Date: Mon, 23 Oct 2000 23:06:14 -0700 From: "Justin C. Walker" <justin@apple.com> To: "'freebsd-net@freebsd.org'" <freebsd-net@freebsd.org> Subject: Re: Socket programming, strange recv reaction Message-ID: <200010240606.XAA03131@scv1.apple.com>
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A quick check shows that you're sending 128 bytes each time around the =
server loop, but only reading 100 bytes around the receiver loop. =
Therefore, you fall behind by 28 bytes each time. Since the "non =
message" bytes are likely to be zero, you appear to be reading no bytes =
(when you print the string in 'buf', the first character is 'nul').
If you examine the received buffer with gdb, you'll see that your =
message arrives, but it is offset because of the difference between =
bytes sent and bytes read.
Regards,
Justin
On Monday, October 23, 2000, at 05:10 PM, TAZ Gravel, Emmanuel wrote:
> I'm trying to write a small client-server pair using TCP sockets.=20
> I'm not changing the default blocking mechanisms for recv().=20
> The client connects to the server, which sends it a welcome=20
> message. Then, the client sends ASCII "commands" that are=20
> interpreted by the server (recv'ed, strcmp'ed and answered to).=20
> If the command is "unknown" it echoes it back to the client=20
> using send(). The client, on the other end, is "waiting" with a=20
> recv().=20
> =20
> Appart from the first message sent by the client, most others=20
> were never echoed back to the client, and when one arrived, it=20
> was from a previous message, anywhere between 2 and 8 iterations=20
> previous to the one that was just sent. Using ethereal to analyze=20
> the traffic, and blocking the server with a 5 second sleep, showed=20
> that the recv in the client was accepting a simple ACK message=20
> as an acceptable message. The "conversation" is all [PSH, ACK]=20
> or [ACK]. Ethereal was set to look at the loopback interface to=20
> see this happening, and for some reason all packets were=20
> "duplicated" (same time frame, same exact packet, always in=20
> pairs). Don't know if this has anything to do with it or not=20
> though.=20
> =20
> I know the problem centers around the recv in the client, however=20
> I don't know where to look. Just starting to look at socket=20
> programming, and using tutorials and newbie code found online=20
> (using Beej's Guide to Network Programming right now).=20
> =20
> Read the man page for recv() also, and since it's supposed to=20
> be blocking until something is recieved, I don't know what to=20
> make of this.=20
> =20
> Inlining my code since I'm using Outlook right now...=20
> =20
> Thanks for your help!=20
> =20
> Emmanuel=20
> =20
> <server code>=20
> #include <stdio.h>=20
> #include <stdlib.h>=20
> #include <errno.h>=20
> #include <signal.h>=20
> #include <string.h>=20
> #include <unistd.h>=20
> #include <sys/types.h>=20
> #include <netinet/in.h>=20
> #include <sys/socket.h>=20
> #include <sys/wait.h>=20
> #include <arpa/inet.h>=20
> =20
> #define MYPORT 4039 /* the port users will be connecting to */=20
> =20
> #define MAXBUFLEN 128=20
> =20
> #define BACKLOG 10 /* how many pending connections queue will hold =
*/=20
> #define MAXCHILD 5=20
> =20
> /* Global variables */=20
> =20
> int sockfd; /* listen on sock_fd */=20
> int child[MAXCHILD];=20
> =20
> =20
> void usage(newfd)=20
> int newfd;=20
> {=20
> char *msg;=20
> int numbytes;=20
> printf("Sending usage information.\n");=20
> msg =3D "Usage:\n\thello: returns a message.\n\tquit: exits the =
session.\n";=20
> if ((numbytes =3D send(newfd, msg, MAXBUFLEN, 0)) =3D=3D -1) {=20
> perror("send");=20
> exit(1); =20
> }=20
> printf("Sent [%i] bytes.\nMessage sent is %s\n",numbytes,msg);=20
> }=20
> =20
> void hello(newfd,buf)=20
> int newfd;=20
> char *buf;=20
> {=20
> char msg[128] =3D "You said: ";=20
> int numbytes;=20
> printf("Entering hello \n");=20
> printf("Replying to [%s].\n",buf);=20
> strcat(msg,buf);=20
> printf("first strcat\n");=20
> strcat(msg,"\n");=20
> printf("sending message now\n");=20
> sleep(5);=20
> if ((numbytes =3D send(newfd, msg, MAXBUFLEN, 0)) =3D=3D -1) {=20
> perror("send");=20
> close(newfd);=20
> exit(1);=20
> }=20
> printf("Sent [%i] bytes.\nMessage sent is [%s]\n",numbytes,msg);=20
> }=20
> =20
> void bye(newfd)=20
> int newfd;=20
> {=20
> /* signal(SIGINT, finalize); */=20
> /* Only usefull in programs not exiting after signal trap */=20
> char *msg;=20
> msg =3D "Closing connection. Goodbye!\n";=20
> printf("in bye\n");=20
> if (send(newfd, msg, sizeof(msg), 0) =3D=3D -1) {=20
> printf("error in sending\n");=20
> perror("send");=20
> close(newfd);=20
> exit(1);=20
> }=20
> printf("closing now\n");=20
> close(newfd);=20
> printf("Closing connection. Child PID is [%i]. \n",getpid());=20
> exit(0);=20
> }=20
> =20
> void finalize()=20
> { =20
> printf("Closing all connections\n");=20
> while(waitpid(-1,NULL,0) > 0); /* clean up all child processes */=20
> close(sockfd);=20
> exit(0);=20
> }=20
> =20
> =20
> int main()=20
> {=20
> int new_fd; /* new connection on new_fd */=20
> int sin_size;=20
> struct sockaddr_in my_addr; /* my address information */=20
> struct sockaddr_in their_addr; /* connector's address information =
*/=20
> int numberbytes;=20
> /* int i, addre_len; */=20
> char buf[MAXBUFLEN];=20
> unsigned short int children;=20
> =20
> if ((sockfd =3D socket(AF_INET, SOCK_STREAM, 0)) =3D=3D -1) {=20
> perror("socket");=20
> exit(1);=20
> }=20
> =20
> signal(SIGINT, finalize);=20
> =20
> my_addr.sin_family =3D AF_INET; /* host byte order */=20
> my_addr.sin_port =3D htons(MYPORT); /* short, network byte =
order */=20
> my_addr.sin_addr.s_addr =3D INADDR_ANY; /* automatically fill with =
my IP=20
> */=20
> bzero(&(my_addr.sin_zero), 8); /* zero the rest of the =
struct */=20
> =20
> if (bind(sockfd, (struct sockaddr *)&my_addr,=20
> sizeof(struct sockaddr)) =3D=3D -1) {=20
> perror("bind");=20
> exit(1);=20
> }=20
> =20
> if (listen(sockfd, BACKLOG) =3D=3D -1) {=20
> perror("listen");=20
> exit(1);=20
> }=20
> =20
> children =3D 0;=20
> =20
> while(1) { /* main accept() loop */=20
> sin_size =3D sizeof(struct sockaddr_in);=20
> =20
> if (children < MAXCHILD) {=20
> if ((new_fd =3D accept(sockfd,=20
> (struct sockaddr *)&their_addr,=20
> &sin_size)) =3D=3D -1) {=20
> perror("accept");=20
> continue;=20
> }=20
> printf("server: got connection from [%s]\n",=20
> inet_ntoa(their_addr.sin_addr));=20
> if (!fork()) { /* this is the child process */=20
> /* Anything that happens here is only executed by the child,=20=
> * and that's the only thing that the child executes. */=20
> if (send(new_fd,=20
> "Welcome to my world!\nWhat is your pleasure?\n",=20=
> 44, 0) =3D=3D -1) {=20
> perror("send");=20
> close(new_fd);=20
> exit(1);=20
> }=20
> =20
> while(1) {=20
> =20
> if ((numberbytes =3D recv(new_fd,buf,MAXBUFLEN,0)) =3D=3D =
-1) {=20
> perror("recv");=20
> continue;=20
> }=20
> =20
> buf[numberbytes] =3D '\0';=20
> =20
> printf("numberbytes =3D [%i]\nbuffer =3D =
[%s]\n",numberbytes,buf);=20
> =20
> if(!strcmp(buf, "")) {=20
> printf("printing usage\n");=20
> usage(new_fd);=20
> }=20
> else if(!strncmp(buf, "quit", 4)) {=20
> printf("calling bye\n");=20
> bye(new_fd);=20
> }=20
> else {=20
> printf("calling hello\n");=20
> hello(new_fd,buf);=20
> }=20
> }=20
> }=20
> }=20
> /* clean up all child processes */=20
> while(waitpid(-1,NULL,WNOHANG) > 0);=20
> }=20
> }=20
> =20
> <client code>=20
> #include <stdio.h>=20
> #include <stdlib.h>=20
> #include <errno.h>=20
> #include <string.h>=20
> #include <netdb.h>=20
> #include <unistd.h>=20
> #include <sys/types.h>=20
> #include <netinet/in.h>=20
> #include <sys/socket.h>=20
> #include <sys/wait.h>=20
> #include <arpa/inet.h>=20
> =20
> #define PORT 4039 /* the port client will be connecting to */=20
> =20
> #define MAXDATASIZE 100 /* max number of bytes we can get at once */=20=
> =20
> int main(int argc, char *argv[])=20
> {=20
> int sockfd, numbytes; =20
> char buf[MAXDATASIZE],msg[MAXDATASIZE] =3D "sta";=20
> struct hostent *he;=20
> struct sockaddr_in their_addr; /* connector's address information */=20=
> =20
> /* printf("Before init\n");=20
> */=20
> if (argc !=3D 2) {=20
> fprintf(stderr,"usage: manuclient hostname\n"); /* put actual =
error=20
> message here */=20
> exit(1);=20
> }=20
> =20
> /*printf("Before gethostbyname\n");=20
> */=20
> if ((he=3Dgethostbyname(argv[1])) =3D=3D NULL) { /* get the host =
info */=20
> perror("gethostbyname");=20
> exit(1);=20
> }=20
> =20
> /*printf("Host is %s\nBeofre socket creation\n", *((struct in_addr=20=
> *)he->h_addr));=20
> */=20
> if ((sockfd =3D socket(AF_INET, SOCK_STREAM, 0)) =3D=3D -1) {=20
> perror("socket");=20
> exit(1);=20
> }=20
> =20
> /* printf("Socket created. Before socket connection.\n");=20
> */=20
> their_addr.sin_family =3D AF_INET; /* host byte order */=20
> their_addr.sin_port =3D htons(PORT); /* short, network byte =
order */=20
> their_addr.sin_addr =3D *((struct in_addr *)he->h_addr);=20
> bzero(&(their_addr.sin_zero), 8); /* zero the rest of the =
struct */=20
> =20
> if (connect(sockfd, (struct sockaddr *)&their_addr, sizeof(struct=20
> sockaddr)) =3D=3D -1) {=20
> perror("connect");=20
> exit(1);=20
> }=20
> =20
> /*printf("Socket connected. Before while loop, value is=20
> %i\n",strcmp(msg,"quit"));=20
> */=20
> while(strcmp(msg,"quit")) { /* Begin chat routine with the server =
*/=20
> =20
> printf("Before recv\n");=20
> /*sleep(5);*/=20
> =20
> if ((numbytes=3Drecv(sockfd, buf, MAXDATASIZE, 0)) =3D=3D -1) {=20
> perror("recv");=20
> exit(1);=20
> }=20
> =20
> printf("After recv\n");=20
> =20
> buf[numbytes] =3D '\0';=20
> =20
> printf("Received: %s\n",buf);=20
> =20
> printf("Command > ");=20
> =20
> scanf("%s",msg);=20
> =20
> /* if (sizeof(msg) >=3D MAXDATASIZE)=20
> msg[MAXDATASIZE] =3D '\0';=20
> */=20
> printf("Size of message is %i\n",sizeof(msg));=20
> =20
> if ((numbytes =3D send(sockfd, msg, MAXDATASIZE, 0)) =3D=3D -1) {=20=
> perror("send");=20
> exit(1);=20
> }=20
> =20
> printf("sent message %s to %s\nNumber of bytes sent is=20
> %i\n",msg,inet_ntoa(their_addr.sin_addr),numbytes);=20
> =20
> if(!strcmp(msg,"quit"))=20
> printf("Recieved quit command, exiting!\n");=20
> =20
> }=20
> =20
> close(sockfd);=20
> =20
> return 0;=20
> }=20
> =20
Justin C. Walker, Curmudgeon-At-Large *
Institute for General Semantics |
Manager, CoreOS Networking | When LuteFiske is outlawed
Apple Computer, Inc. | Only outlaws will have
2 Infinite Loop | LuteFiske
Cupertino, CA 95014 |
=
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