Socket programming - Java server, C (or other) client - server gives "invalid stream header"

Question

Server (java):

public static void main(String[] args) {


//single threaded for now

try {

    //very magic #
    ServerSocket service = new ServerSocket(33000); 

    while(true) {

    debug("Begin waiting for connection");

    //this spins
    Socket connection = service.accept();

    debug("Connection received from " + connection.getInetAddress().getHostName());

    ObjectOutputStream out = new ObjectOutputStream(connection.getOutputStream());
    ObjectInputStream in = new ObjectInputStream(connection.getInputStream());

// ...

client (C) - this is exactly the sample code from http://www.linuxhowtos.org/data/6/client.c

int main(int argc, char *argv[])
{
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;

char buffer[256];
if (argc < 3) {
   fprintf(stderr,"usage %s hostname port\n", argv[0]);
   exit(0);
}
portno = atoi(argv[2]);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
    error("ERROR opening socket");
server = gethostbyname(argv[1]);
if (server == NULL) {
    fprintf(stderr,"ERROR, no such host\n");
    exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
     (char *)&serv_addr.sin_addr.s_addr,
     server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
    error("ERROR connecting");
printf("Please enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0)
     error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);
if (n < 0)
     error("ERROR reading from socket");
printf("%s\n",buffer);
close(sockfd);
return 0;
}

Java is not happy:

Begin waiting for connection
Connection received from localhost
Fatal Exception: invalid stream header: 68657920
java.io.StreamCorruptedException: invalid stream header: 68657920
        at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:801)
        at java.io.ObjectInputStream.<init>(ObjectInputStream.java:298)
        at Scanner.main(Scanner.java:243)

line 243 is:

ObjectInputStream in = new ObjectInputStream(connection.getInputStream());

The C client works with the C server, and the C server works with my Python client. Similar Java servers I've written have worked with Java clients. So as far as I can tell there's some magic words to get Java server -> non-Java client. Sorry, I've had no luck on the Google with this, despite it being obviously very basic and simple. Thanks.

Answer 1

You're using an ObjectInputStream on the Java side, which expects a very specific protocol of serialized Java objects. Unless you write the correct format to the socket from the C client, this is exactly the error you will get. You haven't shown how you try to read from the stream, but I suspect you just want a BufferedInputStream instead.