    = 0;

	context->Message_Digest[0]      = 0x67452301;
	context->Message_Digest[1]      = 0xEFCDAB89;
	context->Message_Digest[2]      = 0x98BADCFE;
	context->Message_Digest[3]      = 0x10325476;
	context->Message_Digest[4]      = 0xC3D2E1F0;

	context->Computed   = 0;
	context->Corrupted  = 0;
}


int SHA1Result(SHA1Context *context){// 成功返回1，失败返回0
	if (context->Corrupted) {
		return 0;
	}
	if (!context->Computed) {
		SHA1PadMessage(context);
		context->Computed = 1;
	}
	return 1;
}


void SHA1Input(SHA1Context *context,const char *message_array,unsigned length){
	if (!length) return;

	if (context->Computed || context->Corrupted){
		context->Corrupted = 1;
		return;
	}

	while(length-- && !context->Corrupted){
		context->Message_Block[context->Message_Block_Index++] = (*message_array & 0xFF);

		context->Length_Low += 8;

		context->Length_Low &= 0xFFFFFFFF;
		if (context->Length_Low == 0){
			context->Length_High++;
			context->Length_High &= 0xFFFFFFFF;
			if (context->Length_High == 0) context->Corrupted = 1;
		}

		if (context->Message_Block_Index == 64){
			SHA1ProcessMessageBlock(context);
		}
		message_array++;
	}
}

void SHA1ProcessMessageBlock(SHA1Context *context){
	const unsigned K[] = {0x5A827999, 0x6ED9EBA1, 0x8F1BBCDC, 0xCA62C1D6 };
	int         t;                
	unsigned    temp;             
	unsigned    W[80];            
	unsigned    A, B, C, D, E;    

	for(t = 0; t < 16; t++) {
	W[t] = ((unsigned) context->Message_Block[t * 4]) << 24;
	W[t] |= ((unsigned) context->Message_Block[t * 4 + 1]) << 16;
	W[t] |= ((unsigned) context->Message_Block[t * 4 + 2]) << 8;
	W[t] |= ((unsigned) context->Message_Block[t * 4 + 3]);
	}
	
	for(t = 16; t < 80; t++)  W[t] = SHA1CircularShift(1,W[t-3] ^ W[t-8] ^ W[t-14] ^ W[t-16]);

	A = context->Message_Digest[0];
	B = context->Message_Digest[1];
	C = context->Message_Digest[2];
	D = context->Message_Digest[3];
	E = context->Message_Digest[4];

	for(t = 0; t < 20; t++) {
		temp =  SHA1CircularShift(5,A) + ((B & C) | ((~B) & D)) + E + W[t] + K[0];
		temp &= 0xFFFFFFFF;
		E = D;
		D = C;
		C = SHA1CircularShift(30,B);
		B = A;
		A = temp;
	}
	for(t = 20; t < 40; t++) {
		temp = SHA1CircularShift(5,A) + (B ^ C ^ D) + E + W[t] + K[1];
		temp &= 0xFFFFFFFF;
		E = D;
		D = C;
		C = SHA1CircularShift(30,B);
		B = A;
		A = temp;
	}
	for(t = 40; t < 60; t++) {
		temp = SHA1CircularShift(5,A) + ((B & C) | (B & D) | (C & D)) + E + W[t] + K[2];
		temp &= 0xFFFFFFFF;
		E = D;
		D = C;
		C = SHA1CircularShift(30,B);
		B = A;
		A = temp;
	}
	for(t = 60; t < 80; t++) {
		temp = SHA1CircularShift(5,A) + (B ^ C ^ D) + E + W[t] + K[3];
		temp &= 0xFFFFFFFF;
		E = D;
		D = C;
		C = SHA1CircularShift(30,B);
		B = A;
		A = temp;
	}
	context->Message_Digest[0] = (context->Message_Digest[0] + A) & 0xFFFFFFFF;
	context->Message_Digest[1] = (context->Message_Digest[1] + B) & 0xFFFFFFFF;
	context->Message_Digest[2] = (context->Message_Digest[2] + C) & 0xFFFFFFFF;
	context->Message_Digest[3] = (context->Message_Digest[3] + D) & 0xFFFFFFFF;
	context->Message_Digest[4] = (context->Message_Digest[4] + E) & 0xFFFFFFFF;
	context->Message_Block_Index = 0;
}

void SHA1PadMessage(SHA1Context *context){
	if (context->Message_Block_Index > 55) {
		context->Message_Block[context->Message_Block_Index++] = 0x80;
		while(context->Message_Block_Index < 64)  context->Message_Block[context->Message_Block_Index++] = 0;
		SHA1ProcessMessageBlock(context);
		while(context->Message_Block_Index < 56) context->Message_Block[context->Message_Block_Index++] = 0;
	} else {
		context->Message_Block[context->Message_Block_Index++] = 0x80;
		while(context->Message_Block_Index < 56) context->Message_Block[context->Message_Block_Index++] = 0;
	}
	context->Message_Block[56] = (context->Length_High >> 24 ) & 0xFF;
	context->Message_Block[57] = (context->Length_High >> 16 ) & 0xFF;
	context->Message_Block[58] = (context->Length_High >> 8 ) & 0xFF;
	context->Message_Block[59] = (context->Length_High) & 0xFF;
	context->Message_Block[60] = (context->Length_Low >> 24 ) & 0xFF;
	context->Message_Block[61] = (context->Length_Low >> 16 ) & 0xFF;
	context->Message_Block[62] = (context->Length_Low >> 8 ) & 0xFF;
	context->Message_Block[63] = (context->Length_Low) & 0xFF;

	SHA1ProcessMessageBlock(context);
}

/*
int sha1_hash(const char *source, char *lrvar){// Main
	SHA1Context sha;
	char buf[128];

	SHA1Reset(&sha);
	SHA1Input(&sha, source, strlen(source));

	if (!SHA1Result(&sha)){
		printf("SHA1 ERROR: Could not compute message digest");
		return -1;
	} else {
		memset(buf,0,sizeof(buf));
		sprintf(buf, "%08X%08X%08X%08X%08X", sha.Message_Digest[0],sha.Message_Digest[1],
		sha.Message_Digest[2],sha.Message_Digest[3],sha.Message_Digest[4]);
		//lr_save_string(buf, lrvar);
		
		return strlen(buf);
	}
}
*/

char * sha1_hash(const char *source){// Main
	SHA1Context sha;
	char *buf;//[128];

	SHA1Reset(&sha);
	SHA1Input(&sha, source, strlen(source));

	if (!SHA1Result(&sha)){
		printf("SHA1 ERROR: Could not compute message digest");
		return NULL;
	} else {
	  buf=(char *)malloc(128);
		memset(buf,0,sizeof(buf));
		sprintf(buf, "%08X%08X%08X%08X%08X", sha.Message_Digest[0],sha.Message_Digest[1],
		sha.Message_Digest[2],sha.Message_Digest[3],sha.Message_Digest[4]);
		//lr_save_string(buf, lrvar);
		
		//return strlen(buf);
		return buf;
	}
}

base64.h

#ifndef _BASE64_H_
#define _BASE64_H_
 
#include <stdio.h> 
#include <stdlib.h>
#include <string.h>

const char base[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="; 
char* base64_encode(const char* data, int data_len); 
char *base64_decode(const char* data, int data_len); 
static char find_pos(char ch); 

/* */ 
char *base64_encode(const char* data, int data_len) 
{ 
    //int data_len = strlen(data); 
    int prepare = 0; 
    int ret_len; 
    int temp = 0; 
    char *ret = NULL; 
    char *f = NULL; 
    int tmp = 0; 
    char changed[4]; 
    int i = 0; 
    ret_len = data_len / 3; 
    temp = data_len % 3; 
    if (temp > 0) 
    { 
        ret_len += 1; 
    } 
    ret_len = ret_len*4 + 1; 
    ret = (char *)malloc(ret_len); 
      
    if ( ret == NULL) 
    { 
        printf("No enough memory.
"); 
        exit(0); 
    } 
    memset(ret, 0, ret_len); 
    f = ret; 
    while (tmp < data_len) 
    { 
        temp = 0; 
        prepare = 0; 
        memset(changed, '', 4); 
        while (temp < 3) 
        { 
            //printf("tmp = %d
", tmp); 
            if (tmp >= data_len) 
            { 
                break; 
            } 
            prepare = ((prepare << 8) | (data[tmp] & 0xFF)); 
            tmp++; 
            temp++; 
        } 
        prepare = (prepare<<((3-temp)*8)); 
        //printf("before for : temp = %d, prepare = %d
", temp, prepare); 
        for (i = 0; i < 4 ;i++ ) 
        { 
            if (temp < i) 
            { 
                changed[i] = 0x40; 
            } 
            else 
            { 
                changed[i] = (prepare>>((3-i)*6)) & 0x3F; 
            } 
            *f = base[changed[i]]; 
            //printf("%.2X", changed[i]); 
            f++; 
        } 
    } 
    *f = ''; 
      
    return ret; 
      
} 
/* */ 
static char find_pos(char ch)   
{ 
    char *ptr = (char*)strrchr(base, ch);//the last position (the only) in base[] 
    return (ptr - base); 
} 
/* */ 
char *base64_decode(const char *data, int data_len) 
{ 
    int ret_len = (data_len / 4) * 3; 
    int equal_count = 0; 
    char *ret = NULL; 
    char *f = NULL; 
    int tmp = 0; 
    int temp = 0; 
    char need[3]; 
    int prepare = 0; 
    int i = 0; 
    if (*(data + data_len - 1) == '=') 
    { 
        equal_count += 1; 
    } 
    if (*(data + data_len - 2) == '=') 
    { 
        equal_count += 1; 
    } 
    if (*(data + data_len - 3) == '=') 
    {//seems impossible 
        equal_count += 1; 
    } 
    switch (equal_count) 
    { 
    case 0: 
        ret_len += 4;//3 + 1 [1 for NULL] 
        break; 
    case 1: 
        ret_len += 4;//Ceil((6*3)/8)+1 
        break; 
    case 2: 
        ret_len += 3;//Ceil((6*2)/8)+1 
        break; 
    case 3: 
        ret_len += 2;//Ceil((6*1)/8)+1 
        break; 
    } 
    ret = (char *)malloc(ret_len); 
    if (ret == NULL) 
    { 
        printf("No enough memory.
"); 
        exit(0); 
    } 
    memset(ret, 0, ret_len); 
    f = ret; 
    while (tmp < (data_len - equal_count)) 
    { 
        temp = 0; 
        prepare = 0; 
        memset(need, 0, 4); 
        while (temp < 4) 
        { 
            if (tmp >= (data_len - equal_count)) 
            { 
                break; 
            } 
            prepare = (prepare << 6) | (find_pos(data[tmp])); 
            temp++; 
            tmp++; 
        } 
        prepare = prepare << ((4-temp) * 6); 
        for (i=0; i<3 ;i++ ) 
        { 
            if (i == temp) 
            { 
                break; 
            } 
            *f = (char)((prepare>>((2-i)*8)) & 0xFF); 
            f++; 
        } 
    } 
    *f = ''; 
    return ret; 
}

#endif

intLib.h

#ifndef _INT_LIB_H_
#define _INT_LIB_H_
int tolower(int c) 
{ 
    if (c >= 'A' && c <= 'Z') 
    { 
        return c + 'a' - 'A'; 
    } 
    else 
    { 
        return c; 
    } 
} 

int htoi(const char s[],int start,int len) 
{ 
  int i,j; 
    int n = 0; 
    if (s[0] == '0' && (s[1]=='x' || s[1]=='X')) //判断是否有前导0x或者0X
    { 
        i = 2; 
    } 
    else 
    { 
        i = 0; 
    } 
    i+=start;
    j=0;
    for (; (s[i] >= '0' && s[i] <= '9') 
	   || (s[i] >= 'a' && s[i] <= 'f') || (s[i] >='A' && s[i] <= 'F');++i) 
    {   
        if(j>=len)
	{
	  break;
	}
        if (tolower(s[i]) > '9') 
        { 
            n = 16 * n + (10 + tolower(s[i]) - 'a'); 
        } 
        else 
        { 
            n = 16 * n + (tolower(s[i]) - '0'); 
        } 
	j++;
    } 
    return n; 
} 


#endif

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