AppletTalk.com Java discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Problem with Java TCP client to the C server          AppletTalk.com Forum Index -> Java Help View previous topic :: View next topic   Author Message Wonderer Guest Posted: Sun Apr 25, 2004 12:19 pm    Post subject: Problem with Java TCP client to the C server Hi there I am trying to use a Java client to write to a server written in C, but for some reason, the C server is just unable to read from the Java client, ALTHOUGH it can write perfectly to the Java client. The Java client reads from the C server using an InputStream object, but te inverse,OutputStream, fails to work when writing back to the C server. Why is that? Both my InputStream and OutputStream are derived from the same socket that I used to initialize a connection the C server. Is that why it's not working? Thanks Back to top Danny Woods Guest Posted: Sun Apr 25, 2004 12:35 pm    Post subject: Re: Problem with Java TCP client to the C server "Wonderer" <truth (AT) here (DOT) com> writes: Quote: The Java client reads from the C server using an InputStream object, but te inverse,OutputStream, fails to work when writing back to the C server. Why is that? Both my InputStream and OutputStream are derived from the same socket that I used to initialize a connection the C server. Is that why it's not working? Perhaps there's some buffering going on. Have you tried calling flush() against the OutputStream after you write to it? Danny. Back to top Andrew Thompson Guest Posted: Sun Apr 25, 2004 12:40 pm    Post subject: Re: Problem with Java TCP client to the C server On Sun, 25 Apr 2004 12:19:24 GMT, Wonderer wrote: Quote: I am trying to use a Java client to write to a server written in C, but for some reason, the C server is just unable to read from the Java client, ALTHOUGH it can write perfectly to the Java client. The Java client reads from the C server using an InputStream object, but te inverse,OutputStream, fails to work when writing back to the C server. Fails to work? How? Quote: Why is that? Both my InputStream and OutputStream are derived from the same socket that I used to initialize a connection the C server. Is that why it's not working? I am pretty sure that is it. Are you getting exceptions? <http://www.physci.org/codes/javafaq.jsp#exact> From my vague memory of a networking D'n'D list I made, was that it required two sockets, one for reading, one for writing [ My example _actually_ had four, so it was easy to feed either serialized objects or Strings, backwards and forwards. ] Try and make a pure Java exmaple that can communicate both ways, remove the 'inter-language' question until you get the pure Java side solved, then attack I/O with the C server as the second part. You might also have a look over the Networking FAQ, you can find the link here.. <http://www.physci.org/codes/javafaq.jsp#faq> Please note that three groups is probably too wide a cross-post. <http://www.physci.org/codes/javafaq.jsp#xpost> One of the groups is for Germany (de.?) but you seem comfortable with English, so I am setting the follow-ups to c.l.j.help -- Andrew Thompson http://www.PhySci.org/ Open-source software suite http://www.PhySci.org/codes/ Web & IT Help http://www.1point1C.org/ Science & Technology Back to top Gordon Beaton Guest Posted: Sun Apr 25, 2004 3:16 pm    Post subject: Re: Problem with Java TCP client to the C server On Sun, 25 Apr 2004 12:40:10 GMT, Andrew Thompson wrote: Quote: From my vague memory of a networking D'n'D list I made, was that it required two sockets, one for reading, one for writing That shouldn't be necessary at all - A TCP socket is two independent streams, one in each direction. You will get slightly better network performance by using a single socket in both directions, instead of two sockets, one for each direction (piggy-back ACKs, for example). Whatever the OP's problem is, he hasn't provided nearly enough information to help him (unless guessing counts). /gordon -- [ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e Back to top Steve Horsley Guest Posted: Sun Apr 25, 2004 3:31 pm    Post subject: Re: Problem with Java TCP client to the C server Wonderer wrote: Quote: Hi there I am trying to use a Java client to write to a server written in C, but for some reason, the C server is just unable to read from the Java client, ALTHOUGH it can write perfectly to the Java client. The Java client reads from the C server using an InputStream object, but te inverse,OutputStream, fails to work when writing back to the C server. Why is that? Both my InputStream and OutputStream are derived from the same socket that I used to initialize a connection the C server. Is that why it's not working? Thanks Without seeing code it's difficult to guess, but I have two comments: 1: Don't forget to call flush() at the end of sending your data. 2: C programmers often don't know exactly what they're sending over the wire. They often send images of structures as they are stored in memory without knowing what alignment padding has been used. A C source-code structure definition simply isn't adequate to define the network protocol. The best way to be sure what is expected is to use a protocol analyser (ethereal is good and free) to trace the C client working succesfully, and then wirte your java program to reproduce exactly what the C client sends. Steve Back to top Andrew Thompson Guest Posted: Sun Apr 25, 2004 3:34 pm    Post subject: Re: Problem with Java TCP client to the C server On 25 Apr 2004 17:16:49 +0200, Gordon Beaton wrote: Quote: On Sun, 25 Apr 2004 12:40:10 GMT, Andrew Thompson wrote: From my vague memory of a networking D'n'D list I made, was that it required two sockets, one for reading, one for writing That shouldn't be necessary at all - A TCP socket is two independent streams, one in each direction. Ooops! Glad I added the caveat.. Quote: Whatever the OP's problem is, he hasn't provided nearly enough information to help him (unless guessing counts). ;-) I'd go the example route.. <http://www.physci.org/codes/sscce.jsp> -- Andrew Thompson http://www.PhySci.org/ Open-source software suite http://www.PhySci.org/codes/ Web & IT Help http://www.1point1C.org/ Science & Technology Back to top Roedy Green Guest Posted: Sun Apr 25, 2004 7:23 pm    Post subject: Re: Problem with Java TCP client to the C server On Sun, 25 Apr 2004 12:19:24 GMT, "Wonderer" <truth (AT) here (DOT) com> wrote or quoted : Quote: Why is that? Both my InputStream and OutputStream are derived from the same socket that I used to initialize a connection the C server. Is that why it's not working? Try a packet sniffer to see if the fault lies with the receiver or sender. See http://mindprod.com/jgloss/sniffer.html Try a flush after each record or batch. Your stuff may be stuck in a BufferedOutputStream. The underlying socket layer may not have even seen it you. See http://mindprod.com/fileio.html for how to do raw socket i/o. -- Canadian Mind Products, Roedy Green. Coaching, problem solving, economical contract programming. See http://mindprod.com/jgloss/jgloss.html for The Java Glossary. Back to top Roedy Green Guest Posted: Sun Apr 25, 2004 7:25 pm    Post subject: Re: Problem with Java TCP client to the C server On 25 Apr 2004 17:16:49 +0200, Gordon Beaton <not (AT) for (DOT) email> wrote or quoted : Quote: Whatever the OP's problem is, he hasn't provided nearly enough information to help him (unless guessing counts). It is amazing how often you can solve a problem with a guess. Ask yourself, what are the 5 errors I have made in past working in that general area? Chances are one of them is the magic solution. I try to put them in http://mindprod.com/jgloss/gotchas.html -- Canadian Mind Products, Roedy Green. Coaching, problem solving, economical contract programming. See http://mindprod.com/jgloss/jgloss.html for The Java Glossary. Back to top Wonderer Guest Posted: Mon Apr 26, 2004 3:40 pm    Post subject: Re: Problem with Java TCP client to the C server "Gordon Beaton" <not (AT) for (DOT) email> wrote Quote: On Sun, 25 Apr 2004 12:40:10 GMT, Andrew Thompson wrote: From my vague memory of a networking D'n'D list I made, was that it required two sockets, one for reading, one for writing That shouldn't be necessary at all - A TCP socket is two independent streams, one in each direction. You will get slightly better network performance by using a single socket in both directions, instead of two sockets, one for each direction (piggy-back ACKs, for example). Whatever the OP's problem is, he hasn't provided nearly enough information to help him (unless guessing counts). /gordon Hey there, my basic problem right now is that on the C server side, I need to read and write to a Java client(really a web applet) when it connects and the C server accepts the connnection. The thing I realized is that if I read from this incoming connection, I cannot write to it anymore, and vice versa if I write to it first. Thus, I don't know how to get the server to identify whether the incoming connection will require data sent to OR from the Java client. Quote: -- [ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e Back to top Gordon Beaton Guest Posted: Mon Apr 26, 2004 3:57 pm    Post subject: Re: Problem with Java TCP client to the C server On Mon, 26 Apr 2004 15:40:36 GMT, Wonderer wrote: Quote: Hey there, my basic problem right now is that on the C server side, I need to read and write to a Java client(really a web applet) when it connects and the C server accepts the connnection. The thing I realized is that if I read from this incoming connection, I cannot write to it anymore, and vice versa if I write to it first. Thus, I don't know how to get the server to identify whether the incoming connection will require data sent to OR from the Java client. You should be able to do both without any kind of restrictions. That is until you close either the InputStream or the OutputStream, at which point the Socket itself is closed, preventing you using the other stream anymore. Exactly what happens when you try to write to it? Do you get an exception or what? Post it! Also post the relevent code - both client and server, both reading and writing. /gordon -- [ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e Back to top Thomas Schodt Guest Posted: Mon Apr 26, 2004 4:04 pm    Post subject: Re: Problem with Java TCP client to the C server Wonderer wrote: Quote: my basic problem right now is that on the C server side, I need to read and write to a Java client(really a web applet) when it connects and the C server accepts the connnection. The thing I realized is that if I read from this incoming connection, I cannot write to it anymore, and vice versa if I write to it first. You mean after you post a blocking read() you don't get control back meaning you can't write? I guess not, as you claim if you write() first you will not be able to read() ? Quote: Thus, I don't know how to get the server to identify whether the incoming connection will require data sent to OR from the Java client. Normally you'd have your client send a packet identifying what it wants immediately after connecting to the server. Something simple like "PUT" or "GET" ought to work. And the server will know it has to read 4 bytes first to find out what the client wants. Back to top Roedy Green Guest Posted: Mon Apr 26, 2004 7:36 pm    Post subject: Re: Problem with Java TCP client to the C server On Mon, 26 Apr 2004 17:04:56 +0100, Thomas Schodt <"news04jan"@"xenoc.demon.co.uk"> wrote or quoted : Quote: You mean after you post a blocking read() you don't get control back meaning you can't write? I guess not, as you claim if you write() first you will not be able to read() ? You have two streams with a socket, a read and a write. Both can work simultaneously, but obviously you need at least two threads, one for reading and one for writing. http://mindprod.com/jgloss/thread.html -- Canadian Mind Products, Roedy Green. Coaching, problem solving, economical contract programming. See http://mindprod.com/jgloss/jgloss.html for The Java Glossary. Back to top Roedy Green Guest Posted: Mon Apr 26, 2004 7:39 pm    Post subject: Re: Problem with Java TCP client to the C server On Mon, 26 Apr 2004 17:04:56 +0100, Thomas Schodt <"news04jan"@"xenoc.demon.co.uk"> wrote or quoted : Quote: Normally you'd have your client send a packet identifying what it wants immediately after connecting to the server. Something simple like "PUT" or "GET" ought to work. And the server will know it has to read 4 bytes first to find out what the client wants. In HTTP the server reads one message. It knows when to stop reading from the Content-Length field in the header. Then it digests the message, and sends back a response. If you have continuous streams of messages coming in and messages going out with no direct connection to each other, your server needs two threads per socket too (or a way of faking it). -- Canadian Mind Products, Roedy Green. Coaching, problem solving, economical contract programming. See http://mindprod.com/jgloss/jgloss.html for The Java Glossary. 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