藍色情懷

•  
  •  
    • Berkeley Sockets 概論

      ---

      Socket 的表面

      	「Berkeley Sockets」是一組專供網路通訊的系統呼叫（程式庫）。
      	當 process 想要進行網路通訊之前，要先向系統取得一個合法的 socket。各種 Berkeley Sockets 的系統呼叫，也都以這個 socket 為第一個參數。
      	和 UNIX 的檔案系統 file descriptor（檔案代碼）類似，socket descriptor 也是以一個 int 來表示。

      ---

      Socket 的內部

      	事 實上，在 UNIX 裡，socket descriptor 和 file descriptor 根本就是配置在同一個 descriptor table 裡頭的！所以，許多針對檔案做的 UNIX 系統呼叫，也能作用於 socket 上；很有 UNIX 的「大一統」精神。
      	每個 socket 背後，都伴有一個連帶的資料結構，用來紀錄網路通訊的狀態。主要的狀態計有：

      欄位	例子
      協定家族 （protocol family）	PF_INET（代表 TCP/IP 系列）。
      網路服務 （service）	SOCK_STREAM（代表 TCP）、SOCK_DGRAM（代表 UDP）、SOCK_RAW（代表 IP）。
      本地位址	140.113.23.33
      遠端位址	140.113.23.3
      本地通訊埠 （port）	5678
      遠端通訊埠	23

• Server

  •  有用的程式庫：

    passiveTCP	建立被動的 TCP socket 連線。 /* passiveTCP.c - passiveTCP */ int passivesock(const char *service, const char *transport, int qlen); /*------------------------------------------------------------------------ * passiveTCP - create a passive socket for use in a TCP server *------------------------------------------------------------------------ */ int passiveTCP(const char *service, int qlen) /* * Arguments: * service - service associated with the desired port * qlen - maximum server request queue length */ { return passivesock(service, "tcp", qlen); }
    passiveUDP	建立被動的 UCP socket 連線。 /* passiveUDP.c - passiveUDP */ int passivesock(const char *service, const char *transport, int qlen); /*------------------------------------------------------------------------ * passiveUDP - create a passive socket for use in a UDP server *------------------------------------------------------------------------ */ int passiveUDP(const char *service) /* * Arguments: * service - service associated with the desired port */ { return passivesock(service, "udp", 0); }
    passivesock	供 passiveUDP 和 passiveTCP 使用。 /* passivesock.c - passivesock */ #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <stdlib.h> #include <string.h> #include <netdb.h> extern int errno; int errexit(const char *format, ...); u_short portbase = 0; /* port base, for non-root servers */ /*------------------------------------------------------------------------ * passivesock - allocate & bind a server socket using TCP or UDP *------------------------------------------------------------------------ */ int passivesock(const char *service, const char *transport, int qlen) /* * Arguments: * service - service associated with the desired port * transport - transport protocol to use ("tcp" or "udp") * qlen - maximum server request queue length */ { struct servent *pse; /* pointer to service information entry */ struct protoent *ppe; /* pointer to protocol information entry*/ struct sockaddr_in sin; /* an Internet endpoint address */ int s, type; /* socket descriptor and socket type */ memset(&sin, 0, sizeof(sin)); sin.sin_family = AF_INET; sin.sin_addr.s_addr = INADDR_ANY; /* Map service name to port number */ if ( pse = getservbyname(service, transport) ) sin.sin_port = htons(ntohs((u_short)pse->s_port) + portbase); else if ( (sin.sin_port = htons((u_short)atoi(service))) == 0 ) errexit("can't get \"%s\" service entry\n", service); /* Map protocol name to protocol number */ if ( (ppe = getprotobyname(transport)) == 0) errexit("can't get \"%s\" protocol entry\n", transport); /* Use protocol to choose a socket type */ if (strcmp(transport, "udp") == 0) type = SOCK_DGRAM; else type = SOCK_STREAM; /* Allocate a socket */ s = socket(PF_INET, type, ppe->p_proto); if (s < 0) errexit("can't create socket: %s\n", strerror(errno)); /* Bind the socket */ if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) errexit("can't bind to %s port: %s\n", service, strerror(errno)); if (type == SOCK_STREAM && listen(s, qlen) < 0) errexit("can't listen on %s port: %s\n", service, strerror(errno)); return s; }

     Iterative connection-oriented server 和 iterative connectionless server 例子。

 Concurrent connectionless server 例子。

    同 Iterative connection-oriented server 範例

 Master server。

/* MasterTCPechod.c - main, reaper */

#include <sys/types.h>

#include <sys/signal.h>

#include <sys/socket.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/wait.h>
#include <sys/errno.h>
#include <netinet/in.h>


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

#define	QLEN		   5	/* maximum connection queue length	*/
#define	BUFSIZE		4096

extern int	errno;


void	reaper(int);

int	errexit(const char *format, ...);
int	passiveTCP(const char *service, int qlen);

/*------------------------------------------------------------------------
 * main - Master concurrent TCP server for ECHO service
 *------------------------------------------------------------------------
 */
int
main(int argc, char *argv[])
{
	char	*service = "echo";	/* service name or port number	*/
	struct	sockaddr_in fsin;	/* the address of a client	*/


	int	alen;			/* length of client's address	*/
	int	msock;			/* master server socket		*/
	int	ssock;			/* slave server socket		*/

	switch (argc) {
	case	1:
		break;
	case	2:
		service = argv[1];


		break;
	default:
		errexit("usage: TCPechod [port]\n");
	}

	msock = passiveTCP(service, QLEN);

	(void) signal(SIGCHLD, reaper);

	while (1) {
		alen = sizeof(fsin);
		ssock = accept(msock, (struct sockaddr *)&fsin, &alen);


		if (ssock < 0) {
			if (errno == EINTR)
				continue;
			errexit("accept: %s\n", strerror(errno));
		}
		switch (fork()) {
		case 0:		/* child */
			(void) close(msock);
			dup2(ssock, 0);


			dup2(ssock, 1);
			dup2(ssock, 2);
			exit(exec(SlaveTCPechod));
		default:	/* parent */
			(void) close(ssock);
			break;
		case -1:
			errexit("fork: %s\n", strerror(errno));

		}

	}
}



/*------------------------------------------------------------------------
 * reaper - clean up zombie children
 *------------------------------------------------------------------------
 */
/*ARGSUSED*/
void
reaper(int sig)
{
	int	status;

	while (wait3(&status, WNOHANG, (struct rusage *)0) >= 0)
		/* empty */;
}

 Slave server。

•  

  • /* SlaveTCPechod.c - main */
    
    #include <unistd.h>
    #include <
    stdlib.h>
    
    #include <stdio.h>
    #include <string.h>
    
    #define	BUFSIZE		4096
    
    extern int	errno;
    
    int	errexit(const char *format, ...);
    
    /*------------------------------------------------------------------------
    
    
     * main - Slave concurrent TCP server for ECHO service
            - echo data until end of file
     *------------------------------------------------------------------------
     */
    int
    main()
    {
    	char	buf[BUFSIZ];
    
    
    	int	cc;
    
    	while (cc = read(0, buf, sizeof buf)) {
    		if (cc < 0)
    			errexit("echo read: %s\n", strerror(errno));
    		if (write(0, buf, cc) < 0)
    			errexit("echo write: %s\n", strerror(errno));
    
    
    	}
    	return 0;
    }

     Multi-Process concurrent connection-oriented server 例子。
    

/* TCPechod.c - main, TCPechod, reaper */

#include <sys/types.h>

#include <sys/signal.h>

#include <sys/socket.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/wait.h>
#include <sys/errno.h>
#include <netinet/in.h>


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

#define	QLEN		   5	/* maximum connection queue length	*/
#define	BUFSIZE		4096

extern int	errno;


void	reaper(int);

int	TCPechod(int fd);
int	errexit(const char *format, ...);
int	passiveTCP(const char *service, int qlen);

/*------------------------------------------------------------------------
 * main - Multi-Process Concurrent TCP server for ECHO service
 *------------------------------------------------------------------------
 */
int
main(int argc, char *argv[])
{
	char	*service = "echo";	/* service name or port number	*/

	struct	sockaddr_in fsin;	/* the address of a client	*/

	int	alen;			/* length of client's address	*/
	int	msock;			/* master server socket		*/
	int	ssock;			/* slave server socket		*/

	switch (argc) {

	case	1:
		break;
	case	2:
		service = argv[1];

		break;
	default:
		errexit("usage: TCPechod [port]\n");
	}

	msock = passiveTCP(service, QLEN);

	(void) signal(SIGCHLD, reaper);


	while (1) {
		alen = sizeof(fsin);
		ssock = accept(msock, (struct sockaddr *)&fsin, &alen);

		if (ssock < 0) {
			if (errno == EINTR)
				continue;
			errexit("accept: %s\n", strerror(errno));

		}
		switch (fork()) {
		case 0:		/* child */
			(void) close(msock);
			exit(TCPechod(ssock));

		default:	/* parent */
			(void) close(ssock);
			break;
		case -1:
			errexit("fork: %s\n", strerror(errno));

		}
	}
}

/*------------------------------------------------------------------------

 * TCPechod - echo data until end of file
 *------------------------------------------------------------------------

 */
int
TCPechod(int fd)
{
	char	buf[BUFSIZ];
	int	cc;

	while (cc = read(fd, buf, sizeof buf)) {

		if (cc < 0)
			errexit("echo read: %s\n", strerror(errno));
		if (write(fd, buf, cc) < 0)

			errexit("echo write: %s\n", strerror(errno));
	}
	return 0;
}

/*------------------------------------------------------------------------

 * reaper - clean up zombie children
 *------------------------------------------------------------------------

 */
/*ARGSUSED*/
void
reaper(int sig)
{
	int	status;

	while (wait3(&status, WNOHANG, (struct rusage *)0) >= 0)

		/* empty */;
}

•  

  •  Single-Process concurrent connection-oriented server 例子。

/* TCPmechod.c - main, echo */

#include <sys/types.h>


#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>

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

#define	QLEN		   5	/* maximum connection queue length	*/


#define	BUFSIZE		4096

extern int	errno;
int		errexit(const char *format, ...);
int		passiveTCP(const char *service, int qlen);
int		echo(int fd);

/*------------------------------------------------------------------------


 * main - Single Process Concurrent TCP server for ECHO service
 *------------------------------------------------------------------------
 */
int
main(int argc, char *argv[])
{
	char	*service = "echo";	/* service name or port number	*/


	struct sockaddr_in fsin;	/* the from address of a client	*/
	int	msock;			/* master server socket		*/
	fd_set	rfds;			/* read file descriptor set	*/
	fd_set	afds;			/* active file descriptor set	*/
	int	alen;			/* from-address length		*/


	int	fd, nfds;
	
	switch (argc) {
	case	1:
		break;
	case	2:
		service = argv[1];
		break;
	default:
		errexit("usage: TCPmechod [port]\n");
	}

	msock = passiveTCP(service, QLEN);



	nfds = getdtablesize();
	FD_ZERO(&afds);
	FD_SET(msock, &afds);

	while (1) {
		memcpy(&rfds, &afds, sizeof(rfds));

		if (select(nfds, &rfds, (fd_set *)0, (fd_set *)0,


				(struct timeval *)0) < 0)
			errexit("select: %s\n", strerror(errno));
		if (FD_ISSET(msock, &rfds)) {
			int	ssock;

			alen = sizeof(fsin);
			ssock = accept(msock, (struct sockaddr *)&fsin,


				&alen);
			if (ssock < 0)
				errexit("accept: %s\n",
					strerror(errno));
			FD_SET(ssock, &afds);
		}
		for (fd=0; fd<nfds; ++fd)
			if (fd != msock && FD_ISSET(fd, &rfds))


				if (echo(fd) == 0) {
					(void) close(fd);
					FD_CLR(fd, &afds);
				}
	}
}

/*------------------------------------------------------------------------
 * echo - echo one buffer of data, returning byte count


 *------------------------------------------------------------------------
 */
int
echo(int fd)
{
	char	buf[BUFSIZ];
	int	cc;

	cc = read(fd, buf, sizeof buf);
	if (cc < 0)
		errexit("echo read: %s\n", strerror(errno));


	if (cc && write(fd, buf, cc) < 0)
		errexit("echo write: %s\n", strerror(errno));
	return cc;
}

• Client

  •  有用的程式庫：

    connectTCP	建立 TCP socket 連線。 /* connectTCP.c - connectTCP */ int connectsock(const char *host, const char *service, const char *transport); /*------------------------------------------------------------------------ * connectTCP - connect to a specified TCP service on a specified host *------------------------------------------------------------------------ */ int connectTCP(const char *host, const char *service ) /* * Arguments: * host - name of host to which connection is desired * service - service name associated with the desired port * or port # in ASCII string, eg. "23" */ { return connectsock( host, service, "tcp"); }
    connectUDP	建立 UDP socket 連線。 /* connectUDP.c - connectUDP */ int connectsock(const char *host, const char *service, Const char *transport); /*------------------------------------------------------------------------ * connectUDP - connect to a specified UDP service on a specified host *------------------------------------------------------------------------ */ int connectUDP(const char *host, const char *service ) /* * Arguments: * host - name of host to which connection is desired * service - service name associated with the desired port * or port # in ASCII, eg. "23" */ { return connectsock(host, service, "udp"); }
    connectsock	供 connectTCP 和 connectUDP 使用。 /* connectsock.c - connectsock */ #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> #include <string.h> #include <stdlib.h> #ifndef INADDR_NONE #define INADDR_NONE 0xffffffff #endif /* INADDR_NONE */ extern int errno; int errexit(const char *format, ...); /*------------------------------------------------------------------------ * connectsock - allocate & connect a socket using TCP or UDP *------------------------------------------------------------------------ */ int connectsock(const char *host, const char *service, const char *transport ) /* * Arguments: * host - name of host to which connection is desired * service - service associated with the desired port * transport - name of transport protocol to use ("tcp" or "udp") */ { struct hostent *phe; /* pointer to host information entry */ struct servent *pse; /* pointer to service information entry */ struct protoent *ppe; /* pointer to protocol information entry*/ struct sockaddr_in sin; /* an Internet endpoint address */ int s, type; /* socket descriptor and socket type */ memset(&sin, 0, sizeof(sin)); sin.sin_family = AF_INET; /* Map service name to port number */ if ( pse = getservbyname(service, transport) ) sin.sin_port = pse->s_port; else if ( (sin.sin_port = htons((u_short)atoi(service))) == 0 ) errexit("can't get \"%s\" service entry\n", service); /* Map host name to IP address, allowing for dotted decimal */ if ( phe = gethostbyname(host) ) memcpy(&sin.sin_addr, phe->h_addr, phe->h_length); else if ( (sin.sin_addr.s_addr = inet_addr(host)) == INADDR_NONE ) errexit("can't get \"%s\" host entry\n", host); /* Map transport protocol name to protocol number */ if ( (ppe = getprotobyname(transport)) == 0) errexit("can't get \"%s\" protocol entry\n", transport); /* Use protocol to choose a socket type */ if (strcmp(transport, "udp") == 0) type = SOCK_DGRAM; else type = SOCK_STREAM; /* Allocate a socket */ s = socket(PF_INET, type, ppe->p_proto); if (s < 0) errexit("can't create socket: %s\n", strerror(errno)); /* Connect the socket */ if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) errexit("can't connect to %s.%s: %s\n", host, service, strerror(errno)); return s; }
    errexit	讓 connectsock 顯示錯誤訊息並結束程式之用。 /* errexit.c - errexit */ #include <stdarg.h> #include <stdio.h> #include <stdlib.h> /*------------------------------------------------------------------------ * errexit - print an error message and exit *------------------------------------------------------------------------ */ /*VARARGS1*/ int errexit(const char *format, ...) { va_list args; va_start(args, format); vfprintf(stderr, format, args); va_end(args); exit(1); }

     TCP client 例子。

 

/* 
TCPecho.c - main, TCPecho */

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

extern int	errno;

int	TCPecho(const char *host, const char *service);


int	errexit(const char *format, ...);
int	connectTCP(const char *host, const char *service);

#define	LINELEN		128

/*------------------------------------------------------------------------
 * main - TCP client for ECHO service


 *------------------------------------------------------------------------
 */
int
main(int argc, char *argv[])
{
	char	*host = "localhost";	/* host to use if none supplied	*/
	char	*service = "echo";	/* default service name		*/



	switch (argc) {
	case 1:
		host = "localhost";
		break;
	case 3:
		service = argv[2];
		/* FALL THROUGH */
	case 2:
		host = argv[1];
		break;
	default:
		fprintf(stderr, "usage: TCPecho [host [port]]\n");


		exit(1);
	}
	TCPecho(host, service);
	exit(0);
}

/*------------------------------------------------------------------------
 * TCPecho - send input to ECHO service on specified host and print reply


 *------------------------------------------------------------------------
 */
int
TCPecho(const char *host, const char *service)
{
	char	buf[LINELEN+1];		/* buffer for one line of text	*/
	int	s, n;			/* socket descriptor, read count*/


	int	outchars, inchars;	/* characters sent and received	*/

	s = connectTCP(host, service);

	while (fgets(buf, sizeof(buf), stdin)) {
		buf[LINELEN] = '\0';	/* insure line null-terminated	*/


		outchars = strlen(buf);
		(void) write(s, buf, outchars);

		/* read it back */
		for (inchars = 0; inchars < outchars; inchars+=n ) {
			n = read(s, &buf[inchars], outchars - inchars);

			if (n < 0)

				errexit("socket read failed: %s\n",
					strerror(errno));
		}
		fputs(buf, stdout);
	}
}

•  

  •  UDP client 例子。

/* UDPecho.c - main, UDPecho */

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

extern int	errno;

int	UDPecho(const char *host, const char *service);


int	errexit(const char *format, ...);
int	connectUDP(const char *host, const char *service);

#define	LINELEN		128

/*------------------------------------------------------------------------
 * main - UDP client for ECHO service


 *------------------------------------------------------------------------
 */
int
main(int argc, char *argv[])
{
	char	*host = "localhost";
	char	*service = "echo";

	switch (argc) {


	case 1:
		host = "localhost";
		break;
	case 3:
		service = argv[2];
		/* FALL THROUGH */
	case 2:
		host = argv[1];
		break;
	default:
		fprintf(stderr, "usage: UDPecho [host [port]]\n");


		exit(1);
	}
	UDPecho(host, service);
	exit(0);
}

/*------------------------------------------------------------------------
 * UDPecho - send input to ECHO service on specified host and print reply


 *------------------------------------------------------------------------
 */
int
UDPecho(const char *host, const char *service)
{
	char	buf[LINELEN+1];		/* buffer for one line of text	*/
	int	s, nchars;		/* socket descriptor, read count*/



	s = connectUDP(host, service);

	while (fgets(buf, sizeof(buf), stdin)) {
		buf[LINELEN] = '\0';	/* insure null-terminated */
		nchars = strlen(buf);
		(void) write(s, buf, nchars);



		if (read(s, buf, nchars) < 0)
			errexit("socket read failed: %s\n",
					strerror(errno));
		fputs(buf, stdout);
	}
}

 Concurrent TCP client 例子。

/* TCPtecho.c - main, TCPtecho, reader, writer, mstime */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/socket.h>



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

extern int	errno;

int	TCPtecho(fd_set *pafds, int nfds, int ccount, int hcount);

int	reader(int fd, fd_set *pfdset);

int	writer(int fd, fd_set *pfdset);
int	errexit(const char *format, ...);
int	connectTCP(const char *host, const char *service);
long	mstime(u_long *);

#define	BUFSIZE		4096		/* write buffer size		*/


#define	CCOUNT		64*1024		/* default character count	*/

#define	USAGE	"usage: TCPtecho [ -c count ] host1 host2...\n"

char	*hname[NOFILE];			/* fd to host name mapping	*/
int	rc[NOFILE], wc[NOFILE];		/* read/write character counts	*/


char	buf[BUFSIZE];			/* read/write data buffer	*/


/*------------------------------------------------------------------------
 * main - concurrent TCP client for ECHO service timing
 *------------------------------------------------------------------------


 */
int
main(int argc, char *argv[])
{
	int	ccount = CCOUNT;
	int	i, hcount, maxfd, fd;
	int	one = 1;
	fd_set	afds;

	hcount = 0;
	maxfd = -1;
	for (i=1; i<argc; ++i) {
		if (strcmp(argv[i], "-c") == 0) {


			if (++i < argc && (ccount = atoi(argv[i])))
				continue;
			errexit(USAGE);
		}
		/* else, a host */

		fd = connectTCP(argv[i], "echo");
		if (ioctl(fd, FIONBIO, (char *)&one))


			errexit("can't mark socket nonblocking: %s\n",
				strerror(errno));
		if (fd > maxfd)
			maxfd = fd;
		hname[fd] = argv[i];
		++hcount;
		FD_SET(fd, &afds);
	}
	TCPtecho(&afds, maxfd+1, ccount, hcount);


	exit(0);
}

/*------------------------------------------------------------------------
 * TCPtecho - time TCP ECHO requests to multiple servers
 *------------------------------------------------------------------------


 */
int
TCPtecho(fd_set *pafds, int nfds, int ccount, int hcount)
{
	fd_set	rfds, wfds;		/* read/write fd sets		*/
	fd_set	rcfds, wcfds;		/* read/write fd sets (copy)	*/
	int	fd, i;

	for (i=0; i<BUFSIZE; ++i)	/* echo data	*/


		buf[i] = 'D';
	memcpy(&rcfds, pafds, sizeof(rcfds));
	memcpy(&wcfds, pafds, sizeof(wcfds));
	for (fd=0; fd<nfds; ++fd)
		rc[fd] = wc[fd] = ccount;

	(void) mstime((u_long *)0);	/* set the epoch */



	while (hcount) {
		memcpy(&rfds, &rcfds, sizeof(rfds));
		memcpy(&wfds, &wcfds, sizeof(wfds));

		if (select(nfds, &rfds, &wfds, (fd_set *)0,
				(struct timeval *)0) < 0)


			errexit("select failed: %s\n", strerror(errno));
		for (fd=0; fd<nfds; ++fd) {
			if (FD_ISSET(fd, &rfds))
				if (reader(fd, &rcfds) == 0)
					hcount--;
			if (FD_ISSET(fd, &wfds))


				writer(fd, &wcfds);
		}
	}
}

/*------------------------------------------------------------------------
 * reader - handle ECHO reads
 *------------------------------------------------------------------------


 */
int
reader(int fd, fd_set *pfdset)
{
	u_long	now;
	int	cc;

	cc = read(fd, buf, sizeof(buf));
	if (cc < 0)
		errexit("read: %s\n", strerror(errno));
	if (cc == 0)

		errexit("read: premature end of file\n");

	rc[fd] -= cc;
	if (rc[fd])
		return 1;
	(void) mstime(&now);
	printf("%s: %d ms\n", hname[fd], now);
	(void) close(fd);
	FD_CLR(fd, pfdset);

	return 0;
}

/*------------------------------------------------------------------------

 * writer - handle ECHO writes
 *------------------------------------------------------------------------

 */
int
writer(int fd, fd_set *pfdset)
{
	int	cc;

	cc = write(fd, buf, MIN(sizeof(buf), wc[fd]));

	if (cc < 0)
		errexit("read: %s\n", strerror(errno));
	wc[fd] -= cc;
	if (wc[fd] == 0) {

		(void) shutdown(fd, 1);
		FD_CLR(fd, pfdset);
	}
}

/*------------------------------------------------------------------------

 * mstime - report the number of milliseconds since Jan 1, 1970

 *------------------------------------------------------------------------
 */
long
mstime(u_long *pms)
{
	static struct timeval	epoch;

	struct timeval		now;

	if (gettimeofday(&now, (struct timezone *)0))

		errexit("gettimeofday: %s\n", strerror(errno));
	if (!pms) {
		epoch = now;
		return 0;
	}
	*pms = (now.tv_sec
 - epoch.tv_sec) * 1000;
	*pms += (now.tv_usec - epoch.tv_usec + 500)/ 1000;

	return *pms;
}