Thread: Client works on a LAN but don't send all the data

Hello, I have been having problems with my client because isn't able to send all the data (or that's what I think). The scenario is the next:

- 2 pc on the same LAN (both windows XP)
- 1 server (my own server, not a professional server ) on the pc #1. That server can get a param from the header (like HTTP params) 'ECHO<crlf>' that internally means 'Return the same message you receive': if the recv header have a 'Content-Length: 0<crlf>' then sends a 'Hello from server'; else sends the content message.
- 1 client (also my own client, less professional than the server) on pc #1. That client sends an HTTP header like

Code:

POST / HTTP/1.0<crlf>
Connection: Close<crlf>
User-Agent: DemoClient/1.0<crlf>
Host:123.456.789.0<crlf>
Accept: */*<crlf>
ECHO<crlf>
Content-Length: 4<crlf>
<crlf>
test<crlf>

Ok, I run the server on pc#1 and the client on pc#1, the client send all the data, the server recv it all and resend 'test'. It works well.

After that, from pc #2 I run the internet browser, connect to my server index page, download the client program from pc#1 (so may I think that the server doesn't have any problem, or any important problem, because I can browse through the server's index page, several links, several formats and there's no problem). Right, now I have the client on pc#2, I run it, send all the data but on the server only arrive since the '<crlf><crlf>', the message 'test' remains I-don't-know-where, the server returns nothing, and whil terminating the conexion I get some unexpected last bytes, exactly 4 bytes, and if I printf them are the message content sended by the client.
Why does it happens when working from different pc but not when I'm work on the same? The server should work well because I can recv the data from forms of webpages settedup with method POST.
The header request from browsers MSIE and NSN when they submit a form in method POST, haven't notably differences with the header on my client. That are a sample of the header that a MSIE browser sends to my server to submit a form in POST method:

Code:

POST /DIRSERVER/response.txt HTTP/1.1<crlf>
Accept: image/gif, (more types)<crlf>
Referer: http://123.456.789.0/<crlf>
Accept-Language: es<crlf>
Content-Type: application/x-www-form-urlencoded<crlf>
Accept-Encoding: gzip, deflate<crlf>
User-Agent: Mozilla/4.0 (compatible; MSIE 5.5...)<crlf>
Host: 123.456.789.0<crlf>
Content-Length: 37<crlf>
Connection: Keep-Alive<crlf>
Cache-Control: no-cache<crlf>
<crlf>
field0=text0&field1=text1&butsub=Send<crlf>

I can't see notably differences between msie request and mine, but on the server I can get all the data (from both pc), but when I send the same request though my client the content message is left (only when the client sends the request from a different pc than the one where server is running).
To send the data from the client I copy the header into a buffer and send it in one time. On the client I have a big buffer to recv the data also in one time (I suppose that form the moment that won't be the problem, if not my server wouldn't be able to get the profesional browsers request).

Have someone had or have seen a problem like that?

Thank's in advance

Niara

P.S. Ok, year-end so have a good new year

Your problem likely lies in your code somewhere, either in the server, the client, or both. I couldn't determine if you have code for the client, server, or both by your last post however. Post your code so we here don't have to divine the answer. (Or guess at common mistakes, like not checking recv()/send()'s return codes.)

Also, consider a network analyzer like WireShark. It'll allow you to see what exactly gets sent over a network connection, so you can determine if your program is sending what it should. (Although I use WireShark's predecessor, Ethereal.)

Also, when you send "test<crlf>", that's 6 bytes. You're saying the Content-Length is 4. Is this correct? (Is <crlf> part of the contents?)

When the client runs on the same pc as the server, you may be getting a loopback interface, which might cause it to act differently then when it's on two different PCs, where it must actually send the data. (But this is not the problem.)

Hello Cactus-Hugger, I didn't post any piece of code because I was thinking that's a strange net problem. Well, let me fix the problem and explanations. The scenario is the same. Also I have rewrite my server and client recv/send codes to it's simples expression (to avoid more programming errors). That's the server recv function:

Code:

char bff[2000];
int nbl;
nbl=recv(s,bff,2000,0);
bff[nbl]='\0';

is a simple use of recv (I know that will have problems on bigger requests, but for that test that's right because on the client's send buffer is 1024 and sends all the data at once). now the server's end connection function:

Code:

bool closeConection(SOCKET s)
{
if(shutdown(s,SD_SEND)==SOCKET_ERROR) {return false;}

char bff[2000];
bff[0]='\0';
while(1)
    {
    int nnb=recv(s,bff,2000-1,0);
    if(nnb==SOCKET_ERROR) {return false;}
    else if(nnb!=0)
        {
        bff[nnb]='\0';
        printf("\tRebuts %d bytes inesperats durant la desconexio:\n",nnb);
        printf("%s\n\n",bff);
        }
    else {break;}
    }

if(closesocket(s)==SOCKET_ERROR) {return false;}
return true;
}

and now the client send function:

Code:

WSADATA wsa;
SOCKET s;
SOCKADDR_IN servidor;
LPHOSTENT he;

if(WSAStartup(MAKEWORD(2,0),&wsa)!=0) {printf("Error 0\n");getch();return false;}
if(wsa.wVersion!=MAKEWORD(2,0)) {WSACleanup();printf("Error 1\n");getch();return false;}

s=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(s==INVALID_SOCKET) {WSACleanup();printf("Error 2\n");getch();return false;}

servidor.sin_family=AF_INET;
servidor.sin_addr.s_addr=inet_addr("172.16.0.4");
servidor.sin_port=htons(80);

if(connect(s,(SOCKADDR*)&servidor,sizeof(servidor))==SOCKET_ERROR)
    {
    WSACleanup();
    printf("Error 3");
    getch();
    return false;
    }

int bs,br;
char sb[1024],rb[100];

sprintf(sb,"POST /DIRSERV/resposta.txt HTTP/1.1\r\n");
strcat(sb,"Accept: image/gif, image/x-bitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, */*\r\n");
strcat(sb,"Referer: http://172.16.0.4\r\n");
strcat(sb,"Accept-Language: es\r\n");
strcat(sb,"Content-Type: application/x-www-form-urlencoded\r\n");
strcat(sb,"Accept-Encoding: gzip, deflate\r\n");
strcat(sb,"User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.1.4322)\r\n");
strcat(sb,"Host: 172.16.0.4\r\n");
strcat(sb,"Content-Length: 36\r\n");
strcat(sb,"Connection: Keep-Alive\r\n");
strcat(sb,"Cache-Control: no-cache\r\n\r\n");

printf("Envia HDR: ");
bs=send(s,sb,strlen(sb),0);
printf("%d bytes ok\n",bs);

printf("Envia PRM: ");
sprintf(sb,"txt0=Texte+0&txt1=Texte+1&sbm=Enviar\r\n");
bs=send(s,sb,strlen(sb),0);
printf("%d bytes ok\n",bs);

br=0;
printf("\nRebent resposta servidor...\n");
while(br!=SOCKET_ERROR)
    {
    br=recv(s,rb,100,0);
    if(br==0 || br==WSAECONNRESET)
        {
        printf("\n\nConexio finalitzada.\n");
        break;
        }
    if(br<0) {break;}
    rb[br]='\0';
    printf("%s",rb);
    }
shutdown(s,SD_BOTH);
closesocket(s);
WSACleanup();

also the simple expresion for the send algorithm. the header for that request is the same I get from a request in MSIE to my server from the next html form:

Code:

<html><head></head><body>
<form action="http://172.16.0.4/DIRSERV/resposta.txt" method="POST">
<input type="text" name="txt0" value="Texte 0"><br>
<input type="text" name="txt1" value="Texte 1"><br><br>
<input type="submit" name="sbm" value="Enviar">
</form></body></html>

That's what I have been doing. First start my server on PC#1 (172.16.0.4), run MSIE on PC#2 (172.16.0.3), connect and load the form page (that page is in PC#1, the server reads the 'GET' statement from MSIE to get that page, and still no errors), click submit and my server can get all the data sended from MSIE running on PC#2. I'll attach an image at the end (image00).

Right, now I have the MSIE headers that work, so I create my client (as it appears at the sample code I've posted), run server on PC#1, client on PC#1 (the client sends the data directly, without web form), and on the server I get all the data. There's no errors here.

And in the next step is where I can't get the data. I run the server on PC#1, the client on PC#2 (the same headers as before, the same client program), and on server I don't get the final params, the data is break after the <crlf><crlf>. And still something alse: the server is able to read the file requested in the 'POST' statement and return it to the client, and in all the cases works well. After send the file (a simple text file of 18 bytes), the client is able to get it without problems, the server calls the 'closeConnection()' function and in that case I get the alert of 'Unexpected extra bytes received'. I'll attach an image of that at the end (image001).

Why the same header and the same client programs run diferently when the client isn't in the same pc that the server? And why MSIE don't give me that problem? Knowing that my server can understand MSIE (also I have tested it with NSN and also works well) I should think that the problem is with the client... but then if the problem is in the client, why a system PC#1SERVER/PC#1CLIENT works, and fails the system PC#1SERVER/PC#2CLIENT?

As you can see on the attached images, the first image is for the PC#1SERVER/PC#1CLIENT, and is exactly the same result for PC#1SERVER/PC#2MSIE. And the second image is the PC#1SERVER/PC#2CLIENT, the data is broken after the <crlf><crlf> (I have translated 'cr'->'<br>' and 'lf'->'<bn>'), so I can see

Code:

...Keep-Alive<br><bn><br><bn>

and after that nothing else, while in the first image you can see that I can get all the data. It seems strange to me, I haven't any idea of what's happening.

More explications: I have been testing it with the router's port 80 opened and closed, but the error is always the same.

I'll take a look at WireShark to see what I'm really doing.

Thank's

Niara

Message fragmentation and reassembly is your problem to fix, when using a TCP connection.

Both send() and recv() can return having sent (or received) the total amount of data to be sent.

All the TCP protocols use some kind of mark (say a length or a character sequence) to mark the end of the transmission. Until that is reached, you have to be prepared to deal with the message in fragments.

TCP is a stream - just a variable length array of bytes.

HTML specifies a content length in the response, so you need to
a) keep reading the stream until you see a content-length appear
b) then read that much more data
c) close the connection.

> Use a recv buffer of 4 bytes
If you want, but that in itself doesn't solve the problem.