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)\n",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\nAccepting connections ...\n",port);
cliaddr_len = sizeof(cliaddr);
connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &cliaddr_len);
printf("From %s at PORT %d\n",
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("---------------------\n");

if(0==connected)
{
printf("read:%d\n%s\n",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,'\0',RESPONSE_HEADER_LEN_MAX);

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

printf("Response Header:%s\n",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\n",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!\n");
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.\n");
exit(0);
}
memset(ret, 0, ret_len);
f = ret;
while (tmp < data_len)
{
temp = 0;
prepare = 0;
memset(changed, '\0', 4);
while (temp < 3)
{
//printf("tmp = %d\n", 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\n", 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 = '\0';

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.\n");
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 = '\0';
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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