我正忙于在嵌入式平台上实现自己的 http 服务器。从技术上讲，服务器符合 HTTP 1.0，因此它希望客户端发送标头“Connection: Keep-Alive”以保持连接打开。
实现看起来像这样。我删除了解析 HTTP 标头并执行请求的代码，以使帖子尽可能短：
int Service_Request(int conn) {
struct ReqInfo reqinfo;
volatile int resource = 0;
int retval = 0;
Req_Result req_result = GOT_REQ;
InitReqInfo(&reqinfo);
/* while we still have HTTP requests to process */
while (req_result == GOT_REQ)
{
/* Get HTTP request, there are 3 different return values:
* GOT_REQ: we got a valid HTTP request
* TIMEOUT_REQ we timed out waiting for a request
* ERROR_REQ there was some error receiving from the socket
* usually because the connection was closed by the peer*/
req_result = Get_Request(conn, &reqinfo);
if ( req_result == TIMEOUT_REQ)
{
/* timed out waiting for the client, exit */
retval = 0;
break;
}
else if (req_result == ERROR_REQ)
{
/* some error, exit */
retval = -1;
break;
}
/* Process the request GET, PUT and POST is supported*/
if (reqinfo.method == GET)
{
/* code to handle GET*/
}
/* PUT and POST are handled in the same way */
else if ((reqinfo.method == PUT) || (reqinfo.method == POST) )
{
/* Code to handle PUT and POST*/
}
else
{
/* not supported, code should never get here */
reqinfo.status = 501;
Return_Error_Msg(conn, &reqinfo);
}
/*Diag_Msg("Client Request: \r\n");
Diag_Msg(reqinfo.clientRequest);*/
/*
* the reqinfo.keep_alive flag will be set to 1 if the
* "Connection: Keep-Alive" header was sent by the client
*/
if(reqinfo.keep_alive == 0)
{
break;
}
reqinfo.keep_alive_max--;
if(reqinfo.keep_alive_max <= 0 )
{
/*
* the connection has been reused for the maxmum amount of times, stop
*/
break;
}
/*
* If we get here, we will clear the memory used for the client request
* and go to the beginning of the while loop to receive another request
*/
Writeline(conn,"\r\n",2);
FreeReqInfo(&reqinfo);
}
FreeReqInfo(&reqinfo);
return (retval);
}
Get_Request 函数如下所示：
Req_Result Get_Request(int conn, struct ReqInfo * reqinfo) {
char buffer[MAX_REQ_LINE] = {0};
int rval;
fd_set fds;
struct timeval tv;
/* Set timeout to 5 seconds if this is the first request since the client connected, wait 5 seconds
* Otherwise, wait 5ms */
if(reqinfo->first_request == 1)
{
tv.tv_sec = 5;
tv.tv_usec = 0;
reqinfo->first_request = 0;
}
else
{
tv.tv_sec = reqinfo->keep_alive_timeout;
tv.tv_usec = 0;
}
/* Loop through request headers. If we have a simple request,
then we will loop only once. Otherwise, we will loop until
we receive a blank line which signifies the end of the headers,
or until select() times out, whichever is sooner. */
do {
/* Reset file descriptor set */
FD_ZERO(&fds);
FD_SET (conn, &fds);
/* Wait until the timeout to see if input is ready */
rval = select(conn + 1, &fds, NULL, NULL, &tv);
/* Take appropriate action based on return from select() */
if ( rval < 0 )
{
Diag_Msg("Error calling select() in get_request()");
return (ERROR_REQ);
}
else if ( rval == 0 ) {
/* input not ready after timeout */
return (TIMEOUT_REQ);
}
else {
/* We have an input line waiting, so retrieve it */
memset(buffer,0,MAX_REQ_LINE - 1);
if(Readline(conn, buffer, MAX_REQ_LINE - 1) == -1)
{
return (ERROR_REQ);
}
if(reqinfo->clientRequest == NULL)
{
reqinfo->clientRequest = calloc(MAX_REQ_LINE - 1, sizeof(char));
strncpy(reqinfo->clientRequest,buffer,MAX_REQ_LINE - 1);
}
else
{
strncat(reqinfo->clientRequest,buffer,MAX_REQ_LINE - 1);
}
Trim(buffer);
if ( buffer[0] == '\0' )
break;
if ( Parse_HTTP_Header(buffer, reqinfo) )
break;
}
} while ( reqinfo->type != SIMPLE );
return (GOT_REQ);
}
用英文描述这个服务器的工作原理：服务器接收到第一个请求。它解析标头，如果找到“Connection: Keep-Alive”标头，它会设置一个标志。服务器继续处理这个请求。完成后，它会检查 keep-alive 标志。如果清除，服务器将关闭连接。如果设置，服务器将执行清理操作，然后继续等待同一连接上的另一个请求。等等。
我用 curl 测试了这个：
C:\curl>curl -v -H "Connection: Keep-Alive" --data-binary @vid1.bin 10.84.67.129/s1p0:1/vid[1-2].bin
[1/2]: 10.84.67.129/s1p0:1/vid1.bin --> <stdout>
--_curl_--10.84.67.129/s1p0:1/vid1.bin
* About to connect() to 10.84.67.129 port 80 (#0)
* Trying 10.84.67.129...
* connected
* Connected to 10.84.67.129 (10.84.67.129) port 80 (#0)
> POST /s1p0:1/vid1.bin HTTP/1.1
> User-Agent: curl/7.28.1
> Host: 10.84.67.129
> Accept: */*
> Connection: Keep-Alive
> Content-Length: 51200
> Content-Type: application/x-www-form-urlencoded
> Expect: 100-continue
>
* HTTP 1.0, assume close after body
< HTTP/1.0 100 Continue
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Server: DTSVU v0.1
< Content-Type: text/html
* HTTP/1.0 connection set to keep alive!
< Connection: Keep-Alive
< Keep-Alive: timeout=5, max=10
<
* Connection #0 to host 10.84.67.129 left intact
[2/2]: 10.84.67.129/s1p0:1/vid2.bin --> <stdout>
--_curl_--10.84.67.129/s1p0:1/vid2.bin
* Connection #0 seems to be dead!
* Closing connection #0
* About to connect() to 10.84.67.129 port 80 (#0)
* Trying 10.84.67.129...
* connected
* Connected to 10.84.67.129 (10.84.67.129) port 80 (#0)
> POST /s1p0:1/vid2.bin HTTP/1.1
> User-Agent: curl/7.28.1
> Host: 10.84.67.129
> Accept: */*
> Connection: Keep-Alive
> Content-Length: 51200
> Content-Type: application/x-www-form-urlencoded
> Expect: 100-continue
>
* HTTP 1.0, assume close after body
< HTTP/1.0 100 Continue
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Server: DTSVU v0.1
< Content-Type: text/html
* HTTP/1.0 connection set to keep alive!
< Connection: Keep-Alive
< Keep-Alive: timeout=5, max=10
<
* Connection #0 to host 10.84.67.129 left intact
* Closing connection #0
如您所见，curl 说： Connection #0 似乎已死！在第一个请求完成后。然后它继续关闭连接并打开一个新连接。我确定我正确地实现了 HTTP 1.0 保持活动功能。所以我的问题是：第一个请求完成后 curl 对连接的期望是什么？为什么它决定连接已死？
PS上面的代码改编自http://www.paulgriffiths.net/program/c/webserv.php